The science return, perhaps? The recent FBC probes are neat, and produce lots of nice data, but, on a per-dollar basis, the Pioneers and Voyagers are unbeatable.
Voyager cost billions of dollars
Just under a billion, actually. This includes two flight articles, two launches, and operations.
In return, we got data on Jupiter, Saturn, Uranus, and Neptune; the Uranus and Neptune encounters are unlikely to be repeated for a very, very long time indeed.
[Cassini] cost over three billion dollars
This I agree with. Cassini is the last of the giants.
All you have to do is run the peroxide (which is, btw, far, far more concentrated than what you buy at the drugstore)
Very true -- HTP is very unpleasant stuff. One speck of the wrong kind of impurity in your tank, and the whole thing goes up.
Combine that with a simple, pressurized fuel tank instead of turbopumps, and you have a rocket engine with the minimum of moving parts.
Yeah, and atrocious performance, too.
Pressure-fed rockets are much simpler than pump-fed ones -- they have many, many, fewer moving parts -- but they require very substantial tanks, since the tank pressure has to be greater than the combustion chamber pressure in order for the propellant to flow. Since, for weight reasons, you can't want to make your tanks out of 1 inch thick steel, you're stuck with fairly low chamber pressures, and the resulting low thrust.
On top of that, monopropellant peroxide has a very low specific impulse. SMAD3 doesn't give an ISP for mono-H2O2, but it does give a value for "Monopropellant (H2O2, N2H2, etc)" as 150-225 s; combining this with some other information would suggest that H2O2 is at the lower end of this scale.
Beal et. al. got around this by running their rockets off H2O2 and LOX; SMAD has no numbers for this kind of engine, but Mark Wade's site gives numbers from 250-300 s for Beal's design. This is quite respectable, but has the downside of requiring a (mildly) cryogenic oxidizer.
Why do these news stories always begin with the project cost
Probably because the paying public wants to know. Of course, with Cassini, you've got the fact that it is the single most expensive science mission that NASA's ever launched. $3.2 billion is probably on the low end of the total cost estimates.
The cost is actually Cassini's single biggest problem. While the data that it will report back from Saturn is certainly valuable -- the only missions that flew out there were Pioneer 11 and the Voyagers, all of which were flyby missions -- it is debatable whether it should have been that expensive.
Cassini is, after all, the last of the Battlestar Galactica spacecraft. Newer missions are much smaller in scope, and, consequently, much cheaper. Even the (cancelled) Pluto-Kuiper Express mission was only to cost something like $700 million.
The reason why you don't want to launch such expensive, all-in-one-basket missions is that if something goes wrong, you've lost everything. When I heard about the reaction-wheel problems it recently had, I was very worried about what could happen to the mission. Fortunately, this has been resolved.
Bzzzt -- sorry, wrong answer. LMTs require a gravitational field (or other axial acceleration).
Now, this does not mean that space-borne LMTs are impractical -- but you do need to provide an axial thruster to supply "gravitational" acceleration. Fortunately, the required accelerations are not high, so you can use things like xenon-ion propulsion systems, which can give months of operation on a load of fuel.
Do a search on NASA's web site for more info on LMTs; you'll find a short study of spaceborne LMT feasability.
The Viking probes in the 70's landed conventionally.
As did the Surveyors on the Moon -- and they (mostly) worked. Rocket-assited deceleration isn't a piece of cake, but the theory behind it is well-developed.
Interesting enough, though, airbags were proposed for Viking; however, it was decided to go with well-established technology.
A Delta II booster will launch 5 tons to LEO, at a cost of $55M. A Titan IV will take up 21 tons, but at a cost of $214M [1]. So, per pound, the Titan is slightly cheaper; however, the two Deltas will cost less for this kind of mission.
Besides, you get better redundancy with two launchers.
[1] Isakowitz; AIAA International Reference Guide to Space Launch Systems (2nd ed.)
The problem with the satellites is the launch costs. The satellite itself is $100 million, the launch is another $300 million.
Where are you getting these figures from? The launch costs that you are quoting are almost an order of magnitude too large!
Modern launch vehicles range from the Orbital Sciences Pegasus XL, which will put 300 lbs into LEO for $15 million, to the Russian Proton, which, IIRC, will do like 30 tons to LEO for $75 million. Even the Shuttle, which is the most expensive way to fly these days, is only $100 million per launch.
Each airship is a few million dollars.
Don't forget development costs. We have nothing like this now --- you'll have to shell out big bucks for R&D.
Each airship itself is an unmanned drone which flies at 20Km, there isn't a surface to air missile in existence which can fly that high.
You may wish to mention this to a certain Gary Powers.
What do you do when some space garbage hits a satellite at 50km/hr?
Nothing. You design it to take low-speed impacts -- you build robustly, and include sufficient redundancy to ensure you can take a failure. I haven't heard of any LEO satellites which got taken out by impact with debris. Sure, the LEO environment is quite dirty, but most of it consists of very small particles (paint flakes, etc) which probably won't do too much damage to a suitably redunant satellite. And anything larger is tracked by NORAD anyways, so you can figure out if you're going to hit, and maneouver around it if necessary.
