STS-128: Flight Day 2 Inspections complete on Discovery’s TPS

by Chris Bergin

The STS-128 crew have completed Flight Day 2’s activities, which focused on the opening inspections of Discovery’s Thermal Protection System (TPS), along with the checkouts of the orbiter’s docking systems ahead of Sunday night’s arrival at the International Space Station (ISS). Discovery launched Friday night on what is initially being described as a very clean ascent.

STS-128 Flight Day 2:

Shortly after reaching orbit on Friday, Discovery’s Payload Bay Doors were opened, followed by the deployment of her Ku-band antenna. Discovery’s Remote Manipulator System (RMS) was also activated ahead of Flight Day 2’s inspections.

neptecFlight Day 2 opened with the unberthing of the Orbiter Boom Sensor System (OBSS) via the RMS, in order to carry out surveys of Discovery’s wing and nose cap, before heading to the OMS Pods to check for any tile damage or protruding blankets.

“TPS Surveys: All RCC (Reinforced Carbon Carbon) is inspected during the OBSS Starboard Wing, Nose Cap, and Port Wing surveys. The two wing surveys also cover most of the areas of the crew cabin. The OMS Pod is inspected using a handheld camera to take pictures from the aft flight deck windows,” noted Flight Readiness Review (FRR) mission outline documentation (L2).

“The OBSS survey procedures incorporate the use of supplemental IDC (Digital Camera) images during LDRI (Laser Dynamic Range Imager) scans, thus reducing the likelihood of needing Focused Inspection. The OBSS unberth procedure incorporates the LDRI 3D calibration and the starboard survey the flat field calibration.

“Three crewmembers are required continuously during the surveys, two for the SRMS/OBSS ops and one to operate the situational awareness cameras and sensors. Only two crewmembers are required during unberthing and berthing operations (non-laser ops).

Scans of the entire starboard wing are not easily performed, or are impossible to perform while docked, which results in those areas being scheduled first. The surveys are scheduled to continue through the night passes, but the crew may elect to pause if the night time visuals are not sufficient.

“The LDRI survey attitude requires no sun within a +/-20 degree field of view (FOV) of the laser bore-sight. Additionally, no sun can be within a 10 degree half-cone directly behind the instrument; however it is highly desired to keep the sun at a 90 degree half cone behind the instrument as long as it’s not directly behind.”

Although Flight Day 3’s RPM (Rbar Pitch Maneuver) – carried out “underneath” the ISS ahead of docking – will provide a near-complete overview of Discovery’s heatshield, the OBSS inspections will give the opening insights into the extent of any damage sustained during the ride uphill.

Ascent Review:

Back on the ground, the Damage Assessment Team (DAT) have begun their evaluations into the ascent of Discovery, a ride uphill that has initially been described as uneventful from a debris standpoint.

The key focus will be on the External Tank (ET-132), following the foam liberation events during STS-127’s ride to orbit with ET-131.  Following pull tests and hours of evaluations into the health of several areas – mainly the intertank and LO2 IFRs (Ice Frost Ramps), engineers are hoping to see less liberations via Discovery’s flight.

Based on the initial data, no “major” foam loss events have been observed – though none of the recent flights can be classed as suffering from anything more than minor foam loss. A lot of work is required to study each element of camera, radar and onboard camera footage, usually taking several days to collate.

AB2Additional photography of the LO2 IFRs will have been gained for engineers on the ground, thanks to the debut use of a Modified Post-ET Separation +X maneuver on STS-128.

“Based on imagery observations of ET foam loss on STS-127, the imagery team was asked to evaluate possibilities for improving the Digital ET TPS umbilical still image photography of the ET LO2 tank,” noted a Program Requirements Control Board (PRCB) presentation on L2.

“In theory, getting the camera over the LO2 tank sooner would allow less time for the tank to fall away, and thus improve camera resolution – especially applicable for dark (no sunlight) conditions because of the limited effective range of the DETTPS flash unit.

“Therefore, the most straightforward approach is to assess options for the +X maneuver with longer burn times and greater overall Delta V.”

As noted in documentation and intimated by Mission Management Team (MMT) chair Mike Moses, a camera may be placed facing out through the pilot’s window on STS-129, in order to take video of how the LO2 IFRs behave during ascent, though a final decision is yet to be taken.

AB3Based on initial launch data, engineers know they will have to check what happened to a small area of ice that built up on the T-O umbilical on the Tail Service Mask (TSM) – though it is likely it fell off the vehicle during the very early stages of ascent from the pad.

Debris, or more specifically, ice on the T-0 plate was also at the center of recent SE&I Flight Readiness Review (FRR) presentations, with the department calling for a Tiger Team – the name for the high level investigation team – to look into the liberation threat from the T-0 umbilical hardware over the coming launches.

Ice on the T-0 umbilical hardware is not uncommon, but following the observation of ice liberating from Endeavour during STS-126’s ascent, and ice spotted on the plate as STS-125/Atlantis left the pad, a greater understanding was called for on the remaining shuttle flights, as part of the Shuttle Program’s ongoing threat mitigation process.

The T-0 umbilical – located on each side of the orbiter – is mated to the orbiter via retractable plates in the Tail Service Masts (TSMs), which can be seen either side of the orbiter’s aft. These umbilicals are retracted at SRB (Solid Rocket Booster) ignition.

AB4Ahead of STS-119’s launch with Discovery, United Space Alliance (USA) engineers worked on a ‘rain/water diverter’ modification, which was added to the TSMs as a form of extra protection from one of the determined drivers of ice formation on the T-0 umbilical area.

Ice is only spotted on the plate via engineering cameras placed inside the TSMs on what is known as the QuVIS video – collated via an array of cameras, most of which are never publicly aired on NASA TV’s launch replay feed (several QuVIS videos available on L2, click here for SSME ignition video sample).

However, ice outside of the mated plate may give indications of a potential threat, with SE&I working on ‘allowable’ mass observations, which in turn will be fed back to the Mission Management Team and Launch Director for what is called a ‘Day-Of-Launch (DOL)’ decision – as was the case ahead of STS-128’s launch.

Full reviews of the DAT findings will be included in upcoming articles next week.

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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