NASA plans to leave OBSS on Station after STS-133

by Chris Bergin

Following its extended vacation on the S1 Truss in-between STS-123 and STS-124, the 50 ft robotic arm of the Orbiter Boom Sensor System (OBSS) may avoid being a casualty of the shuttle’s retirement.

Managers are working on two plans, both of which will result in the OBSS being left on the International Space Station (ISS) at the end of the final shuttle mission to the Station – currently STS-133’s CLF (Contingency Logistic Flight) mission, manifested for April 29, 2010.

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OBSS Plan:

It’s already been an eventful life for the OBSS since its implementation as an additional Return To Flight safety feature on STS-114.

Used in tandem with its sister hardware of the Canadarm Shuttle Remote Manipulator System (SRMS), the boom carries the OBSS sensor package, used to scan the orbiter’s critical RCC panels and Thermal Protection System (TPS) for any signs of damage.

That instrumentation package consists of visual imaging equipment, the Laser Dynamic Range Imager (LDRI), and the Laser Camera System (LCS). The post-Columbia modification has sensors that can resolve at a resolution of few millimeters, and can scan at a rate of about 2.5 inches per second.

This new ability was highlighted during STS-118, when a ‘gouge’ was spotted on Endeavour during Flight Day 3’s Rbar Pitch Maneuver (RPM) – resulting in a Focused Inspection two days later.

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Utilizing Neptec’s LCS, the OBSS was guided underneath Endeavour’s belly for a fascinating close view of the damage, allowing for a stunning 3D movie the probed the tile damage for additional data that aided thermal modelling by engineers on the ground. Ultimately it aided the eventual decision to clear the damage as acceptable for re-entry – as later proven as the correct decision when no heat damage was observed when the tiles were removed in her OPF.

However, it was the next mission where the OBSS’ arm proved its worth for work on the ISS’s hard to reach areas, when it was grappled to the end of the SSRMS (Space Station Remote Manipulator System) boom as an extension for Scott Parazynski’s epic EVA-4 during STS-120.

Tasked with repairing a tear in the station’s P6 4B solar array, Parazynski was carefully transitioned to the worksite he’d never have been able to reach without the additional length of the OBSS, where he spent several hours freeing the snagged bays, before installing five cufflinks to allow for the full deployment of the power generating panels.

That successful use of the OBSS on EVA-4 is when initial discussions started on the potential of leaving an OBSS boom on the ISS before the final shuttle mission to the Station undocks.

Added to its successful docked late inspection use during STS-123 – which would be required on that final mission – the plan is now starting to move forward.

‘(Managers) and others have pulled together the story on the OBSS ‘Leave it on Station’ at end of Program action,’ noted the latest Shuttle Stand-up/Integration report. ‘They took that story to the board (last week).

‘There are two flavors of it, around $1 million and around $1.6 million, depending on whether you relocate the PDGF (Power and Data Grapple Fixture) for the Station arm to the end so they have maximum reach or not.’

Currently, the final shuttle mission to the Station is manifested as STS-133 with Endeavour – which would be the second of two CLF missions.

As the tag ‘contingency’ denotes, these two flights – the other being STS-132 with Discovery (March 18, 2010) – have not yet been officially placed into the schedule.

Should they fly, they would be used to beef up the ISS’ spare hardware reserves, allowing it to ably cope with the subsequent loss of the shuttle’s unique one trip payload capability, which Soyuz, Progress, ATV, HTV and COTS would not be able to compete with.

While the potential for extending shuttle flights to 2012 remains a question of funding in political circles, a reduction of the shuttle manifest would result in either the removal of the CLF missions, which would see the final shuttle mission flying with Atlantis – recently saved from retirement in 2008 – on STS-131 (currently Jan 21, 2010).

The earliest shuttle could be retired, for the purpose of completing ISS construction, is with Endeavour’s STS-130 flight – currently manifested for Oct, 22, 2009 – which will carry Node 3 for installation to the Station. However, there has been no movement towards reducing the remaining flights on the manifest.

The downstream manifest is, as always, a fluid situation. However, whatever mission becomes the final flight of the shuttle has a direct relation on the final flight of the OBSS, with the decision on whether to carry out the plan to leave the ISS with a parting Canadian gift to be advanced by the end of the month.

‘(The plan) will be making its way through the Station Board, and to the JPRCB (Joint Program Requirements Control Board) within a few weeks,’ added the Stand-up.

A follow-up to that meeting will be published when information is available.

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