Archive for March 27th, 2012
Although I don’t often block-quote other sources, for this I’ll make an exception:
The Cassini Plasma Spectrometer (CAPS, off since June 2011) was powered back on on March 16 based on the unanimous agreement of the review board at the CAPS turn-on review held on March 8. All went as planned for both the instrument and the spacecraft during the turn-on. The high rail to chassis short internal to the instrument that was part of what prompted it to be turned off last June was not present, and no changes were seen in the bus voltages or currents when the turn-on occurred. On Tuesday, March 20, the high rail to chassis short in the CAPS instrument returned, generating the same condition that existed at the time the instrument was turned off. However, based on the tin whisker model developed by the NESC team, this condition is believed to be understood and is not expected to cause any problems for either the instrument or the spacecraft. The CAPS instrument has been left powered on and is sequenced to operate as originally planned for the 75 kilometer Enceladus flyby coming up on March 27.
Having seen a forest of tin whiskers myself, that’s a pretty scary diagnosis. One assumes NASA takes extensive precautions, based on their experience, but … 15 years in hard vacuum and free fall will do odd things to spacecraft.
Remember those Toyota unintended acceleration problems? Guess what caused some of them: yup. Read their report to find out what makes metal whiskers so hard to detect. Hint: combine a minimum threshold voltage with a very low current capacity.
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