Saving Huygens

TazMainiac writes "This months IEEE Spectrum is running an article on how a Swedish scientist discovered that the Titan probe Cassini had a communications flaw that would cause it to lose all data sent back from the Huygens lander as it plunges into Titan's atmosphere. The problem - Doppler effect. The fix: go read the article."

Comments

RTFM is the fix?

[Kenja]

So wait, reading the article will fix the Cassini probe?

Re:RTFM is the fix?

[HiredMan]

It's like that damn Peter Pan play when you were a kid:
"If we all clap hard enough maybe Tinkerbell will be okay..."

We just hafta clap loud enough to be heard in space?

Sounds doubtful to me.

=tkk

Re:RTFM is the fix?

[Random_Goblin]

from TFM

Alenia Spazio's insistence on confidentiality may have played a role in this oversight. NASA reviewers were never given the specs of the receiver..."Alenia Spazio considered JPL to be a competitor and treated the radio design as proprietary data."
...NASA probably could have insisted on seeing the design if it had agreed to sign standard nondisclosure agreements, but NASA didn't consider the effort worthwhile, automatically assuming Alenia Spazio would compensate for the changing data rate.

so in this case the problem was indeed caused by the fact they couldn't RTFM to check the supplier had done the job correctly.

I think it is all summed up with the line "An Alenia Spazio spokeswoman said that none of the company's officials were available to comment because of a company-wide summer vacation period."

Re:RTFM is the fix?

[Anonymous Coward]

The probe cannot be fixed. The idea is that if you run alongside the ambulance the frequency of the sound will be constant (you get no Doppler shift). Of course Cassini will not take the plunge in Titan's atmosphere, but a correction in it's course will have the same effect (at any given time the axis defined by the two bodies will be perpendicular to Huygen's trajectory). Of course the Dopper shift won't be annulled (because there will still be some acceleration along the Cassini-Huygens line of sight), but it will be kept within the possibilities of the communications equipment.

Re:RTFM is the fix?

[jellomizer]

Was I the only kid who didn't clap there hands to see what would happen if Tinkerbell died?

Re:RTFM is the fix?

[dgatwood]

Yes.

Re:RTFM is the fix?

[Anonymous Coward]

No--there are plenty of heartless bastard assholes in the world.

Re:RTFM is the fix?

[Buran]

This is why spacecraft design should be "open sourced" and put up for download so that engineers everywhere can review it and point out problems.

Contractors should be heavily punished if their designs fail -- make them pay to redesign and refly, for instance. "You can cram your agreement up your ass because we paid to buy this from you and because it's on a publicly funded spacecraft. We're posting this on the web now so stop whining."

And why do we keep buying from Lockheed when they've fucked up so many missions in the recent past? JPL knows how to build stuff that actually works. Lockheed apparently doesn't. How about Boeing and the other companies out there that can do it?

And I agree... these idiots couldn't be bothered to even explain their mistake.

Re:RTFM is the fix?

[motox]

They -would- if they signed the NDA, which they didn't.

Re:RTFM is the fix?

[drew]

In many European countries there is a month long period where everyone goes on vacation. As I understand it, pretty much the entire country except for basic service industries shuts down for a month. I don't understand the specifics, as I've never been to Europe during a vaction, but I did work on a project once with SwedenPost (the Swedish Post Office) that ended up being pushed back quite a bit because the original project schedule had us going into client QA right as the entire company took a month and a half off for vacation. And this was the Post Office!

So I doubt that the fact that all of the company's officials were on summer vaction at the same time reflects on their abilities to design complicated hardware. It's just business as usual over there.

And as the article points out, NASA probably could have gotten the specs if they had signed an NDA but they didn't believe they were necessary. Given that statement, it's quite possible that no one would have looked at the specs close enough to notice the problem, even if they had them.

Re:RTFM is the fix?

[Anonymous Coward]

Alenia Spazio actually gave a presentation where they lied and claimed a test was done that was not done. And they _did_not_ offer to let JPL sign a NDA to see the specs.

Re:RTFM is the fix?

[Anonymous Coward]

The article does nothing!

Re:RTFM is the fix?

[twiddlingbits]

NASA Has an Independant Verification and Validation Center to provide technical oversight. I worked there (it's in West F'ing Virgina of all places). The folks there do a great job with what data they are given. Often to save costs, this IV&V team is not even allowed to participate in the Design Reviews, and when they are and discover issue the Project Offices sweep them under the rug. No use admitting to problems that might show someone is not thinking correctly or is not managing the project well. The theory is "Let's avoid the problems by witholding information and communication from anyone who might find a problem". Solid testing? Thats a joke too, it costs money to test things well, and who knows they might break!. Contractors will make mistakes, after all they employ humans, but the mistakes can be corrected BEFORE flight if they are found. Having an extra set of eyes, and doing extensive testing is valuable but costly. In FACT having IV&V on manned systems is the LAW since the Challenger disaster, it's just commonly disregarded at NASA for anything but ISS. Even STS has no IV&V, after all it's a "mature" system and there are no bugs left. Regardless of what you hear about NASA "changing" after Columbia it really isn't. I fully expect another STS disaster, and several more mini-disasters in unmanned systems in the near future.

Re:RTFM is the fix?

[b-baggins]

---
so in this case the problem was indeed caused by the fact they couldn't RTFM
---
OK. Which part of the sentence: NASA probably could have insisted on seeing the design if it had agreed to sign standard nondisclosure agreements,

Did you not understand?

Nasa didn't want to BOTHER with making the EFFORT to read the specs.

Re:RTFM is the fix?

[Pinkoir]

An Alenia Spazio spokeswoman said that none of the company's officials were available to comment because of a company-wide summer vacation period.

As drew says, the fact that all the people at the company at fault were on vactation should not be construed as an attempt by them to duck the issue.

These Europeans all have completely non-intuitive amounts of vacation time which sometimes lead us NAers to believe we are getting screwed over in some subtle, uspecified way. I do a fair amount of work with some German companies and they are on vacation about half of the time.

On the plus side it means that another Northern European War is pretty much a logistical impossibility. Back before WWI all the brightest minds on both sides were put to work generating the astoundingly complicated railway schedules needed to minimize the time taken to mobilize the huge citizen armies. The logistical difficulties involved in coordinating the movements of multiple armies along the same railways so that each got to its designated start line at the right time pale in comparison to the utter impossibility of getting a couple of hundred thousand Frenchmen and Germans to not be taking vacation all at the same time.

I for one, see this as a positive development. Even if it does push all my timelines out about two weeks more than I'd like.

-Pinkoir

Re:RTFM is the fix?

[flibuste]

In many European countries there is a month long period where everyone goes on vacation. As I understand it, pretty much the entire country except for basic service industries shuts down for a month.

Great to see that you've been modded "insightful". Mod me "offtopic" if you want but this is a big misconception of european countries. Basically, people there take their holidays at the same time as everyone else, that is, mostly summer time and christmas time.

I leave in north america, and 90% of the companies I have been in do close for the whole christmas week.

As much as you would love europeans to be different, the holidays thing is not the issue in the article, and what you say is simply irrelevant.

Just wanted to clarify a few things for our friends from the new continent who have a wicked conception of the old one.

Re:RTFM is the fix?

[Enigma_Man]

What company do you work for that closes for a week at X-mas? I want to work there! Every company I've ever worked for closes down for two days at most. X-mas day, and the day after. If those happen to fall on a weekend, then no extra days off.

Some places only close X-mas day, or not at all (Walmart).

If I had mod points, I think you'd probably be getting "flamebait" and not "offtopic". -Jesse

Re:RTFM is the fix?

[DAtkins]

No way. I hated that stupid pixie.

Re:RTFM is the fix?

[FnH]

Actually, the logistical difficulties involved in coordinating the movements of multiple armies along the same railways so that each got to its designated start line at the right time are very much comparable to the logistical difficulties involved in coordinating the movements of multiple tourists along the same railways so that each got to its designated hotel at the right time.

You Americans just wouldn't be able to pull it off :)

Re:RTFM is the fix?

[Anonymous Coward]

if you run alongside the ambulance

Are you a lawyer?

Re:RTFM is the fix?

[jakethecake]

Pity you guys, where I'm from you get 4-7 weeks summer vacation, Sweden that is. So the story with the post office is true, that's how we do it :) free healthcare, free education, and allot of vacation, I love it! And we have about the same GDP as England, so there is nothing wrong with productivity ;)

Re:RTFM is the fix?

[Anonymous Coward]

"West F'ing Virginia"

Excuse me, but as someone who has invested a lot to move to this beautiful state, I definitely resent that. As far as I'm concerned, there is no better place to be doing high tech work. We're close enough to DC to drive there for several hours of meetings and make it back for dinner and can buy beautiful land for under $2000 per acre, much less if we accept driving an hour to work instead of 10 minutes. In many states, people can frequently sell their home and buy the same thing here sitting on 100 acres just using the profit from their sell. No more house payments for life. And the people are real instead of the pretentious fakes I've encountered elsewhere.

If you've got an axe to grind, don't grind it on a whole state.

Re:RTFM is the fix?

[Corbin Dallas]

I second this. West Virginia is a georgous state, and anyone who hasn't been truly doesn't know what natural beauty is.

Re:RTFM is the fix?

[Anonymous Coward]

Hewlett-Packard. Unless your department has a project that's about 1 week behind schedule...

Re:RTFM is the fix?

[Indigo]

This is so far off, I don't even know where to start.

Let me just say that "Even STS has no IV&V, after all it's a "mature" system and there are no bugs left" will be a big surprise to the folks at the IV&V center and elsewhere who are responsible for IV&V on Space Shuttle flight software...

Re:RTFM is the fix?

[twiddlingbits]

Ever lived thru a winter there? You might change your mind. Everyone I have ever met who left there (even those born there) said Winter Sucks. Having snow on the Ground from Nov-Mar is not my idea of fun. However, it is a lovely state Spring, Summer and Fall.

Re:RTFM is the fix?

[twiddlingbits]

Yes, you are so far off I don't know where to start. Just answer this: Do you WORK at the Center? Tell me what city it is in? Who are the contractors? Who got the center started? Who is the director? Who does he/she report to? How many floors in the building? What is on each floor? If you don't know this then go back to lurking as you have no credibility to disparage my comment. I was there,in the organization for quite some time, I know what I saw. I still maintain close contacts with the people in the facility. Sounds to me like you are just repeating the NASA party line, which is to be expected. The truth is one thing you will rarely get at NASA. Nothing is going to convince me when this is all based on personal experience.

Re:RTFM is the fix?

[Anonymous Coward]

clap there hands

"their". And "his or her" is more grammatically correct, regardless what some fucking language evolutionists would have you believe.

Also, not only did I not clap, but I screamed at the TV "Die, Tinkerbell, die, you Satan-spawned fairy!!!", which was unusually biting commentary for a seven-year-old. Her unaided-by-clapping recovery traumatized me and led to my atheism vis a vis Santa Claus and the Easter Bunny. I haven't been the same since. Now all I do is read Slashdot all day, correcting people's spelling and admonishing them to please learn how to make links.

Re:RTFM is the fix?

[Indigo]

I never claimed there are no challenges or difficulties in IV&V work. Just like in any workplace, there are. But you just claimed that NASA is too cheap to do IV&V on the Shuttle program and that is patently false. Your other points sound like horror stories to frighten kids, certainly that is not the way it works in the manned spaceflight arena.

The tone of your posts makes me think you have some personal issue with the IV&V facility. I imagine others with experience in this field would have differing views.

Re:RTFM is the fix?

[RhettLivingston]

The winters are one of the reasons I moved here, though I personally would prefer that it be a little colder so that the snow wouldn't melt any. I'd take a winter in West Virginia over a summer anywhere in the south any day.

Also, in terms of shear beauty, seeing my land snow covered strikes me with awe every time. One of my most memorable times last winter was sitting outside in my picnic shelter listening to and watching the snow come down. There aren't many places where its so peaceful that you can sit for over a half hour and hear nothing but the snow and the crackling of the fire.

