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).
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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.
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