Shuttle missions – TPS inspection re-think

by Chris Bergin

The much-hailed inspection technique for checking orbiter TPS (Thermal Protection System) damage on-orbit will need modifying for a number of Shuttle missions.

The 50 foot long arm, which includes the OBSS (Orbiter Boom Sensor System) instrumentation package – integral for scanning the TPS of the orbiter – can’t be carried into orbit due to weight restrictions, interferences and/or unacceptable clearances between the boom and the ISS cargo elements.

The resulting information comes from a 68 page document presented to Thursday’s PRCB meeting. The full document scans and other PRCB documents are available on L2. Ciick the advert to join —>

**Click here for the related thread (or click related images below) for sample L2 scans**

The OBSS and instrumentation package – which is attached to the Remote Manipulator System – debuted on STS-114 (Return to Flight) last summer, producing superb imagery and an array of information on the state of Discovery’s TPS following the ride uphill.

It was installed into the orbiter’s cargo bay to help evaluate any impacts from foam liberating from the External Tank, which was responsible for dooming Columbia on STS-107.

A presentation from the Orbiter Project Office focused on targeting a range of inspection options for 1E, 1J/A, and 1J – otherwise known as STS-122, 123 and 124. STS-122 and STS-126 also have similar mission restrictions.

‘Once the JEM has been installed, the OBSS can not be used for focused inspection of most RCC,’ noted the report – with the first of several JEM elements being the focus of Shuttle missions, beginning NET (No Earlier Than) November 29, 2007, STS-123, 1J/A, Endeavour, JEM ELM PS & SPDM.

However, re-evaluations begin with the NET September 27, 2007 mission for Discovery on STS-122, with the launch of the Columbus module, where a solution has been looked into already.

‘Remove PDGF and reinstall on-orbit prior to Columbus deploy (at an estimated cost ~ $400K). ISSP & IP risks have not been completely identified,’ noted the presentation to the PRCB.

‘However, PDGF must be reinstalled for module deploy. PDGF requires sidewall integration, was done on STS-98/5A (US Lab) Two PDGF shave previously been installed on orbit. Mission Ascent Performance: Marginal. Final disposition requires JPRCB approval.’

STS-123’s potential solution was noted as ‘Remove redundant Starboard FRGF, not required for assembly or on-orbit operations through assembly complete.’ That would also incur half a million dollars in costs.

STS-124, NET February 7, 2008 with Atlantis and the JEM PM & JEM RMS elements for the ISS, pose a bigger problem for Shuttle managers to solve.

‘No payload solution exists to allow for the OBSS to be flown on the STS-124 / 1J mission. The SRMS elbow camera also can not be manifested due to clearance/interference concerns between it and the JEM Module. Elbow camera provides situational awareness for inspection-related robotic operations. Crew Office assessment (OBSS only) due 5/31/06. Additional elbow camera solutions under review.

‘Mission is Ascent Performance Critical. Non-standard SSP APM get-wells required to meet APM requirement. ISSP mission content reduction required to meet APM requirement.’

Options are available to the Program, with the decision to be taken after a series of engineering evaluations. Those include:

‘Option 1: Existing Non-OBSS Assets: Manifest the OBSS on all but those three missions and inspect what we can with existing capabilities from the shuttle and station. Work with ISS to also fly OBSS on 1E and 1J/A missions.’

Option 1 holds the least impact to 1E and 1J upmass problems, protects docked operational timeline, while no new hardware would be required. However, this would mean a limitation to FD2 inspection of RCC with RMS. Limited focused inspection of tile (requires EVA). Limited focused inspection of RCC and very limited repair capability.

‘Option 2: OBSS on ISS: Manifest the OBSS on all but those three missions and install OBSS sensor packages on ISS-mounted IBA while docked.’ This option involves a minimal amount of new hardware is required. Meets all inspection requirements post undocked and allows for almost real-time 3D data.

However, on the negative side, option 2 cannot be used effectively for RCC inspection while docked once the JEM has been installed. Additional EVA time for OBSS prep would be required. Impacts the docked timeline. Also, this would involve leaving the IBA on 10A and/or 1JA; no late inspection, with an option to bring IBA back on different vehicle than launched is unresolved. Only 1 IBA available to support manifest until IBA returned and put back into service.

‘Option 3 MiniBoom. Develop and manifest a MiniBoom which can be used on 1E and all subsequent flights. Use the IBA on ISS for focused inspection of aft tile if required.’ This would see FD2 and docked inspections being able to be accomplished on all flights. Out-year cost savings over OBSS. Approx. 300 lb savings in weight over OBSS, with no modifications to international partners hardware required.

Miniboom, click on image.

Again, being able to carry out adequate inspections of the orbiter’s TPS is the key problem, as option 3 would see the process being unable to reach all areas in requirement of inspection. This would also require new hardware development. Requires good lighting for inspection, plus focused inspection ground data processing of photogrammetric data takes longer to process.

‘Two other options considered and found not feasible,’ added the presentation. ‘AERCam not feasible due to schedule constraints.100% EVA inspection not feasible due to high number of EVAs required.’

While option 3 appears to be the most problematic, it also appears to be the only feasible solution, as the document recommended option 3 to the PRCB.

‘Select Option 3 MiniBoom. Supports FD2, focused, and late inspections while docked on all flights. No impact to docked mission operations for routine inspection. Offers some cost savings in the out years. No modifications to international partners hardware required.

‘However, recommend FRGF removal from 1J/A. Improves KSC ground processing when three vehicles are in a flow. MV to bring MiniBoom funding CR and project plan to PRCB in two weeks.’

‘Get Wells,’ as the document presents them, are aimed increasing capacity on the orbiter: ‘Reduce crew size to 5 (500 crew/600 lead ballast)1130 lbs. Remove 5th cryo tank set (604 lbs hw/200 lbs ballast) 804 lbs (requires less than 96 hrs pad hold time). Remove JEM rack 900 lbs. Remove SRMS (SSRMS for installation and inspection) 855 lbs.

Potential threats are listed as ‘Pending performance impacts (LOX purity, performance collector). Unknown/Unidentified Vehicle weight growth. Increases in OMS propellant budget.’

Given inspections need to be performed on all of the remaining 17 flights in the Shuttle manifest, the options available will continue to undergo evaluation on subsequent PRCB meetings.

All options will remain open in the meantime, those being changing the payloads to eliminate the structural clearance concerns. Reduce upmass to bring OBSS. Leave OBSS attached to ISS on a previous flight (which implies going EVA to install the sensor packages because you can’t leave them on the boom on ISS as they will freeze and die). Or, create a shorter boom and use that – which is currently favoured.

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