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Cassini Probe Has Camera Problems
xX_sticky_Xx writes "The BBC is reporting that the last billion dollar NASA probe, Cassini, (enroute to Saturn) is suffering from an unknown source of contamination on its narrow field camera. NASA has attempted to alleviate the contamination, which is causing a haze to appear around images, by "defrosting" it, with so far limited success. Another attempt will be made in January. If this problem can't be resolved this will be extremely disappointing. Cassini is set to expand our knowledge of Saturn more than Galileo did for Jupiter."
If dust got on the lens, or inside, most likely the fuzz pattern would be even or random. The fact that it is on the edges of the image suggests that something is condensing.
If the camera was hit by a speck of space dust, perhaps the impact could have created a little cloud of dust when it penetrates (assuming it did not hit the lense or image sensor chip itself. If it did hit one of those, I doubt it would be just the edges.)
The fact that a little heat reduced the problem is also kind of against that theory.
Condensation of something is the most likely exlanation IMO.
Table-ized A.I.
The source of contamination *has* to be the spacecraft itself.
If the contamination were external, it would have had a signifigant (measurable) effect on the momentum of the spacecraft. The space through which it is travelling is pretty much completely empty anyway.
That leaves one plausible possibility: Cassini is leaking something that is condensing on the cold (*very* cold) bits. The most likely cause is a small propellant leak. As far as I know, the spacecraft has three propellants on board, N2O4, N2H4 an monomethyl hydrazine. I'm too lazy to look up the charecteristics of these, but their boiling points differ.
A heating cycle of the lens seems to have helped. I would be *very* surprised if the data from the heating cycle didn't give them a good clue as to the exact contaminant by looking at the amount removed by a known heat input (latent heat of vapourisation)
The big worry is that the leak will leave the spacecraft with insufficient fuel for orbital insertion (unlikely - it's almost entirely a gravity-assist trajectory) or for manoeuvering. That would be bad.
I may, of course, be completely wrong.
Normally I'd laugh at that, but I do need to point out some technicalities. First, "crap" is a relative term. Yeah, if Dell tried to sell computers that worked as frequently (or infrequently) as NASA probes, it'd be out of business. Then again, Dell, Intel, AMD, Western Digital, et al all have the chance of trying their machinery out in real-life situations before putting it out on store shelves. How fortunate for them, but NASA doesn't have this luxury. Take a look at lunar missions starting in the early-to-mid sixties - see how many craft NASA shot up, and how many MORE Russia pumped up there. Then look at how many succeeded - you'll see a difference in approach right there. Russian mentality: keep trying, and if it drops out of the sky or flys by the moon or crashes, try it again! Just keep trying, and eventually you'll get one to work. NASA, on the other hand, has the opposite approach - make like the first shot is the only shot. Try to make sure it works as best as it can, then send it up. Maybe this is a result of a much more nosey press in America, or maybe its just the way Americans work.
The spacecraft up there are the pinnacle of technological achievement. Go to http://nmp.jpl.nasa.gov/ds1/ , Deep Space 1's webpage and read about this amazing spacecraft if you don't believe me. Just to cut some people off right now - yes, the cpu's aboard these spacecraft are exceedingly slow (I'm talking PI or slower), but they are doing things longer and more continuously than any desktop here on Earth. Finally, if you want to see a spacecraft that has lasted longer than most of our cars, and acquired a lot more data, see Galileo's latest stat, as it's in its third extended mission and still going stronger than ever: http://www.jpl.nasa.gov/galileo/
Just my thoughts,
JoeRobe
The best way to predict the future is to invent it.
I don't agree with the BBC's claim that this is a "major" problem... the narrow angle camera still works - the contaminent just effectively reduces the resolution of the NAC. But from what I understand, the NAC resolution is nominally very, very high and even with the contamination it still will produce amazing pictures.
As far as what the contaminent is... the best guess so far is that it is outgassing from some part of the spacecraft... probably the camera. Something got heated up, vaporized and then condensed on the lens (either the inside or the outside of the lens). When they see if the stuff cooks off and what temperature it cooks off at, they'll have a better idea where the contaminent came from.
Cassini has already had larger problems (the reaction wheel last December, and the probe relay problem) that have been overcome and Cassini is still on track to make all of its mission objectives and then some. This problem is minor by comparison and will probably be fixed.
Cassini was launched in 1997, and arrives at Saturn in 2004... seven years later. Then its primary mission ends 4 years after that... and it is hoped Cassini can fly a 4 year extended mission after that... So this spacecraft will fly 15 years in deep space without any possibility of any repairs more sophisticated than commanding a motor back and forth to jiggle something loose or turning on a part to heat it up. Things are bound to break... hopefully, these things will be small and not cause the spacecraft to blow up when it turns on its engines the next time.... we all want to see the pictures of the pterodactyls flying on Titan, don't we?
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