[time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem

Bob Camp lists at rtty.us
Sat Sep 21 12:52:42 UTC 2013


Hi

So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.

Bob

On Sep 21, 2013, at 8:11 AM, Jim Lux <jimlux at earthlink.net> wrote:

> 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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