Endeavour’s STS-118 crew preparing for 3, possibly 4, spacewalks

William Atkins
Thursday, 09 August 2007 19:55

Science - Space

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The ISS’ robotic arm will attach the S5 (Starboard-5) truss segment to the S4 segment. The S5 truss segment has dimensions of 10.5 feet by 15 feet, and is the tenth of eleven trusses to be attached on the station. Spacewalking astronauts Dave Williams and Rick Mastracchio will remove locking devices from S5 in order to attach it to the station. A radiator will be re-positioned on S5 so that solar arrays, to be delivered on a future mission, can be attached.

The second spacewalk (EVA-2) takes place on flight day 6 (Monday, August 13). Its main goal will be to remove a failed CMG (Control Moment Gyroscope) and install a new CMG.

Williams and Mastracchio will remove a defective CMG and replace it with a new one brought with the Endeavour. The crew also brought with them an un-pressurized platform (called External Stowage Platform-3 [ESP-3]) that holds the new gyroscope. The failed gyroscope will be placed on an older ESP-2 for eventual return to the Earth.

The third spacewalk (EVA-3) will occur on flight day 8 (Wednesday, August 15). Its primary purpose is to relocate the SASA (S-Band Antenna Structural Assembly), move two CETA (Crew and Equipment Translation Aid) carts, retrieve the MISSE (Materials International Space Station Experiment), and retrieve the P6 Transponder.

ISS Expedition 15 crew member Clayton Anderson and Endeavour crew member Mastracchio will work on preparatory work to relocate the P6 truss segment, which will actually be moved during the next mission to the station (STS-120) in October 2007. Part of the prep work will be to retrieve the P6 Transponder. In addition, two CETA carts will be moved with the use of the station’s robotic arm. An SASA antenna will also be moved to a new location and some upgrade work will be performed on avionics/communications systems.

A possible fourth spacewalk (EVA-4) may occur on flight day 10 (Friday, August 17). This action will occur if the new power-distribution module called SSPTS (Station to Shuttle Power Transfer System) is successful. The SSPTS allows the space shuttle Endeavour to use the power generated by the station’s solar array to reduce the shuttle’s use of its fuel cells. The SSPTS converts up to eight kilowatts of electrical power from the station’s 120-volts direct-current main voltage to the shuttle’s 28-volts direct-current system.

Consequently, the mission can be extended three days if the SSPTS works successfully. Endeavour is the first space shuttle to use the SSPTS, and this is the first mission in which the SSPTS is being used.

If the SSPTS is successful, Anderson and Williams will install support equipment on the S1 truss so that an inspection boom (which provides inspection ability to the station’s protective shell from damage of space debris) can be installed on STS-123 in February 2008. A wireless video system will also be installed.

The Endeavour also has transported Spacehab to the space station.  It is a pressurized aluminum module that was carried to the station within the shuttle’s cargo bay. It contains about three tons of new cargo and scientific research projects. It will be returned to the Earth with about 1.5 tons of no longer needed cargo, along with the MISSE- PEC (where PEC is short for Passive Experiment Containers), which contains specimens that will be studied on Earth for reactions to their exposure to outer space.

Basic information for this article was provided by the NASA STS-118 webpage located at: http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts118/index.html.

All of the spacewalks can be viewed on NASA TV. The TV schedule of the spacewalks, and other STS-118 activities is found at: http://www.nasa.gov/multimedia/nasatv/mission_schedule.html.