Discovery makes perfect landing in California – STS-131 flow preview

by Chris Gebhardt and Chris Bergin

With the weather failing to improve on the Florida coastline, Discovery has landed at the Edwards Air Force Base (EAFB) in California – where she will undergo initial deservicing prior to a ferry trip back to the Kennedy Space Center on the back of the Shuttle Carrier Aircraft (SCA). The deorbit burn took place at 19:47p.m Eastern – which resulted in a perfect landing at 20:53pm.

STS-128 Return:

Discovery allowed managers to concentrate on the weather conditions by continuing to perform in an exemplary manner on orbit, with no new issues noted on the Mission Evaluation Room (MER) list of “funnies”.

With two attempts to land back at her home base of the Kennedy Space Center both called off on Friday as the weather conditions were deemed to be even worse than Thursday’s landing waved off opportunities.

With no sign of improvement, Flight Controllers at the Johnson Space Center (JSC) made an early decision to switch their attentions to landing Discovery at the Californian home of the Dryden Flight Research Center (DFRC),

Now on the ground, Discovery will undergo safing over the weekend, prior to lifted up on the Mate/Demate Device (MDD) for work on her landing gear and propulsion systems – notably the hypergolic systems – along with the installation of the tailcone, which will protect the aft of Discovery during the mated trip cross country on top of the converted 747.

The veteran orbiter’s performance has mirrored the vast majority of the flights over recent years – which earned praise from Space Shuttle manager John Shannon.

“The entire team has done a tremendous job during this flight. It could not have gone any better!” Mr Shannon noted on the latest Shuttle Standup/Integration report on L2. “This is exactly how we want to complete the remaining flights.”

A2A return to California holds no impact to the Boundary Layer Transition (BLT) Detailed Test Objective (DTO) observations, with the Hypersonic Thermodynamic Infrared Measurements (HYTHIRM) team making the right choice to assume Discovery would be heading to California.

With the HYTHIRM aircraft in position over the Pacific Ocean, Discovery’s return was monitored in close detail, as the heatshield on the vehicle rode through re-entry.

“In the absence of any constraints (ground track, weather, Shuttle orientation, aircraft capability) what is the recommended Mach number (point of closest approach)? Mach 16.5 Maximize science: Anticipate fully developed turbulent flow behind the wing protuberance at this Mach number,” noted a Program Requirements Control Board (PRCB) presentation associated with STS-125’s results – dated Thursday, and available on L2.

The presentation also noted the slight cosmetic damage that was observed near the vicinity of the DTO via Thermal Protection System (TPS) surveys, ahead of docking with the International Space Station (ISS).

A3As noted by the DAT (Damage Assessment Team), both areas of damage are not in the downstream path of the tile protrudance, with the HYTHIRM confirming they expect no interference.

“Will observed tile damage influence observation? Unlikely that turbulence from STS-128 TPS damage will obscure our view of the DTO wedge at Mach 16.5,” added the PRCB presentation. “No change to recommendation for Mach 16.5 HYTHIRM deployment.”

This DTO will see an increase in the Boundary Layer Transition tile to 0.35″ during processing towards Discovery’s next flight – STS-131 – based on performance data from STS-128.

The goal of the experiments is to measure the effects of increased heating from an early boundary layer transition as the orbiter returns to Earth. The DTO was set to debut on STS-126, before being deferred to STS-119.

Discovery is also debuting another entry-related DTO on behalf of Orion. A “Catalytic Coating” was applied to two of Discovery’s Thermal Protection System (TPS) tiles, providing Orion – and shuttle – engineers with refined aeroheating data.


Currently targeting launch on March 18, 2010, Discovery’s STS-131 mission will deliver supplies to the International Space Station (ISS) via the Multi-Purpose Logistics Module (MPLM) Raffaello and the Light-weight Multipurpose Experiment Support Structure Carrier (LMC).

Initially, Discovery was to begin processing for STS-131 on August 31. However, due to multiple launch date delays due to External Tank foam concern, weather, and a fill and drain valve, Discovery did not launch until August 29.

Should Discovery land in Florida on Friday, processing for STS-131 will begin once initial safing and excess propellant is offloaded from the vehicle in OPF-3 (Orbiter Processing Facility Bay 3).

