NASA STS-121/ULF1.1 FD 11 Execute Package
MSG 098 (13-0678) – FD11 MISSION SUMMARY
Page 1 of 2
Page 1 of 2, MSG 098 (13-0678)
Good morning, Discovery.
We hoped you enjoyed your time off, ’cause guess what, it’s time for more arm ops. Unofficially, we believe this flight has had the most robotic operations to date. The PDRS and ROBO folks would like to say thanks to you all, and especially the “ROBO chicks”. They have definitely earned the title.
For today’s attitude maneuver with the Shuttle, all we have to say is, “VERNS? We don’t need no stinking VERNS!”
Have fun and enjoy.
YOUR CURRENT ORBIT IS: 191 X 177 NM
MSG 099 (13-0679) – FD11 TRANSFER MESSAGE
Page 1 of 2
Page 1 of 2, MSG 099 (13-0679)
Good morning Thomas, Stephanie, and Steve, Congratulations on finishing up the MPLM! Woohoo! That was surely the hard part.
MSG 106 (13-0690) – FD10 MMT SUMMARY
Page 1 of 3
Page 1 of 3, MSG 106 (13-0690)
FD10 MMT Crew Summary
Flight Day 10’s MMT focused on the two APU anomalies we told you about in yesterday’s summary. Before those items, there was a quick review of the attitude control plan for the port wing LDRI survey that you will complete today on FD11. The procedure will be run on Orbiter ALT DAP control and there are no concerns with the RMS/OBSS being over the nose for nominal 80 msec DAP firings.
APU 3 GG/Fuel Line/Pump/Valve Heater – As a quick review, both the A and B heaters appear to be controlling the upper limit on the overtemp thermostat. We are currently on the A heaters and the system is controlling well. Functionally, there are no issues with operating on the overtemp thermostat. We are still investigating the fault tree to try and determine what would cause both the A and B control thermostats to fail. Some work was done at KSC in this area, but neither of the control thermostats was disturbed. The leading theory continues to be that either the thermostats or the heaters may have locally debonded. Workarounds exist for the next failure – if the B heater failed, we would switch back to the A. If that B heater failed, we would change attitudes after undocking to keep APU 3 warm or ask you to perform switch throws to manually control the heaters. If the heater fails on, the crew reaction time is about an hour after you get the alarm so there are no concerns for out of control temps on the fuel line.
APU 3 is not considered failed for entry or to even have a loss of redundancy. There is one small delta for entry – we’ll swap to the B heater in the entry checklist to meet the APU injector temperature limits and likely turn the heaters off after APU 3 start.
APU 1 Tank Pressure Decay – The APU 1 fuel tank pressure continues to decay slowly (see attached plot). As of today it does not appear that we will be able to conclusively determine if the leak is N2 or hydrazine. The pressure decay has remained stable throughout the mission and there is no reason to assume that the leak rate will change. If the leak is GN2, we have lost about 18 psi so far and will have lost 33 psi by EOM – there will be plenty of GN2 still remaining to support entry operations on the APU. The minimum start pressure is 100 psi and we expect to be at 213 psi for EOM.
If the leak is hydrazine and of course we are not sure of that, we have lost about 10 lbs so far and will have lost 17 lbs by EOM. The leak rate of hydrazine is calculated to be 18 cubic centimeters per hour – very small. At this leak rate and based on the pod environment, analysis has shown that the hydrazine will phase directly into vapor and not form ice or liquid. The vapor exits the vent doors on orbit and there is a minimal concentration remaining. In fact at this leak rate, the hydrazine vapor concentrations will remain well below the flammability limits in the aft compartment for entry. This theory is somewhat corroborated by the fact that there are no indications of localized cooling on any temp sensors that would be indicative of a liquid fuel leak. Of course that also supports the possibility that the leak is N2, which is obviously the best case.
As mentioned yesterday, the N2 fill Quick Disconnect (QD) did have a leak preflight prior to the APU confidence run, but after cycling the QD poppet the leak was cleared (fairly common occurrence) and a flight cap is currently installed on the QD. It is still not clear that this preflight N2 leak could be related to the in-flight leakage we are seeing. The pre-flight data has been reviewed and there was no fuel leak observed pre-launch.
For information the APU 1 and 2 fuel tanks are located on the port sidewall of the aft compartment about 8 feet below the APU’s which are near the top of the 1307 bulkhead. The teams continue to work around the clock on the ground to quantify the effects of the small N2 or fuel leak and the forward plan for entry.
