STS-131: Cold weather delays flow – DDO constraint pushes launch into April

by Chris Bergin

Rollover of Discovery is still pending, due to temperature constraints relating to several systems on the orbiter, resulting in new rollover date of February 22. Meetings are also likely to recommend to delay the launch until early April, to allow the Russian Soyuz TMA-18 to dock at the ISS – pending evaluations on the constraint of Dual Docked Operations (DDO). Update – now officially April 5.

STS-131 Flow Latest:

Discovery is in preparation for her STS-131 mission, which will deliver supplies to the International Space Station (ISS) via the Multi-Purpose Logistics Module (MPLM) Leonardo and the Light-weight Multipurpose Experiment Support Structure Carrier (LMC).

Secured inside the MPLM will be Zero-G stowage racks, an EXPRESS rack, a Muscle Atrophy Resistive Exercise (MARES) unit, a Window Orbital Research Facility (WORF), one Crew Quarters Rack, a Minus 80 deg Laboratory Freezer for ISS (MELFI), Resupply Stowage Racks (RSRs), as well as Resupply Stowage Platforms (RSPs).

Rollover to the Vehicle Assembly Building (VAB) was due last week. However, two issues delayed the flow, with the ultimate problem relating to the cold weather at the Kennedy Space Center (KSC).

For an orbiter rollover – and preparations for mating with the stack’s Solid Rocket Boosters (SRBs) and External Tank – the VAB has to be above 40 degrees for more than 12 hours solid. This relates to the orbiter’s OMS and RCS, which would be without an active warm air purge and/or heaters – which in turn risks damage to the systems.

Although the temperatures in the local area will rise above 40 degrees, they won’t remain within constraints for the extended period of time that would allow managers to be comfortable with rolling Discovery out of her home comforts of OPF-3 (Orbiter Processing Facility).

A constraint within a constraint was also recorded last week, when Discovery’s landing gear was lowered – after being raised for the ‘final’ time ahead of rollover – after a Thermal Protection System (TPS) engineer noticed a Nose Landing Gear (NLG) door had an out-of-spec gap measurement.

“NLG and MLG (Main Landing Gear) were lowered in support of tile operations; then retracted for final closure before rollover. NLG door step and gap measurements were similar to previous. Two tile shaves will get the roughness below the tolerance,” confirmed the NASA Test Director (NTD), via L2-acquired processing information at the time.

This constraint was soon cleared: “The step data was presented to MEQ (Mechanical) Engineering and they are good with the door as-is,” although rollover was delayed regardless, due to the aforementioned temperature constraints.

Discovery’s boosters and tank (ET-135) are currently sat in the VAB’s High Bay 3 (HB-3) wondering why they’ve not been joined by Discovery – although the delay has allowed for continued work on the intertank plug pulls/pull tests.

“ET-135/SRB BI-142 / RSRM 110 (VAB HB-3): L/R FN #8 Cover RT-455/Instafoam application; Re-perform pull test again today (Monday),” added processing information.

“Orbiter Mate Preps are complete. Intertank Plug Pulls; Will perform additional 70 pulls on +Z side of the Intertank after Orbiter Mate. May reconfigure platforms and perform prior to Orbiter Mate if mate is delayed because of weather (since confirmed).”

The plug pulls are now a regular procedure on the tanks, since foam losses were observed from the intertank region of the ET during a number of the recent flights. STS-130’s tank also lost some foam from the intertank stringer, although the amount of foam that liberated was far less than the previous two flights. None of the intertank losses hold a threat to the orbiter.

Launch Date:

When Discovery launches is the main question, with meetings set to take place this week to realign the flow. Had rollover occurred on Monday, managers had already set up a preliminary flow that placed STS-131’s launch date as March 22, which held two days of contingency in the flow.

“Based on the continued prediction of lower than acceptable temperatures, (Mission Management Team manager) Mike Moses has agreed to our recommendation of a STS-131 rollover NET 2nd shift MONDAY 2/15, followed by orbiter lifting to commence on 1st shift TUESDAY 2/16,” noted one of several SSP (Space Shuttle Program) and MOD memos (L2) on the debate of slipping from the scheduled March 18 launch date.

“Here are the corresponding schedule milestones: SSV (Space Shuttle Vehicle) to the Pad 2/23. TCDT (Terminal Countdown Demonstration Test) T-0 3/5. Payload to the Pad 3/10. Launch NET 3/22 (U/R). Two contingency days in the Pad flow.”

With the one week slip to rollover, it can be assumed the latest NET (No Earlier Than) launch date will be March 29. However, talk of the launch of moving the launch to April was already being circulated, even prior to the latest rollover slip.

The April launch date – noted as NET April 4 or 5 – is based on the constraint of Dual-Docked Ops, which relates to an orbiter being docked at the International Space Station (ISS) during a Soyuz docking.

This issue is heavily referenced on a number of SSP and MOD memos debating the departure of Soyuz TMA-16 on March 18 and Soyuz TMA-18’s April 2 launch (for April 4 docking). The original launch date allowed for Discovery to depart the ISS ahead of Soyuz TMA-18’s arrival.

A large amount of work has taken place over recent months to find a solution to the DDO issue, although it appears the constraint will still be in place for STS-131 – with a direct reference made to ISS program manager Mike Suffredini’s wish to “avoid dual docked ops” for this mission, thus they “expect STS-131 to move to 4/4 or 4/5.”

This of course remains fluid, with the possibility of working in a solution to DDO over the coming weeks. However, sources note this is unlikely to be taken, due to the flow all-but aligning to an early April launch date. It’s also very unlikely the Russians would change their launch schedule.

UPDATE: Now officially NET April 5.

Pad turnaround timelines and a Beta Angle Cutout would also likely result in STS-132 slipping to sometime in June, although this would not be an issue for the Program, with plenty of stretch time built into 2010’s current five mission manifest.

L2 members : Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4500 gbs in size

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