The one downside of the area is that they haven't embraced the idea of developers and analysts working from home yet. Working from home in St. Louis was nice; working from home here would be awesome. I've spent a few days sitting beside the stream or in front of the fire with my laptop, but wish they were the majority.

Re:RTFM is the fix?

[RhettLivingston]

If the project office sweeps something under the rug publicly, but addresses it privately, I'd sign off on it anyday. It is not our purpose to publicly humiliate or embarass. If we made that our purpose, we wouldn't survive to do what good we do.

If you find a problem that you can prove will cause a problem, and you don't sign off, it doesn't fly. There are a lot of people that don't seem to understand though that not every problem is a showstopper.

Your theory of projects withholding information to avoid problems is exactly what happens when you rub the developers' noses in the problems you find or when you blow meaningless problems out of proportion and waste time. Sounds like you didn't play nice. I have several employees working with the facility who get minute to minute direct access to the software development team's repository and are invited to more software team meetings than they can attend. They got that access because they proved to the developers that they were on the same side. They found problems, told the developers, and the problems were fixed. And yes, in many cases, they were fixed quietly. IV&Vers don't get a lot of fame, but the ones who work hard at it do get results and personal satisfaction.

Of course, you've shown the depth of your knowledge of how to constructively criticize very clearly. If you want to influence people positively or be taken seriously, you don't start off by "F'ing" a whole state. Your desire to create positive change appears to be weaker than your hatred and/or anger.

Re:RTFM is the fix?

[drew]

most US companies get 6 to 8 holidays (memorial and labor day, independence day, thanksgiving, chirstmas, new years. after that it depends where you work, usually some combination of the day after thanksgiving, the day before christmas, veterans day, presidents day, martin luther king jr, etc.) I've never worked at or heard of a company that had more than 8 holidays.

even if everyone in a US company were to take their vacation at the same time (something most US companies would never allow) most US workers only get 2-3 weeks of vacation a year. so all together, most US workers get less than a month total vacation, and 1/4 - 1/3 of that we have no choice when we use.

so there is a big difference between US and europeans, even if europeans don't actually schedule a month off in the middle of the year. the difference is that most europeans (at least the ones that i've spoken to) get much more vacation overall than their american counterparts, and the work culture there allows for most or all of a company to take vacation at the same time, something that as far as i am aware never happens here in the US, except for the 1-2 day holidays scattered around the year.

Re:RTFM is the fix?

[twiddlingbits]

I don't dispute that SOME projects get access. But the ones I worked on didn't. I think you are talking about ISS and other Code M projects. And we did NOT rub the developers wrong, we were not allowed to even CONTACT them to discuss issues. Go ask some of the folks who work on Code S projects how hard certain project offices tried to prevent them from doing thier job (go ask about HST and SWIFT). The same things happened again on GLAST. It's NOT the attitude of the IV&Vers, it's all dependant on the Project Offices attitudess. We were always very co-operative and would take time to explain what we saw and offer suggestions on how to fix things. I know many times I went to a major review (after fighting to go) and when I finally met the developers they had no clue who IV&V was? They had never got our inputs! I know with the new funding model where the $$$ come from Hdqtrs that is supposed to change, and I hope it does. As far as WV is concerned the people there are great, it's the weather that I hated. Born and raised in the South I have no tolerance for cold just as someone else has none for heat.

Thank you Eberlin

[Anonymous Coward]

Slashbot Rhyme

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Not quite

[palad1]

RTFA will fix the probe.

Re:Not quite

[eingram]

So you're telling us the probe is doomed?

The fix: **Spoiler Alert**

[Anonymous Coward]

Change the cosmological constant of the universe.

Re:The fix: **Spoiler Alert**

[Maavin]

You may think "You can't change the cosmological constant !!"
, but You know something ? We're trying to save existence as we know it, and all you can do is criticize.

Save yourself from RTA, the fix is:

[Tibor the Hun]

reversing the polarity of the transponder...
duh...

Re:Save yourself from RTA, the fix is:

[Solder Fumes]

Actually I would have thought that at first, but on further review it appears you would have to modulate the deflector array with an inverted tachyon pulse.

Re:Save yourself from RTA, the fix is:

[Anonymous Coward]

First decouple the Heisenberg compensators!

Re:Save yourself from RTA, the fix is:

[Anonymous Coward]

Once again the mods show their true intelligence. I am starting to think that the IQ here at slashdot is actually lower than the general public! Does it just take a few technical words to get modded as insightful or what? Fancy this...someone actually understanding what the fuck they are reading before modding? Nope, it'll never happen.

Re:Save yourself from RTA, the fix is:

[MustardMan]

No, NEVER use the targetting systems... you have to trust your feelings

Re:Save yourself from RTA, the fix is:

[jelle]

Why all that newfangled mumbo jumbo? Just order the guy on the controls to compensate and the picture is clear again.

What is this?

[Anonymous Coward]

So now /. wants us to actually... read?

Re:What is this?

[Gherald]

> So now /. wants us to actually... read?

Yeah, I mean since when have we stopped catering to the illiterate geek community? People who can't read have rights too!

Re:What is this?

[Anonymous Coward]

So now /. wants us to actually... read?

Well, that would differentiate slashdot from the teachers' union.

Re:What is this?

[Kehvarl]

So now /. wants us to actually... read?

Only if you're either a space probe that might suffer this problem, or interested in fixing a space probe that might suffer this problem. Otherwise feel free to skim the summary, ignore most of the comments, and then make obviously well-informed comments about what they got wrong in the article. :]

Lots of amazing stuff

[erick99]

It is amazing that the problem with the reciever was detected. It was more amazing to read what they went through to document and present the problem. It also says something about the relationship between NASA and it's subcontractors when they can accept a receiver design and not sign a standard non-disclosure agreement so that they can see the specific design elements. If they had done so, they would have been able to see the problem before launch. However, having read the article, the complexity of the mission is such that I am possibly more amazed that more didn't go wrong.

Re:Lots of amazing stuff

[TAGmclaren]

I have the utmost respect for the guys that do this kinda stuff, because unlike virtually every other industry, there are no chances for a trial run, and zero margin for fuck ups.

The one thing I wonder is how extensively they make use of simulations. I'm wondering whether soon they'll be able to run through an entire mission, speed it up and slow it down around problems, so they can find/fix problems before launch.

Re:Lots of amazing stuff

[erick99]

They were supposed to run a simulation, as one of three safety nets to catch such problems, but decided not to because of the cost.

Re:Lots of amazing stuff

[KjetilK]

...or reject proprietary designs alltogether, so as to make the specs available to the whole organization. The problem here was that the subcontractor didn't want JPL folks to poke at it, since they were "competitors". But that also means that the JPL folks are peers, and if those peers were interested enough in the design, those peers would have performed a peer-review, which is a central tenet of science.

The problem is that someone willing to sign an NDA is also in a situation where you cannot compete on the stuff you signed on. So, you cannot get peers to sign an NDA, that would kill their own career. You can get someone who may be top-notch in a different field, but they have not necessarily the specialisation needed to perform a exhaustive review.

Re:Lots of amazing stuff

[cellocgw]

They were supposed to run a simulation, as one of three safety nets to catch such problems, but decided not to because of the cost.
Which doesn't make sense: did nobody at NASA have the brainpower to conceive of sending an emulated signal just like the one they actually ended up using? How much could it have cost to run a few hours' testing of Cassini's commlink prior to assembly of the craft? It's *always* a good thing to check system components in a full emulation environment.
I think there were many problems, and one of them was that the system (or system test) engineers didn't stop to think of the Q&D way to get some proper failsafe testing done.

Re:Lots of amazing stuff

[erick99]

To run the test they would have had to dismantle part of the craft and then go through an expensive recertification process to put it back together. Apparently the cost for all of this was very, very high. Probably not as high as the fix for this problem, though.

Re:Lots of amazing stuff

[Smilodon]

I agree with what you are saying. The point I was trying to make was that in situations like this, often governments will refuse to allow a free flow of (often) useful information. This state of affairs is tolerated, ironically, in the spirit of cooperation to get the job done.

According to what the article said, in this case, it appears to be a decision by Alenia for strictly commerical reasons. But it could have been ASI, the Italian or US governments that allowed it to stand.

Re:Lots of amazing stuff

[Tablizer]

However, having read the article, the complexity of the mission is such that I am possibly more amazed that more didn't go wrong.

The Huygens probe has yet to be deployed to Titan. Thus, it is too early tell if there are not other significant problems.

Re:Lots of amazing stuff

[cft_128]

Which doesn't make sense: did nobody at NASA have the brainpower to conceive of sending an emulated signal just like the one they actually ended up using? How much could it have cost to run a few hours' testing of Cassini's commlink prior to assembly of the craft? It's *always* a good thing to check system components in a full emulation environment.

s/NASA/ESA/g

NASA was only observing - this part of the project was pretty much run by ESA. Still a "cock-up" all around.

Re:Lots of amazing stuff

[cft_128]

It also says something about the relationship between NASA and it's subcontractors when they can accept a receiver design and not sign a standard non-disclosure agreement so that they can see the specific design elements.

Sort of. This was really an ESA project and NASA was was only assisting the them. If this was a NASA run project I'm sure they would have insited in seeing what the specs were (now weather that would have helped is a different question). I wonder if Alenia Spazio (the contractor) gave the ESA the specs?

Re:Lots of amazing stuff

[Anonymous Coward]

...or reject proprietary designs alltogether, so as to make the specs available to the whole organization.

Whole organisation? USA taxpayers paid for this design. Why isn't it public domain?

Re:Lots of amazing stuff

[clem9796]

It's funny [read: strange]that they could send a test signal after launch, but they couldn't do the same on the ground before launch without taking the craft apart? That doesn't make sense to me.

Re:Lots of amazing stuff

[mefus]

Which doesn't make sense: did nobody at NASA have the brainpower to conceive of sending an emulated signal just like the one they actually ended up using?

It doesn't make sense because the pp gave a very facile explanation of the problem inviting misinterpretation.

NASA ran three tests, all of which passed, but none of which tested the internal correction of signal to carrier wave. Why this is true is due to a number of factors which were laid out in TFA.

The assumption that the receiver worked was in part due to the fact the (spanish) company that made it would not release the specifications without an NDA. Because NASA is a public organ they couldn't sign the NDA.

The hardware fault was not NASA's doing, however, despite what so many of the trolls around here would have you think. It isn't even NASA's probe.

Re:Lots of amazing stuff

[CreatureComfort]

Agreed. Not to mention the fact that apparently nobody thought to test the components before they assembled and certified them?

Re:Lots of amazing stuff

[Mikkeles]

' To run the test they would have had to dismantle part of the craft...'

But they actually ran the test that detected the problem from Earth while Cassini was en route; obviously, the craft did not have to be disassembled.

Re:Lots of amazing stuff

[belroth]

The assumption that the receiver worked was in part due to the fact the (spanish) company that made it would not release the specifications without an NDA. Because NASA is a public organ they couldn't sign the NDA.

s/spanish/Italian/g
also, from TFA:

NASA probably could have insisted on seeing the design if it had agreed to sign standard nondisclosure agreements, but NASA didn't consider the effort worthwhile

so it wasn't that NASA couldn't, they just didn't bother.

The hardware fault was not NASA's doing, however, despite what so many of the trolls around here would have you think. It isn't even NASA's probe.

again from TFA:

LAST JUNE, SCIENTISTS WERE THRILLED when NASA's Cassini probe successfully began orbiting Saturn...

In a collaboration with the European Space Agency...

If it isn't NASA's probe whose is it?
NASA built Cassini, the ESA built Huygens - Huygens appears OK as far as we can tell, it's NASA's bit that has the problem. OK it was the fault of the Italian subcontractor but NASA seems to have screwed the pooch again on the oversight.

Nice catch from Smeds though, nice to see someone wanting to do the job properly, and I do like the ingenious solution.

Re:Lots of amazing stuff

[luckyguesser]

do you even know what this article / post is about? the point is, no one was going to do the test until a non-affiliated scientist discovered the problem and spent considerable time and effort convincing NASA and others that there even was a problem. only then did the necessary testing occur. dear lord, i know it's been said a million times before, but RTFA once in a while.

