STS-123: Third spacewalk concludes – MMT update mission status

by Chris Bergin

As the STS-123 mission heads through the midway point, the third EVA was completed on Flight Day 8 – with Rick Linnehan (EV1) and Bob Behnken (EV2) picking up the baton on what was a 6hr 54 mins spacewalk.

Endeavour continues to perform well, with the latest anomaly information referencing a calibration issue with the Orbiter Boom Sensor System (OBSS) LDRI camera – which will gain workarounds ahead of the docked late inspection when it is next used.

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Flight Day 8:


This spacewalk closed in on the finalization of assembly tasks on the Canadian robot, which gained its 11 foot arms during EVA-2, before Dextre Joint and Brake Tests and Diagnostics were conducted – with varying levels of success – on Flight Day 7.

Linnehan and Behnken’s EVA-3 consisted of the installation of the OTP/THA (ORU Tool Platform/Tool Holder Assembly), cleaning up SLP that Dextre arrived on inside Endeavour’s payload bay, along with the transfer MISSE-6 and LWAPA (Light-Weight Adaptor Plate Assembly) for installation on Columbus.

However, troublesome nuts/bolts with the MISSE-6 package saw the removal of installation efforts, and its return to Endeavour’s payload bay ahead of a big picture re-think on the ground. 

‘MISSE 6 – Materials International Space Station Experiment: The objective of MISSE is to expose materials to the space environment for long durations (12-18 months),’ noted an explanation of the experiment on recent mission baseline documentation.

‘The MISSE flight hardware consists of a pair of trays with test specimens mounted inside a reusable Passive Experiment Carrier (PEC) and attached to an ISS WIF. The PEC is a suitcase-like container that transports experiments (test specimens) via the Space Shuttle to and from the ISS.’

Other activities included the transfer one spare SSRMS (Space Station Remote Manipulator System) yaw joint and two DCSUs (Direct Current Switching Units) from Endeavour to ESP-2 (External Stowage Platform 2), and the installation of two CLPAs (Camera, Light, PTU Assemblies) on Dextre.

‘Space Station Remote Manipulator System (SSRMS) Yaw Joint: ISS spare prepositioned to protect against a future failure of an existing SSRMS Yaw Joint.

Added to EVA-3 is the removal of Dextre’s thermal socks, which have been acting like mittens to protect the robot’s sensitive equipment. The socks were due to come off during EVA-2, before time constraints led to a decision to defer to the next spacewalk.

However, this also still requires some additional work as some of the thermal mittens remained on Dextre at the end of EVA-3.

As per new flight rules set up following cut glove incidents on a couple of recent flights, EMU glove status is an item that is constantly under review.

Though the Over glove has proved to be a very useful form of mitigation against cuts, RTV delamination – from wear and tear endured during EVAs – has put pay to one set of gloves, post EVA-2.

‘JSC discussed the results of EVA 2 activities conducted on Flight Day 6. EV3/Mike Foreman had RTV delamination on both thumbs on EVA 2,’ noted a report to the MMT (Mission Management Team).

‘This was a little larger than desirable, but is still in-family. Those gloves are No-Go for subsequent EVAs, and his first pair of backup gloves will be used.

‘Mr. Foreman (also) reported a minor concern with his boot fit during EVA 2. The sizing team uplinked questions on this to target potential remediation steps for EVA 4.’

Endeavour Status:

‘The mission is proceeding per the updated timeline and no decisions are required from the MMT,’ noted minutes from the MMT going into Flight Day 8, a good sign of the smooth flow the mission and Endeavour are enjoying.

The SSPTS (Station-to-Shuttle Power Transfer System) is working as advertised between Endeavour and the ISS, allowing for an additional time to be added to the mission, should it be required.

‘Cryo margins are above 16+1+2 mission duration, and are Oxygen (O2) limited. Margins for one undocked day (or docked with Station to Shuttle Power Transfer System (SSPTS) off for this day) or for two docked days (SSPTS on) with both assuming SSPTS power transfer for nominal mission duration.

‘There are currently no concerns for middeck transfer, and nitrogen (N2) transfer is complete (about 23 pounds).

Monday information added notes on an anomaly with the LDRI (Laser Dynamic Range Image) camera, spotted during Flight Day 2’s inspections, and which underwent further troubleshooting on Flight Day 5.

“OBSS PTU Pan +10 Deg Hard Stop Error – On FD 2, a 10 deg calibration error was noticed in the LDRI camera,” noted NTD information on Monday. “Normal surveys were completed after the 10 deg error was identified.

“Troubleshooting on FD5 suggests that the extra 10 degrees range of motion (189.0 deg vice 179.8 deg) was caused by a misaligned hard stop (the MER (Mission Evaluation Room) verified that this error was in place preflight).”

The OBSS is currently stowed on the side of the ISS, where it will take up permanent residence – rather than riding home with Endeavour – prior to the arrival of Discovery on STS-124.

It will, however, have one final role with Endeavour, during docked late inspections in the latter stages of the mission. Understanding the issue with the LDRI camera will allow for workarounds to be created.

“Knowledge of the 10 deg error allows for workarounds for STS-123 late inspection and STS-124,” added the report. “Orbiter will work with the Mission Operations Directorate (MOD) to update the procedures if required for this flight and STS-124.”

While not an issue for the continuation of the mission, mangers are still discussing the pressure decay on Endeavour’s Auxiliary Power Unit (APU) 1 – with presentations being created for review during Flight Day 8 meetings.

“APU 1 Fuel Tank Pressure Decay Assessment: Analysis continues on this issue and there has been no changes in pressure decay since the last report.

“Currently, FRs (Flight Rules) allow running an APU while docked with a hydrazine leak. However, analysis for induced loads on the ISS while docked did not include driving the aero surfaces at a high rate during the APU run time. Plans are to define these loads this week.

“Previous analysis and experience indicate a hydrazine leak would continue for period, and then freeze and stop. This issue is a steady pressure decay, so it is believed by the community that this is an N2 leak.

“(MMT Chair) Mr. (Leroy) Cain asked whether any resources across the Agency are needed. JSC Engineering have coordinated with NESC (NASA Engineering and Safety Center), and peer review performed by Boeing, USA (United Space Alliance), and White Sands Test Facility (WSTF).

ISS Status:

Updating the status of the ISS to the MMT, Dextre – as expected – can now be ticked off the anomaly list, follow the successful power up on the end of the SSRMS (Space Station Remote Manipulator System). No further issues are expected.

“The Canadian Space Agency (CSA) reported the SPDM (Special Purpose Dexterous Manipulator) – Dextre – checkout showed the faults were eliminated,” noted the report, before rounding up the latest issues that have been worked on the Station.

“The Russian segment had a loop 2 coolant failure. They are using the backup pump panel. There have been a series of these faults before. (Over the weekend), power was lost in Moscow to the command and telemetry servers. These are expected to be back up operational by Monday.

“There were Columbus Control Center to Mission Control Center (MCC) Houston problems. These issues have been corrected and the communication links between the control centers are operational again.”

Interestingly the report rounds off by updating the status of the European Space Agency’s ATV (Automated Transfer Vehicle), claiming it had another Propulsion Drive Electronics (PDE) fault – as it moves to take up a parking orbit in wait of Endeavour’s departure – though the fault was corrected.

“The ATV is performing nominally. There was another peak propulsion electronics error. This was addressed, and ATV continues to transition to its parking orbit and should arrive there in the next couple of days.”

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