STS-123 completes EVA-2 – Dextre gains its arms

by Chris Bergin

Flight Day 6 saw the completion of the second of five EVAs during STS-123, as the newly powered up Special Purpose Dexterous Manipulator (SPDM) robot “Dextre” takes shape, ahead of its role on the International Space Station (ISS).

Rick Linnehan and Mike Foreman were tasked with the Dextre assembly operations during a seven hour spacewalk, while the rest of the crew continued outfitting of the newly attached JLP module which moves through to Flight Day 7, along with Dextre testing.

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Flight Day 6:

The spacewalk saw Dextre’s 11 foot arms being attached to the torso of the robot – though one of the arms proved slightly troublesome – along with Joint and Brake Tests, plus diagnostic checks. The robot required a stay on the Space Station RMS, following a problem with a cable used to draw power from the pallet it arrived in.

Dextre is capable of robotic execution of ISS external maintenance tasks, such as the removal and replacement of dexterous compatible Orbit Replaceable Units (ORUs), and the servicing of scientific payloads

Supporting EVA-based maintenance is also part of its role, with the preposition of ORUs or Integrated Assemblies, the provision of lighting and camera support, and is it is also capable of actuating external mechanisms, performing inspection tasks, and extending reach of SSRMS.

No more issues with the robot’s power supply are anticipated following the forward plan that was created by engineers on the ground.

Pre-empting the EVA – a review of the first spacewalk (EVA-1) noted the requirement of a repair to MMOD (micrometeoroid/orbiting debris) damage on a D-handle – an EVA tool stowed on the Z1 port toolbox and used for SPDM assembly tasks – which has been wrapped in ‘EVA tape’ to avoid the potential of cut EMU gloves.

‘3mm MMOD hit in the D-handle discovered post EVA 1. CHIT and Flight Note in work for repair and usage constraints,’ noted an MMT (Mission Management Team) presentation that rounded up EVA-1 with a view to approving EVA’s 2 and 3.

‘Repair Procedures: Swatch test to be conducted. Knock down sharps and remove. Construct a ‘pad’ made of EVA Tape (white fiber glass tape) to cover the damage site. Wrap damaged area with two layers of EVA tape. Pending completion of repair, D-handle will be GO for EVA-2 and EVA-3.’

This requirement has been added to the pre-launch notes at the Flight Readiness Review for EVAers to avoid part of the Quest airlock’s handrail – also due to MMOD damage.

‘MMOD damage reported on Airlock – noted during EVA 1 on STS-122/1E. Detailed photos taken and swatch test performed during STS-123 EVA-3. Photo analysis complete,’ added the FRR presentation, pointing out the ‘no go’ area.

The post EVA-1 report also referenced issues with the 55ft safety tether, as overheard on the loop during the spacewalk. However, this will not require any workarounds.

‘During STS-123 / 1JA EVA1, EV1 reported that his 55-ft safety tether was a ‘slow retractor,’ added the presentation. ‘Resolution: None, known issue. This is submitted only to document another occurrence of this issue. No further action required.’

‘EV 2 reported bag was not leaking, but that he would drink the water down as quickly as possible to preclude excessive water leakage into the suit,’ noted another issue. ‘The vent ducts in the EMU have screens over the inlets, preventing the bite valve from entering the ventilation loop.

‘The bite valve was located during suit doffing following the EVA. No further impacts are anticipated.’

The mission is proceeding without any issue of concern, reflected in very short anomaly lists created by associated MMT departments.

The only Endeavour related note of interest relates to an APU 1 (Auxiliary Power Unit) Fuel Tank Pressure Decay, which continues to be monitored. Engineers are drafting an APU Burn to completion procedure to have available if required. However, this is not expected to become a mission impact.

‘Auxiliary Power Unit (APU) 1 Fuel Tank Pressure Decay: Maintenance, Mechanical, Arm, and Crew Systems (MMACS) has been monitoring a pressure decay with a signature similar to the STS-121 Nitrogen (N2) leak,’ added the minutes from an MMT meeting.

‘The decay does not appear to be thermally induced, although thermal causes have not been ruled out. No mission impacts have been identified at this time.’

Additional good news can be found in two presentations that outlined how Endeavour performed during her ascent to orbit, with every propulsion system working as advertised.

“Ascent Quick-Look Report – Marshall Space Flight Center (MSFC): USA-MSFC/ provided an Integrated Propulsion Quick Look Summary,” noted a summary of the data.

“For MPS, there were no violations, and all systems performed nominally. SSME, the External Tank (ET), and the Reusable Solid Rocket Boosters (RSRB) also performed nominally.”

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