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Clock Ticking for Hubble
DoraLives writes "Ok then, what are we going to do with Hubble? Eventually, it MUST come down. The New York Times has a piece that addresses this less than pleasant (at least for the astronomical community) subject. Additionally "The decision about what happens then has been complicated by the breakup of the Columbia." Read all about it."
Why would that complicate things? All the incident proved was what we know already. Besides, Hubble's done some great things, and of course it'll have to come down eventually. We just have to move on and produce a successor.
Bash script for FP whores
Why not just shove it into a bit higher orbit?
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Of course, Taco Bell will put a big floating bullseye in the ocean and if some titanium part of hubble hits it everyone in the US wins a Taco!
Wooo Hoooo!
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Nero-burning ROM for Linux!
Why don't we get some other country
to foot the bill on boosting it
into a sustainable orbit and paying
for the initial maintenance after
2010. I'm sure that an India or
Taiwan would be willing to take it on
for less than $500 million.
Click here
Reality has a liberal bias
Not that 're-deployment' would be easy, mind you, but unless there's some kind of fuel issue, I don't see why it wouldn't be possible (bearing in mind I'm far from an expert on the subject).
On one hand, it would develop skills for astronauts that would be needed on the Space Stations, on the other, it's not cheap and doesn't provide advancement in deployed equipment.
Then again, maybe in 50 years, retrofitting sattelites for technology upgrades by Space Station personnel might become a regular thing.
"Gotta do an EVA to install an upgrade on the Hubble, back in about half an hour. Want me to pick up anything while I'm out?"
How difficult would it be for us to use some other craft to boost the hubble into a higher orbit? it's not as if it's any secret what coupling mechanism it has, it should be easy (relatively speaking) to have something unmanned do it.
In terms of maintenance of the Hubble, why don't they consider a structure that allows them to completely envelop and grapple to the telescope, so that they can work without nearly as serious a risk of losing parts while it's disassembled? Whatever they would employ wouldn't have to enclose an atmosphere, but it would provide a room-like feel for astronauts, rather than the current unsurrounded feel. If they drifted away, they would make contact with a wall, and then rebound. Parts that drift would be easily found.
If they felt really adventurous, they could build a module that would be self-contained with an atmosphere that the Hubble could be brought into for service, complete with a personnel airlock, and when not in use be placed into a convenient orbit or else brought down in pieces for later use...
Do not look into laser with remaining eye.
No way! Then you run the risk of Paramount taking William Shatner out of drydock.
And they'll shoot more "extra" footage that is really really really dull.
It will fall out of orbit eventually if you don't do anything about it. Satellites periodically lifted a bit to keep them up there. "Just leaving it up there" actually costs money. That's why many old satellites are "deorbited".
We spent so much time, money and effort fixing it, why not spend some more and upgrade it for another decade of use?
---
Programming is like sex... Make one mistake and support it the rest of your life.
NASA has long planned to end Hubble's spectacular run and bring it down in 2010 to make way in the budget for the James Webb Space Telescope, scheduled to be launched in 2011.
Theres a gap there in time where we wont have a telescope up there. this will be the end of the world, as we wont be able to see the asteroid comming at earth in time to send our best deep crust drillers to drop a nuke in it and split it up!
Most satellites go up into space with a designated shelf life. They are supposed to be brought down under their own power to save the trouble of building a space-garbage collector if it died and became unresponsive.
So Hubble's self-propulsion system is supposed to go bad in 8 years so they bring it down in 7.
If would have been nice if the article explained why it costs so much to maintain and why we have to periodically spacewalk to it. Does it need new batteries? Does it have to get cleaned? Can it not correct it's own orbital decay?
What's the deal? Anyone know? Seems like if it was mostly self-maintaining, it should cose a whole lot to just keep it up there.
Do not fold, spindle or mutilate.
If sending up a Shuttle to re-establish a fresh orbit for Hubble would be cheaper than building a new and improved Hubble and launching it?
Development cost of Hubble: $2 billion
Cost of one space shuttle launch: $600 million
So you can get in excess of three launches for the same cost of the Hubble.
Toronto-area transit rider? Rate your ride.
I just find is pathetic that the U.S. can't find $600m to refurb the HST. We're spending about twice that EVERY DAY on operations in Iraq.
Just pull the troops out two days earlier and there you have it... enough cash to service the Hubble twice!
