STS-120 – mission extended for ISS troubleshoot

by Chris Bergin

The Mission Management Team (MMT) have decided to approve a request by International Space Station (ISS) managers to increase STS-120’s mission by one day, as they work a plan to fully investigate the problem with the starboard SARJ (Solar Alpha Rotary Joint).

The MMT is still meeting, with decisions being taken on the content of EVA-4, although the TRAD tile repair test will be removed from this mission’s itinerary.

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STS-120 Status:

NASA will utilize EVA time to fully check into the SARJ on the opposite side of the station, starting with around 40 minutes of ‘spare’ time in EVA-3, to be conducted on Tuesday.

With EVA-4 now dedicated to a full inspection of the starboard SARJ, the previously planned TRAD test has now been deleted from the STS-120 timeline. It may now return back to its orginal mission, STS-126.

This change to the mission’s timeline was intimated earlier in the day, after discussions which went on through the night to work on a forward plan, following EVA-2’s findings on the starboard SARJ.

‘Flight – SARJ shavings are metallic. Likely EVA-3 will ask to do a Port SARJ survey,’ noted information. ‘Likely also to add a docked day between EVAs 4 and 5.’ This has since been confirmed, with the additional docked day required to allow for a rest day in-between the two spacewalks.

‘EVA – EVA4 will be full duration EVA if the day gets added between EVA4 and 5,’ added information. Discussing what activities will go on each EVA.’

This won’t be a problem for Discovery, with her SSPTS (Station-Shuttle Power Transfer System) working fine, allowing for over three days of margin for STS-120’s mission duration. EGIL – cryo margins 1d19h (no SSPTS), 3d7h (SSPTS). Looking at adding extra day. Preliminarily looks like we could support.’

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EVA-3 Preview:

With the inclusion of the inspection of the port SARJ, EVA-3 will be a seven hour spacewalk, conducted by Scott Parazynski (EV1) and Doug Wheelock (EV2). The EVA is expected to start at 5:28am EDT.

EVA-3’s objectives include: Attach P6 to P5 (with SSRMS); Connect P5 to P6; Remove SSU (Sequential Shunt Unit) Shroud; Release P6 outboard Radiator Cinches; Inspect portside SARJ (Solar Alpha Rotary Joint).

‘Late timeline change; Transfer spare MBSU (Main Bus Switching Unit) with SRMS from Shuttle PLB to ESP-2 (External Storage Platform 2); and Reconfigure P1 & S1 SFUs (Squib Firing Units) after their use for the radiator deployments.

Other Flight Day 8 objects include: SSRMS moves P6 truss to P5 pre-install position; P5 installation on P6 and umbilicals mating; P6 Thermal Radiator deploy; P6 2B SAW (Solar Array Wing) redeploy; and P6 4B SAW redeploy.

‘Because of yesterday’s discovery of metal shavings sticking to the Stbd SARJ’s race-ring, brackets and other areas under the #2 thermal cover (of 22 total) , the IMMT (ISS Mission Management Team) has decided to modify EVA-3 timeline by adding an inspection of the identical SARJ on the opposite port side,’ noted Monday’s ISS On Orbit Status report.

‘Subsequent steps will depend on the findings of the ongoing investigation, up to and including possible R&R of the trundle bearing with an onboard spare, if required. New insight is also expected by the analysis of the ‘shaving’ samples collected by EV3 Tani, after their return on STS-120.’

According to one of the many ISS handbook (on L2) – concentrating on electrical systems on the ISS – most of the SARJ’s components can be replaced on orbit. The only issue relates to which spares are on board the ISS and which need to be brought up on a future flight. 

‘Replacement/Location: The SARJs major components, which include RJMCs, DLAs, trundle bearings, and UTA are all designed to be on-orbit replaceable.

‘The race rings are not replaceable but the SARJ can be converted from its nominal inboard operations mode to outboard operations by reversing the directions of the trundle bearings and moving an RJMC and a DLA from the inboard side to the outboard side.

‘Conversion to outboard mode allows the SARJ to sustain damage to the outboard race ring teeth without complete loss of SARJ capability.’

Leading up to EVA-3 were a number of Flight Day 7 activities, all successfully completed.

‘Heat rejection Radiators (PVRs) #1/outboard & #3/inboard on the S1 segment were unfolded (12:52am-1:52am) during crew sleeptime (but observed by crewmembers); P6 truss segment, with retracted solar arrays, was handed off to the SRMS (Shuttle Remote Maneuvering System) from the SSRMS (Space Station RMS), after overnight parking,’ added the status report, available daily on L2.

‘Mobile Transporter (MT), with the SSRMS based on it, has rolled on its rails to Worksite 8 (WS-8) on the station’s port side; P6 truss handed back to & grappled by the SSRMS for overnight parking until tomorrow’s installation on the P5 truss.’

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