Discovery’s STS-124 posed for smooth FRR, aided by Endeavour

by Chris Bergin

STS-124 continues to proceed on schedule for the May 31 launch date target, following an issue-free closure of her payload bay doors at the weekend.

The next key junction for the pre-flight preparations relates to paperwork, as managers meet to clear Discovery for her launch date via two Flight Readiness Reviews (FRR) – the first of which is a two day Space Shuttle Program FRR, which begins on Tuesday.

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STS-124 Latest:

The first, the SSP (Space Shuttle Program) FRR, is scheduled for May 13 and 14, which will be conducted via ‘ViTS’ – a Video Conference facility. The Joint Program FRR is scheduled for May 19, which will be a face-to-face meeting, hosted by Bill Gerstenmaier.

With the bulk of documentation being created for the SSP FRR, any signs of a potential issue that could delay the launch at this stage is likely to be known by Wednesday. However, no major issues are being worked.

The other major element that is utilized during a FRR are the issues that occurred during the previous flight, in this case STS-123 with Endeavour.

Classed as the IFA (In Flight Anomaly) review, every major shuttle and mission department creates an overview presentation of any issues during the mission.

This process aids the ‘lessons learned’ and any subsequent ‘get wells’ for both the next mission and the upcoming processing flow for the orbiter that flew. The collated documentation is then presented to the all-powerful Program Requirements Control Board (PRCB).

With regards to STS-124, Endeavour has already done her older sister a big favor, with the cleanest flight on record since the full utilization of the Orbiter Boom Sensor System (OBSS) checks of the orbiter’s TPS (Thermal Protection System), started on STS-121.

Only three issues moved to the IFA review – conducted in the second half of April – on the debris related review of the mission, noted as ‘Lift-Off Debris. Orbiter Stub Tile damage, and Orbiter TPS coating loss.’

‘Lift-Off Debris: Unexpected/expected debris prior to pad clearance. Exceeds mass allowable or risk baseline. Ascent Debris impact to SSV (Space Shuttle Vehicle),’ noted the associated presentation.

‘Stub Tile Damage during SSME (Space Shuttle Main Engine) Ignition. Tile damage was observed outboard of SSME 3 on the base heat shield just above the body flap. Unexpected debris; not included in risk baseline. Ascent Debris impact to SSV.

‘Tile Chips on Orbiter Stingers during SSME Ignition. Three tile chips on Orbiter port OMS pod stinger observed during SSME ignition. Unexpected debris; not included in risk baseline. Ascent Debris impact to SSV.’

Two separate photographic and data presentations – over 100 pages in length (available on L2) – detailed every observation during ascent, most of which either avoided impact with the vehicle, or failed to cause any damage.

The importance of clean TPS adds confidence in the ongoing debris mitigation plan for the External Tanks. This takes another step in the right direction with Discovery’s tank for STS-124, ET-128, which is the first tank to debut the additional modifications to its Ice Frost Ramps, along with the debuting of LO2 Feedline Titanium Yokes.

Out of the 12 IFA presentations for STS-123, available on L2, a grand total of zero issues were noted as a constraint for STS-124, which aids the upcoming FRR process for STS-124.

However, they did present a fascinating insight as to just how much post flight detail each related department goes into to ensure any lessons are learned ahead of the next mission.

That process can be seen with the SRBs (Solid Rocket Boosters), which had a less eventful return to Earth after aiding Endeavour’s ride uphill, than they did with STS-122 (Atlantis) – when one of the parachutes on the left hand booster failed.

STS-123’s boosters all deployed their parachutes without a problem, listing a total of only 10 ‘squawks’ for their role with Endeavour’s ascent – most of which related to small losses of insulation, and not even ascent related in some cares. Below is an example of two ‘squawks’ listed:

‘Incomplete RTV-133 Material Closeout Application on Forward Skirt Door: RTV-133 closeout required by drawing. Unexpected debris source in location. No history of liberation. No failure mechanism identified,’ noted the SRB IFA presentation.

