Graphic: mechanics in space

In space, no one can hear you scream. But thanks to the power of radio there were frustrated sighs, grunts and groans aplenty on the airwaves yesterday during a day of drama aboard the Hubble Space Telescope.

The plan was to unscrew a handrail on the outside of Hubble’s Space Telescope Imaging Spectograph (STIS), to make way for the removal of 111 more fasteners and allow access to the instrument for repairs. But a single mangled screw caused a major headache as it resisted attempts by astronaut Mike Massimino to budge it.

“I don’t think it’s coming out. It’s pretty beat up,” he reported.

Closer inspection showed that the screw’s hexagonal head was severely mangled, raising the prospect that the repair job may have to be abandoned. It was only after 90 minutes of struggling by Mr Massimino — and a brainstorming session by dozens of the world’s finest engineers 350 miles below on Earth — was the hurdle surmounted. “Nice work,” mission control in Houston congratulated him last night.

Yesterday’s spacewalk was the fourth in a series of five extra-vehicular ventures by astronauts based aboard the space shuttle Atlantis, which captured Hubble at 17,500mph last week and latched it down into its open cargo bay.

The Space Telescope Imaging Spectograph operates by capturing light from objects billions of light years away and breaking it down into different wavelengths, giving astronomers unprecedented insight into the makeup of stars and planets.

“It’s really important if we want to learn about how fast an object is moving, what it’s made of, what the pressure and temperature is. It’s getting the physics of what’s going on up there in the universe,” explained Malcolm Niedner, Hubble’s deputy project scientist at Nasa.

It was installed on Hubble in 1997 but failed when its five-volt power supply cut out in 2004 after 69,000 hours of service, leaving it dead for the last five years.

Bringing it back to life is a job that had never been considered in orbit before. Its maintenance would ordinarily require sterile conditions in a “clean room” at Nasa, free of contaminants. Exposing it in orbit is a potentially fatal operation for the instrumentation, which could be irretrievably damaged by even the tiniest speck of space dust or jammed if any of the 111 loosened screws drifts into it.

Since this is the final servicing mission to Hubble, Nasa does not have the opportunity to bring the Spectograph down to Earth and return it on a later flight. The space agency took the decision that it would be worth the risk.

David Leckrone, Nasa’s chief Hubble scientist, explained: “STIS was our first black hole hunter. It confirmed for the first time the existence of a super massive black hole in the centre of a galaxy and it went on to make the first detection and chemical analysis of the atmosphere of a planet around another star. We want to keep on doing that kind of work.”

Live footage of the spacewalks is being beamed back to Earth via cameras mounted on the astronauts’ helmets and at vantage points around Atlantis, allowing ground controllers to monitor progress and chip in with comments and advice as obstacles arise.

As Mr Massimino appealed for suggestions to the jammed screw issue, engineers watching live at Goddard Space Flight Centre, in Maryland, simulated the scenario using a Hubble mock-up in a laboratory, to try to find new ways of solving the problem. In the end muscle power was the answer: they snapped the handrail off and told Mr Massimino to down tools and do the same.

The astronaut first wrapped duct tape around the handrail to try to keep it from splintering before snapping it. “It’s like tying poles together in Boy Scouts,” his spacewalk partner, Mike Good, quipped.

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