Original URL: http://www.theregister.co.uk/2008/10/24/hubble_fired_up/

Hubble fired up and ready for action

Back to work tomorrow, says NASA

By Lester Haines

Posted in Science, 24th October 2008 06:43 GMT

NASA yesterday re-activated the Hubble space telescope's back-up computer system, following a few problems coaxing the venerable spare kit into life.

The decision to press the on button means Wide Field Planetary Camera 2 observations should resume tomorrow, followed by Advanced Camera for Surveys Solar Blind Channel observations later next week.

Hubble was last month blinded by the failure of the Control Unit/Science Data Formatter (CU/SDF) in its operational Side A Science Instrument Command and Data Handling unit (SIC&DH), which packets data from the 'scope's five main instruments for transmission back to Earth.

NASA deployed the redundant Side B system, and hoped to have Hubble back in full science mode last Friday. However, while instrument reconfiguration "proceeded nominally" and the Wide Field Planetary Camera 2, Near Infrared Camera and Multi Object Spectrometer were successfully commanded from safe to operate modes, things didn't go quite so smoothly with the Advanced Camera for Surveys (ACS).

The agency explained that on on 16 October "an anomaly occurred during the last steps of the commanding to the ACS". Its report elaborated: "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.

Several hours later, the Hubble computer "sensed the loss of a 'keep alive' signal from the NASA Standard Spacecraft Computer in the SIC&DH and correctly responded by safing the NSSC-I and the science instruments."

A NASA team duly investigated the matter, and now concludes that the ACS Solar Blind Channel's voltage woes were not caused by a hardware problem with the camera. NASA's update explains: "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."

Regarding the "sudden halt" of the computer, the team found "that three separate events occurring with near-simultaneity were responses to a single triggering event".

Specifically, this triggering event was "most likely caused by a self-clearing short-circuit, or a transient open-circuit, in the SIC&DH system". NASA concludes: "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."

The upshot of all this is that NASA decided to fire up the computer and "monitor it for about 24-hours to assess its operations". The agency will issue another update following resumption of planetary camera science tomorrow. ®