This issue holds no problems for the boosters, as the material’s loss – noted once the boosters returned to port – was identified to have happened during the towback to dock, as opposed to during flight itself.

“Suspect SWAR (Sea Water Activated Release) Units Failed to Release,” is more interesting, especially after it was deemed as a likely candidate for the STS-122 parachute issues.

“One LH and two RH units failed to release. Eight SWAR units per parachute. Disconnects main parachute from SRB after splashdown,” added the presentation.

However, such a failure occurs after the “SRB Mission Cycle,” meaning it is not an issue for STS-124. Added to the redundancy in the system, the parachutes still disconnected as expected, following splashdown.

“X-ray confirmed caused by known failure mechanism within pyrotechnic train,” added the reasoning for the failure mode. “Primer fails to breach 3 mil stainless steel booster closure cup with enough energy to ignite charge in booster.”

A key element of a mission – the EVAs – always holds the potential of causing fallout on the following mission. However, the IFA presentation for STS-123’s EVAs showed no such problems.

The main areas of interest related to the EMU (Extravehicular Mobility Unit) gloves and a MMOD (MicroMeteoroid/Orbiting Debris) strike of a piece of EVA hardware.

“Description: During EVA 1, EVA D-Handle stowed on the Z1 port toolbox was brought inside and the crew observed damage (MMOD strike). Impact: Real time structural analysis and crew time to repair,” noted the related presentation.

“Resolution: Tool was successfully repaired and used on subsequent EVAs. Returned to original stow location. No operational constraints on hardware. Will formally document the analysis results and acceptance rationale for continued use of the hardware for nominal handling/tethering operations.”

Ever since the implementation of the specially designed “Over Gloves” – cuts EMU gloves have become less of a safety concern.

Also, with visual inspections being carried out at regular intervals during spacewalks, the chances of another EVA being terminated – as was seen during STS-118’s EVA-3, when Rick Mastracchio observed a cut in his gloves – are now slim.

Regardless, all damage to EMU gloves are recorded, evaluated and cleared during the IFA review for the benefit of subsequent missions and spacewalks.

“Description: During routine glove inspection in EVA-2, Mike Foreman reported RTV flap (1/2 inches long x 1/4 inches deep) on both gloves,” noted one example on the IFA presentation.

“Impact: Over gloves were donned. Gloves were NO GO for subsequent EVA use. Resolution: Backup gloves were available and used on future EVAs.”

EVA-related hardware – or General Flight Equipment (GFE) – also gains a mention. In this IFA presentation’s case, it specifically relates to the Modular Mini-Workstation (MWS) Gimbal Assembly End Effector (EE).

“Description: During EVA 5, EV1’s Modular Mini-Workstation (MWS) Gimbal Assembly End Effector (EE) came loose from it’s retraction cord. The crew reported that it looked like the lock-tite failed on the nut/bolt at the base of the EE.

“The loose EE was stowed in EVA Trash bag and the nut remained attached to the retracting cord swivel.

“Impact: Loss of End Effector for remainder of the EVA. Crew had other means of local tethering, but lost capability to lock themselves tightly into a worksite. Resolution or Workaround: The MWS EE (and baseplate) was returned on STS-123 and is being investigated. A replacement unit was transferred from Shuttle to ISS.”

One of the larger IFA presentations – by the Orbiter Project Office – also cleared all of their IFAs as no constraint for STS-124.

While their presentation listed some of the better known issues with STS-123 – such as the FES (Flash Evaporator System) issue, and the APU 1 Gas Generator Chamber Pressure Transducer Shift, all notes relate solely to Endeavour’s processing flow towards her STS-126 mission (and Launch On Need roles).

One thing that is clear, as STS-124 pushes ever closer to the final leg of launch preparations, is that the fleet is in great shape, and the engineers have all the tools and processes required for continuing to achieve safe flight.

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