420p 10/21 Update: Engineers still in dark about cause of latest Hubble trouble

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CBS NEWS Coverage of Breaking Space News
Posted: 4:15 PM, 10/21/08

By William Harwood
CBS News Space Consultant

Changes and additions:

10/17/08 (12:45 PM): Initial Hubble reboot goes smoothly but anomalies interrupt reactivation
10/17/08 (05:45 PM): Engineers troubleshoot Hubble trouble; optimistic about eventual fix
10/21/08 (04:15 PM): Engineers not yet sure about cause or what to do about Hubble glitches

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4:15 PM, 10/21/08, Update: Engineers not yet sure about cause, what to do about Hubble glitches

After a weekend of troubleshooting, engineers at NASA's Goddard Space Flight Center have not yet pinned down the cause of two glitches last week that prevented restart of the Hubble Space Telescope's science instruments, officials said today.

The restart, switching instrument control to a backup payload computer and components, was required because of a failure in the A channel of the telescope's control unit science data formatter, or CU/SDF-A, on Sept. 27. To restore the lost redundancy, NASA managers decided to delay the shuttle Atlantis' planned Oct. 14 launch on a final Hubble servicing mission, known as SM-4, to give engineers time to prepare replacement hardware. That flight now is targeted for no earlier than mid February.

In the meantime, Hubble managers wanted to restart the telescope's science instruments by reconfiguring six components in the observatory's data management system and five in the instrument command and control system. Several of the components in question had not been turned on since launch in 1990.

The initial stages of the complex restart procedure went smoothly, but improper voltage levels were seen in one of the instruments, aborting the startup sequence. Later, the data management subsystem computer also suffered an unexpected glitch. It is not yet clear whether the two events were related.

"On Monday, October 20, engineers at NASA’s Goddard Space Flight Center met to discuss their next steps toward resolving two anomalies which caused the B-side of the Science Instrument Control and Data Handling System (SI C&DH-B) and the Advanced Camera for Surveys (ACS) Solar Blind Channel (SBC) to return to a 'safe hold' status on October 16," NASA said today in a status report.

Over the weekend, "the Hubble team continued detailed reviews of all the data available when last week’s anomalies occurred. A suspect 8-volt power source within the SBC's low voltage power supply (LVPS) reached its nominal output value just after failure of an internal check monitoring its health. Hubble engineers are evaluating alternative procedures and determining whether another attempt to restart the LVPS presents a risk to the instrument or to the planned SM-4 repair of ACS's other cameras."

The Advanced Camera for Surveys, installed in 2002, suffered an earlier failure that knocked out its visible light wide-field and high-resolution cameras. Only its solar blind channel, which is sensitive to ultraviolet light, is still in operation. The Atlantis astronauts hope to repair the ACS during the  upcoming servicing mission.

In the meantime, before engineers can restart the solar blind channel - assuming they can resolve the voltage anomaly - they must first coax the B-side science instrument command and data handling system back into operation.

"Intensive study of the SI C&DH-B shutdown also continues," today's status report said. "Analyses done thus far suggest that an electrical event of unknown origin and characteristics caused a reset of both the Control Unit/Science Data Formatter-B (CU/SDF-B) and the NASA Standard Spacecraft Computer-1 (NSSC-1) Central Processing Module-B (CPM-B). Both of these modules were activated on-orbit for the first time on October 15. Additional analyses and a risk assessment of SI C&DH-B reactivation have begun."

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