NASA evaluates STS-131 Mission Timelines as Discovery heads toward S0007

by Chris Gebhardt

With Discovery’s opening launch attempt on the STS-131 mission now officially set for Monday, April 5 at 6:21:22 a.m., final pre-countdown operations are underway at Launch Pad 39A as engineers complete last minute tasks to configure Discovery and the launch pad for S0007 (launch countdown) operations.

Discovery’s Mission:

In all, STS-131 will be Discovery’s 38th and penultimate flight under the current Space Shuttle launch manifest.

The mission, the second of the calendar year, is scheduled to last just over 13-days, with two contingency on-orbit days and two additional landing wave-off days for weather or technical issues.

Of the 13 Flight Days (FDs), Discovery and her seven-member crew will spend eight full days docking with the International Space Station performing three Quest Airlock campout EVAs (Extra Vehicular Activities – or spacewalks), over 30-hours of middeck transfers to and from Discovery, and over 100.5 hours of transfers to and from the MPLM Leonardo – STS-131’s primary payload.

At the beginning of the mission, Discovery will launch with 5 full Nitrogen tanks (with no Nitrogen transfers planned for the mission) and 5 nearly-full Cryo tank sets.

Discovery’s sixth Nitrogen tank was removed during OPF (Orbiter Processing Facility) processing as part of a campaign to increase Ascent Performance Margin (APM) for this mission.

Additionally, 515-lbs of Cryo will be offloaded from Discovery after initial PRSD (Power Reactant Storage and Distribution) loading is complete. This offload will “[protect] Dual Docked Ops (13+2+2) w/ 120 hrs of pad hold (O2 limited),” notes the SSP FRR (Space Shuttle Program Flight Readiness Review) Mission Operations Directorate presentation – available for download on L2.

The loading of these Nitrogen and Cryo tank sets will constitute one of the final elements of pre-flight processing on orbiter Discovery before her pre-dawn liftoff with the MPLM (Multi-Purpose Logistics Module) Leonardo, the Lightweight Mission Peculiar Equipment Support Structure (MPESS) Carrier (LMC) with an Ammonia Tank Assembly, and the TriDAR Automated Rendezvous & Docking Sensor DTO (Detailed Test Objective).

Nominal Mission Timeline Overview:

Under nominal conditions, Discovery will liftoff from Pad 39A at the precise moment that Earth’s rotation carries the launch pad into the center of the orbital corridor of the International Space Station (referred to as the “in-plane” launch time).

Despite a preference to launch at this “in-plane” time (which currently rests at 06:21:16 EDT on April 5), the “in-plane” time is not the only moment at which Discovery can launch on April 5. The entire launch window for the opening launch day extends from 06:16:22 EDT – 06:29:36 EDT. a total of 13-minutes and 14-seconds. (Exact second marks are subject to change based on real-time ISS position on the day of launch.)

In all, this gives Launch Director Pete Nickolenko and his team ten minutes of nominal, FD-3 rendezvous launch window with an additional three minutes and fourteen seconds of FD-4 rendezvous launch window on April 5.

Subsequent launch attempt days will alternate – until the end of the April window – between strictly 10-minute, FD-3 rendezvous launch windows and 10-minute FD-3 + three additional minutes of FD-4 rendezvous launch window opportunities.

Once Discovery/STS-131 launches, FD-1 will be spent conducting Post-Insertion operations, activating MPLM heaters and conduction MPLM environmental checks, powering up the SRMS (Shuttle Remote Manipulator System – or Robot Arm), performing the NC-1 course correction burn, and downloading and then downlinking all External Tank Umbilical Well photos, hand-held ET Video, and Wing Leading Edge Sensor data to Mission Control.

FD-2 will see Discovery’s crew perform the standard inspections of their ship’s RCC (Reinforced Carbon-Carbon) panels, nose cap, T0 umbilicals, and upper flight surfaces using the Orbiter Boom Sensor System (OBSS). The crew will also take high resolution digital photographs of Discovery’s OMS (Orbital Maneuvering System) Pods’ thermal blankets and tiles for review by imagery experts on the ground.

FD-2 will also include the NC-2 and NC-3 course correction burns, EMU (Extra-vehicular Mobility Unit – spacesuit) checkouts, installation of the centerline camera for docking operations, Docking Ring extension, and Rendezvous Tool checkout.

FD-3 (under the nominal mission timeline) will see Discovery’s docking to the ISS and subsequent grapple of the OBSS by the SSRMS (Space Station Remote Manipulator System) and handoff to the SRMS.

Given a launch at 6:21a.m. EDT on April 5, Discovery will dock with the ISS at ~3:46a.m. EDT Wednesday, April 7. Following docking, all RPM (R-bar Pitch Maneuver) photos taken by the ISS crew of Discovery’s TPS (Thermal Protection System) will be downlinked to the ground.

