07 October 2008

NASA Delays Hubble Space Telescope Repair Mission

Replacing failed system will add another fix to busy spacewalk schedule

Flight day 10 of Hubble Servicing Mission 3B in March 2002 (NASA)

By Cheryl Pellerin
Staff Writer

Washington — Two weeks before space shuttle Atlantis and seven astronauts were to start the final servicing mission to the Hubble Space Telescope, a critical system on the observatory failed, causing NASA managers to delay the October 14 launch.

Servicing Mission 4 to Hubble — the first telescope designed to be visited in space by astronauts to perform repairs, replace parts and update its technology — will deliver new instruments, gyros, batteries and other components critical to extending the observatory’s life through 2013.

Now, the repair team might have to wait until early 2009 to complete its mission, carrying along a spare part whose installation must be squeezed into an already full schedule of spacewalks and repairs. But this is not necessarily bad news.

“Think about if this failure had occurred two weeks after the servicing mission,” Ed Weiler, associate administrator of NASA’s Science Mission Directorate, said at a September 29 briefing.

“We [would have] just put two brand new instruments in and thought we had extended the [telescope’s] life for five to 10 years. If this thing had failed after the last shuttle mission to Hubble, we could have lost the mission in six, 12 or 18 months,” he said. “In some sense, if this had to happen, it couldn't have happened at a better time.”

SPARE PARTS

The telescope’s main onboard computer detected errors September 27 on side A of Hubble's science data formatter, which stores and transmits science data to NASA’s Goddard Space Flight Center in Maryland from the telescope’s five instruments. The formatter is part of the science instrument command and data handling (SIC&DH) system, which has operated successfully on orbit for more than 18 years.

The Hubble operations team has begun the complex process of transferring operations to side B of the science data formatter and five other modules. This will fix the problem but leave the formatter and other modules without backup systems if future problems arise.

Thanks to the foresight of Hubble’s designers, NASA has a spare SIC&DH. Agency managers are working on a plan to test the unit rigorously and get it ready for delivery to the Kennedy Space Center in Florida during the first week of January 2009 for a possible mid-February launch.

Artist’s rendering shows Hubble’s 2008 discovery of the first organic molecule in atmosphere of a planet orbiting another star.

“By going ahead and accepting a delay of perhaps several months,” Weiler said, “we can get our SIC&DH spare tested and ready to go.”

In the months before the spare unit is ready to fly, Hubble will have to use side B of the science data formatter. At Goddard, the operations team is carefully reviewing the process of switching the observatory from side A to side B. The B sides of the modules affected by the failure were last activated during ground tests in the late 1980s and early 1990 before Hubble was launched.

The team is practicing the transition using a Hubble replica called the vehicle electrical system test facility, said Preston Burch, Hubble manager at Goddard.

“Engineers are great at worrying about one thing or another,” he added. “There are concerns that throwing a switch or a relay to turn something on, you might blow a fuse — that sort of thing. ... So we will check that out and see if we note anything unusual in the way of high current draws or difficulty in doing switching, and that will go into our risk assessment.”

After a review of the procedure, top management at Goddard and NASA headquarters will determine whether to proceed with the side switch.

“We do not know the precise location and the exact nature of this failure,” Burch said, “and we probably won't know until we bring the unit down to the ground.”

HUBBLE REPAIRS

During Servicing Mission 4 — actually the fifth time astronauts will have visited the orbiting telescope — and over the course of five six-hour spacewalks, the team will install two new science instruments to enhance Hubble’s capabilities, refurbish Hubble’s subsystems and try the first on-orbit repair of two instruments — the space telescope imaging spectrograph and the advanced cameras for surveys.

The new instruments are the cosmic origins spectrograph and wide-field camera 3. A refurbished fine guidance sensor will replace one degrading unit of three now aboard and maintain the ability to point the telescope.

Astronauts will also install gyros, batteries and thermal blankets to make sure Hubble works efficiently for at least five years after servicing.

The repair mission originally was planned for 2004, but was postponed after the Columbia space shuttle accident in 2003 and then canceled because of safety concerns. After a revamped shuttle program began flying again in 2005, NASA re-examined the risks involved in a Hubble repair effort and approved one last servicing mission.

More information about the Hubble Space Telescope is available at the NASA Web site.