Spacewalkers replace a failed station component
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 13, 2007
Astronauts Rick Mastracchio and Dave Williams successfully replaced an ailing control moment gyroscope on the international space station today to accomplish the primary goal of their second spacewalk.
The spacewalk began at 11:32 a.m. and ended at 6 p.m. for a duration of six hours and 28 minutes.
This was the 90th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the 13th so far this year. Seventy two men and women from the United States, Russia, Canada, Japan, Germany, France and Sweden have now logged 557 hours and 29 minutes of EVA time building and maintaining the lab complex.
The space station uses four control moement gyroscopes, or CMGs, to control the lab's orientation without burning hard-to-replace rocket fuel. One of them, CMG No. 3, acted up last year and was taken off line on Oct. 10, 2006. The unit installed today will restore full redundancy to the critical orientation system.
The replacement CMG rode into space mounted on a 600-pound pallet in the shuttle's cargo bay. Mastracchio and Williams first removed the suspect CMG-3 from its place in the Z1 truss atop the station's central Unity module and temporarily mounted it on a handrail fitting. Then they moved down to the shuttle's cargo bay - Williams on the end of the station's robot arm - and removed the new CMG and a carrier platform.
"Hey Scorch, the motion of the arm is incredibly smooth," Williams radioed arm operator Charlie "Scorch" Hobaugh as he was being moved down to the cargo bay.
"It's because I ain't doing it," Hobaugh joked, referring to the arm's computer control.
"I thought you wre driving real well there."
"Man, I could have taken credit for that," Harbaugh said.
"This is the most amazing ride I've ever had," Williams marveled.
"There's work on the other end," Harbaugh reminded him.
"Yeah, I can see it coming up."
Williams, still on the robot arm, manually carried the hardware up to External Stowage Platform No. 2 near the Quest airlock. The new CMG then was removed from its carrier plate and installed in Z1. CMG-3 was mounted on the ESP-2 carrier plate where it will remain until it is returned to Earth later this year.
The new CMG will not be fully spun up to 6,600 rpm until later this week. But initial electrical checks showed it was properly wired into the lab's electrical system.
"How's the ride, Dave, and the stability of that big boy?" one of the astronauts inside the space station asked Williams at one point.
"Great. It's got a lot of mass," Williams said, manually holding the 600-pound gyro and the mounting plate.
"This is NOT a jettison mission, OK?" the other astronaut joked.
Later, referring to the old gyro, station astronaut Clay Anderson quipped: "If you have time, you might want to whip out a piece of gray tape and a Sharpie and stick it on the CMG and write 'suspect, return to ground.'"
Mastracchio had a brief scare around 4 p.m. when a faulty carbon dioxide sensor indicated an apparent CO2 buildup in his spacesuit.
"Our assessment right now would be to clock it..." someone was saying.
"Break, break, break...
"Break! Break!" someone yelled urgently.
"CO2 sensor bad. CO2 high," Mastracchio radioed.
"Stand by," someone said.
"48.3 millimeters. I guess the CO2 sensor went bad, I'm hoping. It says 'open purge valve,' but I'm not going to do that."
"Stop arm motion. Stop arm motion," someone said.
"How you feeling, Rick?" astronaut Tracy Caldwell asked from inside the shuttle.
"I feel fine."
Flight controllers monitoring telemetry from the suit told the astronauts Mastracchio's spacesuit was in good shape and the two astronauts were cleared to continue the spacewalk.