Slashdot Mirror
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
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.
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.
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.