Space

Problems with a spare part for the Hubble Space Telescope - which has been stored for years at a NASA centre - may further delay a shuttle mission to repair and upgrade the telescope now targeted for launch in February.

On 27 September, errors turned up in Hubble's science data formatter, which relays data between Earth and the probe's science instruments. The failure has prevented the telescope from making observations.

There is an identical formatter - known as 'Side B' - on the telescope, and NASA is planning to boot up that backup system next week. If all goes according to plan, that would restore the telescope to life.

But there is no backup for Side B, so last week NASA decided to delay its mission to service the telescope from October to no earlier than February in order to prepare a replacement part for flight.

Now, preliminary checks into the history of the spare, which has been stored at NASA's Goddard Space Flight Center in Greenbelt, Maryland, suggest the device might not be ready to fly in February.

Bad record

The spare, known as the Science Instrument/Command & Data Handling (SI/C&DH) system, was developed years after Hubble's unit and is not an exact replica of it, says Hubble manager Preston Burch of Goddard.

For example, Hubble's unit stores data using older, "core" memory technology, some types of which are very robust against power failures. The flight spare, however, uses modern CMOS memory, which can be lost when the unit loses power.

The flight spare was tested around the time of the telescope's launch in 1990, and again in 2001, during tests of a cooling unit for the probe's Near Infrared Camera and Multi-Object Spectrometer. Records show that glitches occurred in the device during those tests, Burch told New Scientist.

Extra delays

The team is still digging through paperwork on the unit, but the system seems to have trouble relaying commands. "There were a number of problems that were discovered with it," Burch told New Scientist. "Those anomalies were never fully resolved."

The team is now re-assembling the unit and plans to power it up on a mock-up of the telescope's electrical system, called the Vehicle Electrical System Test facility, or VEST, as early as 20 October.

But given the device's troubled history, the planned February launch might be "very ambitious", Burch told New Scientist. "We won't have a lot of confidence in our February schedule until we've had an opportunity to run this thing on the VEST for a week or two to see what we've got."

If problems with the unit are difficult to fix, this might result in additional delays to the servicing mission. This could strain NASA's already tight shuttle launch schedule, since the agency hopes to launch the repair mission with a back-up shuttle at the ready and the shuttles are set to retire in 2010.

Better to wait

Still, some experts say NASA is more likely to delay the repair mission than launch without the spare. "They'll go when they're ready," says Howard McCurdy, a space policy researcher at American University in Washington, DC.

In the meantime, the Hubble team is planning to boot up the telescope's backup system. That entails switching not only the telescope's formatter but also six other units over to their B sides, a process that is expected to take 47 hours.

Ground testing of the switchover was completed on Monday, but the Hubble team is still awaiting approval from top NASA officials to make the switch.

If they give the green light, the transition to Side B could begin as early as 15 October, allowing Hubble to return its first new images by late next week.

In addition to replacing the SI/C&DH during the shuttle servicing mission, NASA aims to replace two of Hubble's instruments, repair two others, and install all-new gyros, batteries and insulation on the telescope. The revamp could give Hubble its best vision yet and extend the telescope's life to at least 2014.

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