STS-135: Downmass requests build with ISS interest in returning a BGA motor

by Chris Bergin

Although technically still a notional mission, should Atlantis provide the swansong to the Shuttle Program with STS-135, she’d be returning home full of downmass – ranging from a full Multi-Purpose Logistics Module (MPLM), the failed Pump Module, a Pressurized Mating Adaptor (PMA-3) and also now potentially including the BRRM motor component of the 2A Beta Gimbal Assembly (BGA).

STS-135 Processing:

Atlantis is enjoying a smooth flow, with only 27 Interim Problem Reports (IPRs) listed in her flow since returning from the highly successful STS-132 mission.

Technically, Atlantis is being processed all the way through a nominal processing flow inside her Orbiter Processing Facility (OPF-1) for the provision of STS-335 Launch On Need (LON) support for Endeavour’s STS-134 mission.

However, with FY2011’s funding levels starting to show signs of stabilizing via the Continuing Resolutions (CR), NASA managers may be close to pressing forward with manifesting STS-135.

A major milestone for both Atlantis and the Space Shuttle Program (SSP) was reached this week, with the completion of Space Shuttle Main Engine (SSME) installation tasks on the orbiter. SSME-2 was the last engine to be installed on Sunday, followed be securing tasks over the last few days.

“SSME #2 installation was completed Sunday. This was the final planned installation of a Space Shuttle Main Engine for flight,” noted the NASA Test Director (NTD) processing reports (L2). “Engine securing operations are in work, for completion on Tuesday.”

Atlantis’ Payload Bay Doors (PLBDs) were also closed this week ahead of the Christmas/New Year holiday, in tandem with the completion of testing on the orbiters Microwave Scan Beam Landing System (MSBLS) magnetron.

The External Tank (ET-138) designated to ride with Atlantis is currently located in the Vehicle Assembly Building’s (VAB) High Bay 2E checkout cell, with no processing work of note being carried out for some days. Atlantis’ booster segments continue to be undergoing build-up tasks in Surge.

The last ‘newly produced’ tank has to wait its turn for mating operations, with Discovery – as the STS-133 stack – soon to rollback for a 360 degree Non Destructive Evaluation (NDE) of ET-137’s LO2 and LH2 flanges via scans, in order to check for stringer defects.

STS-134’s ET-122 mate with its twin Solid Rocket Boosters (SRBs) remains on hold until next year, with a preliminary target of January 11, following Program instructions at the Mating Review.

STS-135 Mission Planning:

With STS-133 slipping to early February, resulting in STS-134 moving to a placeholder of April, STS-135 could still remain on target to launch in late June – although NASA managers have made no secret of holding out hope they can launch STS-135 later in the summer, which would be beneficial for leaving the ISS in the best possible configuration for the post-Shuttle years.

The mission has already received its first program-level mission outline, with Atlantis manifested with carrying a MPLM (Multi-Purpose Logistics Module) and LMC (Lightweight Multi-Purpose Carrier) on a 11+1+2 day mission. This outline should expect to undergo refinements of the mission objectives via the Program Requirements Control Board (PRCB) meetings in the next few months.

However, fully utilizing STS-135 is not just related to the superior upmass the shuttle can provide, but also the downmass – the biggest hit the ISS will face in the coming years once the fleet has been retired.

Plans have already been drawn up to return the failed Pump Module from the ISS, following its changeout during the External Thermal Control System (ETCS) Loop A troubleshooting, providing vital analysis into the failed hardware on the ground.

However, according to Tuesdays MOD 8th Floor News – and internal and expansive overview of the Shuttle, ISS and Constellation – other elements of ISS hardware are set to hitch a ride home with Atlantis.

STS-335/135 Specific Articles: 

The 8th Floor ISS and SSPCB (Space Station Program Control Board) notes in the 8th Floor opened by explaining the reason behind the recent request to look into the possibility of returning PMA-3 back to Earth.

Citing if PMA-3 was left on ISS in its current location (Node 3 Port), then PMA-2 would have to go to Node 3 Aft in order to free up Node 2 Forward for the Cupola. Bringing PMA-3 down on STS-135 would allow PMA-2 to go to Node 3 Port, leaving Node 3 Aft open for the PMM.

A more recent topic for a potential addition to the downmass is the 2A BGA, which is used to rotate the array so that they face the Sun to provide maximum power to the International Space Station.

“There was a long side discussion regarding the 2A BGA that has potential stall issues at high betas,” noted the 8th Floor (L2). “ISS Manager Mike Suffredini asked whether we should R&R this BGA (BRRM). Since this is one of the BGA’s that was “driven hard” during its life on P6, the Program is interested in getting the unit home for analysis and refurbishment and installing a pristine unit with no liens on its performance.

“(We) got an action to determine whether it makes sense to perform the R&R from an engineering perspective and when it makes the most sense to perform the R&R (stage or ULF7 (STS-135) – MOD action). The Program would like a top level response in the next few weeks.”

Given the timeline of the top level response, a full shopping list of upmass and downmass may be finalized early next year. However, NASA managers have to first ensure they have the appropriate level of funding to carry out the mission, which may only become clearer once Discovery’s STS-133 mission has been completed.

(Images via L2 and

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