Discovery will switch to new fuel tank before July blastoff
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: May 6, 2005; Updated at 7:15 p.m. after meeting
NASA managers today decided to stage a second tanking test next weekend or shortly after to troubleshoot problems with the shuttle Discovery's external fuel tank. The shuttle then will be hauled back to the Vehicle Assembly Building where engineers will attach the ship to a different set of boosters and a fresh external tank, officials said late today.
The shuttle will be returned to the launch pad in mid June for launch on the first post-Columbia mission around July 13, the opening of the next available space station launch window. But that date could slip if program managers order yet another tanking test after rollout to verify the performance of the new fuel tank.
NASA had hoped to launch Discovery on the first post-Columbia mission this month, but managers decided last week to delay the flight to the July window because of lingering concerns about the potential threat of ice on the external fuel tank and because of two problems that cropped up during a tanking test April 14.
The ice issue will be addressed by a heater around a liquid oxygen feedline bellows assembly similar to the one used to prevent ice buildups on the struts holding the nose of the shuttle to the external tank. The other two issues with the current tank are more subtle.
During the tanking test last month, two of four hydrogen sensors inside the tank, which are used to control the main engine shutdown sequence when the shuttle reaches space, failed to operate properly. Engineers have not yet pinned down what caused the problem, but all four must be operational for a launch to proceed.
In addition, a valve used to bleed off pressure in the hydrogen tank cycled more often than usual.
NASA managers spent the week debating a variety of processing options, including whether to stick with the current tank, whether to carry out one or two additional tanking tests and whether to swap out Discovery's tank and boosters for a set being assembled for the second post-Columbia flight (STS-121).
During a meeting late today, shuttle managers decided to implement a version of the latter scenario. Here is a timeline of major processing milestones (dates are approximate "no earlier than" targets and as such should be taken with a grin of salt):
Before Discovery is returned to the pad, engineers must decide whether an additional tanking test is needed to verify the performance of the new tank. Such a test would add several days to the processing schedule, pushing launch to around July 18. But if the test is not required, July 13 remains a viable launch target.
Discovery's launch window opens July 13 and closes July 31. The next launch window opens Sept. 9 and closes Sept. 24. A three-day window is available Nov. 8-10, a four-day window opens Jan. 4 and a lengthy window opens March 3 and closes March 19.
The launch window is based on an internal NASA requirement to launch at least the first two post-Columbia missions in daylight. But the issue is complicated by a requirement to also ensure the external tank separates half a world away in enough light to allow documentary photography.
To reach the space station, the shuttle must launch within five minutes of the moment Earth's rotation carries the launch pad into the plane of the station's orbit. When all of those requirements are met, along with others involving temperature constraints on the station, only a limited number of launch windows is available.