However, should Discovery land in California, full-up processing for STS-131 will not being until the Orbiter has been flown back across the country — a task that usually takes between nine and ten days to accomplish following a landing at Edwards Air Force Base.

Nevertheless, Discovery’s flow toward STS-131 is longer than the usual OPF flow — ~145-days v. the minimum ~100-days a vehicle can be processed out of the OPF.

During her stay in OPF-3, Discovery will have her #2 APU (Auxiliary Power Unit) — one of three devices (APUs) that provide hydraulic power to the vehicle during launch and entry — replaced due to time and cycle requirements.

A4Additionally, Discovery’s Main Propulsion System PV 9 and PV 12 fill and drain valves will be replaced for the same reason — as both of these valves have reached the end of their 16 flight certified lifespan.

It should be noted that this replacement was scheduled well before the PV-12 valve sensor malfunction occurred on the launch pad on August 25 — a malfunction which caused a scrub to Discovery’s 2nd launch attempt.

However, the first of several modifications that will be made to Discovery during her turn-around flow will be a the implementation of a redesign to the Rudder Speed Brake (RSB) Inconel Thermal Barrier tabs — tabs which provide thermal protection from the SRB and main engine plumes during ascent.

Stemming from a liberation event on Discovery’s STS-124 mission in June 2008, the modification of the RSB tabs “provides redesigned (RSB) inconel thermal barrier tab attachments to improve strength and durability,” notes the STS-131 Launch Site Flow Requirements presentation, available for download on L2.

A5For the modification, all 60 tabs located on the RSB periphery will be replaced.

An initial modification was made to the tabs following STS-124. However, that modification did not work as several tabs were found missing on the following mission (STS-126) during post-flight inspections of Endeavour in December 2008.

For this modification, the fastening mechanism will be improved by increasing the number of “spot welds,” shortening the overlap of each tab to 0.300,” and adding a secondary fastener via an increase in tab length.

The next modification discussed in the LSFR is to the Starboard Lightweight Tool Stowage Assembly (TSA).

“Due to allocation of the two standard port lightweight TSAs to OV-104 (Atlantis) and OV-105 (Endeavour) and manifest delays, OV-103’s (Discovery’s) STS-128 flight required use of the starboard LWT TSA for stowage of standard contingency tools,” notes the review document.

A6To accommodate this need, a new cushion was provided. This will allow the tools to be stowed in the starboard TSA; however, a fit check issue has yielded a one flight modification to “reverse the forward tool tray installation and remove its handle.”

The orientation of the TSA to the upside-down position was necessary in order to properly mount the TSA to the Starboard location.

This reversal now places the tray handle on the bottom. As such, the handle had to be removed to allow the tool tray to fit properly and allow the TSA lid to close. The handle will be relocated to the opposite end of the tray to place it in the proper position for the starboard TSA.

The final approved modification at this time “Improves the damage resistance of the Aft Stub carrier panel tiles adjacent to the body flap” of the orbiter — which is parallel to the three Space Shuttle Main Engines.

Historically, several damage locations in this area of the vehicle have been attributed to ground processing procedures.

As a result of this realization a few years ago, eight tiles in the area were upgraded to reduce the risk of damage associated with ground processing.

However, recent tile damage in this area has been seen on the tiles that were not modified. Furthermore, flight experience has shown that the tiles that were upgraded have performed very well.

As such, the remaining tiles in this region will be upgraded for STS-131 and subsequent flights. This new material will have approximately twice the strength of the previous material.

In addition to these modifications, several other configuration changes are under review for STS-131.

A7Among these are a redesign of the Gaseous Hydrogen Flow Control Valve poppet following the event seen on STS-126, a redesign of the F3D/F4D thruster cover, a sneak peak of the Wing Leading Edge spar inspections, a redesign of the Wing Leading Edge Carrier Panel Horse Collar Gap Filler on panels 1-4, and a connector saver redesign of the OMS Pods and Ku-Band Antenna.

Click here for articles on the FCV issue since STS-126.

Also under evaluation for the STS-131 are the delivery dates for Government Flown Equipment and the Flow Control Valves and the potential removal and replacement of the Multiplexer/Demultiplexer due to Wave Form Output.

L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

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