Re:Lots of amazing stuff

[Anonymous Coward]

Testing what? This is a fairly complex system. Sure it is a good idea to test everything, but what is everything? How do you test it?

To test everything requires time and money. I'll bet that for any test cycle that takes less than 500 years, with 100 testers working at all times, there will be undiscovered bugs. Note that everytime even one bug is fixed the entire cycle starts all over again! Good luck getting any science done at that rate.

Re:Lots of amazing stuff

[Mikkeles]

'...but RTFA once in a while.'

I did (and even before posting!). The pre-launch doppler tests were not done due to cost and the required [?] partial disassembly of the craft, etc., (as stated above). Obviously, such a test did not require this.

Let me guess....

[Anonymous Coward]

does it involve a man with crazy hair pitching photons off a rail car that has a ticking clocks on each end?

Re:Let me guess....

[AKAImBatman]

I don't know. But do the photons curve or do they fall straight?

Re:Let me guess....

[DaHat]

But do the photons curve or do they fall straight?
That would depend on your frame of reference. That is to say, compared to what are they 'falling'?

Re:Let me guess....

[AKAImBatman]

That would depend on your frame of reference. That is to say, compared to what are they 'falling'?
So it's safe to say that the photon's path is both curved AND straight depending on your frame of reference? Perhaps to the photon, we are the ones who are falling! :-)

farsighted

[Doc Ruby]

Installing the reentry sensor upside down, ignoring the Doppler effect - this rocket science stuff is so hard, they're missing all the easy stuff.

Re:farsighted

[hopemafia]

It's actually fairly common...when you have a bunch of smart people working on difficult problems they tend to breeze through the easy parts, and don't necessarily double check each other's work because of "Jim has 2 PhD's...he'll get that right" syndrome.

Reminds me of taking caculus exams...it was always something dumb like switching +/- or "1+1=3" that I got wrong...not the partial differentials.

It just shows that no matter how smart you are, if you hurry and don't pay attention to every trivial detail you'll make mistakes.

Re:farsighted

[Ill_Omen]

reminds me of my high-school calculus exam... I did all the work correctly on my scratch paper, then incorrectly transcribed the answer onto the answer sheet.

Re:farsighted

[drew]

too true. i had a nobel laureate as a teacher in my freshman physics course in college. brilliant man, and a great researcher, but i couldn't help being amused seeing him stumble over basic physics problems and getting stuck to the point that the class would have to point out what he was doing wrong.

Re:farsighted

[Anonymous Coward]

or "1+1=3" that I got wrong

You say that like it is wrong. 1+1=3 for extremely large values of 1 just like in electronics with all of the rounding off of readings.

Re:farsighted

[freqres]

11 binary = 3 decimal. You just have to define '+' as concatenation (and switch mental mode to smartass).

Re:farsighted

[Rich0]

Sounds like all you need is a weakly typed language with operator overloading and fairly liberal syntax. I'm sure there is some way to do this in PERL...

Re:farsighted

[Rich0]

I think the statistics are that somewhere around 5% of all carefully transcribed data points will contain errors. In many jobs where accuracy is critical, any manual data entry is either carefully reviewed or performed in duplicate. (That is, two people type all values independantly, and the system raises an alert if they differ.) Data review literally means just comparing all values to the original source to verify accuracy of transcription.

It is painful work, but it is fairly effective in lowering the error rate. Probably the only other approach is statistical analysis, assuming you have a large dataset. (That wouldn't be practical in the current situation - you can't design 100,000 radios and compare their schematics.)

Re:farsighted

[MustardMan]

obofficespace:
MICHAEL
Well, technically it did work.

PETER
No it didn't!

SAMIR
It did not work, Michael, ok?!

MICHAEL
Ok! Ok!

SAMIR
Ok?!

MICHAEL
Ok! Ok! I must have, I must have put a decimal point in the wrong place
or something. Shit. I always do that. I always mess up some mundane
detail.

Re:farsighted

[blackbear]

Jim has 2 PhD's...he'll get that right" syndrome. "

More like, "Jim has 2 Ph.D.'s... He'll bust a cap on my ass if I double check his work."

Re:farsighted

[danila]

Probably they need some "not-so-smart" people with the IQ of 95 and slow-witted to go through all the design docs and calculations line by line, methodically and carefully, because otherwise they won't understand anything. :)

Re:farsighted

[Anonymous Coward]

lol...
apparently jim is African-American now too... i'm sure that's a quite common name for someone of that nationality =P

Horizon

[Gaima]

God bless good 'ole auntie.
Saw this on Horizon yesterday evening.

Always nice to see a simple solution.
Now if only NASA could find a simple solution to conversions between imperial and metric, or not undoing bolts :)

Re:Horizon

[payndz]

An informative show, even if the CG got a bit repetitive (they used the same clip looking down from Saturn's pole before sweeping into the rings six or seven times, and even had to start flipping the image to disguise it!)

Anyone else notice just how much familiar movie music was in there? The sequence of Cassini being loaded into the Delta was accompanied by a track from Armageddon, a space flyby CG sequence had the 1989 Batman theme, and one of the Titan shots used the 'opening of the Ark' theme from Raiders! There were also cues from Moonraker and a couple of others. Methinks the Beeb's music library's been infiltrated by movie fans...

The BBC is doing a very good job with documentaries at the moment. Part 1 of The Power Of Nightmares (about the parallel origins of al-Qaeda and the neo-conservative movement) on Wednesday was both informative *and* disturbing!

Re:Horizon

[Anonymous Coward]

Horizon is one the last hard-science (By TV terms) shows left. I hope that the previous shows will be made available online as part of the archive scheme although I won't hold my breath as many of them were co-productions.

I want my own personal copy of the Horizon episode they did with the scientists who work inside Chernobyl. Excelent stuff.

Re:Horizon

[Anonymous Coward]

More Info including transcripts.

It was an awesome show, really fascinating.

Re:Horizon

[orac2]

But if I may point out, to all those BBC viewers yawning "old news", this story was published by us on October 1st. (I actually submitted it at the time but the /. Gods rejected it).

Disclaimer -- I work for IEEE Spectrum.

Re:Horizon

[Anonymous Coward]

Don't feel bad I had a story rejected a few days ago and it was posted by Cowboy Neil today (Cisco buying blahblahblah). If you want something accepted all you have to do is find something that has a birthday today and they will accept it every year like clockwork. 'X' turns 'Y' today is a pretty consistent headline here.

Re:Horizon

[mefus]

I don't remember when I got the current Spectrum, but this is indeed old news.

[I don't work for IEEE Spectrum]

Re:Horizon

[orac2]

Really? Just where did you read/watch about Boris Smeds before? Seriously. I think we got a scoop of sorts and I'd like to know if we didn't.

Re:Horizon

[mefus]

Sorry, I meant to imply that the hardcopy of SPECTRUM came out long before any of the other sources for this 'scoop'.

So yeah, feel good about it.

Re:Horizon

[orac2]

Cheers.

Re:Horizon

[Anonymous Coward]

Were doing a pub quiz in a couple of days, care to join us?

Thats quite a talented ear you appear to have. :)

Old news

[Timesprout]

The problem was discovered years ago, took 6 months to investigate and nearly 2 years to resolve. The BBC told us all about it with nice graphics the other night.

Re:Old news

[orac2]

That's nice. Did they actually explain how the Doppler shift affected the BPS coding used in the Huygen's telemetry, or describe how the problem was missed, or tell the story of Boris Smeds pushed through his test and ended up modifying it on the fly? And does every reader of IEEE Spectrum get the BBC on their TV? (hint, Spectrum has a global circulation)

-- disclaimer, I edited (and did some reporting for) this story.

Re:Old news

[Anonymous Coward]

No, but they had much better video sequences of the Jupiter and Saturn flybys.

Re:Old news

[orac2]

As soon as proper electronic paper comes out, I promise we're going to have video so good it'll make your eyes melt out of their sockets.

Re:Old news

[Anonymous Coward]

I was actually joking. You seem very uptight about the fact that a lot of us UK readers just happened to see the Horizon show last night, which just happened to be about the exact same subject. So for us, this is fresh in our minds yesterdays news. Them's the breaks; sorry.

Re:Old news

[orac2]

I'm uptight because its annoying when you work on an article and people comment without bothering to read it -- yes, I know that's endemic to /., but it's still a pain in the ass.

The point is that we dug up an aspect of the story you're not going to see any where else, let alone a general overview program, but a really cool story of a guy who deserves a lot of credit, Boris Smeds. I would hate for anyone to not bother to find out about him because a related program on the telly happened to be braodcast the night before /. decided to post the story.

Re:Old news

[physman]

See: http://www.bbc.co.uk/sn/tvradio/programmes/horizon /saturn_prog_summary.shtml it has a full transcript of the whole programme available, as well as a questions and answer page and summary of the programme.

Re:Old news

[orac2]

Thanks for the link to the transcript: Smeds, who saved the Huygens mission, isn't mentioned once.

Re:Old news

[Anonymous Coward]

Nice article. I, for one, appreciated it and forwarded it to the ham-radio microwave list for further publicity. :)

That Alenio Spazia outfit needs to be restricted from working on any vehicle faster or more expensive than a Fiat.

Re:Old news

[orac2]

Cheers!

Re:Old news

[EccentricAnomaly]

Boris was key to finding the problem, but the solution was mostly a trajectory one. The article has a rather mangled explanation of the trajectory changes, and it treats the people who worked on it rather anonymously.... just calling them 'navigators'. The fact is that the trajectory changes done to save the probe mission were far from trivial.

Boris deserves a lot of the credit for saving Huygens, but several other people deserve credit but have been rather anonymous outside of ESA/JPL. 'Saving' Huygens was a team effort, and a lot of people played a part. There are a handful of other key people that the article doesn't mention at all.

Also there are a few factual errors in the article.... NASA couldn't simply sign a NDA to get the specs for the receiver, and there was a lot of effort by NASA to get the specs. Even after the problem was detected, Alenia resisted sharing information for many months.

Re:Old news

[orac2]

I agree the recovery was a team effort, but the fact remains that what Smeds did was a rarity: a singular individual effort that, if it hadn't occured, would have resulted in disaster. Thus we felt he deserved some serious kudos and so the article focused on him.

I'm in no way deingrating the amazing and creative work that the trajectory guys did. But think of it like this: If any one of those guys were absent from the project, because of a sabbatical, or, God forbid, an accident, chances are that the mission still would have been salvaged.

The same cannot be said about Smeds during the period between being told to do a test and coming back to ESA with the results -- it's fair to say that many, if not most, engineers would have just developed a carrier wave only test as originally planned, or wouldn't have bothered to persist with the more complex test after being turned down (after all, who's looking to get into trouble to do extra work?), or might not have had the insight required to modify the test on-the-fly when the downlink started showing problems.

The situation is analogous to Apollo in some ways: a lot of people helped design and build the LEM (Tom Kelly is one of my personal engineering heroes), but John Houbolt deserves his place in history for pushing NASA onto the LOR architecture path in the first place.

As for what we said about NASA and the NDA, I'll just have to say we stand by Oberg's reporting. But if you have something that shows we really did get it wrong, I'd be more than happy to look at it and print a correction if warranted.

Re:Old news

[belroth]

I watched the program and I found the article far more informative, thanks - Horizon used to be good but has dumbed down a fair bit in the last few years.
Apart from the pretty graphics there were lot's of pictures of 'mission control' and people getting excited.
We used to have Tomorrow's World which started off as pretty hard science reporting but degenerated into Blue Peter for grown ups, Horizon is following it IMHO. Equinox took over the decent reporting crown but that seems to have been shelved too. Now I have the net, hmm. Is that good or bad?

Re:Old news

[orac2]

Yeah, it really sucked when TW went from the equivalent of Scientific American or New Scientist to a product launch show: the episode they did in real time in th '80s on what would happen during a nuclear missile exchange still gives me chills...

