Two pluses and a minus for NASA on STS-118 flight day six.

William Atkins
Monday, 13 August 2007 18:36

Science - Space

NASA extended the STS-118 mission after successfully testing the new power transfer system. Officials will decide Monday (maybe Tuesday) whether to fix a nasty gouge on Endeavour’s underbelly. A second spacewalk is scheduled to replace a faulty gyroscope.

The Station to Shuttle Power Transfer System (SSPTS) is a new power-distribution module that lets a space shuttle piggyback off the space station’s power supply, its solar arrays, so the shuttle can reduce the use for its own 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.

With the successful operation of the SSPTS, NASA has approved a fourth spacewalk on flight day 10 (Friday, August 17), and extended the mission by three days. This is the first mission for the use of the SSPTS.

STS-118 is now scheduled to land on flight day 13, Monday, August 20. This three-day extension for the mission will make this the longest mission to date for the shuttle flights.

Astronauts aboard Endeavour spent much of Sunday (flight day 5) looking at a much-publicized 3.5-inch-long gouge, along with other damaged areas, with a laser boom attached on the end of the shuttle’s Canadian built robotic arm. The three-dimensional images of the damaged areas will help NASA officials to decide whether to fix them or not.

As of Sunday, the 3.5-inch hole, which has damaged two thermal tiles (while bordering on another one), seems to extend all the way through the thermal shielding—it extends down into the 1.12-inch silica tiles and has dimensions of about 2 inches by 3.5 inches.

Engineers on Earth are simulating the gouge (with computers and in the laboratory) to see if that damaged area can withstand the extreme heat of re-entry without being fixed. The damaged area is located near the right main landing gear door on the right wing. Under the tiles is a thin layer of 0.1 inch felt, which is on top of the aluminum body of the shuttle. Another five tiles have been damaged but are considered of minor damage and, are said by NASA officials to not need repairs.

A close-up photograph of the damaged area is found at the Houston Chronicle website: http://www.chron.com/disp/story.mpl/front/5048239.html.

The estimated six-hour second spacewalk, to be performed by Canadian astronaut Dave Williams and U.S. astronaut Rick Mastracchio on Monday, August 13, will involve removing a failed control moment gyroscope (CMG) and replacing it with one brought with the Endeavour on the external stowage platform-3 (ESP-3). The old CMG will be placed on an older ESP-2 for return to Earth on a future shuttle mission. The gyroscope, along with three others helps to orient the shuttle as it orbits the Earth.