A couple of weeks ago the Hubble Space Telescope stopped communicating with the world.  Its Control Unit/Science Data Formatter (CU/SDF) went down, rendering it unable to communicate back to NASA.

Fortunately the Redundancy Department of Redundancy built a backup system into the Hubble satellite.  Side A, the systems active since launch, had broken.  But Side B, unused all that time, were at least theoretically there to solve this very kind of problem.  In reality though, Side B hadn’t been active in almost two decades.  Would it really just power up and smoothly transition?  There were doubts.

And those doubts, apparently, were justified.  NASA bravely tried to convince the Hubble to switch over to Side B a week ago.  And ran into some problems.  While the Wide Field Planetary Camera 2, Near Infrared Camera, and Multi Object Spectrometer all happily transferred over from safe to operate modes now using Side B, the Advanced Camera for Surveys (ACS) was not so successful.  NASA explained that on the 16th of October, “an anomaly occurred during the last steps of the commanding to the ACS.  When the low voltage power supply to the ACS Solar Blind Channel was commanded on, software running in a microprocessor in ACS detected an incorrect voltage level in the Solar Blind Channel and suspended ACS.“  This in turn caused the the safety systems to throw everything back into safe mode to prevent damage.

NASA further explained that, “the anomaly was because of a limit-checking algorithm that triggered before the data that it was checking was valid. A commanding change on the instrument will eliminate this condition and both teams expect a nominal low voltage power supply turn-on when it is commanded on next week.” And that, “three separate events occurring with near-simultaneity were responses to a single triggering event,” which was, “most likely caused by a self-clearing short-circuit, or a transient open-circuit, in the SIC&DH system.  One or more such events would not be highly improbable in hardware inactive since 1990, and will not harm the telescope, although it could cause another interruption of science operations.”

To which pretty much anyone would have to agree.  That Side B could be made to work at all is amazing.  Space is not exactly an environment friendly to electronics, and a computer system down for so many years, to just bring back up by remote communications alone?  It’s pretty amazing.

Of course, like any good doctor, NASA is going to, “monitor it for about 24-hours to assess its operations“.  But as sure as they can be, they’re pretty sure that the transfer of operations to Side B is licked, and that the Hubble will be back to full operation.  And hopefully stay that way until someone can actually go up there and really fix it.  Because when you put things up in space, it kind of makes it difficult to schedule house calls.