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Spirit Rover Communications Error
cybrthng writes "Through yesterdays press release and the current Nasa Briefing there is news that they are having communications errors with contacting spirit. Is she lost or is it something akin to the Pathfinder failures that happened? Or did little green people claim an expensive tonka truck toy?"
By now they have probably rebooted it (forced it through safe mode to clear any software fault; space vehicles never really go all the way "down"), so if it's still happenning I would say it's either a hardware fault or corruption of essential software or data in (putatively) nonvolatile memory (not unreasonable in high-rad environments).
Not impossible, but relatively unlikely with deep-space grade hardware. It'd require a double fault to create a detectable error, and more than that to create an undetectable one.
If they haven't forced it through safe mode, then they're not too worried and are more interested in characterizing the problem than getting on with the scientific mission. Which is a good or a bad thing depending on which sort of information is more valuable. I'm sure the guys in the software group have their bias.
They've had one day, and much of that was spent thinking the problem was because of thunderstorms/atmospheric vapor near Canberra and dish tracking problems were causing communications errors. It's important to get some idea of the problem before you go shoving things into safe modes because you may make things worse (if it's a power bus fault, for instance).
Stay tuned ...
chongo (was here)
Spirit status updates are here: http://spaceflightnow.com/mars/mera/statustextonly .html
"To confine our attention to terrestrial matters would be to limit the human spirit." -Stephen Hawking
Spirit runs an Operating System called VXWorks, by Wind River.
The software running onboard the MER rovers is not written in java. Not even a little bit. Sun's posters and propaganda at last year's JavaOne seemed to deliberately give that false impression. There is plenty of Java running on the ground, though, for both planning activities and processing the downlinked data.
I meant a synchronization problem between the physical transmitter unit and the main avionics system.
When it comes to clocks, it is somewhat complicated. The rover keeps a clock, and usually finds earth by locating the sun in the sky. It has a set of keplerian/rotational elements for both Earth around the Sun and the MGS/Odyssey around Mars, and thus knows when they rise and set in the sky. This tells it when to transmit and where to point the antenna.
Full duplex communications are possible on xband, so transmitting and receiving do not need to be synchronized. Blocks of data are sent with error correction codes-- as they arrive intact, messages are sent telling the rover to delete them. Retransmits can also be requested if the data is particularly interesting and missing (but often aren't, as witnessed by the number of empty portions of images.
UHF is usually just used to offload additional data from the rover during the night to the satellites. The delays are short and the protocols are thus more conventional.
There's much more detail about this here.
Apparently, Tidbinbilla is one of only 3 stations tracking Spirit from Earth. If it's out, they have to wait until Spirit is visible from over the horizon at another station before they can communicate.
"The plural of anecdote is not data" -- Bruce Schneier