Re:Old news

[EccentricAnomaly]

I agree the recovery was a team effort, but the fact remains that what Smeds did was a rarity: a singular individual effort that, if it hadn't occured, would have resulted in disaster. Thus we felt he deserved some serious kudos and so the article focused on him.

In no way do I want to take away from what Boris did. He was key to finding the problem... as were Claudio and Jean-Pierre. Take away any of the three and we would be finding out about the problem the hard way.

I'm in no way deingrating the amazing and creative work that the trajectory guys did. But think of it like this: If any one of those guys were absent from the project, because of a sabbatical, or, God forbid, an accident, chances are that the mission still would have been salvaged.

This is very much _not_ true. Traditional techniques to design the distant flyby required more fuel than Cassini had on board. ESA was orignally pushing for an all electrical engineering approach that would leave the trajectory unchanged but just pre-heat the probe's crystal.... this would have given a mission, but with severe data loss. The nav solution with the retrograde flyby saves all probe science while preserving all orbiter science for only 80 m/s. Nothing lke this has ever been done before, and it is the result of a couple people who refused to give up on finding a solution, and kept banging on the problem. If you take away one person in particular the mission never would have been saved.

(also, we don't get sabbaticals... we're lucky to get weekends)

Re:Old news

[orac2]

Sorry for the long delay in response!

as were Claudio and Jean-Pierre.

Very true, and while the article doesn't focus on them we did try to tell readers how significant their roles were.

ESA was orignally pushing for an all electrical engineering approach that would leave the trajectory unchanged but just pre-heat the probe's crystal....

Now, you've really tickled my professional interest. It was my understanding that (because of the physics) changing the angle of incidence was a big contender for the solution from the get-go... Anyhoo, seriously, if you want to continue this conversation off /., (my email addy is s[dot]cass[at]ieee[dot]org), I'd really like to follow up with you about this.

we don't get sabbaticals... we're lucky to get weekends

Well, I was trying to come up with something a little friendlier than a heart attack :)

classic

[theMerovingian]

"We have a technical term for what went wrong here," one of Huygens's principal investigators, John Zarnecki of Britain's Open University, would later explain to reporters: "It's called a cock-up."

We Americans speak English, but this is proof positive that the British have had much more time to master the use of it :)

Re:classic

[Anonymous Coward]

"We have a technical term for what went wrong here," one of Huygens's principal investigators, John Zarnecki of Britain's Open University, would later explain to reporters: "It's called a cock-up."

We Americans speak English, but this is proof positive that the British have had much more time to master the use of it :)

Of course we would tend to think that a "cock up" might very well be a good thing. ;)

Re:classic

[Anonymous Coward]

"We have a technical term for what went wrong here," one of Huygens's principal investigators, John Zarnecki of Britain's Open University, would later explain to reporters: "It's called a cock-up."

We Americans speak English, but this is proof positive that the British have had much more time to master the use of it :)

The British have another saying. When someone else's mistake lands you in trouble, they say "Their cock-up, my ass."

Watch out for the fithp

[AKAImBatman]

Well this is good news! I'd hate to have missed our early warning signal about alien elephants coming to subjugate us all!

So I hear we're building a nuclear pulse ship (aka Orion). Can I help? :-D

We have a technical term for it

[RealAlaskan]

"We have a technical term for what went wrong here," one of Huygens's principal investigators, John Zarnecki of Britain's Open University, would later explain to reporters: "It's called a cock-up."

Oooooh! I love that technical jargon.

Spoiler Warning:

... the Cassini team crafted a response plan that centered on reducing the Doppler shift sufficiently to keep the data signal within the recognition range of the receiver. They accomplished this trick by altering the planned trajectory of Cassini.

Now you know how they fixed it, so no need to read the article.

Re:We have a technical term for it

[crawling_chaos]

Now you know how they fixed it, so no need to read the article.

Like that would ever happen on Slashdot anyway...

Re:We have a technical term for it

[Haeleth]

Now you know how they fixed it, so no need to read the article.

Thank you for the summary! I tried to RTFA, but I got tired of the tedious dumbed-down human interest after the first thousand words of breathless "Could the mission be saved, or was it too late?" tosh that these journalists always seem to feel they have to pad their word counts with.

I guess I should be glad they hadn't quite managed to turn it into One Man's Struggle Against the Establishment. And if the guy had got divorced or lost a child while he was working on Huygens, they'd probably have forgotten to put any science in the article at all...

Re:We have a technical term for it

[mstefanus]

...the Cassini team crafted a response plan that centered on reducing the Doppler shift sufficiently to keep the data signal within the recognition range of the receiver. They accomplished this trick by altering the planned trajectory of Cassini.

But don't you think lauching a class-2 probe and use it to relay long burst high power electromagnetic wave emitted from the deflector dish a simpler solution?

Obvious

[dsanfte]

THIS kind of stuff is what NASA needs to be held accountable for. Had it not been for this engineer, the Huygens mission would have failed due to complacency and bureauocracy, having been rejected and deemed "unnecessary".

What is wrong with NASA? Here's a great example.

Re:Obvious

[erick99]

To be fair, it was not just NASA, according to the article this was

a collaboration with the European Space Agency, Cassini, in addition to its own suite of scientific instruments designed to scan Saturn and its moons, carries a hitchhiker--a lander probe called Huygens.

Re:Obvious

[TykeClone]

What is wrong with NASA?

As you answered in the previous paragraph - it's the non-scientist administrators.

Re:Obvious

[Anonymous Coward]

Troll.

The board discovered that Alenia Spazio SpA, the Rome-based company that built the radio link, had properly anticipated the need to make the receiver sensitive over a wide enough range of frequencies to detect Huygens's carrier signal even when Doppler shifted. But it had overlooked another subtle consequence: Doppler shift would affect not just the frequency of the carrier wave that the probe's vital observations would be transmitted on but also the digitally encoded signal itself. In effect, the shift would push the signal out of synch with the timing scheme used to recover data from the phase-modulated carrier.

NASA's cocked-up elsewhere, but this wasn't their cock-up.

Re:Obvious

[Talian]

Ya, lets not bother calling out the company who made the piece and for business reasons didn't want to release the specs.

Should NASA have pushed harder? Maybe, but that also gets them grief from the other side, too hard to work with, etc.

Re:Obvious

[Smilodon]

From the article:

"Nor was there any 'nation-to-nation finger-pointing."

Thank goodness they weren't the typical Slashdotter these days (apparently)...

Re:Obvious

[Jugalator]

Yes, it's more of an example of the fruit from some great cooperation. Congrats to both NASA and ESA for being successful here. :-)

Re:Obvious

[Jugalator]

Had it not been for this engineer, the Huygens mission would have failed due to complacency and bureauocracy, having been rejected and deemed "unnecessary".

Uh, yeah, that's a way to look negatively on it...

Another way to do it is to look at with which success both parties assembled a NASA/ESA cooperation to solve this critical problem, and did it.

If we're only going to only see the problems, no organization or company is successful. If we're going to look at those solving the problems in time to become successful in time, we start seeing those that are truly successful. I mean, if NASA had done anything truly wrong here, it would be to have ignored ESA, but they didn't.

Re:Obvious

[Anonymous Coward]

So they put K56 on the lander and v.90 on the orbiter?

Re:Obvious

[mefus]

THIS kind of stuff is what NASA needs to be held accountable for.

Yeah, shame on NASA for following its edict as a publicly held organization. Shame on them for reverse engineering the specifications of the receiver instead of just signing the NDA.

And, shame on them for being required to assume the contractor made something suitable to the job at hand, on a project run by the ESA.

Damn commies.

Sheesh.

Re:Obvious

[Anonymous Coward]

FLAME ON.

Fuck you asswipe. I bet you've never worked on a mission critical project you your entire life. Your ignorant comment shows that you live in a padded room and never leave the house.

Who is accountable here? NASA has been underfunded for years, and it is required by the same elected idiots to spread the work out for political reasons. House member X needs some pork? We'll make sure that the local bicycle repair shop in his district gets some 'Hi-Tech' contract.

If read the article (and you had any brains) you would be asking yourself why NASA would be sending this out to these bozos in Italy? It's not that they are in Italy, but it is obvious that this work was put there because of a political deal with the ESA. If NASA was really in charge they would pick the best, no matter who or where they are.

This also obviously happened with the crashed Genesis probe. Some political animal made sure that Lockheed-Martin got a contract because they were in his (very few women in congress) district.

The worst part is that you support he incompetent creeps who force these bad decisions in the first place: you blame NASA. Instead of asking why the work goes where it does, and asking who makes these decisions, you have to make you tiny dick look big by saying "NASA needs to be held accounable". The problems are much further up the food chain, but you are too ignorant and far too stupid to figure it out.

Do us all a favor. Go back to you game boy and porno and let responsible adults talk about the real problems.

what esa makes to people

[Anonymous Coward]

looks quite old for 26 year old.

Re:what esa makes to people

[erick99]

The article says he is a 26-year EASA veteran, it does not say that he is 26 years old. Though, I thought the same thing on my first pass and had to re-read it.

Re:what esa makes to people

[Unnngh!]

Actually it says he is a "...26-year ESA veteran", but you were closer than the other guy;)

Well...

[White Rabbit 132]

There is a reason we do not race in space iny more; we might just get where we want.
I, for one, am all for letting other people do it. If their trajectories are off, well then, hey, I'll still have my modem.

Not amazing at al really.

[reality-bytes]

The problem was uncovered because the communications equipment had something like 14 sceduled tests en-route to Saturn using simulated data from Huygens to Cassini.

Obviously, the first scheduled test showed up the problem so from there (in 2000) they knew they had something to fix. 3-4 years to fix a problem using a known set of tools isn't too bad ;)

Re:Not amazing at al really.

[Tablizer]

The problem was uncovered because the communications equipment had something like 14 sceduled tests en-route to Saturn using simulated data from Huygens to Cassini. Obviously, the first scheduled test showed up the problem so from there...

This conflicts with my reading of the article. The techie who suspected a problem had to fight tooth and nail to schedule a decent test run. The standard set of tests would not have detected dopler issues.

Re:Not amazing at al really.

[Bingo Foo]

This conflicts with my reading of the article.

This is Slashdot. We don't point out inconsistencies and conflicts with the content of articles; we only point out conflicts with our preconceptions and prejudices. Please rephrase your post.

Re:Not amazing at al really.

[Tablizer]

Since the moderators seem to think I read it wrong, here is an except:

In proposing this more complex test with simulated telemetry, Smeds "had to argue with those who didn't think it was necessary," recalled JPL's Mitchell. Smeds was persistent and continued championing the test even after it was initially rejected. In the end, with the backing of Sollazzo and Huygens's project scientist, Jean-Pierre Lebreton, Smeds's plan was accepted because it was easy to do, even though hardly anybody seemed to think it was worth doing.

Dont Bother Reading Long Article

[johnatjohnytech]

Skimmed through it. They are just gonna use fancy flying to solve any issues with the dopler shift. Writer gushes to much scientist love in this article.

Re:Dont Bother Reading Long Article

[orac2]

Sure, everyone knows that a)something Doppler related went wrong with Huygens and b) they fixed it with "fancy flying", but that's like saying don't bother to read a history of World War II because everyone knows a) Hitler started it and b) the Allies won.

The point of the story was to explain the problem with a level of accuracy and detail that was simply missing from most report and to tell the story of some stone-cold great work by an engineer, something of interest to most engineers, and I would hazard, to most slashdotters.

As far as I am aware, no-one else has told the story of how Boris Smeds pushed through the comms test that showed something was wrong, despite intial rejection and then later, modified it on the fly to reveal the problem was Doppler related, saving months of delay. Learning about his example of how to be a great engineers is the article's real utility, not teaching Spectrum readers how to fix Titan landers.

Disclaimer -- I edited this story for IEEE Spectrum

Re:Dont Bother Reading Long Article

[Anonymous Coward]

My only question is: how did they dispose of thos who opposed him in making the tests?

Re:Dont Bother Reading Long Article

[orac2]

As far as I know they didn't.

