Diagnostic activities performed by Spirit on Thursday, Jan. 29 narrowed the range of factors that may have contributed to its unexpected behavior earlier in the week. No clear explanation has been established yet. Spirit is healthy and responding to commands. It recorded and returned images of nearby scientific targets. The rover team plans further diagnostics on Friday of Spirit's inertial measurement unit -- a combined gyroscope-and-accelerometer device that measures rover movements and attitude.
A diagnostic test on Sol 1805 provided an evaluation of how accurately Spirt's accelerometers sense the rover's orientation or attitude. The testing was a follow-up to Spirit's mistaken calculation of where to expect to see the sun on Sol 1802. The sol 1805 results indicate the accelerometers may have a bias of about 3 degrees. This would explain why Spirit pointed a camera about three degrees away from the sun's actual position on Sol 1802. However, the Sol 1805 test also showed that Spirit's gyroscopes are operating properly, which convinced engineers that the rover could safely resume driving. Only the gyroscopes are used for orientation information during driving.
That is, of the inertial measurement unit's two components, the gyroscopes and accelerometers, the gyroscopes appear to be working properly; it's the accelerometer that seems to be off a bit. Something to file away. It wasn't clear from the update whether the issue with the inertial measurement unit is related to the other weird thing that happened to Spirit on sol 1800, which was that the rover didn't save any information at all from its day of activities into its flash memory. An interesting hypothesis is that "One possibility is that a cosmic-ray hit could have put Spirit temporarily into a mode that disables use of the flash memory. The team intentionally used that mode -- relying only on volatile random-access memory -- during recovery from a memory problem five years ago on Spirit." That is, during recovery from the problem that Scott Maxwell has been discussing on his blog this very week. Quite a coincidence!
Scott's latest entry contains a funny remark: "Since nobody else has much to do either, the scientists plan an abbreviated downlink assessment meeting followed by a mass trip to a nearby Mexican restaurant. Man, you haven't lived until you've gone to a Mexican restaurant with a bunch of exogeologists. On second thought, I decide to skip that." This is followed by the footnote, "Big mistake! As it happens, since then I have gone to a Mexican restaurant with a bunch of exogeologists, and you know what? Turns out it's a lot of fun, and great conversation, too. D'oh!"
It's true. Even though the community of scientists who study planets is pretty small, it turns out that there are major social differences even within this community. Planetary geologists are, well, geologists, and in my experience it's pretty much always fun to go have beer and Mexican food (or whatever else is the grub of the land) with geologists, whether they study the ground beneath our feet or stuff up in space. The prospect of fun among groups of people from other disciplines has always been more hit-and-miss. I'm not sure why that is. Maybe it has something to do with the strange attractiveness that the study of geology has for people from apparently unrelated disciplines. When I was in college, people kept getting sucked into the geology major from other departments like history and art, meaning that they'd thought about a wide range of topics before winding up in geology. Maybe that gives them a leg up in social conversation, I don't know.