Fossum demonstrates heat shield repair work
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 8, 2006
Astronaut Mike Fossum, anchored to the end of a 100-foot space crane positioned at one end of the space station's solar array truss, pretended to make heat shield repairs today, measuring the forces imparted to the untried space crane to judge its stability as a repair platform.
The tests appeared to go well and while some exercises were easier to accomplish than others, the shuttle robot arm/inspection boom combination seemed stable enough to serve as a repair platform if real repairs are ever needed.
If an engineering analysis confirms that, future shuttle crews would have a way to reach virtually any part of a shuttle's heat shield to make repairs, regardless of whether the space station was available. That could be a factor in any decisions down the road to approve a mission to repair the Hubble Space Telescope. Because the observatory is in a different orbit, a Hubble crew would not be able to reach the space station in an emergency.
But it will take engineers time to fully evaluate the data from today's test and to debrief the crew after the flight. As such, it's too soon to say whether the crane might be a viable option.
Television views from the station were spectacular, showing Fossum and Piers Sellers floating high "above" the shuttle's open cargo bay, making various movements, or inputs, to help engineers characterize the crane's rigidity.
"You guys look pretty lonely out there," shuttle pilot Mark Kelly radioed from Discovery's flight deck.
"Well, I'm just looking at Mike," said Sellers. "That's all I've got to look at right now, There's nothing else!"
"We can see you out the window of our warm, comfortable cabin," Kelly joked.
"As a matter of fact, I am."
With both astronauts on the end of the boom, large swaying motions resulted from crew movement. But the swaying appeared to damp out quickly. The mock repair work up on the space station's solar array truss went to the point of the exercise.
One technique for repairing damaged heat shield tiles calls for spacewalking repairmen to spread on a viscous material called "emittance wash" to help restore the tiles' ability to reject heat.
Using a stand-in for an emittance wash application tool, Fossum went through the motions of applying the material, lightly holding a hand rail with one hand for stabilization and wielding the tool with the other.
"You have a desired point you want to apply it in, desired plus or minus a tenth of an inch, adequate a half of an inch, and you're going to use a handrail lightly for stabilization while you do this," Kelly said, reviewing the procedure.
"Ready to start... ready, ready, now," Fossum said. "Input stop. It was very easy to get the desired performance. No problem at all."
Next, he repeated the test using an open hand for stabilization, reporting he "had to work harder."
"To do the task in general, you have to, you've got to lean in, put a light pressure on it and then offset with the other hand," he said.
Finally, he repeated the test without doing anything for stabilization.
"Ready, ready, now... You know, this isn't bad," he reported. "The back and forth that time was eight, a little more compensation required, I still think I got desired performance. A moderate amount of compensation."
Fossum then went through the motions of other tile and wing leading edge panel repair techniques, reporting varying degrees of success. Before the robot arm/inspection boom can be used for an actual repair, engineers will need to evaluate videos and data from instruments that precisely measured how much force the astronauts put into the system.