My opinion is that the HST should be retrofitted with a small nuclear power source (like those on the Voyager series) and send out of the solar system. But unlike previous missions were the probes were sent past the outer planets, we should send HST perpendicular to the Earth's orbit, so we can look back "down" on ourselves and surrounding stars/planets.
I can't recall if the solar system plane is about parallel to the galactic plane, but if so this would also give us a tremendous perspective on the galaxy that we haven'y had before. Yea, yea it would take a decade or two to get to a distance that would mean anything astronomically, but it has to happen some time, why not now.
Article X: The powers not delegated... by the Constitution...are reserved...to the people
Hubble is in Low Earth Orbit (LEO). It's got an orbital velocity of around 4KM/Sec.
To raise the orbit far enough to get to the Moon, takes a total deltaV of 7KM/S (or another 3KM/S on it's current speed).
The Earth orbits the sun at around 30KM/S, give or take. So to send something - anything - into the sun requires a deltaV of the same amount: you've got to cancel out the existing 30KM/Sec velocity, otherwise you're just going to send the object into a different orbit around the sun
The fastest any object has left the earth is around 8KM/S for the interplanetary probes (Pioneer, Voyager, Cassini, Galileo etc). That's as fast as the human race has ever gotten anything going[*]. Without a major advance in rocket technology (i.e. away from chemical rockets), that's about as fast as we're going to get anything going, too.
As a reference, the on-orbit manoever capability of the Shuttle, is a total of about 100M/S
Oh, and Hubble has much MUCH less manoever capability than this
This is why things are de-orbited, rather than "sent towards the sun" or further out. De-orbiting from LEO requires only a little "kiss" of deceleration before the orbit intersects the atmosphere, from where friction does the rest. The only exceptions are Satellites in higher orbits (e.g. GPS in the 12-hr / 12,000KM orbits, or Geostationary sats) which tend to be "retired" in slightly higher orbits because these are thought to be more stable over longer (geological) time periods than lower ones, and there's not enough residual manoever capability to lower the orbit enough to graze the atmosphere
[*] = However, we've learnt the trick of gravitational assists which lets Mother Nature (or Newton, or Einstein depending on your religious orientation :-) speed up our probes considerably at the expense of the orbital energy of the planet we're assisting from.
--
I'd rather have a bottle in front of me than a frontal lobotomy
I've been an avid avid amateur telescope maker since I was twelve years old. It led to me studying astronomy for a time at Caltech. While I'm a programmer now, it's still a very enjoyable and intellectually stimulating hobby.
While a basic newtonian is a straightforward instrument that can be built by anyone who's good with their hands, telescope making can get as complicated as you want if you're really looking for a challenge. Optical design is still a wide open area of research in mathematics, software engineering, and physics, and some of the more interesting designs take quite a bit of skill to fabricate. That means anyone can make a satisfying telescope, but the hobby will yield a lifetime of interest because there's always new things to learn.
You can construct your own telescope with a primary mirror of 8 inches in diameter for less than $200. It will take quite a bit of work, but it is enjoyable and meditative work. Grinding mirrors is one of the things I do to relax and relieve the strain of coding all day.
A good place to start looking for information is the ATM FAQ. The procedures for grinding, polishing and figuring are pretty involved - you should buy one of the books from astronomy publisher Willman-Bell.
There are a number of people and business who sell inexpensive mirror grinding kits. They will come with a glass mirror blank and an assortment of different sizes of abrasive grits. I would recommend asking on the ATM mailing list (that you can find in the FAQ) when you're ready to order your first kit.
The 8" plate glass kit I bought from Dan Cassaro for my current project set me back $64. When I get done working on the mirror, it will cost me about $35 to have a vacuum coating laboratory aluminize it. Good quality eyepieces cost about $50 - just one will do to start with but it helps to have more.
While fancy equatorial mountings can be expensive to make, it's possible to make a quite servicable altazimuth mount out of common materials like plywood and a few hand tools.
Request your free CD of my piano music.
I'm certain that it would have brain-dead simple to convince GM or Ford or DuPont to spend billions of dollars to build, launch, and maintain something which produces pictures of objects in space. In fact, I seem to recall that NASA had to sue a number of such companies to keep them from launching several other pure science satellites which had no commercial value. Stockholders in those companies were outraged that the attempts of their management to dump billions of dollars into altruistic enterprises were thwarted by evil bureaucrats. Idiot. Get a clue as to what private companies do and why and how they do it.
"What the hell is that thing?"