As to the technology to keep it up there.
And how are you going to keep it in place? Don't forget that stratospheric winds can get quite fast.
Engines? What about powering them? Maybe a tether? The FAA will love you, as will the pilots who have to avoid them.
The blimps are a nifty idea, but not really practical. Satellites are proven technology, and work.
Now, as for the feasibility of the LEO comsats, that's an entirely different issue.
The Microprocessor Systems course ( ECE 385) at the University of Toronto uses Linux as the base OS. Although this isn't an OS course per se -- it's a hardware course -- students still write device drivers that talk to ISA cards that they build. More details can be found at the course and lab web-pages.
As for security (students requiring root on the boxes and all), we handled this by putting all the boxes behind a switch and requiring the use of ssh for all communications. Students caught doing anything stupid (like DoS attacks) can get expelled; FWIW, we didn't catch any.
Apparently, Steve has a display built into a pair of wire-frame bi-focals. I haven't actually seen it, as it is somewhat fragile (bond wires as structural elements!), but it is supposed to be rather inconspicuous.
I can't seem to find a link to the paper that describes it; however, it should be at http://wearcam.org
I do some work with Steve at the Wearable Computing lab. Very cool stuff -- the site above has quite a bit of material on both the technology and math of wearable computing, personal imaging, and so forth.
I think that as soon as computer literacy becomes more widespread, the irreverance that geeks now enjoy will come to an abrupt halt.
Don't hold your breath. Computers are becoming more and more complex (despite the "user friendliness" that's being touted so highly). This is a natural phenomenon -- as things get more powerful, they also increase in complexity. We are adding more and more hardware, from different vendors (all misinterpreting standards in their own creative ways), and thenlayering software on top of it all. This means that when something goes wrong, you need someone highly trained to resolve the problem.
The other thing to keep in mind is that computers have changed their place in society -- as little as ten years ago, computers were mostly a business item, and businesses could afford to train their employees properly. Now, with the spread of computers into the marketplace, people are being exposed to this technology without any kind of background knowledge. This situation is not likely to get any better any time soon; just look at how many people can't set the clock on their VCR!
Besides which, as we move more and more to knowledge- and technology-based economies, you will need ever-increasing techie people. So we won't be out of a job soon.
The solution for this is simple: import skilled workers from abroad. US companies are wealthy enough to pay quite a bit, and people are lining up for a chance to work in the states. I just need to look at my classmates -- a good 20% or so of my graduating class either got jobs in or went to grad school in the States.
Meanwhile, the dumb, gullible sheep which the system mass-produces are quite happy to buy, buy, buy.
This is not intended as a flame of the US school system -- the schools here in.ca suck just as badly, though in different ways. It's just that the Americans are wealthy enough to buy talent from abroad.
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The science return, perhaps? The recent FBC probes are neat, and produce lots of nice data, but, on a per-dollar basis, the Pioneers and Voyagers are unbeatable.
Voyager cost billions of dollars
Just under a billion, actually. This includes two flight articles, two launches, and operations.
In return, we got data on Jupiter, Saturn, Uranus, and Neptune; the Uranus and Neptune encounters are unlikely to be repeated for a very, very long time indeed.
[Cassini] cost over three billion dollars
This I agree with. Cassini is the last of the giants.
Very true -- HTP is very unpleasant stuff. One speck of the wrong kind of impurity in your tank, and the whole thing goes up.
Combine that with a simple, pressurized fuel tank instead of turbopumps, and you have a rocket engine with the minimum of moving parts.
Yeah, and atrocious performance, too.
Pressure-fed rockets are much simpler than pump-fed ones -- they have many, many, fewer moving parts -- but they require very substantial tanks, since the tank pressure has to be greater than the combustion chamber pressure in order for the propellant to flow. Since, for weight reasons, you can't want to make your tanks out of 1 inch thick steel, you're stuck with fairly low chamber pressures, and the resulting low thrust.
On top of that, monopropellant peroxide has a very low specific impulse. SMAD3 doesn't give an ISP for mono-H2O2, but it does give a value for "Monopropellant (H2O2, N2H2, etc)" as 150-225 s; combining this with some other information would suggest that H2O2 is at the lower end of this scale.
Beal et. al. got around this by running their rockets off H2O2 and LOX; SMAD has no numbers for this kind of engine, but Mark Wade's site gives numbers from 250-300 s for Beal's design. This is quite respectable, but has the downside of requiring a (mildly) cryogenic oxidizer.
Probably because the paying public wants to know. Of course, with Cassini, you've got the fact that it is the single most expensive science mission that NASA's ever launched. $3.2 billion is probably on the low end of the total cost estimates.
The cost is actually Cassini's single biggest problem. While the data that it will report back from Saturn is certainly valuable -- the only missions that flew out there were Pioneer 11 and the Voyagers, all of which were flyby missions -- it is debatable whether it should have been that expensive.
