Arm on standby for Discovery

by Chris Bergin

Technicians at the Kennedy Space Center (KSC) are preparing a replacement robotic arm – originally designated to Endeavour – should it be deemed that Discovery’s RMS (Remote Manipulator System) suffered levels of damage that require her arm to be replaced.

Discovery’s robotic arm suffered a couple of small indentations on the arm, following an accident involving a bucket – which was being used to clear up glass fragments in the cargo bay, after a heat lamp was smashed during work on the orbiter.

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Tests are being carried out on the arm, with a report being compiled to help managers come to a decision on whether to replace the arm, or fly ‘as-is.’ Discovery is currently set to launch in May – although it is becoming ever-more likely her mission (STS-121) will be moved to July.

A variety of tests are being performed on the arm and the damaged section.

‘MDA ran some tests using an aluminium tape and have not yet been able to get as close to the original resistance as they would like, but the MRB agreed that with some more work, MDA should be able to re-establish the plane with this tape,’ noted a document relating to the evaluations on the arm. ‘The ground plane is also used during a failure to carry fault currents so the repair method must be able to handle these fault currents.

‘MDA is performing analysis to ensure that this tape will be sufficient for carrying these fault currents otherwise an additional wire may need to be installed from one end of the composite boom to the other end. Adding a wire will not be an issue if required.

‘MDA is also performing analysis to ensure the repair method will not impact the RMS/OBSS system performance and result in sensor re-test requirements.’

Specialists are expected to arrive at KSC today to further evaluate any work that may be required, including structural analysis of the arm, leading to a decision being taken on the best course of action – if any.

‘Given that we believe the ground plane can be re-established, travel plans have been finalized for MDA and AASC folks to arrive at KSC (today) and should be ready to begin work Thursday AM,’ added the document.

‘We have provided a list of all inputs required for structural analysis. I have a call into to ensure that this is given a high priority as this structural analysis will be critical path for accepting the RMS and MPMs ‘As-Is’ if the inspection shows no damage to the composite boom.’

One option would see the removal of the arm from Discovery’s payload bay, replacing it with a spare arm – which was sent to be installed on Endeavour – or just a section of the arm.

‘KSC is beginning to prepare the S/N 201 arm, originally destined for OV-105, for installation into OV-103 if it is required,’ added the document.

‘The MRB also discussed the possibility of swapping out just the composite boom (instead of the whole arm) so that the strain gauged arm could continue to fly on STS-121. This swap of the composite boom would require sending the lower arm back to MDA for change-out and would total a two week turn around before it could be back at KSC.

‘A presentation (is being compiled) for Wayne Hale as requested to explain to him the significance of the strain gauges on the arm and the impact to DTO 849 if that arm does not fly.’



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