Two astronauts floated out of the International Space Station (ISS) on Monday to repair equipment crucial for the completion of the orbiting laboratory.
Astronauts Mike Fossum and Piers Sellers, who arrived at the ISS last week aboard the Discovery shuttle with five other colleagues, started the second of three planned spacewalks after stepping out of the ISS’s de-pressurisation chamber.
A day earlier, Fossum said the six-and-a-half-hour spacewalk would be ”quite a ballet”.
”The most challenging thing tomorrow [Monday] is going to be just the choreography,” he said on Sunday from the ISS in an interview with international media.
The astronauts will have to move ”back and forth” in the shuttle’s payload bay and move a spare pump module up to the ISS, he said. Discovery docked to the ISS on Thursday.
The duo will also replace a cable on the ISS’s mobile transporter, a sort of rail car that moves the ISS’s robotic arm along a truss for construction and maintenance work on the unfinished spacecraft.
They will venture out of the ISS again on Wednesday to try out shuttle-repair techniques pivotal for the National Aeronautics and Space Administration’s (Nasa) efforts to increase space-flight safety.
They will test repairs on pre-damaged samples of reinforced carbon-carbon (RCC), a composite material used on the shuttle’s wing leading edges as a heat shield.
”This is our chance to really test out in a zero-gravity vacuum the repair material that might be used,” Fossum said.
In their first spacewalk on Saturday, Sellers and Fossum tested a boom extension on the shuttle’s robotic arm as a possible work platform for future repairs. Nasa described the test as a success.
The US space agency has striven to improve shuttle safety since seven astronauts died in the Columbia disaster in February 2003.
Nasa administrator Michael Griffin wants to conduct 16 more flights to complete the ISS by 2010, when the 25-year-old shuttle fleet is scheduled to be retired.
In addition to testing in-orbit repair techniques, Nasa has made several modifications to foam insulation on the shuttle’s external fuel tank to prevent debris from striking the spacecraft during lift-off.
Such debris pierced Columbia’s heat shield, dooming its return to Earth.
Officials cleared the shuttle to return to Earth on July 17.
Nasa analysts who reviewed images of the shuttle’s heat shield found no damage that could prevent Discovery from coming home.
”We are absolutely clear and ready to bring this vehicle home when our mission is accomplished,” Steve Poulos, the orbiter programme manager, told reporters at the Johnson Space Centre in Houston, Texas.
Discovery will get a final check-up at the end of the mission, however, to make sure it was not hit by micrometeorites while in orbit.
Columbia’s demise was caused by foam insulation that peeled off its external fuel tank and pierced its heat shield during lift-off, dooming its return to Earth on February 1 2003.
Nasa has since made several fuel-tank modifications to limit the size of debris during blast-off.
Officials were pleased with the performance of Discovery’s fuel tank during lift-off, saying it shed small pieces of debris as expected but too late into ascent to cause concern.
Nasa officials had said that the Discovery crew could remain in the ISS and wait for a rescue mission if the shuttle suffered irreparable damage. — AFP
