Opening Japan’s new module – Troubleshooting Canada’s new arm

by Chris Bergin

The International nature of the Space Station is fully in evidence, as STS-123 moved into Flight Day 5 – which saw JAXA’s new addition to the orbital outpost ingressed during the day.

Meanwhile, a full plan of action has been drawn up by the Mission Management Team (MMT) on the power up issues with the Canadian Space Agency’s Special Purpose Dexterous Manipulator (SPDM) robot. This has proved to be successful.

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Flight Day 5:

Flight Day 5 will be conducted at a more relaxed pace compared to the previous 48 hours on orbit, which has seen the successful docking of Endeavour to the ISS, the first EVA – successfully completed by Rick Linnehan and Garrett Reisman – and the berthing of the JEM ELM (JLP) module to Node 2.

‘EVA 1 successfully completed (PET 7:01). The following tasks were completed: JLP Unberth Prep, OTCM (ORU & Tool Changeout Mechanism) 2 Install, OTCM 1 Install and the steps of the SPDM Assembly Prep Tasks. Due to the SPDM power problem, the SPDM thermal blankets were not removed,’ noted the MMT overview on FD 5.

‘The JLP is installed on Node 2 Zenith. Leak checks are complete. N2 Transfer has been initiated. Expect to transfer 20 lbs of N2 with pressure equalization at 4/21:00.’

Next up is the ingress of the newly attached module, OBSS (Orbiter Boom Sensor System) handoff from Station RMS (Remote Manipulator System) to Shuttle RMS, Logistics transfers, PAO events and EVA 2 procedure review and preps.

The crew entered the module at 9:15pm EDT.

SPDM Dextre Troubleshooting:

The main issue being worked by engineers relates to power problems with the SPDM Dextre robot that arrived with Endeavour on Flight Day 3 – latched to its special logistics pallet (SLP).

‘Keep-alive’ power supply to Dextre – ahead of its placement at its final location – suffered problems when the SLP was removed from the Shuttle Payload Bay, and repeated attempts to activate the SPDM PSU (Power Switching Unit) for powering on the ‘keep-alive’ heaters were unsuccessful.

The first plan of action was to try a software patch, due to engineers suspecting a software timing issue, notably too little time for the Lab RWS (Robotics Work Station) between applying power to the PSU and establishing data comm. However, this failed to solve the issue.

‘SPDM troubleshooting: The MSS software patch was uplinked with no joy on the SPDM power up,’ noted MMT information. ‘The plan is to grapple the SPDM on FD5 following OBSS handoff and power the SPDM via the PDGF (Power Data Grapple Fixture).’

Thanks to further evaluations by engineers, the problem has now been pinpointed to a design error in a cable – unavoidable given test bed research would not of been able to be simulated in the same environment the system currently resides, due to elements now involved having already been on orbit with the Station.

‘The problem has been traced with high confidence to a design error in the SLP 1553 cable harness,’ added a March 14th presentation to the MMT, ‘Problem not discovered during integrated SLP/SPDM launch configuration testing due to GSE setup.’

The get around plan is to slightly change the upcoming EVA’s, delaying the removal of a thermal ‘sock’ – so as to protect Dextre’s systems – and to mate the robot on the end of the Space Station RMS, from which it should be able to happily draw power from.

‘SPDM Troubleshooting Plan: FD5 (75/03:00) Grapple SPDM PDGF with SSRMS. Demate the POA connectors from SLP PDGF prior to mating SSRMS connectors to SPDM PDGF. Attempt nominal power up of SPDM to Keep Alive.

‘EVA-2: Powered off approx 9:30 Defer ‘Sock’ removal from get-ahead tasks. EVA: powered off 9:10 ‘Sock’ removal is approx. 2 hours into the EVA. Thermal analysis may or may not drive the ‘sock’ removal to later in EVA 3.’

This plan negates the concerns about the robot’s thermal clock, with troubleshooting presentations noting full evaluations on the configuration’s health during this troubleshooting period.

This plan appears to have been successful, as Dextre now is powered on the end of the SSRMS.

Full MMT notes and presentations (expansive – and technical) are available in L2.

More to follow during FD 5.

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