Five days after work to replace the grapple fitting on one end of the space station's robot arm, commander Randy Bresnik and flight engineer Mark Vande Hei ventured back outside the lab complex Tuesday to continue servicing the arm, to replace a degraded camera and to carry out routine maintenance.
Floating in the Quest airlock, they switched their suits to battery power to officially begin the excursion. This is the 204th spacewalk devoted to station assembly and maintenance since construction began in 1998, the ninth so far this year, the fourth for Bresnik and the second for Vande Hei.
Last Thursday, the spacewalkers replaced the grapple fitting on one end of the Canadarm 2 space crane. Today, Vande Hei plans to lubricate the internal mechanism of the replacement fitting. The astronauts also will replace a degraded camera group and re-orient a spare ammonia coolant system assembly so it can be vented prior to relocation later.
Toward the end of the spacewalk, Bresnik will replace a camera lens cover and remove two handrails from the Tranquility module to make way for future installation of additional wireless antennas.
For identification, Bresnik, call sign EV-1, is wearing a suit with red stripes and using helmet camera No. 18 while Vande Hei, EV-2, is using an unmarked suit equipped with helmetcam 20.
Servicing the station's aging robot arm, or space station remote manipulator system -- SSRMS -- is is a critical priority given the space crane's central role in lab operations, moving astronauts and equipment to various work sites around the outpost and capturing visiting cargo ships.
Both ends of the seven-joint arm are fitted with latching end effectors, or LEEs, to grapple components, visiting vehicles, spacewalker foot restraints and the station itself. It can move inchworm fashion from one anchor point to another and ride a mobile transporter to reach various worksites along the lab's power truss.
Bresnik and Vande Hei replaced the LEE-B mechanism last Thursday while LEE-A will be replaced during a spacewalk early next year.
"Our primary objective is to make sure we get the SSRMS recovered and fully functional, " said Kenny Todd, space station operations integration manager. "The SSRMS played a critical role in the assembly of station, but it's playing just as critical a role today in the overall execution of the program when it coms to science, when it comes to inspections, when it comes to putting visiting vehicles on station.
"It's just an absolute critical asset that our Canadian partners have contributed. We're very excited about getting out and getting it fully recovered and functional."
After floating out of the Quest airlock, Bresnik planned to reconfigure a latch on a nearby high-pressure oxygen tank and then move to the left side of the Destiny lab module to rotate the spare coolant assembly to permit venting later. Vande Hei, meanwhile, will make his way to the robot arm transporter to retrieve a foot restraint and install it on one end of the SSRMS.
After helping Bresnik with the flow control assembly, Vande Hei planned to lock his boots to the end of the robot arm, working with Bresnik to replace a degraded camera group. Vande Hei then will get off the arm and set up to lubricate the internal mechanism in the newly installed LEE-B grapple mechanism while Bresnik works on a variety of other relatively minor tasks.
If all goes well, Bresnik and Joe Acaba will carry out another spacewalk Oct. 18 to finish the arm lubrication work, to install another group of cameras and to carry out additional routine maintenance.