The following day, Discovery’s crew will remove the MPLM Leonardo from Discovery’s Payload Bay using the SSRMS and install the temporary module to Node-2 Nadir.

MPLM ingress and partial activation will occur later that day. Meanwhile, middeck transfers to and from Discovery will also begin in earnest on FD-4.

Further events of FD-4 will include EVA-1 campout preparations and nitrogen venting of the S1 truss’ Ammonia Tank Assembly (ATA).

FD-5 will see the first of three EVAs for the mission. During EVA-1, the new ATA in Discovery’s Payload Bay will be released from its transport carrier and manually handed-off to the SSRMS (which will then move the new ATA to a POA [Payload/ORU Attachment] location), the JEM SEED experiment will be retrieved, and RGA-1 (Rate Gyro Assembly #1) will be removed and replaced (R&Red).

On FD-6, 3.5-hours will be reserved for any FI (Focused Inspection) activities that may be necessary. If a FI is not required, that 3.5-hours will be re-allocated to internal transfer time.

Meanwhile, the SSRMS will be “walked-off” to a MBS (Mobile Base Station) at Work Station-3 and EVA-2 preparations and campout will occur.

FD-7 will be devoted to both internal transfer operations and EVA-2 activities.

The 6.5-hour EVA-2 will see the empty ATA removed from the S1 truss and stored on a POA location and the new ATA installed in the old ATA’s place.

Following the new ATA’s attachment, integration operations to connect the ATA to the EATCS (External Active Thermal Control System) loop will take place.

Later that night, after crew sleep begins, the SSRMS will be “walked off” to Node-2’s PDGF (Power Data Grapple Fixture).

FD-8 will consist of three hours of crew off-duty time, internal transfers, and EVA-3 preparations and campout activities before the third and final EVA on FD-9.

For this final EVA, the empty ATA will be installed on the LMC in Discovery’s Payload Bay and the LWAPA (Lightweight Adaptor Plate Assembly) will be retrieved from the exterior of the ISS and installed on the LMC for return to Earth.

Meanwhile, internal ISS/Discovery transfers on this day will include the swap of LiOH (Lithium Hydroxide) CO2 scrubber canisters.

Following the mission’s final EVA, FD-10 will see 3.5-hours of crew off-duty time, the continuation of internal transfers, and MPLM closeout (rack configuration for reentry) preparations.

FD-11 will see the final egress, deactivation, vestibule demate and depress, and uninstall of the MPLM Leonardo from ISS and reberth into Discovery’s Payload Bay.

Post-EVA transfers will also be worked on FD-11, as will positioning of the OBSS into its undocking configuration.

Following completion of these activities, the standard farewell ceremonies will be held between the ISS and Shuttle crews before the hatches between the two vehicles are closed.

The following day, FD-12, will see Discovery undock from the ISS at 4:01 a.m. Friday, April 16. Discovery’s crew will then perform the customary flyaround of the ISS as well as OBSS late-inspections of Discovery’s RCC panels and nose cap following undocking operations.

Following these procedures, the OBSS will be deactivated and stowed for reentry, as will the SRMS.

FD-13 (EOM-1 – End Of Mission -1) will see Discovery’s crew reconfigure the orbiter’s crew cabin from a spaceship/living space arrangement into her proper reentry setup, perform the RCS (Reaction Control System) Hot Fire test, conduct the Landing-1 Comm Checks, stow the Ku-Band communications antenna, and deactivate the Wing Leading Edge Sensors.

If all goes according to the nominal plan, FD-14 will be landing day for Discovery and her crew.

Coming in on a descending node reentry (with a ground track over the heartland of the United States), Discovery’s first landing opportunity will result in a landing at the Kennedy Space Center’s Shuttle Landing Facility on April 18 at ~8:35a.m. – approximately 13-days 2-hours 14-minutes after liftoff.

Minimum Duration Flight Timeline:

As with all Space Shuttle missions, the possibility exists – however remote – that Discovery’s mission may have to be cut short due to a systems failure or other emergency situation.

As long as the problem does not require the immediate termination of the flight and landing of Discovery at the next Primary Landing Site (the three U.S. landing sites), Flight Controllers could opt to execute a Minimum Duration Flight (MDF) – accomplishing only the CAT I mission objectives before terminating the mission.

For STS-131, these CAT I mission objectives include the docking of Discovery to the PMA-2 (Pressurized Mating Adaptor) on the forward end of the Node-2/Harmony module, berthing of the MPLM Leonardo to Node-2 Nadir, Removal and Replacement (R&R) of the spent S1 truss ATA with the new ATA, the transfer of all mandatory quantities of water from Discovery to the ISS, the transfer and stowage of all “critical items per flight 19A TPL,” and the reberth of the MPLM Leonardo into Discovery’s Payload Bay.