Re:Dont Bother Reading Long Article

[loose electron]

1. I did read the article.
2. It is well written and oriented to engineers.
3. There is good depth and detail there.
4. A lot of slash-dot folks use this as place to spout babble without reading the content. For hundreds of examples, just look at all the assorted postings.
5. Consider the source, no need to defend your work to the "babble rousers"

Disclaimer: I am a member of the IEEE

Re:Dont Bother Reading Long Article

[orac2]

1. Thanks for taking the time
2. Thank you - although Jim Oberg, the article's author deserves much of the credit.
3. Thank you, but see (2) re: Oberg
4. I know, I know, and I should be used to it by now, but when it's your own work, one's skin is just that little bit thinner.
5. See (4). (Actually one of my favorite /. experiences was when some slashgit was ragging on an article I edited on the history of id software, when Carmack himself roused himself to reply saying the article was "quiet good." Boo-yah!)

Nice to hear from a member!

Saving Pvt Huygens

[nounderscores]

This time the probe is the mission.

"I tell you this Huygens had better develop a better theory of light or something..." -Cpt Miller

"Nasa has lost so many probes. We can't let them lose any more. We have to bring the data back." - Boris Smeds

Re:Saving Pvt Huygens

[heptapod]

NASA not Nasa. It's an acronym which stands for "National Aeronautics and Space Administration".

Hooray for the Engineer

[Space_Soldier]

Engineer 1 : 0 Politics Mission saved!

NOOO!!!

[Tibor the Hun]

I was trying to be funny! Don't mod me Informative! Woe to all who read the OP and consider it Informative.

It was a reference to star trek!

Re:NOOO!!!

[Anonymous Coward]

now that's informative

Re:NOOO!!!

[Anonymous Coward]

Given this is Slashdot I'd bet there are some that view Star Trek as absolute reality. Aparently some of them have mod points as well. *shudder*

Re:NOOO!!!

[Anonymous Coward]

RICK BERMAN ROT IN HELL!!!

I could have helped out with this

[kalpol]

I drove a Fiat for years. I could have told them an Italian radio wasn't gonna work. :)

Re:I could have helped out with this

[kfg]

I own a FIAT, please, give what you can
I'm broken and tired and footsore young man
I walk the cold earth with my hat in my hand
Saying, I own a FIAT, please. . .give what you can.

Yeah, I, ummmmm, 'drove' a FIAT for years too. As a friend of mine noted just last night, "never piss off a songwriter.

Driving a FIAT and trying to listen to the radio is like being punished for the same thing twice.

It worked out ok though, I now use its cylinder head as a towel rack (pull the cam boxes, leaves lots of long studs to hang things off of).

KFG

Re:I could have helped out with this

[Anonymous Coward]

Ever heard of a guy named Marconi?

Re:I could have helped out with this

[red floyd]

Drove a Fiat 128 for about 3 years. Had to keep replacing the clutch cable every 3000 miles or so (it rubbed against something else).

It finally died on the 101 freeway in LA when it threw a rod.

Doppler shifting radio waves?

[penguinoid]

Forgive my ingorance, but don't you have to me going *really fucking fast* if you want to make any noticeable doppler shift in light?

Re:Doppler shifting radio waves?

[dougmc]

but don't you have to me going *really fucking fast* if you want to make any noticeable doppler shift in light?

Yes and no. Ultimately, it depends on how fast you consider `really fucking fast' to be.

Certainly, satellites around the Earth qualify -- if you want to be truly successful working with amateur (ham) satellites, you need to adjust for the doppler shifts., especially at the higher frequencies. If you don't, you'll only be successful when the doppler shift is small -- basically, when the satellite is as high in the sky as it's going to get in this pass.

Suppose your signal is at 441 mHz, and the signal is only 20 kHz wide. It only takes a 0.005% shift in the frequency to move that signal 20 kHz so you can't detect it at all, and doppler shifts seen by objects in low Earth orbit satellites can be a good deal larger than that.

Re:Doppler shifting radio waves?

[Fortran IV]

If you want to see a change in color of visible light (as with receding galaxies), yes. If you want a detectable change in radio frequency, no. Doppler radar can measure the speeds of clouds and rain, which are not only far sublight but far subsonic as well.

Re:Doppler shifting radio waves?

[Anonymous Coward]

Ever been done for speeding by radar gun?

Re:Doppler shifting radio waves?

[dougmc]

and doppler shifts seen by objects in low Earth orbit satellites can be a good deal larger than that.

Let me correct myself. At 440 mHz, I've seen Doppler shifts of low Earth satellites around 10 kHz. This is enough that you'll still pick up the signal, but it'll be really garbled. You definately do need to adjust for this when talking to these satellites using the 440 mHz band. (In the 2m/144 mHz band, the effect is smaller and can almost be ignored. However, many satellites transmit on one band and receive on another, so Doppler shifts are always something to keep in mind.)

Of course, in the case of the probe mentioned, the Doppler shift for the radio was considered, but the effect on the data stream received was not. Slightly different problem, but still very much related.

Ultimately, once you get into space, relativistic effects are very real and detectable, even without warp drives and impulse engines that can get you to 0.5 c. (Actually, they're often noticed on the Earth too under certain conditions. It's just a matter of having something sensitive enough ...)

Re:Doppler shifting radio waves?

[cellocgw]

Forgive my ingorance, but don't you have to me going *really fucking fast* if you want to make any noticeable doppler shift in light?
Well, you could RTFA :-), but here's the answer: Doppler shifts occur parallel to the direction of motion. If you view at an angle to that motion, the shift reduces by the cosine. Cassini will drop Huygens and then run like hell to the side, so to speak, to be in position by the time Huygens reaches the atmosphere.

Re:Doppler shifting radio waves?

[Ruie]

The key is "noticeable". Our hardware is very precise nowadays and the relative shift is approximately proportional to v/c for small v.

The relative velocity was quoted as 5.5km/sec which means v/c=0.000018. This is not such a small number.

Furthermore, even though the frequency changes little, the phase can shift a lot. The change in phase is proportional to v/c times the number of cycles in the segment you are examining - and there are a lot of cycles in 1/8192 second chunk of the microwave signal they are using to communicate.

Lastly, the length of the transmission also matters - 2 hour transmission of 1/8192 sec chunks amounts to approximately 60 million chunks. If you multiply the doppler shift above by the number of chunks you get approx 1000 - i.e. the chunk timing will shift through completely 1000 times during transmission. (In other words you will be drifting in and out of sync with transmission rate 1000 times during descent.. A sure way to get most data scrambled)

Re:Doppler shifting radio waves?

[ch-chuck]

but don't you have to me going *really fucking fast* if you want to make any noticeable doppler shift in light?

That's what I said to the radar cop but he gave me a ticket anyway.

Re:Doppler shifting radio waves?

[mikael]

The amount of doppler shift is proportional to frequency and velocity. But it wasn't the change in signal frequency alone, it was the change in length of data timing as well.


The general equation is:

fdoppler = (frest * velocity )/ c

where:
fdop = frequency after doppler shift
frest = frequency before doppler shift
velocity = speed of object relative to oberver
c = speed of light


Although radio waves have a longer wavelength (kilohertz/megahertz) than light (terahertz+), the
effect is less noticable, but still significant.

According to the article, the doppler shift was +/-38 Kilohertz. Given the fact that data was being transmitted on an 8/16 Kilohertz carrier wave, that's a rather significant change.

This is enough difference to allow police speed radar traps to work, and for researchers to measure the wind speeds inside tornado's.

Re:Doppler shifting radio waves?

[cdberg]

Well, consider this: You can hear the doppler shift quite fine when the much-quoted ambulance speeds by, even though most ambulances I've seen don't make anything close to Mach 1.

Re:Doppler shifting radio waves?

[QuantumFTL]

The general equation is:

fdoppler = (frest * velocity )/ c

Not to be pedantic, but I think it should be mentioned that this is a first order approximation to the relativistic doppler shift as seen (here):
fdoppler = frest * Sqrt(1-beta^2)/(1-beta)
where beta = velocity / c

Not terribly important here, but definitely so in other astronomical fields.

This is enough difference to allow police speed radar traps to work, and for researchers to measure the wind speeds inside tornado's.

Not only that, but I've personally measured changes in velocity of an object on the order of 10s of microns per second using gamma radiation doppler shift (using the Mossbauer Effect). It's really quite incredible - a simple and fun experiment to try if you can.

Cheers,
Justin

Re:Doppler shifting radio waves?

[mikael]

I viewed the web page; this is some amazing research - to be able to measure the doppler shift due to gravitational acceleration.

May not be that simple...

[Smilodon]

This is not a simple subcontractor arrangement. It is cooperation between government agencies in different governments, each of which has private contractors working for them.

Besides the obvious contractual nightmare this represents, there is also the issue of Export control between governments, which cannot be countermanded with a simple non-disclosure.

IMNAL, but I work on a similar project and you need to learn some of this stuff, sadly, to get your work done. I'm hopeful this incident will help to clear up these sort of cooperation issues in the future.

Good work in resolving this all involved! Remember Slashdotters, we explore to learn...

Re:May not be that simple...

[La Fortezza]

Remember Slashdotters, we explore to learn...

Don't we explore to exploit?

Re:May not be that simple...

[osu-neko]

Remember Slashdotters, we explore to learn...

Don't we explore to exploit?

Yes, exactly. Explore, Expand, Exploit, Exterminate.

Long vacation.

[RobertB-DC]

[NASA's] Horttor never got an explanation of why Alenia Spazio's telemetry system was built with a timing system that couldn't accommodate the Doppler shift in Huygens's telemetry. "It is a design feature of another application in Earth orbit, and they just reused it," he told Spectrum, adding, "I don't know why anyone would ever want to build it that way." (An Alenia Spazio spokeswoman said that none of the company's officials were available to comment because of a company-wide summer vacation period.)

Anyone think that the "company-wide summer vacation" may extend a little longer than originally expected?

"Hey, Tony! Glad to hear you ready for work. But why don't you go ahead and stay in Verona another month or two? Check out this web site while you're there. Ciao!"

the solution is so anticlimactic.

[WormholeFiend]

I was expecting something involving quantum fluctuations, baryon sweeps and tachyon beams.

Re:the solution is so anticlimactic.

[Fortran IV]

I know what you mean. I was expecting something about reprogramming Cassini or Huygens or both. But then I read:

...the firmware could not be altered after launch.

What? A $300M mission, and there's no provision for firmware upgrades? Even my $40 wireless hub can get firmware upgrades. Oh, wait: "Do NOT upgrade firmware on any D-Link product over a wireless connection. Failure of the device may result. Use only hard-wired network connections."

So I guess they'd have had to run a billion-mile cable first. Line noise would be a bitch, wouldn't it?

Re:the solution is so anticlimactic.

[stienman]

So I guess they'd have had to run a billion-mile cable first. Line noise would be a bitch, wouldn't it?

Who cares about line noise, I want to see the whiplash at the end of the cable when I tap it on this end. Whip that probe!

-Adam

Re:the solution is so anticlimactic.

[Fortran IV]

I want to see the whiplash at the end of the cable...

I started to answer this with something about being more worried about where they'll put the 186,000,000 miles of slack they'll have to take up as Earth and Saturn pass in their orbits, but then I realized this could go on for years. Introducing harmonic vibration in the cable so the Moon will miss it (not to mention the Sun, Mars, Jupiter, several quazilliad asteroids, Saturn's rings, and of course Saturn itself), shielding it against Earth's and Saturn's magnetospheres (and then grounding the shielding - instant new electrical supply!), the likelihood that NASA will have designed the cable port on Cassini upside down so that the probe has to be rolled over before we can plug it in - you get the idea.

Reminds me of a story about a town in west Texas (maybe Brownwood?) so dry that they got a bill through the Texas Legislature that if water was ever found on the Moon this town could try to build a pipeline to it.

