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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."
What about plain old space dust? According to this article there's enough of it out there to hamper astronomists when viewing celestial objects from earth. More closer to the point this article describes how people involved in space exploration are concerned with peices of space dust, too small to be tracked, causing serious damage to orbiting satelites. The Cassini article says they're pretty sure that it's related to the deep cold of space, which is why they equipped it with heaters. But if it's not related to the cold, it's not out of the realm of posibility that maybe Cassini simply encountered some of this dust? Although you'd have to think the makers of the satelite thought of this already, but who knows.
I posted to
This is from the report sent out:
.Recent instrument activities included two Radio and Plasma Wave Science HighFrequency Receiver calibrations. Engineering activities taking place onboardthe spacecraft this week include an Attitude Control Subsystem high-watermark clear and the uplink of the Mission Sequence Subsystem (MSS) D7.6.1Modules.
Cassini Weekly Significant Eventsfor 12/06/01 - 12/12/01The most recent spacecraft telemetry was acquired from the Goldstonetracking station on Wednesday, December 12. The Cassini spacecraft is in anexcellent state of health and is operating normally. "Present Position" webpage, http://www.jpl.nasa.gov/cassini/english/where/
In news today, Nasa scientists spent all last week trying to find the source of the contaminant on the Lens. After many hours of brainstorming, one of the engineers spilt coffee on a button labeled "Lens Cap". Shortly after, the camera apeared to be functioning correctly. Head NASA Scientists are trying to work out the function of this "Lens Cap" button, but the British designer of the button cannot be contacted, and Nasa officials are still unsure what has happened.
it'll still be winter -- if we waited 'til spring and maybe it'd thaw out on its own.
when you take something from earth pressure to zero pressure you'd be surprised at what will boil off. this is called outgassing, as polymers, etc... lose mass to vapor. the stuff outgassed can then condense on your optics and ruin your pictures. The usual practice is to put everything in a vacuum chamber and get it all out before flight, but this won't always be enough. Also, you can coat surfaces that will outgass, but you need to use anyway (such as electronics circuit boards) with a non-outgassing coating (such as uralane). If some electronics overheat and melt away some of that coating, the materials underneath might, you guessed it, outgass. It is a difficult problem to avoid and it is unfortunate that it might ruin the mission. hopefully not.
This just keeps happening--the Vogon interstellar starliners keep illegally flushing their toilets into space in the vicinity of solar systems. I think we should file a complaint with the local authorities on Alpha Centauri.
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.
Okay, most of the folks here seem to be bashing NASA and jumping to conclusions that the probe is lost. No damn way. They'll come up with a solution soon enough - for one thing, a similar incident occured with the Stardust probe earlier this year. Just take a look at the status reports.
Start at somewhere aroud May 4,2001 and go backwards (by that report, the problem had been fixed). I bet the glitch on Cassini will be fixed just as easily. Note that the problem occured just before christmas, so they probably just tried a "quick fix" to see if it just went away. Like said, they have until 2004(!) 'till Cassini is at its destination to try a number of things. They'll probably get rid of the contamination just by turning on the heaters for a couple of months, but they don't want to start the operation and immediately leave for a christmas vacation (in case something comes up).
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?
There are 10 types of people in this world, those who can count in binary and those who can't.