NASA STS-121/ULF1.1 FD 12 Execute Package
MSG 116 (13-0705) – FD11 MMT SUMMARY
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Page 1 of 1, MSG 116 (13-0705)
FD11 MMT Crew Summary
Today’s MMT focused on the APU 1 pressure decay. There was also a review of plan to deploy resources to image the Orbiter on re-entry in order to attempt to capture boundary layer transition, especially since we know we have irregularities on the lower surface due to protruding gap fillers.
APU 1 Tank Pressure Decay – The APU 1 fuel tank pressure continues to decay at a steady rate (actually it is slowing very slightly as the pressure and temperature drops).
There is still no way to determine if the leak is N2 or hydrazine. The assumption still stands that if the leak is hydrazine, it will be a vapor. JSC engineering, White Sands and the NESC are collaborating on that part of the story.
The MMT narrowed the options down to a forward plan that will be finalized tomorrow. As of today, we are going to use APU 1 for FCS checkout. This will give us a chance to evaluate the APU and to monitor the leak rate afterwards. If the leak rate increases, we would burn the APU to depletion while in orbit. There is also an option to run the APU longer during FCS checkout, such that entry usage will leave the tank quantity close to depletion after wheelstop. One of the factors affecting that decision is the concern of possible Water Spray Boiler freeze-up if the APU is run long enough to need cooling (WSB 1 does not have a PGME mixture). Nominal FCS checkout does not require WSB cooling.
The entry plan as of today is to use APU 1 nominally, most likely with a pre-TIG start. Starting it earlier than TIG-5 would burn off more fuel but would create complications for the deorbit burn weather decision-making process.
Post-landing, KSC will perform their usual post-landing procedures and sniff checks of the aft vent doors to confirm if the leak was indeed hydrazine. Plans for how long to operate the APU post-landing are still being discussed.