"It appears to be the mothership."
"Then what did we just blow up?"
"The Hubble Telescope."
"You tried your best and failed miserably. The lesson is...never try. Heh!" -Homer
For everything Hubble has done to further astronomy (and since it was practically the only bright spot of the otherwise maligned space program), they owe it a better end than what they are proposing. To deorbit it and let it burn up with as much thought as one would give to flushing a dead goldfish is just plain wrong.
It should definitely be retrieved and become a piece in the Air & Space Museum's collection.
Drastic and sorry failures? Do you have any evidence to back your claims that all of these programs are failures?
Let us imagine for a moment what things would be like without public education.
For one, a lot of children would receive *no* education. Either because their parents could not afford it, or because their parents did not believe that education is a necessary component of a democratic society.
Secondly, many high school graduates (of private high schools) would not be able to attend college. Even public college tuition is expensive these days.
Another interesting thing about publicly funded research is that it benefits everyone. The goal of publicly funded programs is to benefit our society as a whole. The goal of privately funded programs is to make money for the company. If something isn't ultimately profitable, it won't get funded, even if it is beneficial in other ways.
It's going to need a bit of polishing, a space telescope isn't exactly suited for that kind of rough re-entry.
I'm not sure about your list (I'm not an expert on any of these), but I do remember that Medicare and Medicaid beat the pants out of any private medical insurance in terms of what percentage of money going in actually went to pay medical bills (it was not even close). Private health care has turned into a bloated inneficient non-working mess. It's actually a good argument as to why large government programs are a good thing (this has to be rediscovered every couple of decades, it seems).
... (except reduce the "leveling" of education). Private schools look better overall because they can just decide not to take or drop problem students, unlike public schools. If education were to be made private, we'd have the same administrators and teachers except now working for bosses interested in a bottom line. I can't imagine how this wouldn't be disastrous.
I think there might be some merit to what you say, but the mantra "private business is better" just doesn't apply uniformly and universally (in fact, in some cases it just doesn't work compared to government programs).
I'm also curious how you think that privatizing education would change anything
I would be curious to hear your whys -- since I personally don't subscribe anymore to the "private business is better" mantra (and, thus far, medical coverage is actually a good counter-argument to this).
The moon race isn't the only example, SSI, public education, medicade/medicare are all drastic and sorry failures.
Yeah, not like the shining examples of Amtrak, Worldcom, and Enron.
I don't know exactly how much of my tax money goes toward funding Hubble, but even apart from the science I get a pretty good entertainment value from the the pictures it has produced, such as the wonderful picture of NGC 7742 on the APOD page for today.
Sheesh, evil *and* a jerk. -- Jade
> I was just thinking, what happened to the space program is a classic example of why it's better for things to be privatized. I mean, one of the worst possible things that can happen to a government program is
I find myself wondering whether you've every had a job. Surely even the most casual observation reveals that private enterprise doesn't have all the magical properties commonly attributed to it. Failed or discontinued projects in the private sector are a dime a dozen, as are pet projects that get funded on the basis of which manager is the best suck-up rather than on the basis of which best satisfies some other requirement (even if that requirement has no higher social goals than raking more gold into corporate coffers). Waste and "dumbsizing" of good projects seem to be the rule in the private sector as much as in the public sector; you're just less likely to see them in the news or hear them harped on for political exploitation by radio talkjox.
Sheesh, evil *and* a jerk. -- Jade
Why is everyone so firmly opposed to registering with NYTimes.com? Not only is it free and easy, but they provide useful services. They aren't going to track you down and accuse you of downloading illegal warez. Just register once for heaven's sake and never think about it again.
o
This neither qualifies as free-as-in-beer nor free-as-in-speech, but rather free-because-I-won't-let-anyone-tell-me-what-to-d
Hubble is an overgrown version of a digital camera. As CCDs improve, you eventually want to replace the ones up there with better ones. This has already been done a couple of times, but electronics keeps improving.
It also has batteries and solar cells that provide power, and these wear out and have to be replaced.
Hubble needs to point itself at things, and it does so using heavy spinning rotors, which are
turned one way, and by Newton's Law, Hubble
turns the other way. There are 5 of these
"Control Moment Gyros", or CMGs. Being mechanical devices, they wear out and break over time.
You need 3 out of 5 to be working to point Hubble, and if they have an MTBF of 12.5 years (which is pretty good for a mechanical device), then you need to visit every 5 years and replace 2 to keep Hubble running.
