NASA managers today decided to stage a second tanking test next weekend

Update: NASA managers assess shuttle schedule (UPDATED at 7:15 p.m.)

http://cbsnews.cbs.com/network/news/space/current.html

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 should be taken with a
grin of salt):


05/15: Discovery's current tank is reloaded with a half-million gallons of
rocket fuel to collect additional troubleshooting data on engine cutoff
sensors, pressure relief system
05/28: Discovery is moved back to the Vehicle Assembly Building*
06/09: The orbiter is attached to the new booster/tank stack*
06/16: Discovery is moved back to pad 39B
07/13: Launch (assumes no additional tanking test)
* Discovery's rollback depends on when the new tank/booster stack is
completed. Engineers hope to finish the work ahead of schedule, allowing
them to move rollback up by several days or more.


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.




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Jacques :-)

www.spacepatches.info