Third spacewalk contains “windshield wiper maneuver”

William Atkins
Sunday, 08 June 2008 20:51

Science - Space

The third spacewalk for NASA astronauts Michael Fossum and Ronald Garan, as part of the STS-124 mission, will consist of a ride on the robotic arm by Garan over the top of the International Space Station as he carries a 550-pound replacement nitrogen tank.

Space shuttle Discovery astronauts Mike Fossum and Ron Garan were scheduled to begin their spacewalk at about 10:32 a.m. Eastern Daylight Time (EDT) (1432 GMT). However, they were ahead of schedule, causing their walk in space to start early.

The spacewalk consists primarily of replacing an empty nitrogen tank assembly (NTA) for the Station.

Annette Hasbrook, lead ISS flight director fro STS-124, states, “This is basically a scheduled maintenance. It's like the 50,000-mile checkup on your car." [Space.com: “Astronauts Set for Third Spacewalk Outside Station”]

However, in order to replace the nitrogen tank, one astronaut—Garan—must ride on the end of the Space Station’s 57-foot (17-meter) robotic arm from one side of the ISS to the other side while carrying a 550 pound replacement nitrogen tank.

The maneuver is being called the “windshield wiper maneuver" as the robotic arm moves across the width of the Space Station. At the end of its journey, the robotic arm will be fully extended.

Garan states, "If you think about it, I'm going to be on the end of the arm and as we're doing this windshield-wiper maneuver right here at the top, I'll be 80 feet above the station looking down at the station, looking down at the Earth, It's going to be really exciting, it's going to be really challenging, but I'm really looking forward to it." [Spaceflight Now.com: “Astronauts prepare for mission's final spacewalk”]

NASA mission specialist Karen Nyberg, assisted by Japanese astronaut Akihiko Hoshide, will delicately operate the robotic arm with Garan strapped onto the portable foot restraints on the end of the arm while on the journey to replace the tank.

Nyberg states that Garen will get the ride of his life as he will be positioned: "clearly on top of the world." [Spaceflight Now]

The nitrogen tank is about the size of a refrigerator. It is used to pressurize ammonia coolant lines, which provide cool air for various systems on the International Space Station.

While Garan handles the new tank, Fossum will remove the empty old tank by removing four bolts holding it down. The empty tank is located on the right-side (Starboard side) S1 segment of the power truss of the ISS. The new tank is mounted on an external stowage platform (ESP), specifically ESP-3, on the left side (port side) of the power truss.

What else will the two spacewalkers do today? Please read on. Additional comments by the astronauts is also included.