Discovery – STS-133 Repairs

We are now several months past the planned launch of the Space Shuttle Discovery. What follows is the the time line and reasons for this state of affairs.

5 November 2010 - Discovery was preparing for its launch when a leak in the Ground Umbilical Carrier Plate (GUCP) was discovered. The GUCP is located in the intertank region between the LH2 tank (liquid Hydrogen ) and the LOX tank (liquid Oxygen) and vents gaseous hydrogen from the LH2 tank. GUCP The decision was made to replace the seals and reschedule for the December launch window (which would open on 30 November). As noted here, the GUCP was at the center of issues during the launch of STS-119 and STS-127. The problem had not reoccurred since the change of the flight seal design and the associated feet which holds the hardware in place.

Cracked Stringer Foam

At the same time, a crack was also noticed in the foam on the External Tank (ET) intertank region, which would require inspection and likely a repair. That was the ominous opening to the current situation.

7 November - The crack in the foam on the intertank stringer, which faced Discovery, would required a complete analysis and repair since it threatened the flight surfaces of the orbiter. This sealed the fate for Discovery and the launch was definitely rescheduled for December at the earliest.

8 November - NASA engineers began work on plans for the repair of the large foam crack observed on 7 November, and several smaller cracks.

10 November - Troubleshooting on the Ground Umbilical Carrier Plate (GUCP) saw the flight seal removed. The engineers removed the cracked foam from Discovery’s damaged Thermal Protection System (TPS) area on the flange between the intertank and LOX tank. Then, two nine inch cracks were found on the structural stringer. Cracked Stringers

11 November - Plans were underway to replace the Ground Umbilical Carrier Plate. Plans were also underway to install a doubler to reinforce the cracked intertank stringer.

12 November - Two additional cracks were discovered on a stringer to the left of the GUPC.

16 December - New foam was installed on the cracked stringers and instrumentation applied in anticipation of a full tanking test on 19 November in order to determine the stresses and cause of the four cracks created by the previous tanking on 5 November. In addition, the GUPC and the Quick disconnect were replaced.

18 November - The Tanking Test was canceled and work was ongoing to install doublers on the two cracked stringers. Foam application and a 3-4 day cure were scheduled. A Flight Readiness Review (FRR) was scheduled for 29 November, and a launch date of No Earlier Than (NET) 3 December was set.

24 November - Computed Radiography (CR) scanning of the stringers and other structures in the intertank were conducted. The Program Requirements Control Board (PRCB) decided that the 3 December launch window could not be met due to ongoing evaluation, and a NET launch window beginning 17 December was examined. Although it was determined that the installation of a "good" stringer (not damaged in manufacture) should not fail under cryogenic loading, not enough information was yet available to validate the model being used. Additional work would be required.

3 December - NASA managers decided to push the launch to NET 3 February. This would require realignment of the cargo manifest for Discovery, along with the manifest for Endeavour (now with a launch placeholder of 1 April 2011) as well as a realignment of the manifest for the Japanese HTV, scheduled for 20 January 2011. No mention has yet been made of the European Space Agency (ESA) launch on 15 February of the ATV-2 Johannes Kepler.

13 December - Installation of nearly 100 sensors continued in anticipation of a tanking test on 17 December. Following the tanking test, the plan was to rollback Discovery to the Vehicle Assembly Building (VAB) for additional backscatter and X-Ray scans on the areas of the tank which are currently inaccessible at the pad.

17 December - A successful tanking test was conducted, and data collected from the instrumentation in the intertank.

21 December - Rollback to the VAB was completed, and additional testing on the intertank was started. STS-133 Intertank The intertank is the area between the LH2 tank (bottom) and the LOX tank (top).

The technicians performing the tests walk around on light-weight foam block inserts so as not to damage the tank, and are removed before flight.

22 December - Initial evaluation of the instrumentation data indicated that the S6 and S7 stringer doubling produced results confirming the modeling. Deflection data from the cryogenic loading was nominal, indicating that the intertank was stable. Additional evaluations would be made, leading to a rollout back to pad 39A on 13 January.

The program will hold a review on 12/30 to discuss the Non Destructive Evaluation (NDE) results and the potential for any further stringer modifications or repair requirements. MAF (Michoud Assembly Facility) personnel would perform those repairs, which are to begin on 3 January 2011.

30 December - From an update at NASASpaceFlight:

"The X-rays showed four additional small cracks on three stringers on the opposite side of the tank from Discovery, and managers elected to repair those cracks in a similar fashion to repairs made on cracks discovered after the Nov. 5 launch attempt. That work is estimated to take 2–3 days. Any further work will be evaluated thoroughly early next week after additional data is reviewed. The hardware is in place to perform any modification. That work would be performed inside the VAB. Managers continue to evaluate an option to perform known and practiced modifications on additional stringers. A decision may be made as early as Monday, Jan. 3."

Last Updated 30 December 2010

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One thought on “Discovery – STS-133 Repairs

  1. Pingback: Launch of Discovery « The National Space Society of Phoenix

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