Astronauts at the International Space Station have overcome initial fears and are preparing to perform the first spacewalk beneath the shuttle to repair two dangling pieces of material.
The material, used to fill gaps between tiles, is sticking out between tiles that protect Discovery's underside during launch. When the shuttle lifts off, the tiles protect the vehicle from hot gases flowing near the external fuel tank.
NASA engineers are worried the protruding material could change the normally smooth airflow during re-entry, creating turbulent hot air that might pose a risk to Discovery and its crew. Columbia broke up in 2003 upon re-entry when hot gases entered a crack formed during launch.
On Wednesday, astronaut Steve Robinson will be attached to the station's robotic Canadarm2. In a new move for the arm, it will reach around the vehicle to allow Robinson to reach the 'gap fillers.'
'I think a number of us, we did have some misgiving,' about the repairs said Australian astronaut Andy Thomas.' We were concerned about the implications of it and what was motivating it.'
After learning more about the robotics and the spacewalk tasks, the crew's reservations eased, said Paul Hill, lead flight director.
Ground controllers initially had the same reaction, he said.
'I am pretty comfortable with using tools very carefully,' Robinson told a news conference early Tuesday. 'But no doubt about it, this is going to be a very delicate task. But as I say, a simple one.'
NASA's first preference is for Robinson to pull out the two pieces with his gloved hand. One piece is protruding 2.5 centimetres and the other 1.5 centimetres.
If that doesn't work, he'll try using a hacksaw made with a bent metal blade tested to withstand the temperatures of space, while the fabric is held with forceps.
Robinson could also use scissors to cut the material so less is protruding, if he cannot remove it.
The shuttle's arm and the station's arm will move at different times and in different areas during the spacewalk to prevent them from touching each other.
To try to prevent Robinson or his tools from inadvertently striking the tiles, he will keep his safety tethers behind him, not take any extra tools and take care to keep his helmet from bumping into the bottom of the shuttle, said astronaut Dave Wolf, who demonstrated the repair tasks for reporters.
NASA officials decided it was better to try the choreographed repair mission rather than accept the uncertainty of how the protruding tile material could affect the shuttle during re-entry.
During Wednesday's spacewalk, astronauts will also scan for damage to the shuttle and attach a new external stowage platform onto the station. |