Space shuttle astronauts will attempt an unprecedented in-orbit repair of key Hubble Space Telescope (HST) instruments during the servicing mission scheduled for August 2008. The repairs, along with the addition of two new instruments, will make Hubble 90 times as powerful as it was after its flawed optics were corrected in 1993.

In October 2006, NASA announced plans to carry out a fourth and final servicing mission for Hubble, in which it would install two new scientific instruments and replace the observatory's batteries and gyroscopes. But previously the agency has not said whether it would attempt a difficult repair of two key instruments that have broken down in recent years.

The Advanced Camera for Surveys (ACS), which died in January 2007, was Hubble's highest resolution camera and its most-used instrument. And the Space Telescope Imaging Spectrograph (STIS), which failed in 2004, measured light spectra in the ultraviolet, allowing it to gauge the distance and composition of distant galaxies.

Now, the space agency says it will try something never attempted in the three previous Hubble servicing missions – a finicky electronics repair job in space, where astronauts have the challenge of doing everything while wearing bulky spacesuit gloves.

Without the repair mission, Hubble would likely die by 2011, when its last functioning gyroscope is expected to fail. But with new gyroscopes and batteries installed on the upcoming servicing mission, HST should last at least until 2013, and possibly into the 2020s.

Early galaxies

Two powerful new instruments will be installed on the mission. The Wide Field Camera 3 (WFC3) will allow Hubble to see fainter and more distant galaxies than anything it has seen before, shedding light on the early universe.

This could allow Hubble to see galaxies so far away that we see them as they were just 400 million years after the big bang, says Sandra Faber of the University of California in Santa Cruz, US, a member of the panel that recommended that NASA carry out the final servicing mission.

To date, the most distant galaxies seen by Hubble appear to be from about 800 million years after the big bang, which occurred 13.7 billion years ago. "The universe evolves extremely rapidly at these early times, so a [time] difference like this makes a huge difference in the structure and size of galaxies [that exist in those eras]," Faber said at a press conference on Tuesday at a meeting of the American Astronomical Society in Austin, Texas, US.

Another new instrument, the Cosmic Origins Spectrograph (COS), can obtain ultraviolet light spectra of very faint, distant objects such as quasars – huge black holes that are glowing as they gobble up surrounding gas. COS can measure much fainter objects than STIS, although STIS can get more detailed spectra of the objects it can see.

'90 Hubbles'

With its new instruments, Hubble will be 90 times as powerful as it was supposed to be when first launched – it will be like having 90 of the original Hubble Space Telescopes, astronomers say. The improvement comes from a combination of increased sensitivity and wider fields of view, allowing Hubble to see 900 galaxies where its original instruments would have revealed only 10. HST will be about 60% more powerful than it was right after the third servicing mission, before ACS and STIS failed.

The most challenging part of the mission will be to repair ACS and STIS. "We're going to do something that has never been done in space," said John Grunsfeld, NASA's lead spacewalking astronaut for the servicing mission.

Both repairs involve astronauts unfastening dozens of tiny screws to replace some circuit boards on each of the instruments – all while wearing bulky spacesuit gloves. Such a feat has never been attempted before in space.

The astronauts will also have to cut through metal layers to reach the circuit boards, creating sharp edges that could be hazardous to spacesuits. In the case of ACS, Grunsfeld may not even be able to see the screws he is working with because of the way the instrument is angled inside HST.

Risky business

Grunsfeld has been practicing this tricky manoeuvre in a "neutral buoyancy laboratory" – a water tank designed to simulate the weightlessness of orbit. "Amazingly ... training in a neutral buoyancy lab in the spacesuit, I've been able to do this," he said.

He added that he is willing to put his life on the line for the risky mission. "I still believe that Hubble science and the Hubble programme is still something worth risking my life [for], and I know I have six other crew members who believe that as well," he said.

NASA science chief Alan Stern said although the mission is still scheduled for August 2008, it could slip because of the launch delays the space shuttle has been experiencing in its missions to assemble the International Space Station. "Our watchword in all of this is safety," he said, adding that if the servicing mission needed to wait until October or even later to make sure the shuttle is safe, then NASA would wait.

During the mission, new insulation blankets will be wrapped around Hubble to make up for cracks in existing insulation and a fine guidance sensor will be added to help HST point itself precisely. Astronauts will also install a "soft capture mechanism" to allow a future robotic mission to grab onto Hubble at the end of its lifetime so that it can safely re-enter the atmosphere and crash into the ocean.

Comment subject
Comment
No HTML except lower case italic tags or lower case bold tags, please: <i> or <b>
Your name
Your email
	We need your email in case we need to contact you about the comment. We will not use it for any other purpose.

• For exclusive news and expert analysis every week subscribe to New Scientist Print Edition
• For what's in New Scientist magazine this week see contents
• Search all stories
• Contact us about this story
• Sign up for our free newsletter