LAR capability on track to make Hubble flight

by Chris Bergin

NASA has updated the status of its Large Area Repair (LAR) capability, which is being developed ahead of the only flight remaining in the shuttle manifest to be without the option of “safe haven” at the International Space Station (ISS) – next August’s STS-125.

The 12 inch by 12 inch plate is capable of covering large breaches on the orbiter’s wing leading edges and nose cap, to be potentially used as a last ditch capability to repair Atlantis, prior to a Launch On Need (LON) rescue mission being called.

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The panel, which can be shaped to the curve of the leading edge of the orbiter’s wings, would be fastened over the breach with screws, after an astronaut had drilled holes into the Reinforced Carbon Carbon (RCC) panel. LAR – which can be used on flights after the trip to Hubble – is also capable of being a patch for the nose cap of the orbiter.

The LAR cover patch is flexible, allowing for the covering of breaches in the wing leading edge, as well as being able to be placed over small holes – such as MMOD (micrometeoroid/orbiting debris) impacts – on the nose cap.

The effort has been ongoing since the start of the year – as revealed by this site – with project milestones now moving into certification and repair techniques – which would be carried out by two spacewalkers on a six and a half hour EVA.

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Via an update to the all-powerful PRCB (Program Requirements Control Board) meeting this month, engineers outlined specific guidelines for what LAR would be capable of repairing.

‘LAR shall repair a hole from 4×4 inches to 8×8 inches with a 1-2 inch spall around the hole and 1 – 3.5 inch delamination. LAR is not designed for repairing or overlapping T-seals,’ outlined the presentation, available on L2.

‘LAR shall meet ISS missions (worst case) and trajectories for RCC Panels 10 and 16 (with Panel 9 as a goal) from Entry Interface (EI) plus 1200 seconds, with a goal to survive to wheels stop. (It shall also) meet vibe loads to EI+1200 seconds, with a goal to wheels stop.

‘Gap between LAR Cover Plate and RCC shall be less than 0.040 inches. Gap between LAR washer and Cover Plate pending (design to < .005 in.). LAR shall not create an adverse aerothermal environment downstream (0.2 in. protuberance) of the repair.

‘No more than (2) EVA sorties of 6.5 hours: (2) suited crewmembers, one hands-free, one damage site repair per mission. On-orbit RCC temp range: -230F to +320F. Except STS-125, all repairs will be ISS-based. Post STS-125: Components and IVA support hardware stowed internally on ISS.’

It is likely, however, that LON would be called if damage as large as 4×4 to 8×8 inches was observed following the launch of STS-125 – with Endeavour set to be on standby to launch from launch pad 39B should a serious problem arise with Atlantis on orbit.

This still leaves LAR as a contingency option to repair the orbiter in the event of a problem with Endeavour (STS-400) – in the very unlikely event she received even worse TPS (Thermal Protection System) damage during her race to reach Atlantis, or if NASA decided to carry out a RCO (Remote Control Orbiter) ‘unmanned’ landing of the damaged Atlantis, after the crew are evacuated to Endeavour for the ride home.

To install the patch would be no easy task, with spacewalkers being required to drill/tap holes into the RCC around the damaged location. Fasteners and washers would be needed to help secure the patch in place, before being sealed with NOAX.

Further details on how the spacewalkers would carry out the repair were added via the latest presentation to the PRCB. It is likely this would be the most complex on orbit repair ever to be carried out on an orbiter.

‘Provide EVA Tools for LAR installation and verification: IVA hole punch. Cover Plate marking template. Transport to worksite. Prepare damage site for repair (using existing tools). Remove SiC coating from RCC at most 16 locations for fastener installation. Drill and tap (16) 5/16 – 18 holes with 10 degrees perpendicularity,’ noted the presentation on EVA key requirements.

‘Install (16) fastener/washers (6 to 30 in-lb torque, +/- 2 in-lb tolerance). Remove fasteners up to 30 in-lb torque. Locate cover plate within +/- 0.25 inches and 5 degrees. Measure RCC temperature prior to sealant application. Sealant manipulation. Repair site clean-up. Repair inspection.’

The tools available for the repair are also seen for the first time, which include the PGT Drill Aid, Fastener Gripper and Caddy, Fastener/Washer retention and control. IVA Hole Punch and EVA and LAR Cover Plate Handhold.

Key milestones for bringing LAR capability to STS-125 include several ‘decision gates’ – such as results from Arc Jet testing in Houston. So far, the capability has passed through a year of phased development, with EVA training set to start early next year.

The project has also moved into the procurement phase for the materials and tools, with SSP (Space Shuttle Program) approval on costs required throughout the development phase.

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