Astronaut handyman repairs heat shield
After ride on robot arm, spacewalker plucks out protusions that may have imperiled shuttle’s return to Earth.
JOHNSON SPACE CENTER, Houston - A spacewalking astronaut rode the International Space Station's robot arm to a traditional no-man's land Wednesday, going under the belly of the shuttle Discovery to inspect and repair its heat shield.
Two pieces of stiff filler material were protruding from the black silica-tile mosaic that will protect the orbiter and its crew of seven from a tornado of fire when Discovery enters the atmosphere on its way back to Earth.
NASA's Stephen Robinson plucked out the thin fabric scraps with the thumb and forefinger of his gloved right hand, alleviating ground controllers' fears that the protruding straps could cause an overheating incident during the shuttle's scheduled descent from orbit on Monday.
The first space shuttle mission in 30 months has Discovery docked at the space station to deliver supplies and do outside maintenance. In spacewalks July 30 and Aug. 1, Robinson and partner Soichi Noguchi of Japan mounted a platform for spare parts, repaired the station's stability-controlling gyroscopes, and tested ways to patch the shuttle's heat shield.
With the maintenance operation Wednesday, Robinson became the first astronaut to work on the underside of a space shuttle in orbit. The operation, which Robinson described as "super-smooth and easy, as well as historic," took a little more than an hour and had him out of his crewmates' direct line of sight for at least 15 minutes.
That's usually forbidden, but ground controllers kept watch over Robinson through a camera in his helmet and others on the space shuttle's robot arm. They instructed him to keep talking throughout the maneuvers in the event the cameras failed. The absence of a running commentary would have been a sign that something had gone wrong.
Robinson perched himself on the space station's 35-foot-long arm shortly after 7 a.m. EDT and got what he called the "ride of the century" from shuttle pilot Jim Kelly. Working from a control panel aboard the space station, Kelly reached the arm around the right side of the winged ship and positioned Robinson within arm's reach of the heat shield, a mosaic of black silica tiles.
"I'm grabbing it and I'm pulling and it's coming out very easily," he said as he laid fingers on one protrusion. The second one came out just like the first.
"Maybe you have to be an old aerodynamicist like me, but the surface of this belly is a work of art," Robinson said.
The gap fillers he removed aren't used for heat protection. They are designed to keep the delicate tiles from "chattering" under the vibrations of launch. Now that the fillers are no longer a concern, all but one small part of the orbiter's surface has been cleared for re-entry. Engineers were examining an insulating blanket below the left side commander's window, just above the "D" in the word "Discovery" on the shuttle's nose. The white blanket appeared puffed out, torn and frayed in views taken by a camera attached to a 50-foot-long boom in the grasp of the shuttle's 50-foot-long robot arm.
The loose blanket doesn't pose a thermal threat because it covers a spot that stays relatively cool. Engineers are worried more about debris and the damage the blanket could cause if it tears loose and hits a wing flap or other important flight control surface.
At Johnson Space Center, home of Mission Control, lead flight director Paul Hill said engineers were evaluating a range of options for removing or shredding the blanket, but he downplayed the likelihood that any of the ideas will be needed. Hill admitted that ground controllers and the astronauts had "apprehensions" about a possible fourth spacewalk but expressed confidence the misgivings can be overcome, if necessary.
Robinson and the rest of the shuttle crew demonstrated what NASA has long sought--the capability to deal with crisis scenarios in mid-mission. "We proved we can get access to the bottom of the vehicle," lead spacewalk officer Cindy Begley told reporters.
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