Endeavour’s External Tank (ET-129) tanking operation is now in stable replenish, as STS-126 remains on schedule for a 19:55 local time launch to the International Space Station (ISS). Overnight, the ET purge heater controller had to be replaced – though the five hour hit to operations has not caused a serious delay.
STS-126’s S0007 Launch Countdown operations are now in the business end of the count, following the retraction of the Rotating Service Structure just prior to midnight last night.
S0007 Launch Countdown: LO2 / LH2 preps for vehicle loading completed, LH2 at 15:47 and LO2 at 21:53 (local times), noted Friday morning processing information on L2. “SSME (Space Shuttle Main Engines) final preps completed yesterday. Comm. activations completed at 19:24. RSS retracted at 2358.
“Ascent SW List complete at 0330. Air-to-GN2 changeover was started at 05:30. Final ET Load preps at 0700. LOX / LH2 tanking on time for 10:30. Crew Ingress scheduled for 16:35.”
Activation of Endeavour’s three Fuel Cells began at 7am this morning.
The main issue overnight was the requirement to changeout the ET purge heater controller, which was a constraint for tanking. A waiver was issued, as nominal operations can proceed, even in the event of the new controller – which was proving to be troublesome – failing.
“The ET purge heater controller was operating out of nominal temperature range. The heater was R&R’d on this shift, and is now working; however, it is taking too long to reach the heater control band,” noted processing information.
“The OMRS (Operational Maintenance Requirements and Specifications) requires reaching the control band in 7 minutes, and it is taking over 10 minutes. A wavier to explain the condition is in work.”
The waiver was signed without issue, due to the ability for tanking to proceed within the required temperatures parameters.
“Even in the event of total heater failure, can live with the condition as the GHe purge can maintain temperatures as needed as long as the ambient temperature is above 32 Deg. F.”
The only other item of interest was the discovery of a 1/2 inch bolt that was found to be resting on the LOX feed line box beam tie plate.
“An immediate walk down of the RSS found the same part number bolts being used on the FRCS (Forward Reaction Control System) room platform handrail grounding system,” added processing information this morning.
“A missing bolt location (FRCS room RH) was identified directly above the found bolt and was determined to be the point of origin.”
With its origin found, engineers evaluated the path it would have taken during its liberation. Their findings showed that the orbiter was not in the path of the falling bolt, which removed the requirement to inspect critical hardware on the vehicle for damage.
“Evaluating the starting point of travel and final resting point, there is no credible way that the pin struck the Orbiter wing RCC, so no impact analysis of the Orbiter RCC is required,” confirmed the report.
“In the area of travel, complete inspections were performed of the Orbiter TPS, ET, and SRB and no discrepancies were noted. Will coordinate closure.”
Tanking was completed within its usual three hours of operation, with no problems reported – once again – with the Engine Cut Out (ECO) sensors. All four sensors went WET during early tanking, and were successfully commanded DRY via the SIM test during fastfill.