Reminds me as well of when we spent nearly a week's lunches talking about the pros and cons of moving the Moon into a geostationary orbit. Permanent high (very high!) tides at two points on Earth, lunar eclipses once a night, solar eclipses once a day, very bright moonlight (but for only half the Earth) -

Clever Solution

[SparksMcGee]

It looks like the relative velocity of Cassini to Huygens actually *was* high enough to lend a singificant Doppler shift, so correspondingly the data rate was massively compressed--like the frequency of a racecar coming towards you getting higher and higher, except in this case its bitrate instead of sound. The antenna was only designed to "listen" for a fairly static bitrate --like if once the car got close enough and the sound frequency high enough you just stopped hearing it. So instead they're altering the flightpaths so that Cassini is now far enough away from Huygens that the broadcast vector is mostly perpendicular, with minimal Doppler shift -- think about standing very far away from the racetrack instead of right in front of the car. The total distance between you and the car changes by much less, so you hear more of a constant hum than a higher and higher frequency, analogous to the drone of a jet plane passing far overhead. Because the Doppler shift is minimal, the antenna can now receive data at a nearly constant bitrate it can handle. Very nicely done.

Re:Clever Solution

[orac2]

It is so nice when someone actually bothers to read the bloody article. Thank you!

Disclaimer: I edited this story for IEEE Spectrum

Re:Clever Solution

[mefus]

So instead they're altering the flightpaths so that Cassini is now far enough away from Huygens that the broadcast vector is mostly perpendicular, with minimal Doppler shift -- think about standing very far away from the racetrack instead of right in front of the car.

Today on slashdot I learned that angle of incidence is a function of distance. Thanks for the "informative" post.

Swedish scientist...

[rackhamh]

Meh. I'm feeling pretty neutral about this article.

SDR

[wowbagger]

What I find hard to beleive is that the data slicer for the radio was not a chunk of code running on a processor, rather than a hardwired circuit.

I do SDR (Software Defined Radio) for a living - doing a data slicer like this isn't very hard at all. Why they couldn't just reprogram the slicer to take into account the bit timing shift - or better still, why weren't they resyncing on the zero crossings of the signal so they could deal with bit timing errors automatically?

Hell, for that matter why don't they have an option to route the recovered signal verbatim to the main transmitter and send that to earth - and do the signal processing here? NASA *used* to have the philosophy of "all the bits to earth" - the wouldn't even use lossless data compression lest the signal be corrupted and unrecoverable.

Re:SDR

[Anonymous Coward]

Why they couldn't just reprogram the slicer to take into account the bit timing

because as the article said, the firmware was not designed for being reflashed remotely.

Re:SDR

[Anonymous Coward]

Keep in mind that Cassini was launched in 1997. That means that initial system design was begun probably somewhere around 1990 or so. What was the state of SDR in 1990?

Re:SDR

[bware]

Were you doing SDR in 1997 when Cassini was launched? Were you doing it in 1987 when Cassini was being designed?

All the bits don't come to earth because Cassini doesn't have continuous data transmission to the Earth. That would be extremely expensive. DSN time is charged out the wazoo. I don't know Cassini specs, but most missions plan on recording data and shipping it back to Earth when DSN time is allocated. It isn't continous. DSN has other things to do.

You want to send the raw analog signals ("verbatim"?) back to Earth for signal processing in real time? That doesn't even really make sense.

Re:SDR

[Anonymous Coward]

The signal strength is very weak. We'll be using the 100 meter Greenbanks telescope, as well as the VLA, Parkes and Mauna Kea radio telescopes to record the signal on the ground, but the primary plan is still the Cassini orbiter.

This isn't the only screw-up for Alenia this mission. Look for articles involving the Ka Band Translator if you're interested. You may not find many, it hasn't been covered very publicly. Basically, we can no longer send a Ka band uplink to the spacecraft becasue the Alenia built receiver broke. See Paragraph 10 here

Re:SDR

[Anonymous Coward]

One other thing to consider - even if they had the technology for SDR back in 1987, the devices they fly on these missions have to be radiation hardened, which probably wouldn't have been the case.

Re:SDR

[orac2]

why don't they have an option to route the recovered signal verbatim to the main transmitter and send that to earth

The big dish they use to transmit to Earth is also the dish that will be used to pick up Huygen's signal -- it can't be pointing in two places at once.

Re:SDR

[wowbagger]

Yes, I *was* doing SDR in 1997. I was in college in 1987, but this sort of demodulation has been done since the 1960's.

The fact that the slicer couldn't be reflashed in flight is just plain stupid - and that is my point.

And as for sending the raw signals - I did not say "make that the only option" - I said "why is that NOT an option". The whole thing about designing spacecraft is to have as much flexibility as possible so that WHEN the unexpected happens, you have a shot at a work-around.

Re:SDR

[twiddlingbits]

DSN is saturated and time slices are VERY hard to get. It needs to be upgraded, but there is not any money. NASA will spend 10's of millions on a probe but won't spend any on the data network to get the probe's data to the ground. In part, due to the saturation of DSN, most missions now have to have an on-board data recorder that holds anywhere from 24 hours to 7 days of data for compressed delivery when a slot is open. That adds costs and weight to every mission.

Re:SDR

[djvern]

you just contradicted yourself! If you "send all the bits" then your implying that you've already decoded things! If you want to send back the raw stream, sampled, then it would be enourmous amounts of data. Enough to occupy Cassini for the rest of its mission. Do the math: the telemetry subcarrier is about 100kHz away from the carrier signal, so, you'll need a recording bandwidth of about 500kHz just to get the first harmonic. 500kHz sampled at 8 bits per sample, complex, for 4 hours is over 14 gigabytes. You dont want to have to send that back to earth.

Re:SDR

[wowbagger]

No, I did not.

First of all, you obviously do not understand how to apply the Nyquist criterion, as the Nyquist limit is set by the BANDWIDTH of the signal of interest. You can take a 100kHz IF and sample it at 16ksample/sec if the signal of interest is only 8kHz wide - indeed this is a common way to take an bandwidth limited IF at a high frequency and both sample it and downshift it at the same time.

Secondly, what I was talking about was quite literally taking the analog IF, shunting it to the main transmitter, and sending it. No sampling required - this is much the same trick that analog AMSATS used to redirect the signal.

AND just to reiterate - I am not saying you do that as the ONLY means of communication with the probe. You have that as an emergency, "AW SHIT" backup mode.

Re:SDR

[Rich0]

I've seen this mentioned in other missions as well...

You'd think that the ground-based part of the mission would be the simplest part to execute well. No weight penalties, no fuel costs, no need for crazy test regimins since if something doesn't work right you just need to drive out and swap parts, etc.

I'm sure the DSN is a fairly costly network to build, but if they already have transmitter sites desiging more should just be an academic exercise. Everything is super-high gain, so you could probably have two ground transmitters on the same frequency 100 feet from each other as long as the probes they are talking to were reasonably well-seaparted in the sky.

All you really need is a couple of cheap plots of land with electricity and telecom access. (Telecom isn't even essential - you could use satelite.)

Re:SDR

[Rich0]

I think he is talking about taking the input signal from the probe, and simply amplifying the signal at Cassini and rebroadcasting on the same frequency to earth. That of course assumes the frequency is compatible with the high-gain antenna. If no signal processing occurs other than just a simple amplifier, you avoid issues like the above. On earth you simply record the entire signal with modulation and then can descramble it at leisure.

Re:SDR

[Zoxed]

To be honest I have not heard of SDR, so I do not know how old the technology is, but do not forget that Cassini/Huygens was launched in 1997, so was probably spec'ed in the early 90s. And most of the technology chosen would have been reliable, proven stuff, so was probably state-of-the-art nearly 20 years ago !!

>why don't they have an option to route the recovered signal verbatim to the main transmitter and send that to earth

Because the same antenna is used to communicate with Huygens and Earth !
http://sci.esa.int/science-e/www/object/index.c fm? fobjectid=35026&fbodylongid=1632

I guess the benefits of having a real-time relay capability are outwayed by the extra cost of the additional antenna. Also I am not sure about the transmission rates: I could not find any numbers, but IIRC Huygens sends a burst of data during it's short operational life, and I am not sure if the Earth link would cope with that rate in real-time.

Proprietary

[Eryximachus]

A shining example of the promblems with proprietary design. No one can see what's wrong with it without expending a huge amount of effort. I'm just glad someone did decide to spend the effort.

Re:Proprietary

[serbanp]

The problem is not neccessarily related to open vs. closed. What is amazing is that this company (Alenia Spazio) ESA chose to use can produce such laughable, shitty equipment.

Come on, 8192 bits/second should not be that hard to manage, even by 1985 standards. I simply can't understand how come they didn't use a clock recovery scheme for synchronizing with the incoming serial stream of bits. The rate shift due to doppler effect would have been a non-issue.

The "engineers" at Alenia Spazio who designed this disgraceful POS should be given 10 whips on the bare back in a public place for shaming the Engineer name.

Wrong wrong wrong

[Manip]

The problem - Doppler effect. The fix: go read the article.

The problem was a 'undetectable' flaw in the transceiver the solution exploited the Doppler effect, by slowing down the satellite they were able to change the way in which the receiver received the transmissions and recover all the data.

Re:Wrong wrong wrong

[mefus]

The problem - Doppler effect.

the solution exploited the Doppler effect

The problem is the solution? The Doppler effect isn't the problem, it is a part of the requirements specification, and a known quantity that has been dealt with before.

Except that in this case it wasn't: The engineered solution was for a land-based communication, which doesn't match the requirements specification. This fact was hidden by the NDAs NASA could not sign, and the company's perceived threat that providing the engineering details would give JPL a competitive advantage.

So the problem wasn't The Doppler Effect, the problem was NASA (and ESA) was developing with a blackbox they were told was engineered to the task that was not.

Slashdot needs a 'HERO' tag

[mcrbids]

While slashdot has category icons, it really REALLY needs a "hero" tag, like you'd see on Fark.

This engineer that found the problem and rallied against opposition to see that this gets fixed is, in my opinion, a total hero. The world would be a much better place if more people like him were around!

Re:Slashdot needs a 'HERO' tag

[forkazoo]

Quick, somebody register engineeringherodance.org, where we can post animated GIFs of heros of engineering dancing, so that people can become better acquainted with them! What? I'm serious. Yes, really.

[nt] I guess that makes them "metro"...

[Luyseyal]

Re:[nt] I guess that makes them "metro"...

[AKAImBatman]

One of these days, you'll have to tell me how you managed to post an empty comment. Slashdot is supposed to reject that sort of thing. :-)

Don't bother watching the Movie

[jacksdl]

The Bruce Willis character _is_ a dead person!

Whats wrong with Proprietary

[Qzukk]

You mean "What is wrong with proprietary?" right? After all, the entirety of this problem was because NASA bought a black box proprietary technology, and without access to its specs could only pray that it performed as advertised.

In this case, the black box didn't meet the required standards, but there was no way NASA could have known that this company built the black box out of off-the-shelf terrestrial design principles unfit for cosmic use.

Re:Whats wrong with Proprietary

[Suidae]

there was no way NASA could have known that this company built the black box out of off-the-shelf terrestrial design principles unfit for cosmic use

Well, for near-earth satts anyway.

And they would have known it wouldn't work if they had done the test in the first place, but they decided it was too expensive.

The guy from the article just had the insight and peristance to run a test that he knew should have been run before.

As a bonus he also figured out how to fix the problem.

RTFA

[scribblej]

Is *IS* a "software" radio and not hardware. It's implemented in "firmware" and they say they could have changed it easily, except there's apparently no way to do so after launch.

The problem is they didn't find this problem until AFTER launch. good timing, right?

Re:RTFA

[wowbagger]

And that is my point - why did they make it so that they could not reflash it in flight?

And again, why did they not design the slicer to resync on zero crossings, which would have prevented the problem in the first place?

Re:RTFA

[Suidae]

The software was from a design used in earth sats, the ability to deal with doppler shift like that was not part of its design spec (I wonder if NASA got ripped of because they probably paid for a custom radio module and they got an off-the-shelf design).

There were lots of ways the receiver could have been done that would have been better, but it wasn't done that way, and they didnt' have the code, nor any way to fix it remotely anyway.

Faster, Better, Cheaper. Pick two.

