Endeavour finally got a break from the weather and launched on the sixth attempt to mark the begining of STS-127. A number of debris events could be seen on the ET Cam during ascent, but it will take a few days to check to see if they caused any damage of note. STS-127 will include work on one of the troublesome Unpressurized Cargo Carrier Attachment Systems (UCCAS), as outlined by ISS managers.
STS-127 Attempt 6 pre-launch:
An overnight issue with Endeavour’s Fuel Cell load checks has proved to be the only problem being worked on the orbiter – following the retraction of the Rotating Service Structure (RSS) shortly after midnight.
The RSS was placed around the vehicle during Tuesday to allow for work to be completed on replacing the loose tyvek cover on the F1D Reaction Control System (RSC) thruster.
“Orbiter: OV-105 / ET-131 / BI-138 / RSRM-106 (Pad-A) Launch countdown / Scrub T/A: LO2/LH2 tanker replenishment was completed yesterday. RSS retract to park complete at 0010 EDT,” noted Wednesday processing information on L2.
“Fuel Cell load checks (CHIT 007493): Terminated the test at 0015 EDT and returned all parameters to normal. All the data needed has been provided. Formal analysis is underway. Initial data shows a stable platform that is within limits.”
“Air to GN2 changeover completed at 0446 EDT. BDA (Blast Danger Ares) Clear is in work. LO2/LH2 final preps will begin at 0608 EDT.
“Ops/Eng Tanking Briefing started at 0715 EDT. ET load Weather Briefing started at 0800 EDT. LO2/LH2 tanking began on time at 0838 EDT. T-0 is expected at 1803 EDT.”
The power generating Fuel Cells are located under the payload bay area in the forward portion of the orbiter’s midfuselage, and operate as independent electrical power sources, each supplying its own isolated, simultaneously operating 28-volt dc bus.
They have been known to register problems – such as STS-119’s Oxygen Flowmeter Measurement anomaly on Fuel Cell 3 – but can still operate as required.
The last time a Fuel Cell issue caused a scrub was back on STS-115, when Atlantis’ Fuel Cell 1 suffered the loss of the phase A string on the FC coolant pump motor.
Columbia’s infamous STS-93 launch also suffered a momentary short on AC1 phase A, five seconds into the launch, as observed on the MCC (Mission Control Center) internal flight loop video (click here to download). The MMT cleared the issue as a constraint for launch later in the countdown.
Unlike the previous two attempts, the countdown continued through to coming out of the T-9 minute hold. There had been a 40 percent chance of a weather violation, but that had reduced to 10 percent close to launch.
“The Bermuda ridge is located just south of Kennedy Space Center (KSC). The low-level winds on the latest balloon are from the southwest at 8-10 knots. This low-level wind flow will impede the progress of the east coast sea breeze somewhat, but it should progress inland into eastern Orange County by launch time,” noted the latest USAF weather report.
“The mid-level storm steering winds also favor a very slow, eastward movement of interior and west coast storms. Our primary concerns for launch are showers and thunderstorms within 20 miles of the Shuttle Landing Facility (SLF).”
More updates will follow on the progress of STS-127’s countdown. For up-to-the-second updates, refer to the live update pages, linked above.
Launched on STS 115 in September of 2006, two UCCAS platforms occupy the P3 element of the ISS. The P3 UCCAS 1 Zenith deployed during increment 14, and currently houses the ESP3 (External Stowage Platform).
However, during UCCAS 2-P3 Nadir deployment during STS-119, the platform stuck in the detent position. The current plan is to deploy UCCAS 2 during STS-127, following an investigation into root cause.
A successful conclusion will allow for ELC 1 (Express Logistic Carrier) will be attached to UCCAS 2 during STS-129’s mission, currently tracking launch in November of this year.
“Root Cause Investigation Results: Possible Root Causes: Less Likely: Pin seizure. Pin actuated on orbit from launch position when crew member deployed platform so unlikely that pin suddenly seized,” noted a status overview in the Agency Flight Readiness Review (FRR) presentation for the ISS, available on L2.
“Most Likely: Design of countersink angle too steep (120countersink) resulting in side load on pin with a contributing factor of friction in system. Recent ground testing has shown that high force is required to get out of detent.”
Using “high force” is within EVA limitations – as ably carried out just recently with Mike Massimino’s forceful yank on the STIS handrail during STS-125 (Helmet Cam Video – uploaded by the crew post landing – of the actual pull available on L2).
Ground testing results confirm that the yanking free of the UCCAS mechanism will be within EVA limits.
“Two test setups in bldg 13 Structures Test Lab. Full STA UCCAS mounted to a strong back. A single hinge mounted to a tooling table. The following tests were conducted,” added the ISS FRR presentation.
“Single Hinge Pull tests: Static Pull – No Lubrication: Result: Test halted at 190 lbf and detents did not release. Static Pull – With Lubrication: Result: Detent released 139 lbf. Dynamic Pull – No Lubrication: Result: Detent release at 103 lbf. Dynamic Pull – With Lubrication: Result: Detent release at 37 lbf.
“Full UCCAS platform pull Test – No lubrication: Test was limited to 264 lbf max. static load and detents did not release (load applied on Yoke). Hardware capability is approximately 300 lbs.
“Full UCCAS platform pull Test –w/Detent Tool Mockup, No lubrication. Result: Platform released from Detent at approximately 30 lbf static load (applied on Yoke).
“Summary: Tests indicate that it is unlikely a static pull force without lubrication is within normal EVA or hardware capability. Dynamic pull without lubrication may be within EVA capability (as noted for UCCAS 1 deploy). Lubrication does reduce the load required to deploy. Use of Tool significantly reduces load required to release from detent”
Engineers also created a “Partially Deployed P3 UCCAS Resolution” – should all not go to plan during the procedure.
“The following are the recommendations from the Anomaly Resolution team and current forward plan for 2J/A UCCAS deployment recovery.
“Primary Plan: Use the detent tool to depress the spring plungers for the UCCAS deployment. Contingency plan (assumes tool failure).
“Use a rocking/dynamic technique, as performed during the increment 14 EVA UCCAS deployment, with lubrication.”
“Plan for deploying the remaining four PAS sites: Prevent the PAS platforms from reaching the detent position using a tether. 2J/A crew training use of a tether and crew vigilance to control platform position. UCCAS anomaly resolution plan to be followed if platform inadvertently reaches detent.”
However, the task -which is down the list of mission priorities as a Cat 3 task – may not of even been carried out, had Endeavour failed to launch on Wednesday. This is due to the requirement to undock in time for the arrival of the Russian Progress resupply vehicle.
Deferring the launch to the final opportunity in the window on Thursday would have result in mission content being deleted from the mission. However, this would have depended on how much progress is made during the early EVAs, with the potential to find additional time, if the spacewalkers fly through their major mission objectives.
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.