STS-135: Atlantis rollover moving to May 16 – Launch may slip to July 4

by Chris Bergin

With schedules continuing to be refined based on Endeavour’s troubleshooting efforts, Kennedy Space Center (KSC) teams were told on Tuesday that Atlantis’ rollover is being moved to a May 16 placeholder, while the launch date – which continues to target June 28 – may slip to July 4, based on a shortage of contingency days. No firm changes to the launch date will be made until after Endeavour launches.

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Atlantis will mark the final launch of the Space Shuttle Program when she heads uphill for a swansong mission to the International Space Station (ISS), carrying a packed MPLM (Multi-Purpose Logistics Module), along with a LMC (Lightweight Multi-Purpose Carrier).

Although early mission planning showed a preference to launch Atlantis as late as possible, in order to reduce the gap between the massive capability of the orbiters and the opening operational missions from the commercial resupply vehicles, June 28 became the solid launch date target for several months – per discussions between Shuttle and Station managers.

That date is, of course, at the mercy of waiting for Endeavour to launch. With the STS-134 mission now delayed until at least May 10, meetings at KSC on Tuesday morning noted the latest review into the rollover schedule and a potential slip to the launch date, likely with an eye on the possibility STS-134 will slip further.

Atlantis’ rollover from her Orbiter Processing Facility (OPF-1) to the Vehicle Assembly Building (VAB) was tracking May 12, before being pushed up to May 10 to allow for a two day mating operation, caused by a shortage in specialist engineers tasked with the transfer of the orbiter from the transfer aisle to the awaiting ET-138 and Solid Rocket Booster stack. Such an operation normally takes one day to complete.

That rollover date has slipped to May 16 – according to L2 information – and may slip further based on Friday’s upcoming decision on Endeavour’s launch date, which will be made following an update on progress of retests which are to be carried out on the soon-to-be-installed Aft “Load Control Assembly” (ALCA-2).

With only two to three weekend days of contingency time remaining in the STS-135 flow, Endeavour’s impacts now hold the potential of slipping Atlantis’ launch date from the June 28 placeholder, with the Tuesday meeting noting a July 4 launch date is being considered.

Again, any decision to officially slip to the launch date won’t be made until after Endeavour eventually launches.

As far as Atlantis herself, work to prepare the orbiter for her roll from OPF-1 are almost complete, with the vehicle now powered down for the final time prior to the short journey to the VAB. Processing information shows preparations for orbiter rollover will continue for the rest of this week.

Only one issue – logged as Interim Problem Report 37 (IPR-37) – has required the attention of her engineering team, when the MDM (Multiplexer Demultiplexer) “FA4 card 4” showed a failure signature during testing late last month. The MDM’s provide instrumentation measurements, commands and data to the displays on the orbiter’s flight deck.

“IPR 0037 DPS (Data Processing System): During power up, MDM FA4 Port 2 analog card 4 failed off scale low. This failure required an MDM R&R (Removal and Replacement),” noted the NASA Test Director (NTD) report (L2). “The discrepant MDM was successfully removed. However, several dings were noted on the coldplate.”

As is standard, engineers took mold impressions of the dings in the coldplate – which provide the role of heat sinks for the electronics – located in Atlantis’ Avionics Bay 6. This led to a repair to a total of 15 defects in the coldplate, along with some documentation on the observation of bolt hole thread marks on the hardware.

After the coldplate repair was signed off as acceptable, the replacement MDM FA4 card was installed, and put through a series of retests – all of which were deemed to be successful. The closure of IPR allowed for the process of orbiter aft compartment structural leak checks and orbiter positive pressure tests, through to the final power down of Atlantis ahead of her rollover.

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Once she arrives in the VAB, she’ll be greeted by the already-mated ET-138 and twin SRBs, with the duo sat patiently awaiting the orbiter on Mobile Launch Platform 3 (MLP-3) inside High Bay 1 (HB-1).

As with ET-137 (STS-133) and ET-122 (STS-134), ET-138 is sporting a ring of radius blocks on its stringers in the area of the LO2/Intertank Flange.

This work was completed without issue, as the specialist engineers from both KSC and the Michoud Assembly Facility (MAF) continued to refine their processes from their work with the previous two tanks.

Notably, ET-137 performed superbly during both its tanking and launch with Discovery, providing positive proof that the mitigation of the stringers cracking during both the cryo cycle of tanking, the pressurization of the internal LOX and LH2 tanks, and indeed the pressure environments of ascent, all worked as advertised via the radius block modification.

ET-122 also showed no signs of issues during its tanking and detanking last Friday.

As far work conducted on STS-135’s tank and boosters over recent days, most of the engineering has related to the electrical integration between the two supporting actors for Atlantis’ ride uphill.

“ET/SRB electrical mates are complete. ET/SRB Integrated Closeouts continue with Upper and Lower strut closeouts,” added the NTD report on Tuesday. “Upper and lower strut closeouts are complete less RTV/Acrymax cure on lower strut. SRB Hold down post ordnance installation is scheduled for 3rd shift tonight (Tuesday).”

Further updates on STS-135’s status will be provided as information arrives, driven by L2’s new STS-135 Special Section.

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