Re:RTFA

[John Miles]

And again, why did they not design the slicer to resync on zero crossings

It's a BPSK receiver, so the zero crossings are the data. I would think the decoder would look like a fast PLL whose center frequency corresponds to the nominal data rate, with enough locking range to handle Doppler-induced variations. Guess there was little or no locking range after all.

Re:RTFA

[wowbagger]

No, in a BPSK receiver you sample between the zero crossings, because you switch phase at the zero crossings. If you switch phase elsewhere, you cause ENORMOUS spectral growth as the phase switch looks like an step function (a.k.a. the first integral of a Dirac impulse).

So, you trigger on the zero crossings, wait a portion of the bit time, then sample the signal.

Re:RTFA

[John Miles]

Right; I didn't phrase that very well. The zero crossings contain the signal information, but you don't want to rely solely on them to regenerate the clock you use to sample at the bit-cell centers.

If you try to detect zero crossings and derive any timing information from them, then you're going to have to discriminate against false triggering at the phase transitions themselves. A frequency-domain solution, as opposed to a time-domain one, won't have that problem. (I'll admit to not knowing how it's done commercially, though.)

Re:RTFA

[wowbagger]

The phase transitions happen at the zero crossings - otherwise you get HUGE spectral regrowth.

Re:RTFA

[John Miles]

Well, no, they don't, not really. When a phase transition happens, there is no zero crossing. The waveform hits zero, then flips its first derivative and heads back where it came from.

If you look for those events in the amplitude domain with a simple trigger circuit, you will have no noise immunity to speak of.

Re:RTFA

[wowbagger]

OK, if you want to put it like that, yes, there is no zero *crossing*.

But the signal still goes to zero(ish), and that is what you use as your locking point, so we were saying the same thing.

Normally, you'd run the signal through a squaring function, then look for signal minima, then feed those into a filtering function to determine the slice point.

Or, if you are looking for a slightly simpler decoder, you have a bit timer that retriggers every bit time. You reset it at any zero crossing (after appropriately narrow band filtering the signal, of course), and sample at 1/2 bit time from when the timer triggers. For noise immunity, I'd sample at 1/4, 1/2, and 3/4 bit time and use a weighted average to determine the bit value. You can deal with a hell of a lot of bit time shift with a decoder like that, and unless you have a run of phase reversals you get enough zero crossings to sync (and you can design your data encoder to provide for those crossings, either with HLDC type encoding, a P/N spreader, or other approaches).

In any case, it't DSP 101 to make a tracking loop for that kind of signal that can deal with enormous bit time errors.

But then again, I design test equipment, so I am always designing my decoders to deal with severely broken encoders.

Re:RTFA

[John Miles]

For noise immunity, I'd sample at 1/4, 1/2, and 3/4 bit time and use a weighted average to determine the bit value.

Makes sense. Even with a series of alternating phase reversals you still have one "real" zero crossing per bit cell, at least with traditional BPSK. It could be detected reliably, I guess, but I'd still be tempted to use a tracking filter centered in the baseband spectrum to regenerate a sampling clock. That being said, I'm sort of talking out of my ass since I've never built a BPSK codec. :-P For all I know, some bit patterns might generate a big honking Bessel null right where I want to lock my PLL.

But then again, I design test equipment, so I am always designing my decoders to deal with severely broken encoders.

Yeah, I've seen enough of those in MP3-land to do me for awhile...

I know Alenia

[Anonymous Coward]

... having worked with some of them. Actually that is exagerating it slightly: I worked and they, well, did not. Nothing, absolutely nothing will surprise me about that sorry lot.

Well, I guess anyone there fired for incompetence will surprise me.

Article Summary

[Anonymous Coward]

Cassini/Huygens never went through full-up communications tests on the ground, and this worried some ESA folks. Swedish scientist working in Germany is asked to test system while probe is somewhere between the orbits of Mars and Jupiter, and discovers major flaw in Cassini's receiver. The receiver cannot properly recover signals that have certain Doppler shifts. Problem lies with Italian radio manufacturer who re-used a design from an Earth-orbit system, but refused to release design data to reviewers earlier. Solution was to alter Cassini's trajectory to avoid doppler, possible because there is plenty of fuel.

SDR

[jacksdl]

Note that the launch was in 1997 (and the design was a few years older than that). Was SDR a mature technology in that time period?

Re:That's Switzerland.

[Fiddy Cent]

they're both neutral

You needed to RTFA for your car

[Anonymous Coward]

In this case, RTFA stands for "remember the fine acronym".

A German car enthusiast told me what FIAT really stands for "Fehler in allen Teilen", which translated means mistakes/flaws in every part/component.

Hang on...

[trackguy]

What's a Huygens lander?

Re:Hang on...

[trackguy]

Ignore me, I have a cold. Or possibly a strange comms defect.

Fix It Again, Tony

[Anonymous Coward]

n/m

I think I see a trend...

[Cragen]

in the way people post here. The first bunch of well-rated replies are generally funny. The second bunch of well-rated replies is generally something like "WTF?" The third bunch (or fourth) is generally the guys who actually know something about the subject, but are not always reall the experts. The fourth bunch is generally the experts weighing in (like doing a cannonball dive at the pool). The rest of the posts after that are kinda "oh. cool" or "WTF?", again from the second bunch. (I'm pretty much a "second-buncher" myself.) Ever notice that? I wonder if there's any way we could like get the fourth bunch a head's up so they could weigh in sooner. Then us "second-bunchers" would only have to reply once, after the fourth-bunch, rather than before. That would really save a lot of time, you know. Maybe not. I thought you all should know this. Thank you very much.

A great hack!

[renehollan]

And this, my friends, is an example of a great hack (and, by extention, a great hacker).

Kudos. A relatively unknown engineer suddenly earned a great deal of respect from me.

Some Numbers

[follower_of_christ]

LAST JUNE, SCIENTISTS WERE THRILLED when NASA's Cassini probe successfully began orbiting Saturn after a 3.5-billion-kilometer, seven-year journey across the solar system. The 6-ton spacecraft immediately started returning spectacular pictures of the planet

3.5 Billion km Divided by 7 Years Divided by 365 Days Divided by 24 Hours gives you the aproximate velocity at which Cassini was travelling for the last 7 years in Km/h

Travel Velocity: 2,976,190.48 Km/h
Speed of Light: 1,079,252,849.00 Km/h(link)

Using the equation: KE = 1/2 * Mass * Velocity Squared (link) we get

Mass: 1 ton = 907.18474 kg - 6 tons = 5443.10844 kg (Ton Conversion Number Link)
Velocity: 2,976,190,476 m/h is = 178,571,428,560 m/s

KE = 0.5 * (5443.10844) * (178,571,428,560.0)^2 = 86,784,254,453,177,329,714,641,182.592 Joules
8.68 x 10 25 J (Amount of energy it takes for Cassini to go that fast)? Can someone help me with this? If so, how is this accomplished?
9.53 x 10 19 J (Consumption of energy by the USA in 1995) (link)

Re:Some Numbers

[renehollan]

Er, I get 57077 km/hour or 15855 m/s.

So, KE = 684 x 10^9 J.

I thought, perhaps, that you used a British billion 10^12 instead of an American Billion 10^9, but I'd still not get your numbers.

Re:Some Numbers

[sexylicious]

15 km/s is more reasonable because the delta-v needed to go from earth to saturn is on the order of that much. 57 km/s sounds more like Neptune.

As for how they got it going that fast, you have to remember that the velocity that you came up with is an average. Actual orbital velocities vary greatly. The other thing is that the vehicle had some fun with gravity assists (angular momentum transfers), and other planets. The initial velocity when it left earth orbit couldn't have been much more than 12 to 15 km/s.

Re:Some Numbers

[renehollan]

I never really understood gravity assists. I understand how they can change angular momentum of a craft, but, kinetic entergy (and thus speed (the magnitude of velocity)) would remain the same at equal distances from the assisting body, no (since gravity is a conservative force)?

Re:Some Numbers

[renehollan]

I wrote: since gravity is a conservative force.

More correctly: the force of gravity gives rise to a conservative field.

Re:Some Numbers

[daveo0331]

I got the same thing you got. The grandparent is off by a factor of exactly 52 1/7, which is exactly the number of weeks in a [365 day] year. It looks like after dividing by 7 (as in the travel time to Saturn being 7 years) he divided by 7 again instead of dividing by 365.

Re:Some Numbers

[zenyu]

I never really understood gravity assists. I understand how they can change angular momentum of a craft, but, kinetic entergy (and thus speed (the magnitude of velocity)) would remain the same at equal distances from the assisting body, no (since gravity is a conservative force)?

The trick is to find a planet that's moving relative to the spacecraft.

Imagine flying past a non-moving body, this will change your course, but assuming don't hit too many things you should be traveling at the same speed. Now imagine flying past a planet and but it's moving away from you, now you will slow down that planet bringing it closer to the sun, and you will speed up. (For simplicity you can assume that you are heading toward the planet perpendicular to it's motion.)

Re:Some Numbers

[Anonymous Coward]

Minor problem with your math:
3,500,000,000 / 7 / 365 / 24 comes out to roughly 57,000 km/h, not the nearly 3 million that you started your calculations with. This would change the KE equation, to approximately 0.5 * (5443) * (57000^2), which is equivalent to close to 8.8 x 10^12. A much more manageable number, especially when you consider gravity assists from the sun and multiple planets along the way.

Re:Some Numbers

[renehollan]

< light bulb on > Ah! < light bulb off > While the planet will exert a force with a component in opposition to my direction of motion after I pass it similar to the force it exerted in my direction of motion before I passed it; having moved, the magnitude of this force will be less (the planet is further away from me). I thus experience a net accellation and the planet a net decelleration.

As with all insights, once understood, this ranks up there with "Duuuuh!".

Thanks.

Re:Some Numbers

[renehollan]

64 looks painful and 69 smells fishy.

Re:Some Numbers

[sexylicious]

What gravity assists do can be thought of in this way:

Think of ALL orbits as ellipses (this will avoid confusion).
Realize that the ellipse pictured in your head is the path that you will travel as you orbit something, with one focii of the ellipse at the center of mass of the object you are orbiting.
The result of one of the ellipse's focii being the object you are orbiting is that you will have a maximum and minimum altitude relative to that planet. (A result of this thought experiment, rather.)
You will swing really fast around the planet you are orbiting when you are closest to it. Then you will be sent on your way away from the planet, only to fall back down.

BUT! Let's say you added another planet at the OTHER focii. But let's make it simpler (in terms of the big picture) and say that the planet will be at the focii when you get near it. In other words, that other planet's orbital path puts it dead center on the focii of your orbit's ellipse just at the time that you happen to be close to that ellipse.

What will happen is that the gravity of this new, second planet will influence you more and more as you get closer to it. It gets to a point where your orbit will be changed so much by this new planet that you are travelling in a different direction.
If done properly, your gravity assist comes when you happen to swing around this second planet. Remember that as you get close to the body you are orbiting, you gain speed. And since as you get closer to the second planet, you are orbiting it more and more, this new speed you encounter can increase or decrease your true velocity. You are no longer really on the orbit around the first body. Instead, you are orbiting the second body.

Now, if you were to extend this to a third body, and a fourth and so on, you'd see how the gravity assists can be staged throughout the solar system. When the next planet flings you away from it, you usually have more than enough escape velocity for that planet. You can think of gravity assists as changing the focii of the ellipse that your orbital path takes.

Granted, overlapping conic sections (ellipses, parabolas, hyperbolas, points, and circles) is the best way to think of how orbits are put together, they are a bit more complicated than that. The complication comes from the fact that there is a lot of "junk" out there that introduces noise into your system, and there is the fact that no body is a perfect sphere (which would produce a perfectly spherical gravitational field).

Re:Some Numbers

[leeward]

Interesting theory. But I have a hard time correlating it with the explanation provided by NASA.

Re:Some Numbers

[sexylicious]

I did the same thing as NASA... minus the vector math.

The patched conic method is how you visualize the vector math, and those two together are only an approximation. The vector math is kind of the mortar between the patched conic approach. Patched conics offer visualization, but to figure out the actual direction and magnitude of the velocities, you need to do vector math. =)

Hill's equations are solved if you want a more precise orbit calculation.