Hubble has no propulsion and you don't want any until you are ready to kill it. Fluids sloshing in tanks will mess up your pointing of the telescope, and any exhaust from a rocket will contaminate the optical surfaces. When the Shuttle visits, the thrusters are 50-75 feet away, which is much less of a problem than if your booster pack is on the back end of the telescope only 2 feet from the science instruments.
And yes, IAARS, in fact the first group I worked at at Boeing back in 1981 supplied the graphite/epoxy frame that holds Hubble's mirrors in place.
Daniel
It's partly down to privacy - if you're registered - the New York Times could (in theory) check on which stories you're looking at. You don't have to register to view the offline version so why should you to read the online version? Of course the NYT would say that it helps them find out how many readers are looking at their online edition which their advertisers would like to know....
Video Game cheats, hints a
Sure hubble has done great things for astronomy but it is just a hunk of metal (and other materials).
I am sure that I still have my first computer somewhere in the loft but that didn't cost me $600 M to keep.
Wouldn't be much better and more respectfull to the exsisting peice of metal to spend the money you would use preserving it to build a bigger better teliscope. (what happened to the idea of building arrays of teliscopes in orbit?)
A lot of the things in the air and space museam are replicas anyway, one more won't hurt.
Maybe it's time for the US to test some of their cool new weaponry. They must have SOMETHING neat that was designed to take out high altitude stuff. What better chance to prove it's effectiveness? I mean, the Hubble has to come down anyway, so why not give us all a show?
Here the the correct link.
Video Game cheats, hints a
They need to just point the Hubble back to earth and create the worlds best voyeur porn site. They could fund all their other missions with that money.
Why not rename it the Hubbard Space Telescope? Then you can get Hollywood Scientology types to pay big bucks to keep it in the air.
`which fortune`
As much as I hate saying anything against ANY part of our space exploration, I would have to say that STScI is right behind NASA in being the cause of ossification of science. Thanks to the bureaucracy, the average astronomer has NO chance of receiving observing time on the Hubble, but the members of STScI have gained fame and fortune, thanks to the taxpayers' largesse. They've tied their fortunes to the Hubble, and if it stops, they may have to actually produce! "Faster, better, cheaper" is a good motto. High-end astronomy is a good thing, but when a program starts drawing resources from other programs it should be ended. Wouldn't you rather see more planetary probes, maybe a Mars colony? I am an amateur astronomer, and personally I don't care WHEN the universe began or ends. We've got a whole Solar system out there in our backyard. let's go explore!
You have to pay to read the offline version.
This has already been done! (at the request of Carl Sagan in the early 90's)
- "Hear that?! The percolations are imminent! Cease your ingress!"
unless you read it at a public library
Soma: because a gramme is better than a damn.
For the same reason you don't put an 80GB ATA133 in that old 486.
Sometimes it's better to just to get a new machine.
It *will* be sad when Hubbble burns up. (And don't think that it's ever going to come down nicely. That opportunity was lost with Columbia as others have pointed out.)
If you don't want to repeat the past, stop living in it.
Off by a factor of two, give or take. 8 km/sec for a typical LEO velocity would be better.
The Earth orbits the sun at around 30KM/S, give or take.
This one's right where it ought to be.
The fastest any object has left the earth is around 8KM/S for the interplanetary probes
8 miles per second it is. Chalk it up to a conversion error.
Otherwise your post is on the money. Yeah yeah, I know I know, it's a damnable bit of persnickityness, but no sense in giving folks bad numbers when good ones are just as cheap, eh?
Is it fascism yet?
There is a ton of debris in space, there is no reason to bring all of that down
Actually, there is. It's a hazard to satellites and orbiting spacecraft. A few years back, one of the shuttles had a small crater made in its windshield when it was hit by an orbiting *paint chip*.
There's just so much space junk and it's moving so fast, that it's tough if not impossible to safely intercept and capture. NORAD actually tracks and catalogs every piece of it large enough to get a radar return. When a shuttle is up, they constantly monitor its path for errant debris so it can maneuver if necessary. I believe they do the same for the ISS.
~Philly
If Webb is going to be a literal replacement for Hubble, it could be in a similar orbit as Hubble. If so you could kill two birds with one stone--shuttle up with Webb in it, deploy it, then retrieve Hubble on the same trip.
