STS-133: NASA managers decide to slip to a NET December 17 target

by Chris Bergin and Chris Gebhardt

A Christmas mission may be the cards for Discovery’s final mission, as managers at the Program Requirements Control Board (PRCB) decided against shooting for the early December launch window opportunities. More work is required on assessing the status of External Tank (ET-137), resulting in a move to the December 17-20 window – although this target remains preliminary at best.

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Ahead of the PRCB, the pad flow timeline continued to support the preliminary NET date of a December 3 launch date, with pressurization tasks, range safety checks and evaluations on the Pyrotechnic Initiator Controllers (PIC), which are used to light the Solid Rocket Boosters (SRBs) at T-0.

“OV-103 / SRB BI-144 / RSRM 112 / ET-137 (Pad-A): No formal launch date has been selected. The option to perform a tanking test is still under discussion. S0007.100 launch countdown preparations continued. Preparations for hyper/MPS (Main Propulsion System) pressurization operations continued,” noted the NASA Test Director (NTD) on Wednesday, with the timeline set to be realigned.

“Initial (cheat load) press was successfully accomplished on Tuesday. Press to flight mass is scheduled for Sunday, 11/28.”

“S5009, ordnance operations to disconnect SRB ordnance, perform PIC resistance tests, connect the GUCP (Ground Umbilical Carrier Plate (GUCP) and SRB/SRSS ordnance, and perform open and closed loop range safety checks is scheduled for Wednesday.” (All of which are now on hold).

Scanning of the stringers on the LOX/Intertank flange was completed last on Tuesday, which should have been in time for the PRCB meeting on the launch date target. However, the NTD did reference the potential of scans being required on the lower LH2/Intertank flange stringers.

“IPR 0072 ET LO2/IT stringer cracks: Computed Radiography (CR) scanning of the LO2 flange is complete. The pic board, +Y/-Y access platforms, and intertank access kit have been removed. Additional backscatter scanning of the LH2 flange may be required next Monday, 11/29.”

Those scans on the LH2 flange are now likely to proceed, given the PRCB decision to carry out further evaluations into the root cause and required flight rationale – despite a large amount of progress being made, with positive signs on documentation likely to have been unrepresentative of what is understood to be strong dissent against flight at this stage of the discussions.

“The Space Shuttle Program PRCB has determined that we cannot complete the work to provide flight rational in time to meet the 3-7 December launch window,” noted a memo from the meeting (L2). “The next window is 17-20 December. We don’t know if that window is achievable.”

Initially, a slip past the early December opportunities would have led to a multi-month delay to STS-133 and a resultant launch date of No Earlier Than (NET) Sunday, February 27, 2011 based on a month-long Solar Beta Angle Cutout (January 1, 2011 – February 1), the launch and month-long mission of Japan’s second HTV to the ISS (mid-January thru mid-February), and the planned February 15 launch of ESA’s (European Space Agency’s) Automated Transfer Vehicle (ATV) and subsequent late-February docking of ATV-2 to the ISS.

Nonetheless, upon review of the December ISS traffic schedule following the realigned ATV-2 launch date, the Space Shuttle Program had identified a potential (and slightly complicated) launch window in the mid-/late-December 2010 period.

As noted by NASA personnel and revealed by earlier this month, there was a potential launch window under discussion that opens on December 17, which has now being taken as a preliminary target.

“Starting to look at some opportunities after the 25S docking in December and early January, before the beta cutout, just to be strategic,” notes the November 18 Standup Integration Report.

With the new window now confirmed as a target, the International Space Station Program will have opted to take a hit in order to help the Shuttle Program, given a requirement of the late December window results in the removal of around 600 lbs of payload from Discovery to meet the mid-/late-December APM (Ascent Performance Margin) requirements for launch.

Moreover, the exact duration of the this potential window is small, partly due to to the Year End Rollover (YERO) consideration of potentially having Discovery on-orbit and docked the ISS during her computer transition from Dec. 31, 2010 to January 1, 2011 – a computer transition that has to be performed manually at the GMT (Greenwich Mean Time) midnight year end transition.

Based on the original design of the Shuttle orbiter’s computers, it was never intended that a Shuttle mission would fly over the YERO. Therefore, all YERO computer resets could be performed on the ground and any minor glitches as a result of this manual reset accounted for on the ground.

Thus, a launch from December 21 (currently outside the defined window) could be completely eliminated from launch consideration or a truncated version of the STS-133 mission executed instead. A contingency does exist to allow for a YERO scenario via a patch created via troubleshooting into the issue. However, none of the recent missions have required such a contingency consideration.

According to recent documents, the next Solar Beta Angle Cutout begins on January 1, 2011 and extends thru February 1. However, this will be evaluated, as Solar Beta Angles always are, to determine if there are launch opportunities available in early January.

The question remains how much additional work is required on the flight rationale in order to stop the flight from slipping yet further.

(Further updates and articles will follow. Refer to live coverage threads linked above. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used, Lead: Within the article: via L2 acquired PRCB presentations).

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