Future looks bleak for powerless Hubble device

But robotic mission may yet save the telescope

Washington

Jupiter's atmosphere glows in a stunning image taken by Hubble's spectrograph. Credit: NASA/JPL

One of the Hubble Space Telescope's four scientific instruments has shut down and seems unlikely to be resurrected.

Astronomers are not optimistic about repairing the Space Telescope Imaging Spectrograph, one of the telescope's workhorses. “There's some hope, but it is small,” says Bruce Margon, a science director at the Space Telescope Science Institute in Baltimore, Maryland.

The spectrograph, which records specific frequencies of visible and ultraviolet light, failed on 3 August owing to a faulty power unit. Project officials are currently mulling over the few options open to them. The instrument has a back-up power supply, but that has not been used since it was repaired in March 2002 and engineers are not sure whether it will work properly.

The instrument has already lasted two years longer that it was designed to do. Astronomers had come to rely on it: at present, it features in some 30% of planned Hubble science observations.

If the device cannot be revived, the onboard Advanced Camera for Surveys could provide limited spectra images. Hubble's data could also be supplemented with spectra taken from the ground.

The Cosmic Origins Spectrograph, due to be installed on Hubble during a repair mission in 2006, could perform a few of the imaging spectrograph's functions. But NASA is currently reviewing plans for the 2006 repairs and deciding whether astronauts or robots should do the job, or whether it should be cancelled altogether. The agency said this week that it would start developing plans for a robotic mission, but would not make its final decision until next year.

NASA has also awarded a study contract to a team at the Johns Hopkins University in Baltimore to see if the Cosmic Origins Spectrograph and another camera planned for Hubble could fly on a separate satellite instead.

Box 1: Hubble Trouble

NASA chief Sean O'Keefe told engineers at the Goddard Space Flight Centre in Maryland on 9 August that they should start planning a robotic rescue mission to save Hubble. "Everybody says, 'We want to save the Hubble'… well, let's go save the Hubble," said O’Keefe, according to Florida’s Orlando Sentinel.

O'Keefe speculated that a mission might cost more than $1 billion, but Goddard’s director, Al Diaz, would not be drawn on whether this was a reasonable estimate when he spoke at a press conference the following day. O'Keefe says he will prepare an amendment to the US president's budget, which will be submitted on 1 September, and it will be up to Congress to fund the mission.

Since the Columbia crash, O'Keefe has ruled out a manned mission to repair the telescope, saying that it was too risky to plan to use a space shuttle before it had been given a clean bill of health. The shuttle fleet have been grounded since the crash in February 2003, with the 'return to flight' expected in spring next year. Before the disaster, NASA had planned a manned repair mission to Hubble in 2006, which would have installed new batteries and gyroscopes. The mission would also have installed instruments to replace those, such as the Space Telescope Imaging Spectrograph, that are beginning to fail.

As Hubble's batteries run down and its stabilizing gyroscopes fail, it will lose the ability to focus on a fixed point. NASA expects this to happen in late 2007 or early 2008, so any servicing mission would probably take place earlier in 2007.

The leading contender for a repair mission is the Special Purpose Dexterous Manipulator (Dextre), a robot with two arms that has been developed for installation on the International Space Station in 2005. Dextre was created by the Canadian Space Agency for intricate servicing work on the exterior of the space station and would be well suited to the Hubble job.

Dextre is a prime candidate because, unlike other potential saviours, it has already been built. Each arm is about three metres long and has seven joints, giving it complete freedom of movement; it has already proved adept at replacing components in an ISS mock-up. It carries four cameras, and would be controlled remotely by trained operators.

Human Presence in Space