METH%USC-ISI@sri-unix.UUCP (04/16/84)
The resaon you use fuses over circuit breakers is just because fuses are one-shot deals. If your circuit is faulty you don't wan't it reset inadvertantly by some glitch command. The reason you fuse circuits is as was stated in another message, you'd prefer to permanently take out a single circuit rather that fail the entire satellite. I heard an (unconfirmed) story that Solar Max's fuses blew because the gas contained in them diffused into space resulting in a lower current rating than the (well behaved) circuit they were in. Regarding reaction wheels, Space Telescope will do its maneuvering using reaction wheels and magnetic torquers. The latter will permit the reaction wheels to operate at low average rotation rate (there are four of them so the torquers can despin the wheels with no net angular momentum change) to reduce power consumption and jitter. The reason one does not want to use reaction jets of any kind in such a vehicle, is beacuse the effluent produces molecular contamination which could deposit on the telescope mirror, severely degrading performance. -Sheldon Meth The BDM Coorporation (METH@ISI.ARPA) -------
henry@utzoo.UUCP (Henry Spencer) (04/22/84)
Sheldon Meth observes:
I heard an (unconfirmed) story that Solar Max's fuses
blew because the gas contained in them diffused into
space resulting in a lower current rating than
the (well behaved) circuit they were in.
According to the chief scientist for Solar Max (a talk from him was
part of the NSI launch tour I took for the 41C launch), nobody was
quite sure what the problem with Solar Max's attitude-control system
fuses was. There was a great deal of interest in examining the bad
module to try to determine what caused the problem.
He also said, incidentally, that the bring-it-back-to-Earth-if-we-
can't-fix-it option was definitely a last resort, because there was
no funding allocated for either repair or relaunch after return.
"We are planning for a successful in-space repair." He must have
been awfully happy when the last grabbing attempt succeeded.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry