Pending the successful outcome of STS-133’s External Tank (ET-137) clearance for flight, managers have created a preliminary schedule for Endeavour’s realigned milestones. Currently, STS-134’s April 1 launch date is only a placeholder, but remains a target that can be achieved – providing Discovery doesn’t slip from her early February launch window.
Endeavour final mission is tasked with launching the AMS-02 (Alpha Magnetic Spectrometer-02) to the International Space Station (ISS), whilst carrying the Express Logistics Carrier 3 (ELC-3). Also riding with Endeavour are the Materials on International Space Station Experiment 8 (MISSE 8), an Orion Rendezvous Detailed Test Objective (DTO) kit, and a GLACIER freezer module for one of the Station’s science laboratories.
Endeavour will also return the MISSE 7a and 7b experiments to Earth as well as perform four Department of Defense payloads of opportunity: MAUI, SEITI, RAMBO-2, and SIMPLEX.
The youngest orbiter in the fleet was set to rollover from her Orbiter Processing Facility (OPF-2) in January, following what is currently a very smooth flow, with only 20 IPRs (Interim Problem Reports) charged against her flow – although IPR-20 has undergone troubleshooting for weeks.
“OV-105 (OPF Bay 2): No vehicle power is scheduled until January. WLE (Wing Leading Edge) end-to-end and sleep mode testing,” noted the NASA Test Director (NTD) processing report (L2). “IPR-0020 LH (Left Hand) OMS (Orbital Maneuvering System) pod Main Engine Ignition (MEI) acoustics instrumentation troubleshooting was performed. Engineering is evaluating.”
The problem relates to the instrumentation which is now sported by all the orbiters, as engineers continue to gather data on the MEI Acoustic and SSME (Space Shuttle Main Engine) Ignition Overpressure (IOP) Environments.
*Click here to see a SSME Ignition in superslow 8mm footage*
The call to investigate the IOP Environments resulted in a large debate at the STS-129 Flight Readiness Review (FRR), specifically relating to an attach point between the aft Reaction Control System and OMS Pod, which – it was ‘feared’ – may be around 20 flights beyond its predicted fatigue lifespan, following a review of engineering data.
Due to potential structural integrity problems via localized acoustics during the firing of the main engines, engineers wanted to gain a better understanding of the environment, in order to update their computation models – which were mainly based around data from early in the Shuttle Program – thus helping them work out if there is a risk associated with these element of hardware.
Although structural fatigue may sound dramatic, the attach point in question is only one of four on each stinger. Engineering data – along with borescope inspections – was already available on the same location on orbiter Discovery by the time the STS-129 FRR met, showing the hardware is in good shape.
All three orbiters have since undergone borescope inspections, with no cracks – or signs of cracks forming – observed.
Up to 29 previous flights were used to refine what was a large level of conservatism for specific areas of the orbiter that could be affected by MEI Acoustics and IOP, with Ground rules and update previous criteria that had been approved by a Loads Panel.
This ranged from 3000 Thermal Protection System (TPS) tiles, to large areas of the aft. Only the one stinger raised flags, leading to the FRR discussions.
For all NASASpaceflight.com articles on the MEI Issue, click here: http://www.nasaspaceflight.com/tag/mei/
With managers confident the hardware was in an acceptable condition for launches throughout the latter stages of the program’s lifetime, a call to install numerous acoustic sensors and a microphone on to the orbiters – in order to glean additional updated data from the aft of the orbiters during main engine ignition – were ordered. Sensors in the Mobile Launch Platform (MLP) were also added.
The current problem with Endeavour is specific to one of those acoustic sensors, with “MEI acoustic sensor V08Y9704A does not channelize” the subject of a couple of week’s worth of investigation.
A suspect connector has been replaced and retested, although the IPR remained active as engineering overviews continue to evaluate if the sensor is now in an acceptable condition for flight.
This is a minor issue, the only issue Endeavour has right now, as she was powered down for the Christmas holidays. She will also have some additional time to undergone troubleshooting, should it be required, now her rollover has been delayed to February.
STS-134 Specific Articles: http://www.nasaspaceflight.com/tag/sts-134/
Realigned milestones presented prior to the holidays are all subject to change, based on the work ongoing in the Vehicle Assembly Building on Discovery’s ET-137, although the January 11 mating of Endeavour’s Solid Rocket Boosters (SRBs) and ET-122 – slipped due to STS-133’s issues – should now go ahead on the realigned date, just ahead of Discovery’s scheduled return to Pad 39A, which is currently scheduled for two days later.
Discovery is currently located in High Bay 1 of the VAB undergoing inspections of ET-137’s flange stringers, whilst STS-134’s boosters are stacked and awaiting ET-122 in next door’s High Bay 3. ET-122 will be lifted over by the VAB crane from the checkout cell in High Bay 4E (HB-4E).
Updated milestones then list the Payload Readiness Review on January 20, leading into the Orbiter Rollout Milestone Review. Should all go to plan, Endeavour will rollover from her OPF on February 8, for a nine day stay inside the VAB for mating operations with her stack.
With rollout to Pad 39A on February 17, Endeavour will have a slightly longer than usual stay out at the pad ahead of the April 1 launch date target, with the Space Shuttle Program (SSP) and Agency FRRs taking place in March, ahead of the March 30 L-2 Mission Management Team (MMT) meeting.
(All images via L2).