Cassini is, after all, the last of the Battlestar Galactica spacecraft. Newer missions are much smaller in scope, and, consequently, much cheaper. Even the (cancelled) Pluto-Kuiper Express mission was only to cost something like $700 million.
The reason why you don't want to launch such expensive, all-in-one-basket missions is that if something goes wrong, you've lost everything. When I heard about the reaction-wheel problems it recently had, I was very worried about what could happen to the mission. Fortunately, this has been resolved.
Now, this does not mean that space-borne LMTs are impractical -- but you do need to provide an axial thruster to supply "gravitational" acceleration. Fortunately, the required accelerations are not high, so you can use things like xenon-ion propulsion systems, which can give months of operation on a load of fuel.
Do a search on NASA's web site for more info on LMTs; you'll find a short study of spaceborne LMT feasability.
As did the Surveyors on the Moon -- and they (mostly) worked. Rocket-assited deceleration isn't a piece of cake, but the theory behind it is well-developed.
Interesting enough, though, airbags were proposed for Viking; however, it was decided to go with well-established technology.
A Delta II booster will launch 5 tons to LEO, at a cost of $55M. A Titan IV will take up 21 tons, but at a cost of $214M [1]. So, per pound, the Titan is slightly cheaper; however, the two Deltas will cost less for this kind of mission.
Besides, you get better redundancy with two launchers.
[1] Isakowitz; AIAA International Reference Guide to Space Launch Systems (2nd ed.)
Where are you getting these figures from? The launch costs that you are quoting are almost an order of magnitude too large!
Modern launch vehicles range from the Orbital Sciences Pegasus XL, which will put 300 lbs into LEO for $15 million, to the Russian Proton, which, IIRC, will do like 30 tons to LEO for $75 million. Even the Shuttle, which is the most expensive way to fly these days, is only $100 million per launch.
Each airship is a few million dollars.
Don't forget development costs. We have nothing like this now --- you'll have to shell out big bucks for R&D.
Each airship itself is an unmanned drone which flies at 20Km, there isn't a surface to air missile in existence which can fly that high.
You may wish to mention this to a certain Gary Powers.
What do you do when some space garbage hits a satellite at 50km/hr?
Nothing. You design it to take low-speed impacts -- you build robustly, and include sufficient redundancy to ensure you can take a failure. I haven't heard of any LEO satellites which got taken out by impact with debris. Sure, the LEO environment is quite dirty, but most of it consists of very small particles (paint flakes, etc) which probably won't do too much damage to a suitably redunant satellite. And anything larger is tracked by NORAD anyways, so you can figure out if you're going to hit, and maneouver around it if necessary.
As to the technology to keep it up there.
And how are you going to keep it in place? Don't forget that stratospheric winds can get quite fast.
Engines? What about powering them? Maybe a tether? The FAA will love you, as will the pilots who have to avoid them.
The blimps are a nifty idea, but not really practical. Satellites are proven technology, and work.
Now, as for the feasibility of the LEO comsats, that's an entirely different issue.
As for security (students requiring root on the boxes and all), we handled this by putting all the boxes behind a switch and requiring the use of ssh for all communications. Students caught doing anything stupid (like DoS attacks) can get expelled; FWIW, we didn't catch any.
Apparently, Steve has a display built into a pair of wire-frame bi-focals. I haven't actually seen it, as it is somewhat fragile (bond wires as structural elements!), but it is supposed to be rather inconspicuous.
I can't seem to find a link to the paper that describes it; however, it should be at http://wearcam.org
I do some work with Steve at the Wearable Computing lab. Very cool stuff -- the site above has quite a bit of material on both the technology and math of wearable computing, personal imaging, and so forth.
I think that as soon as computer literacy becomes more widespread, the irreverance that geeks now enjoy will come to an abrupt halt.
Don't hold your breath. Computers are becoming more and more complex (despite the "user friendliness" that's being touted so highly). This is a natural phenomenon -- as things get more powerful, they also increase in complexity. We are adding more and more hardware, from different vendors (all misinterpreting standards in their own creative ways), and thenlayering software on top of it all. This means that when something goes wrong, you need someone highly trained to resolve the problem.
The other thing to keep in mind is that computers have changed their place in society -- as little as ten years ago, computers were mostly a business item, and businesses could afford to train their employees properly. Now, with the spread of computers into the marketplace, people are being exposed to this technology without any kind of background knowledge. This situation is not likely to get any better any time soon; just look at how many people can't set the clock on their VCR!
Besides which, as we move more and more to knowledge- and technology-based economies, you will need ever-increasing techie people. So we won't be out of a job soon.
The solution for this is simple: import skilled workers from abroad. US companies are wealthy enough to pay quite a bit, and people are lining up for a chance to work in the states. I just need to look at my classmates -- a good 20% or so of my graduating class either got jobs in or went to grad school in the States.
.ca suck just as badly, though in different ways. It's just that the Americans are wealthy enough to buy talent from abroad.
Meanwhile, the dumb, gullible sheep which the system mass-produces are quite happy to buy, buy, buy.
This is not intended as a flame of the US school system -- the schools here in