I fixed similar problem too!

[killmore]

I am not a rocket scientist but just a software engineer. Some years ago I worked for satellite phone company. My team was working on receiving signals from the satellites. Code had to determine signal frequency (shifted to Doppler) and delay (due to distance). Amazingly they forgot to account for satellite antenna rotation. Depending on the angle of antenna toward direction of satellite movement Doppler would significantly change. Enough that some calls at the antenna edges would be dropped. After I pointed out problem to them chaos ensued. We could not change any of the equipment and some of it was in orbit already. So I came up with software only fix. As a reward I got $1000 bonus and was moved from Engineering/Development to Quality assurance to make sure I will not cause any more problems. They did not even wanted to hear about smaller Doppler changes due to earth rotation.

Re:I fixed similar problem too!

[cheekyboy]

And I bet your boss got a fat $50k bonus for saving the companies ass and got invited to all international meetings and stuff.

Hopefully some bad ass trojan/spy ware hijacks his 4.3m etrade account and cleans it out.

I can do it in my car

[Clueless Moron]

I've got ham radio gear in my car.

I had a friend key up a dead carrier on 446 MHz while standing at the side of the road, put my car radio in SSB mode (which makes the dead carrier sound like a plain sine wave) and then I drove past him at around 100 km/hr.

At that speed, it causes a total shift of around 80 Hz, which is easily heard by ear. Quite cool.

NDAs

[orasio]

Well, signing a NDA is not a nice thing.
In fact, it's the main reason we have free systems nowadays, because RMS wasn't willing to sign a fucking NDA, so he had to start the GNU operating system.

I wouldn't sign a fucking NDA either. Noone can tell me what I can do with what I know. I wouldn't be worth much if I couldn't use my knowledge.

NDAs can have the power to prevent you from developing things, just because the whole way in which Intellectual "Property" is managed in most places. It's not a non-issue, it's a sensible thing to do to refuse to sign an NDA. Of course, it would be sensible to stop buying from the jackass that wants you to sign the damn NDA, in the first place.

NEAR Spacecraft was saved in a nail-biting finish

[EqualSlash]

If Boris Smeds was a hero for the Cassini-Huygens Mission, Ann Harch was a heroine for the $150 Million Near Earth Asteroid Rendezvous(NEAR) spacecraft mission to asteroid Eros. When an engine burn to reduce the spacecraft's approach speed went awry, the spacecraft tumbled violently and contact to it was lost for 36 hours. When they regained contact, the spacecraft was rushing at a great speed that it would pass Eros about two weeks ahead of schedule. The spacecraft had to be given new commands within 12 hours or it would miss clicking Eros altogether in the flyby. In the nerve-racking moments, Ann Harch and her colleagues rewrote new command sequences for the original program that took them 6 months to write. In a nail-biting finish the commands reached 8 minutes before the Eros flyby, just in time to enable capturing images of asteroid Eros. Ann Harch was later honored for her efforts with an asteroid being named after her.

How a down-to-the-wire computer fix at Cornell enabled a troubled spacecraft to take images of an asteroid

CU astronomer who helped save mission receives a celestial gift

BBC

[BigBadBus]

This was on the BBC last night.

I was horrified that the mistake was only found after launch, but catastrophic errors are what we've come to expect of NASA's projects. Someone should sit their engineers and managers down in a school room and tell them in a v-e-r-y s-l-o-w and VERY LOUD voice to get it right!

Great work by Smeds.

[francisew]

Boris Smeds did a great job in replacing lots of expensive tests with a series of trivial, yet critical tests.

Why weren't simple tests like these used while the spacecraft was on the ground?

These are obvious problems. When you take a transmitter and throw it into a planetary descent, this is what should be expected.

It is shocking to me that a transceiver pair isn't tested by the team assembling the spacecraft before launch!

If it can be tested in 2 days when it's in space, 48 light-speed minutes away, why can't it be tested on the ground, fully assembled?

Engineering isn't a science, but I expect that engineers desigining projects like this should be using thorough unbiased scientific testing, not only thorough design.

If they slip up like this in non-destructive tests, one has to wonder about how tests on the resistance to physical damage are carried out?

Do they simply make assumptions that all nuts & bolts are manufactured to spec? Do they assume that all parts will withstand the forces that they are requesting in spec sheets?

How can a cost of hundreds of millions of dollars be justified in creating such craft, when basic, inexpensive testing isn't being carried out? If the test would cost 30,000$ (a few days of well-paid outside experts time, plus expenses and travel), as a critical portion of a 300,000,000$ mission, how is it not done?

The only agreement that should be accepted by an agency purchasing a part is that they won't use the specifications of that part to replicate exactly the same device. I'm sure that they paid a high premium for the transceiver. Why wouldn't they have access to the documentation and spec sheets? This use of NDA's is dangerous.

It's old news for you new posters. . .

[eutychus_awakes]

At the risk of being modded redundant, buried down on page 2 or 3 of the comments list is a reason why this is a VERY old story. It's not like it just happened. . .

Off shore outsourcing proves it worth

[Anonymous Coward]

Alenia Spazio's insistence on confidentiality may have played a role in this oversight. NASA reviewers were never given the specs of the receiver..."Alenia Spazio considered JPL to be a competitor and treated the radio design as proprietary data."

Looks like off shore outsourcing proves it worth
'nuff said

Just like Apollo 13 "save" - good work, Smeds!

[no_sw_patents123]

Just a quick post from downunder here in New Zealand to say "well done, Smeds!"

This story reminded me very much of Apollo 13 and the amazing "save" of that mission, due to some excellent work by Nasa *and* the very ice-cool astronauts. ( Okay, the Apollo 13 thing was an accident, not a design-flaw, but the "fixing things on-the-fly" was similar in both these events ) .

On this "Doppler shift" problem, it's easy to heap criticism on those who didn't spot it (and some constructive criticism is in order), but at least Smeds has beautifully highlighted a potential problem for any future space missions. This problem can now be tested for, and avoided.

Well done, all those who were involved in the "fix" to save Huygens!

Re:Just like Apollo 13 "save" - good work, Smeds!

[dr_db]

Honestly, I would call Apollo 13 a design flaw. The tanks had little heaters in them (to keep the pressure up), and during the design stage the voltages were changed. Inside the tank there was also a thermostatic switch that kept the temp from getting too high.

That particular group of tanks was dropped, breaking off the fill tube inside the tank (on the ground). To empty the tank, they elected to turn on the heater to boil out the O2. The thermostatic switch welded shut, and the internal temp of the tank had reached many hundreds of degrees. This was not expected, nor detected on the ground. The heat burned off the insulation on the wires to the stirring motor.

I can't remember how they justified flying that set of tanks with the fill tube broken inside, but in flight, when the stiring motor was turned on, the wire arced to the tank body and ignited in the o2 enviroment.

Scary shit, O2. A burr from threading the pipes used to transport it sliding down the pipe can ignite the metal. Wiping a fitting with a little oil *will* give you a fire - this has brought down aircraft. The next big fear is the home o2 kits - a leaking system will flood the room to a high level of o2, and the static of walking across the rug will ignite it. As well, the fireproof nomex suits that firemen show up in will burn in that enviroment too.

shaky design?

[multi io]

According to the article, the bitstream coming out of the receiver/demodular component has a bitrate of 8192 bit/s. At a relative speed of a couple of km/s, the relative Doppler shift is roughly v/c=1/100000. So, the bitrate increases to something like 8192.08 bit/s. And that's all that's needed to make the subsequent circuit choke and lose half the data? I would say, no wonder they didn't want to reveal their design to anybody...

Re:shaky design?

[jelle]

It's probable not about the symbol rate, but the carrier frequency, which is often crystal-generated, hence must be specifically designed tunable in some fashion, otherwise is very, very stable.

Re:shaky design?

[multi io]

It's probable not about the symbol rate, but the carrier frequency, which is often crystal-generated, hence must be specifically designed tunable in some fashion, otherwise is very, very stable.

To quote from the article:

The board discovered that Alenia Spazio SpA, the Rome-based company that built the radio link, had properly anticipated the need to make the receiver sensitive over a wide enough range of frequencies to detect Huygens's carrier signal even when Doppler shifted. But it had overlooked another subtle consequence: Doppler shift would affect not just the frequency of the carrier wave that the probe's vital observations would be transmitted on but also the digitally encoded signal itself. In effect, the shift would push the signal out of synch with the timing scheme used to recover data from the phase-modulated carrier.

So, it appears that the HF receiver and demodulator work correctly even in the presence of Doppler shifting, but the "bit extractor" (which, unless I misunderstood something, must operate at only ~ 8kHz) doesn't.

Re:shaky design?

[jelle]

Woa... That teaches me to not RTFA...

I guess then my only defense arguing that it may not be bad design is that it may have to operate in very low SNR conditions? But no, even then, in today's digital world it should be simple enought to make something like that adaptive and/or tunable to much larger variations than that...

So I'll just shut up then.

Re:shaky design?

[Lord Crc]

So, the bitrate increases to something like 8192.08 bit/s. And that's all that's needed to make the subsequent circuit choke and lose half the data?

Well, the article states

In effect, the [Doppler] shift would push the signal out of synch with the timing scheme used to recover data from the phase-modulated carrier.

The problem is the timing needed to detect the phase changes, not handling slightly more bits per second. This is mentioned in the slide here which illustrates the technique used.

Re:shaky design?

[multi io]

Well, the article states

In effect, the [Doppler] shift would push the signal out of synch with the timing scheme used to recover data from the phase-modulated carrier.

My understanding of this sentence was that the phase detection/demodulation works correctly, and "timing scheme" refers to whatever they do to clock the 8192bits/s bitstream into Cassini's onboard computer (the paragraph immediately following the text you quoted also seems to suggest that).

Also, the article states that "the timing scheme was implemented by firmware loaded in Cassini's receiver". There is probably no way one could detect phase changes in a 2060 MHz carrier signal in realtime purely in software.

Confirms what we all know...

[Qrlx]

Berlusconi sucks!

Many can claim, but only on /.

[Excen]

. . . would someone be able to prove that 1+1 does in fact equal 3.

How would testing on the ground uncovered this?

[wernst]

So I'm reading this and am amazed at the engineering savvy and all, and being a former JPL contractor, am not at all surprised that a real "on the ground" test wasn't performed for financial reasons.

But I'm trying to figure out how "on the ground" testing would have discovered this problem. The actual probe and the actual spacecraft could not have been moving so fast relative to each other on a test bench to duplucate the Doppler effect it would encounter in Titan.

It would have to have been simulated on the test bench, right? But the reading of the article suggests that simulating this, even if both craft were on the test bench talking to each other, would not have been performed because no one but this guy thought to do it years after the fact.

In fact, it seems to me that if testing actual inter-craft communications HAD been done, NO ONE would have still been thinking about it years later, and the REAL PROBLEM might not have ever been considered, tested, and taken care of.

In othe words, it sure was a good thing that no one tested the communications systems on the test bench between both craft!

I'm sure I'm misunderstanding something though, so if someone knows, I'd love to hear it.

Re:How would testing on the ground uncovered this?

[Anonymous Coward]

Fomer JPL Contractor? No wonder there are so many problems. Fucktard.

houyhnhnms vs. yahoos

[shiva.singh.goel]

houyhnhnms not Huygens

Yes, you are misunderstanding.

[Anonymous Coward]

The article clearly stated that they simulated the doppler effect by computer distortions in the signal. There would also be very little doppler effect otherwise in the signal from earth. That is how they figured out it was the doppler effect doing it. Transmit without doppler distortion, no problem, transmit with doppler distortion, big problems. Easily doable on earth, all they had to do was test with a signal with doppler distortion that the engineers clearly knew would occur.

Moderators, you screwed up

[JoeBuck]

The parent is not "informative". The buggy receiver is (at least partially) a chunk of code running on a processor. Didn't you read the article?

Hint: what do you think "firmware" means? The code is in ROM, and evidently not changeable.

[nt] View Page Source (sorry abt de "sig" mixup..)

[Luyseyal]