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Friday, February 25, 2011

Discovery STS-133 Launches After Brief Hold

STS-133's near-perfect day was slightly marred by an unscheduled hold at T - 5:00 due to a problem with a command system computer operated by the Air Force's 45th Space Wing in supervision of the Eastern Range. Discovery launched with only two seconds remaining in the launch window.

blog post photo
Credit: Heather Goss

At KSC's post-launch press conference, NASA said they had few details available about the actual computer problem because the computer in question is operated by the 45th Space Wing and not by NASA.

When the computer problem developed, the 45th Space Wing went "no go" to discuss the problem. NASA decided to count down from T - 9:00 to T - 5:00 to give them four more minutes as the launch window diminished. STS-133, scheduled to launch at 4:50pm ET, had only three minutes of additional launch window, with the last possible launch time being around 4:53pm.

Prior to resuming the count down from T - 5:00, NASA Launch Control received word from the 45th Space Wing that they would be clearing for launch. At that point, NASA began preparing to resume the countdown since the time remaining was so small.

Regarding the two-second margin, Mike Moses, chairman of the Mission Management Team, joked, 
"It was one more second than Mike Leinbach [shuttle launch director] needed to get the job done, so there was plenty of margin."
Leinbach said launch simulations have conditioned the team of controllers to handle the pressures of last-second "go" decisions without jeopardizing a mission.

"This was one for the record books," Leinbach said. "It may have seemed a little rushed to people on the outside. It's a testament to the team that we have practiced for this."

Here are the relevant updates from Spaceflight Now:
T - 9:00 scheduled hold, 2127 GMT (4:27 p.m. EST)
The Eastern Range is "no go" at current time because of a problem with the central command computer.

T - 9:00 scheduled hold, 2129 GMT (4:29 p.m. EST)
The Air Force-controlled Range is working the problem in hopes of getting the computer system back online for launch at 4:50 p.m. EST.

T - 9:00 scheduled hold, 2132 GMT (4:32 p.m. EST)
Launch director Mike Leinbach says the option is available to resume the countdown at T-minus 9 minutes and continue down to T-minus 5 minutes even if the problem isn't resolved. That would give the Range a few more minutes to resolve the problem. But NASA doesn't like going beyond T-minus 5 minutes until all systems are "go."

T - 9:00 scheduled hold, 2133 GMT (4:33 p.m. EST)
Mike Leinbach just radioed commander Steve Lindsey and said the team is ready to take things down to the wire if necessary to get the Range problem resolved.

T - 9:00 scheduled hold, 2138 GMT (4:38 p.m. EST)
NASA launch director Mike Leinbach has conducted his poll and given approval to resume the countdown to proceed down to T-minus 5 minutes and hold there if Range isn't "go" by then.

T - 5:00 unscheduled hold, 2145:27 GMT (4:45:27 p.m. EST)
T-minus 5 minutes and holding. The countdown has stopped for the Range problem. The available launch window extends only three more minutes.

T - 5:00 unscheduled hold, 2147:27 GMT (4:47:27 p.m. EST)
T-minus 5 minutes and holding. Only 60 seconds of hold time left.

T - 5:00 unscheduled hold, 2147 GMT (4:47 p.m. EST)
Range is GO for launch.

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