Discovery handed special heatshield coating DTO on behalf of Orion

by Chris Bergin

Shuttle Discovery has been tasked with a special DTO (Detailed Test Objective) – on behalf of the Orion Project Office – to be carried out during STS-128’s re-entry. A “Catalytic Coating” has been applied to two of Discovery’s Thermal Protection System (TPS) tiles, providing Orion – and shuttle – engineers with refined aeroheating data.

STS-128 Processing Latest:

Discovery is ahead of her timeline to make the August launch of STS-128, thanks to a smooth processing flow, and the impact of STS-127’s delay.

Now targeting a refined August 18 NET (No Earlier Than) lift-off, Discovery will be launched on a logistics mission to the International Space Station (ISS), carrying the MPLM (Multi-Purpose Logistics Module) Leonardo.

Work being conducted on Discovery is taking place inside OPF-3 (Orbiter Processing Facility), with mid-body closeouts in progress.

Engine heat shield installation is complete – following the installation of the three SSMEs (Space Shuttle Main Engines) which will assist her ride uphill – while carrier panel installation and T3 closeouts continue.

Payload bay door closure for rollover occurred late on Monday, ahead of the installation of Discovery’s three “fully inspected” Flow Control Valves (FCVs).

Over in High Bay 1 (HB1) of the Vehicle Assembly Building (VAB), Solid Rocket Booster (SRB) stacking was recently completed, allowing for last week’s mating operation with External Tank (ET-132).

STS-128’s DTOs:

The recently added DTO on behalf of Orion – and further understanding for the shuttle program itself – won’t be the only test to be carried out by Discovery on behalf of improving engineering data, with the TriDAR AR&D Sensor Detailed Test Objective (DTO) and the next Boundary Layer Transition (BLT) DTO, also riding with the veteran orbiter.

o8The goal of the BLT experiment 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.

Following the success of STS-119’s opening BLT DTO, engineers have increased the size of the protuberance to 0.35” for Discovery’s STS-128 flight.

The larger wedge is expected to trip the boundary layer at around Mach 18, provided information on higher levels of heat.

Discovery’s latest DTO addition:

The Catalytic Coating DTO is related to the BLT tests, and was approved by the all-powerful Program Requirements Control Board (PRCB) this month.

“Background: The Orion Project Office requested SSP (Space Shuttle Program) support in the development and flight of the Catalytic Coating DTO. SSP Funding was approved in Dec 2008,” noted the PRCB presentation, available to download on L2.

o6“As part of the BLT FE (Flight Experiment) activity, OV-103 (Discovery) has been modified to include MADS (Modular Auxiliary Data System) thermocouple instrumentation on the lower surface of the port wing downstream of a protuberance tile.”

The catalytic coating was recently applied to two tiles in the turbulent heating wedge on the belly of Discovery, appearing as two green stripes across the tiles.

This is not the first time such a DTO has been carried out by the orbiters, with documentation showing that a version of the coating was first flown on STS-2, 3 and 5, as part of a laminar/catalytic flight test effort.

However, material specification records were not maintained, thus Orion’s manufacturing process and material specification needed to be reconstituted to support the Crew Exploration Vehicle (CEV) requirements.

The purpose of the new DTO is to understand the entry heating performance of a fully catalytic (CC-2) coated tile located downstream of a protuberance designed for Mach 18 Boundary Layer Transition, as targeted by Discovery’s BLT DTO.

o5“Primary Objectives: Acquire temperature data via surface thermocouples in CC-2 coated tiles and adjacent RCG coated tiles during hypersonic turbulent heating phase of Orbiter entry,” added the presentation.

“Test a hypothesis that fully catalytic heating in a turbulent boundary layer can not be modeled as an effect independent of boundary layer turbulence.

“Evaluate the accuracy of existing aeroheating tools being used to support CEV and SSP.”

In order to certify the test, the engineers followed an approach which included reconstitution of the C742 catalytic coating previously flown on Columbia’s early missions, such as STS-5’s experiment – which was used to derive the “Catalytic heating bump factors”.

“NASA ARC (material proprietor) conducted the reconstitution of Catalytic Coating components,” outlined the certification process. “Characterization and certification arc jet testing performed.”

“Material property and performance similarity has been demonstrated. Arc jet test plans were presented and approved by the TPS Project Team.

“Material batch was delivered to Boeing HB (Huntington Beach) for standard testing. Qual testing has been completed and final report is in work. Sequence Of Environments testing close to completion with no issues identified to date.

“Material and Application specifications were developed to SSP standards with the support of Boeing HB and KSC (Kennedy Space Center). Engineering released for KSC implementation.”

o3The actual application of the special coating to the two tiles on Discovery was carried out by one of the KSC engineers, who – along with two other TPS technicians – underwent special training at the ARC facility in Houston.

Although it only involved the use of a spray gun, any changes and new procedures are taken very seriously, in order to ensure the orbiter’s TPS will perform as advertised during re-entry.

“KSC TPS Engineer and Technician as well as TPS NSE participated in Catalytic Coating application training conducted at ARC,” the presentation added.

“KSC Technician has performed training applications and is confident in the process. Technician certified in similar spraying application (koropon). Orbiter flown tiles utilized for training session and sprayed in same orientation planned for OPF implementation.”

Risk assessments were also conducted, which included an overview of all of Discovery’s tiles in the region of the DTO since STS-114.

This also included the associated gap fillers, which have been known to protrude after ascent – notably on STS-114, when Steve Robinson had to conduct a unique EVA to the belly of Discovery to pull out one of the small plastic tabs. A protruding gap filler also has the potential to become an unscheduled BLT DTO during re-entry.

“All gap fillers local to catalytic coating have been installed with the post STS-114 process, which have had no failures for around 17000 installations,” noted the presentation, referencing the gap filler installation changes made since the Return To Flight incident.

In summary, the United Space Alliance and Boeing presented positive conclusions for the inclusion of the DTO into Discovery’s upcoming flight.

o7“Catalytic material characterization and certification testing completed with no issues identified. Full material qualification and sequence of environments scheduled for completion before material application.

“Application training session with KSC personnel also conducted. Catalytic heating environments developed for the BLT FE mission 2 (Mach 18) have been applied to the TPS.

“Concurrence established with Aero-heating, Thermal, Stress and TPS PRT based on remaining conservatism and flight history. Aluminum structure is within certified limits and tile bond/structural margins are positive.

“All gaps in the area of the two catalytic tiles will be filled to reduce gap heating to structure (around 15 gap fillers). Missing gap filler and protruding gap filler risk assessments provide additional confidence in TPS capability.

“Approve application of CC-2 Catalytic Coating on STS-128.”

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

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