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NASA managers mull launch options for shuttle Discovery BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: March 12, 2009 Kennedy Space Center engineers are assessing two repair scenarios to fix a leaking gaseous hydrogen vent line system that grounded the shuttle Discovery Wednesday. One option, which requires engineers to use an expedited repair timeline, leads to a launch try Sunday while the other, which follows an established timeline based on past experience, would result in a Monday liftoff.
Discovery was grounded Wednesday after sensors detected gaseous hydrogen leaking from a vent line attached to the side of the shuttle's external tank. A valve in the tank cycles periodically to reduce pressure when hydrogen gas builds up during the fueling process. The gas is vented overboard and routed to a "flare stack" where the excess hydrogen is burned away. During fueling Wednesday, when the liquid hydrogen section of the tank was nearly full and the vent line was chilled to ultra-low temperatures, a leak developed at the vent line/shuttle interface. Based on past repair experience, a seal in the system must be tightened down after reassembly and allowed to sit for more than a day to correct for possible misalignments during installation. If that repair timeline is followed, Discovery's launch likely would slip to Monday. If engineers can shorten the repair procedure, a Sunday launch try might be possible. For most shuttle launches, a one day slip would not have major consequences. But for Discovery's already delayed mission, the difference between launching Sunday and Monday is the difference between a three-spacewalk mission and one that could be reduced to a single spacewalk. The goals of the shuttle Discovery's mission are to install a new set of solar arrays on the international space station; to ferry a new crew member - Japanese astronaut Koichi Wakata - to the lab complex; to bring astronaut Sandra Magnus back to Earth after four months in orbit; and to deliver a replacement urine processor assembly for the station's water recycling system. Four spacewalks were originally planned, one to attach the new solar arrays and three more to carry out a variety of "get-ahead" tasks for upcoming assembly missions. But because of a conflict with an upcoming Russian mission to rotate space station crew members using Soyuz ferry craft, the docked phase of Discovery's mission must be completed by March 25. That means Discovery must take off by Tuesday, or the flight will slip to the end of the first week in April, after the Soyuz crew rotation mission is complete. For a launch try Sunday, docking would occur on flight day three and the astronauts would have to cancel one spacewalk, along with off-duty time, to ensure an undocking on March 25. For a launch Monday, docking would occur on flight day 4. That would force the crew to give up three spacewalks in order to undock by March 25. The same would be true for a launching Tuesday, which features a flight-day-three docking. All of the mission scenarios assume an undocking on March 25 and landing back at the Kennedy Space Center on March 27. They also all include a non-spacewalk day for a "focused" heat shield inspection and time for urine processor installation and testing.
To help clarify the various scenarios, here's a table, based on options developed when Discovery's launch slipped from February to March, showing mission highlights for launch attempts Sunday, Monday and Tuesday: FL Day..DATE....EVENT March 15 Launch (Flight Day 3 docking): FD-01...03/15...Launch at 7:43:44 PM FD-02...03/16...Heat shield inspection FD-03...03/17...Docking FD-04...03/18...S6 solar array truss unberthing FD-05...03/19...EVA-1 (S6 solar array truss installation) FD-06...03/20...Focused inspection (if necessary) FD-07...03/21...EVA-2 FD-08...03/22...S6 solar array extension FD-09...03/23...EVA-3 FD-10...03/24...Logistics transfers FD-11...03/25...Undocking/late inspection FD-12...03/26...Entry preps FD-13...03/27...Landing March 16 Launch (Flight Day 4 docking): FD-01...03/16...Launch at 7:21:14 PM FD-02...03/17...Heat shield inspection FD-03...03/18...TBD FD-04...03/19...Docking FD-05...03/20...S6 solar array truss unberthing FD-06...03/21...EVA-1 (S6 solar array truss installation) FD-07...03/22...Focused inspection (if necessary) FD-08...03/23...S6 solar array extension FD-09...03/24...Logistics transfers FD-10...03/25...Undocking/late inspection FD-11...03/26...Entry preps FD-12...03/27...Landing March 16 Launch (Flight Day 3 docking): FD-01...03/16...Launch at around 7:17 PM FD-02...03/17...Heat shield inspection FD-03...03/18...Docking FD-04...03/19...S6 solar array truss unberthing FD-05...03/20...EVA-1 (S6 solar array truss installation) FD-06...03/21...Focused inspection (if necessary) FD-07...03/22...EVA-2 FD-08...03/23...S6 solar array extension FD-09...03/24...Logistics transfers FD-10...03/25...Undocking/late inspection FD-11...03/26...Entry preps FD-12...03/27...Landing March 17 Launch (Flight Day 3 docking) FD-01...03/17...Launch at 6:55:29 PM FD-02...03/18...Heat shield inspection FD-03...03/19...Docking FD-04...03/20...S6 solar array truss unberthing FD-05...03/21...EVA-1 (S6 solar array truss installation) FD-06...03/22...Focused inspection (if necessary) FD-07...03/23...S6 solar array extension FD-08...03/24...Logistics transfers FD-09...03/25...Undocking/late inspection FD-10...03/26...Entry preps FD-11...03/27...Landing For reference, here is the mission the Discovery astronauts would have flown if the shuttle had taken off Wednesday, March 11: March 11 Launch (Flight Day 3 docking): FD-01...03/11...Launch at 9:20:14 PM FD-02...03/12...Heat shield inspection FD-03...03/13...Docking FD-04...03/14...S6 solar array truss unberthing FD-05...03/15...EVA-1 (S6 solar array truss installation) FD-06...03/16...Focused inspection (if necessary) FD-07...03/17...EVA-2 FD-08...03/18...S6 solar array extension FD-09...03/19...EVA-3 FD-10...03/20...Crew off-duty time FD-11...03/21...EVA-4 FD-12...03/22...Off-duty time; hatches closed FD-13...03/23...Undocking/late inspection FD-14...03/24...Entry preps FD-15...03/25...Landing An updated flight plan, countdown, etc., will be posted as soon as NASA managers pick a launch target and flight planners generate updated timelines.
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