Given the amount of time necessary to complete all ATA R&R activities (which require 3 EVAs to complete), a MDF would only be one day shorter than the nominal mission timeline for STS-131.

Under a MDF, the first three FDs of STS-131’s mission would proceed per the nominal timeline. FD-4 would then see the installation of MPLM Leonardo to Node-2 Nadir and the transfer of all mandatory items per the STS-131/19A transfer list.

EVA-1 (ATA removal from Discovery’s Payload Bay, JEM SEED Retrieval, S0 truss RGA-1 R&R), MPLM rack transfers, and STS-131/19A critical item transfers would dominate FD-5.

FD-6 would be set aside for FI activities, critical item transfers, and crew off-duty time before the Flight Crew moves on to EVA-2 (Empty ATA removal from S1 truss, installation of new ATA on S1, and Airlock Micro-Meteoroid Orbital Debris shield retrieval) and critical items transfer on FD-7.

FD-8 would be reserved for critical item transfers and EVA-3 preparations.

EVA-3 (Move empty ATA to Discovery’s Payload Bay and LWAPA retrieval) would dominate FD-9, as would final transfer of all critical items.

The MPLM Leonardo would then be deactivated, unberthed, and reinstalled into Discovery’s Payload Bay on FD-10. Hatches between Discovery and the ISS would also be closed on this day.

Discovery and her crew would then undock from the ISS on FD-11 and perform the standard OBSS late-inspections before berthing and deactivating both the OBSS and SRMS.

FD-12 would then be devoted to all standard EOM-1 activities ahead of landing at the first available U.S. landing site on a descending node reentry on FD-13.

STS-131 Specific Articles:

Further notes from the Mission Operations Directorate (MOD) regarding a MDF for STS-131 include: “Mission duration driven by Cat 1 objectives to return empty ATA (EVA3) and MPLM. If ATA return is not a program priority, the MDF timeline could be up to 4 days shorter.”

Other Mission Considerations:

In addition to the possibility of a MDF, the option also exists to extend Discovery’s mission by one day.

“The following may be considered when using one of the “+1″ days to extend the docked mission: if FD-4 rendezvous is required, if Focused Inspection (FI) delays MPLM installation, and for any other unplanned contingencies,” notes the MOD presentation to the SSP FRR.

In terms of the FI delaying the installation of the MPLM, “Focused Inspection for starboard wing not feasible with MPLM installed on Node 2 nadir” due to clearance concerns, notes the MOD presentation.

Basically, if any areas of Discovery’s starboard wing require a FI, the installation of MPLM Leonardo to the ISS will be delayed until FD-5 and a FI of the damaged area “attempted” as early as the evening of FD-4 if proper procedures and crew time can be devoted to the preparation and execution of the FI.

Following the one-day delay to the installation of MPLM Leonard, a +1 mission day can be added to the mission timeline to ensure that all transfers to and from the MPLM are completed on an equivalent timeline to the nominal timeline.

A +1 day can also be inserted into the mission in order to add a fourth EVA for the completion of all CAT I objectives. Additionally, a +1 day could also be used to add an extra docked day to the mission to ensure the completion of all “high priority IVA (Intra-Vehicular Activity) CAT II objectives.”

Aside from mission duration discussions, additional considerations going into STS-131 include the use of the temporary runway at Edwards Air Force Base, California and construction efforts on the runway at Moron, Spain – one of three TAL (Trans-oceanic Abort Landing) site runways.

“Edwards Temp Runway: Permanent runway concrete work started in mid-January,” notes the MOD presentation. “Flight Rules, procedures, and Crew/MCC training have been conducted with use of the Temp Runway.”

Navigation aids are in place and have been certified for use on the temporary runway.

In terms of the runway at Moron, Spain, “Construction to replace keel area and BAK-12 arresting system surface on MRN20 will begin on April 12,” notes the SSP FRR.

The Landing Signal Officer (LSO) is currently working to confirm the construction details, but the Moron runway threshold will be “displaced” by ~2,700 feet and will thereby decrease the total length of the Moron runway to 9,085 feet, with 1,000 feet of underrun and 1,000 feet of overrun available.

“Ball-bar and PAPIs (Precision Approach Path Indicators) will not be available. MSBLS (Microwave Scanning Beam Landing System) Elevation shelter (within construction zone) TBD.”

Given this construction, the Moron runway will be available as an Emergency Landing Site only since preliminary information shows an “~95 percent chance of roll-out margin violations.”

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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