Ya, that introduces a ton of logistical problems--three massive objects in close proximity (shuttle, Webb, Hubble), or fuel to shift orbit, tech crew has to be trained in deployment and capture of different satellite, etc; and I suppose Hubble wasn't meant to be returned to Earth to begin with.
But it sure wouldn't cost an additional $600M (the cost of a typical shuttle launch), and an important piece of space history could be preserved.
you will see almost an opposite coorlation.
Coorlation?
Is that, like, the relationship between how much beer I've drank and um, you know, like how bad my english on Slashdot becomes?
Endless arguments over trivial contradictions in books written by ignorant savages to explain thunder in the dark.
Plans exist to orbit a replacement telescope, but I don't recall if that project is actually funded.
In point of fact, however, this illustrates the fundamental unsoundness of U.S. space policy since the premature close of the Apollo project during the Nixon administraton. The shuttle was justified as a way to get to the space statoin amd the space station was justified as a place for the shuttle to go.
The failure of every administration since Nixon's to provide leadership and a coherent space policy is the reason we are in this mess. The White House should be making space policy and assigning goals to NASA. No one has one that since Kennedy, and it shows.
-- Slashdot: When Public Access TV Says "No"
The number is 4B per month.
I haven't seen this suggestion here, maybe I missed it.
The HST does have attitude control jets. Generally those are used just to rotate the HST in various axes. They could be reprogrammed to thrust in pairs on the same side of the system, and thus accelerate rather than rotate it. This would slightly alter the orbit each time. Done at the proper points in the orbit it could gradually 'leapfrog' into a higher orbit with minimal effect on the system or usage.
This would take much more thruster fuel than it presently carries, so on the next Shuttle visit, they could bring a larger fuel tank and adapters to mount it to the HST. (They might even be able to develop a remote refueling port that could be used by a robotic tender, but that's more complicated.) This would require some research on how to do so without unduly disturbing the center of mass and reprogramming to deal with the different moment of inertia, but it seems not much more complicated than things they've done before like replacing the mirror, or doing the upgrade a couple of years ago. I think (but I'm not an astronomer) that in between thrust events most observations could continue with updated ephemera.
Another way would be to add a small ion thruster and reaction 'fuel' to the end of the HST and use a small continuous thrust to move it to higher orbit - perhaps even to one of the LaGrange points (L5?). This method would make many types of observations difficult during the entire thrust period of perhaps a year. I speculate that the solar panels would provide enough electrical power to drive the ion thruster(s).
Either of these methods would be stressing the HST at the same order of magnitude as the existing stabilization systems, and it would seem to me that engineering either of these mods is doable in the time frame for the next Shuttle visit, thereby avoiding a separate, expensive visit.
While the Web telescope is anticipated to be much better, there are good reasons to have HST still available. The fact that it is such a piece of science history, I would dearly like to see it moved to a place where it is safe from total destruction, like one of the LaGrange points. It might even become a popular sightseeing "flyby" for tourists on the way to the moon. There it could rest and continue to be used until a means of, for example, safely bringing it down to a museum on the moon could be developed in 50 years or so. Letting it burn up in the atmosphere would be too bad.
It's easier to be a result of the past, but more fun to be a cause of the future! http://www.spacefinancegroup.com/
Who said its in trouble, the mighty hubble, as I scratch my stubble, blowing a bubble, am I seeing double?... he,he...
It's actually worse than that. Orbits at altitudes reachable by the Shuttle decay rapidly, because the atmosphere's a little too thick up there - satellites like the Hubble, with big solar arrays, are particularly vulnerable.
The most important thing that happens on Hubble servicing missions has nothing to do with fixing hardware. The Shuttle catches the Hubble, then fires its maneuvering engines and carries the Hubble up to a higher orbit.
I know this because my company did some computer modeling for NASA to help them predict how often these reboosts would be needed. The amount of atmospheric drag varies with sunspot activity - increased solar output makes the atmosphere "puff up" and makes orbits decay faster.
And guess what? The Space Station is in an orbit reachable by the Shuttle, and also has big solar panels, so it needs reboosting by the Shuttle too.
To a Lisp hacker, XML is S-expressions in drag.
If www.theregister.co.uk required registration, I probably would, because I read it often enough. I read stuff on the NYT once in a blue moon. It's absurd I should have to remember some account on it which offers no benefit to me.
You are not alone. This is not normal. None of this is normal.
