Troubled unit includes Hubble's heart

The electronic brains and heart of the Hubble Space Telescope are among the collection of components that make up the unit that failed over the weekend, forcing NASA to shut down scheduled science observations.

A back-up unit is onboard the telescope and flight controllers aim to turn it on and check it out this week. That series of events is expected to take a few days to complete.

Here's a primer on the Science Instrument Control and Data Handling Unit: HST%20SYSTEMS.pdf It comes from the official NASA press kit that was distributed prior to the Hubble servicing mission that was launched in December 1999.

See Section 5.5 and note that the unit is a collection of electronic computers that include: +The NASA Standard Spacecraft Computer (NSSC-1). Known to Hubble flight controllers as "Niss-Key," the computer is the electronic brains of the telescope and has been a workhorse that has operated without major problems for 18 years.

The computer moves data, commands and operations programs -- called "applications" -- for individual science instruments. Its memory stored "time-tagged" operational commands for execution when the telescope is not in contact with the ground.

++The Power Control Unit. Surgically repaired by astronauts on the last Hubble servicing mission in 2002, the power control unit is the electronic heart of the observatory. Electrical power generated by the telescope's twin solar wings is distributed to spacecraft systems and science instruments.

All in all, a major failure that raises questions such as: Is a spare available on the ground, and if so, would NASA decide to delay the upcoming mission and add a change-out to an already packed spacewalking schedule for the fifth and final mission to Hubble?

NOTE ON IMAGES: Click to enlarge the NASA photos of the Hubble Space Telescope as seen by the last astronaut crew to visit the observatory. The first shows astronauts John Grunsfeld and Richard Linnehan installing install a new Power Control Unit (PCU) on Hubble. Grunsfeld is on the end of Columbia's Rrobot arm, which was operated from inside the crew cabin by astronaut Nancy Currie. The second image was recorded with a digital still camera. This shot was taken out the windows of shuttle Columbia after the STS-109 crew released Hubble and headed for a landing at Kennedy Space Center. Photo credit: NASA/STS-109 crew.