[time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem
Jim Lux
jimlux at earthlink.net
Sat Sep 21 08:11:46 EDT 2013
from JPL
http://www.jpl.nasa.gov/news/news.php?release=2013-275
"Mission controllers postulate that there was an anomaly generated by
the spacecraft's software which left the vehicle's computers in a
condition where they are continuously rebooting themselves. If this is
the case, the computers would not continue to command the vehicle's
thrusters to fire and hold attitude. Lack of attitude hold makes
attempts to reestablish communications more difficult because the
orientation of the spacecraft's antennas is unknown. It also brings into
question the vehicle's electrical power status, as the spacecraft
derives its power from a solar array that is fixed, with its cells
pointing in one direction."
If it gets cold enough (without power from solar cells, it won't
generate enough internal heat to keep warm), it will die. That's
probably what happened to Spirit on Mars. It got cold enough during the
Martian winter, and with not enough solar power, enough things drifted
cold enough that we couldn't get commands in.
BTW, DI uses star trackers for attitude knowledge, so it has the
potential to point very precisely.
If anyone is interested in the gory details of how the telecom system works
http://descanso.jpl.nasa.gov/DPSummary/di_article_cmp20050922.pdf
Page 20 shows the variation in AuxOsc frequency of the SDST radio vs
temperature. That shape will look pretty familiar to list members.
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