I can read the paper version completely anonymously, but I have to go through the hassle of registering, and remembering passwords etc, so that NYT's marketing department can collect entirely bogus statistics on usage. They'd be better off creating a "My NYT" and assuming anyone who doesn't register with that is a casual visitor.
You are not alone. This is not normal. None of this is normal.
Well, the NYT thinks I'm a 70 year old woman, living in Afghanistan, who is the CE0 of a company, and that I make less than $US20000/year.
Somehow I don't think that's helping their demographic DB one bit.
The only reason we have the rights we have is that people just like us died to gain those rights. -- Cheerio Boy
...but it's a telescope, right?
:-p
Why not just weld it (not literally) to the Space Station? I mean... it could be maintained, and, still used. We've got some damned interesting information from that thing in the past, IIRC. Upgrades and fixes would be a lot freaking easier if we didn't have to yank it out of orbit every time. I mean, if it's attached to the station, we know right where it is. Parts could be delivered via shuttle to the space station, so repairs could be done through airlocks there. Wouldn't add TOO much mass to the equation - I mean, the Hubble is no bigger than any of the other modules (it fit in the shuttle...). Also, the downlink and power requirements are easily met.
So, go ahead, debunk my idea? I know Slashdot is chock-full of certified NASA Engineers.
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When you're trying to aim an optical system accurately, people moving around the ISS would cause totally unacceptable vibrations. Not to mention station orientation thrusters and the occasional docking maneuver by visiting spacecraft
To put it in perspective, imagine trying to compose a picture and while someone is smacking your camera with a nerf hammer(people moving) and sledge hammers(docking maneuvers). It's just not gonna happen.
I'm an individual! Just like everyone else!
Hubble requires an absolutely still environment to work. Any attempt to connect it to the ISS would transmit too much vibration from various motors and the crew bumping around. Parking it in a nearby orbit would avoid the vibration but might gum up other systems, like the infra-red systems that don't like vented atmosphere or space junk.
Hubble doesn't need constant maintenance, so don't park it near the ISS. Humans will have cheap transport to orbit once the X-prize contest is over.
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Is this the beginning of the end of NASA, and US space research in general? I think so! Folks, the show is over. Regardless of how you look at it, space exploration is too expensive. Even for the imperialist superpower, it is too costly. The only reason there was anything done 30 or 40 years ago was to battle the Communists--it had nothing to do with science. There is little interest and the neo-cons running USA can't possibly garner enough support. So instead of spending on space, they will be spending it all on the missile shield.
Once USA cuts back their space program (circa 2010, with the downing of the Hubble), I think space exploration will decrease. Russia is practically out of the space equation. India and China are simply in it for political reasons (not scientific). I don't see too much activity happening beyond 2010. Sure, there will be more commercial activity. But they will all be money-making schemes to send people into orbits, put up advertising in space, and such things.
I guess one country or a small number of countries simply can't carry on space programs anymore. The ISS alone is too expensive. Note how the member countries don't want to spend much money on the ISS. As I--as well as many others--have been predicting for a long time, humans need to unite or else kiss goodbye to space...
NOTE: I do not count militarization of space (which USA will attempt in 10-15 years) as space exploration
KoalaBear33
......The worst thing in my life happened when the stock market started mattering more than the economy
An actual reactor would have too many parts (moving, and otherwise) to be reliable in the environment and over the lifespan of a Voyager-type mission. And lets not even get into the complexities involved with the liquid coolent of a reactor.
Rathar, an RTG is simply a source of heat in a decay much slower than that in a reactor. Said heat is then converted into electricity by a thermocouple (Actually, a battery of many thermocouples, but who's counting?) And while there's no danger of the plutonium ceasing to give off heat anytime soon, even the best thermocouples wear out. And in the hostile environment of space, and under bombardment of particle radiation (from the plutonium, and the solar wind) they wear out even faster.
Incidently:
> These things have a half-life of several thousand years.
Nope.
Plutonium 238, the radioisotope used in the Cassini space probe (I'm not sure about Voyager.), does not have a half-life of "several thousand years". Pu-238's half-life is 87 years. Strontium 90, another radioisotope commonly used in RTGs has a half-life of 28 years. A half-life in the range of "several thousand years" would actually be a *BAD* thing in these applications. You WANT a significant amount of decay to take place. That's where the HEAT comes from!
cya,
john
Imagine all the people...
I ground my own mirror and made an amazing discovery.
The Moon is actually football-shaped, and slightly blurred at the ends!
Those fools in the mainstream science community just refuse to believe me though.
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?