Tuesday, May 20, 2008
Discovery passes final review for May 31 launch
Discovery Ready For Space Mission
The shuttle Discovery has been given a green light for the May 31 launch, when it will engage in the second of three flights to launch components of the Japan Aerospace Exploration Agency’s Kibo laboratory. The announcement was made on Monday, during a press conference held at NASA’s Kennedy Space Center in Florida, following the Flight Readiness Review.
According to Shuttle Launch Director Mike Leinbach, all preparations are going well. He also added that shuttle work crews will be able to get some time off for the Memorial Day holiday, due to a smooth processing flow of the pre-launch preparations, and return in time for the launch.
Discovery’s STS-124 mission is to install the Kibo’s Japanese Pressurized Module (JPM) and its remote manipulator system (RMS) on the International Space Station, following the successful installation of the Japanese Experiment Logistics Module, during mission STS-123.
Before any launch, two Flight Readiness Reviews need to be conducted, a program-level review and an executive-level review. The shuttle prepares for a 14-day flight to the International Space Station, carrying the largest payload so far (the Kibo pressurized module alone weights 32,000 pounds).
Discovery will also be in charge of delivering new station crew member Greg Chamitoff and bringing Flight Engineer Garrett Reisman back home, after three months aboard the International Space Station, NASA announced.
The STS-124 mission will include three spacewalks, as follows: on day 4, astronauts Ronald J. Garan Jr. and Michael E. Fossum will transfer the Orbiter Boom Sensor back to the shuttle from its temporary location (during the last mission, the Boom Sensor was left at the station for lack of room) and then prepare for the JPM removal from the shuttle’s payload bay.
The second spacewalk will take place two days after the first one. Garan and Fossum will have the mission to install covers and external television equipment on the JPM and remove covers on the RMS, as well as prepare for the flight day 7 relocation of the Japanese Logistics Module.
The third and final spacewalk will be performed by the same astronauts, whose primary mission will be to replace a failed hydrogen tank assembly on the station’s truss with a spare one that has been temporarily stored on one of the station’s external stowage platforms.
NASA managers today cleared the shuttle Discovery for launch May 31, at 5:02:09 p.m. EDT, on a long-awaited three-spacewalk mission to deliver and attach Japan's huge Kibo laboratory module to the international space station. The decision to proceed came after a lengthy discussion on the health of the station's Soyuz lifeboat after back-to-back re-entry problems that led to rough, off-course landings.
Russian engineers are still assessing what went wrong during the descent of the Soyuz TMA-11 spacecraft April 19 when two of the three modules making up the vehicle failed to separate properly before atmospheric entry. The propulsion module ultimately broke free of the crew section, allowing Yuri Malenchenko, outgoing station commander Peggy Whitson and a South Korean space tourist to complete a steep but otherwise safe landing in Kazakhstan.
It was the second such entry mishap in a row and Russian engineers have launched a major investigation to determine what went wrong and whether the Soyuz TMA-12 spacecraft currently docked to the station is healthy. It is a critical issue because the three-seat Soyuz is the station crew's only way home in the absence of a space shuttle in the event of an emergency that might force an evacuation.
It is a critical issue for NASA as well because the agency plans to rotate U.S. crew members during Discovery's flight, ferrying Gregory Chamitoff to the station to join Expedition 17 commander Sergei Volkov and Oleg Kononenko and bringing Garrett Reisman back to Earth. Another shuttle is not scheduled to visit the space station until November. The Soyuz TMA-12 spacecraft will serve as the station's lifeboat until October when a fresh crew is launched aboard a fresh Soyuz. Current plans call for Volkov, Kononenko and U.S. space tourist Richard Garriott, who will ride the new Soyuz to orbit, to return to Earth aboard the TMA-12 spacecraft Oct. 23.
Going into today's executive-level flight readiness review to set a launch date for Discovery, NASA managers discussed a variety of options, including whether to delay the shuttle flight until Russian engineers get a better idea about the status of the Soyuz currently in orbit.
But the Russian investigation into what went wrong during the Soyuz TMA-11 descent is not expected to be complete until the end of June or later and a one week to two week delay for Discovery would not improve the station crew's safety margin.
Bill Gerstenmaier, NASA's chief of space operations, said the odds of a station failure that would force a Soyuz evacuation are low - on the order of 1-in-124 over six months - and that a safe landing would be likely even if similar entry problems occurred.
"If something comes out of the investigation that says the Soyuz is not acceptable as a return vehicle, then we would go take some appropriate action," Gerstenmaier said. "But we haven't seen anything along those lines. For emergency return, Soyuz is OK. ... But the Russians are working through it methodically, trying to identify if there's anything that would invalidate its use as an emergency return vehicle. As long as that doesn't occur, then we proceed with our normal plans. And I don't see anything between now and the 31st that's going to change any of that thinking."
Sources familiar with recent NASA discussions on the Soyuz issue said an assessment of the relative risks of various options played a key role. While the odds of a station problem that would force evacuation are thought to be around 1-in-124 over six months, the overall risk of a catastrophic shuttle failure over the course of Discovery's mission - including all phases of launch, orbital operations and re-entry - is on the order of 1-in-78, according to NASA's latest assessment. Given those relative odds, and the belief that the station is five times more likely to suffer a non-recoverable failure in the absence of a crew to repair it, NASA managers opted to press ahead with an on-schedule launch for Discovery.
"It's a fairly low probability that we'd need to use (the Soyuz) in an emergency case," Gerstenmaier said. "In fact, we analyzed that, we did a probabilistic risk assessment of what the chances were of having to use the Soyuz as a rescue vehicle. It's a low probability we're going to have to use it. But if we use it, we think there's a good probability it'll return the crew and do what it needs to do. So as a parachute or a backup system, it has the reliability that we think we need for a backup system. We have yet to prove it has the reliability that we would use for a nominal return situation."
Discovery is in good shape and on schedule for launch May 31. The only technical problem of any real concern since the shuttle was moved to pad 39A was the failure of a multiplexer-demultiplexer computer system that required a changeout. When the MDM, known as FA2, failed, it caused two of the shuttle's four flight computers to lose synchronization. In flight, that could force a crew to switch to a backup flight system computer, limiting their ability to cope with additional failures. But the MDM was successfully replaced and tested and no concerns about it were raised during today's flight readiness review.
"It's an extremely complicated mission," Gerstenmaier said. "Adding the Kibo module is a big deal for the Japanese. This really brings them up to speed. And adding the Kibo module is not easy. ... We need to be careful we don't assume success and take our eye off of what we're doing. We've got to stay focused. The Soyuz is fine, it will take care of itself, we've got time to work that. That needs to get resolved by the fall. The issue right now in front of is us we need to be 100 percent ready to go fly this flight, we've got to be 100 percent ready to get the Kibo attached. ... We need to work all that activity during the flight and that needs to be our focus."
Commander Mark Kelly, pilot Kenneth Ham, flight engineer Ronald Garan, Karen Nyberg, Michael Fossum, Japanese astronaut Akihiko Hoshide and Chamitoff plan to fly to the Kennedy Space Center on May 28 for the 3 p.m. start of their countdown to launch.
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