Spirit Sol 142

Of course, they've corrected the anomaly. Once again, it was not my fault. Surprisingly, it was another race condition, this one in the imaging subsystem: a command to take an image was dispatched at almost the same instant as a command to stop imaging. This caused the spacecraft to try to write to the camera interface hardware when the interface hardware was turned off, which triggers a self-protective reboot. The window of vulnerability was all of an eighth of a second wide, which helps explain why we hadn't seen this before -- it's another one of those one-in-a-million (well, maybe one-in-a-few-hundred) things.

In his Mission Manager Report, summarizing the anomaly and the resulting investigation, Mark Adler wrote:

 "This was the second 'very low probability' fatal in less than
 a week.  After verifying the theory, the flight software team
 then went out to buy lottery tickets."

Then, in the "Concerns" section of his report, Adler wrote:

 "Concerns: I'm not sure that the flight software guys are
 clear on the 'very low probability' concept."

Well, the rover drivers on shift (John and Ashitey) had a few easy days. Due to the anomaly, they were off for at least one of those days, and then spent yesterday and the day before (sols 140 and 141) just re-running sequences that had already been built for sols 137 and 138 -- doing the stuff that didn't happen because of the anomaly. Today we're all caught up from the anomaly and are driving away -- a simple drive, if a short one.

Art, as usual, is spending his time kidding around. With a mix of rue and pride, he describes the Pathfinder-era Thompson Loop -- the combination of a sequencing error (in a sequence Art wrote) and flight software behavior that seemed it might cause us to lose the Sojourner rover. Since both the last Spirit anomaly and this one happened to occur on sols Art planned -- and, in each case, his last day on-shift before going off-shift (just like today) -- he tells Mark Adler to expect the TWA (Thompson Weekly Anomaly) to occur tomorrow. "Keep that in mind," Adler says, "someday HQ is going to ask us how do we kill these things." "Put Thompson on it," several people say at once.