Astronauts to replace flawed Hubble camera

WITH the second of five scheduled spacewalks successfully completed yesterday, hopes are rising that the marathon rescue and repair mission for the Hubble space telescope will remedy all the faults on the dollars 1.6bn ( pounds 2.4m) instrument.

The emphasis will now switch from the engineering essential to keep the telescope working, to improving the astronomy it can perform.

The next stage of the repair mission, which should have started at about 4am (British time), is extremely delicate. In the third spacewalk, Story Musgrave and Jeff Hoffman have to replace the 270kg (595lbs) wide field and planetary camera.

The new camera contains a a coin-size mirror that has been ground to a prescription that should compensate for a flaw in Hubble's main 94in (238cm) mirror. In addition, the new camera will be able to 'see' well in ultra-violet light.

In theory, the camera should slide like a drawer into the telescope. But the astronauts will first have to remove the protective cover without touching the mirror itself. If, encumbered by space-suits and gloves, they do touch the mirror, they will ruin it: knocking it out of alignment and contaminating its surface.

In their spacewalk, which ended early yesterday morning, Endeavour astronauts Kathy Thornton and Tom Akers successfully equipped the Hubble telescope with two new solar panels to provide power for its operation. The astronauts spent more than six hours in space, fitting the new panels and jettisoning an old one that had buckled.

Nasa's mission controllers had ordered Ms Thornton and Mr Akers to ditch the panel, which was stuck in the open position, after Mr Musgrave and Mr Hoffman failed to roll it up and stow it in Endeavour's cargo bay during their first space walk on Sunday. Like the originals, the new panels have been supplied by the European Space Agency and built by British Aerospace.

Made of Teflon sheets covered with photovoltaic cells, the new solar arrays convert the sun's energy into electricity for scientific instruments inside the telescope. The original arrays fluttered like wings when the telescope moved in and out of darkness, interfering with the telescope's alignment.

As Ms Thornton let the panel go, shuttle commander Dick Covey slowly moved the craft away, leaving the panel to join some 7,000 pieces of debris from space missions, which will gradually be pulled towards the earth and burn up on re-entering its atmosphere.

As Ms Thornton released the panel, it caught the light from the sun, standing out against the deep blue of the Indian ocean 590km (360 miles) below as the craft orbited at 29,000km an hour.