Endeavour suffered significant MMOD impact on radiator

by Chris Bergin

Similar to that suffered by Atlantis during STS-115, engineers have found a significant MMOD (MicroMeteoroid/Orbiting Debris) impact point on one of Endeavour’s radiators, large enough to require a full repair.

The MMOD impact was spotted during STS-118 post flight processing of Endeavour inside of OPF (Orbiter Processing Facility) High Bay 2. Hi res images – acquired by L2 shows the impact as seen in the OPF – a sample can be viewed below (read more).

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Currently, NASA aren’t classing the impact in the same manner as Atlantis’ MMOD hit, which was at the time noted as ‘first or second largest hit’ in the history of the Shuttle program.

It was later revealed that analysis showed Atlantis’ MMOD was actually a piece of circuit board from a previously launched vehicle.

However, images – acquired by NASASpaceflight L2 – appear to show an impact much larger than that suffered by Atlantis.

‘(Endeavour) radiator inspections showed fairly significant MMOD hit on LH aft radiator number 4; must decide how to repair,’ noted Monday’s Shuttle Stand-up/Integration report, with more information set to follow after closer inspections.

MMOD hits are commonplace for orbiters, classed as the third biggest threat to a mission, below the risks of launch and re-entry. The dangers associated with a MMOD hit to the radiators relate to the potential of an impact to any of the Freon-22 coolant plumbing in the radiator panel.

Such an impact could cause an entire coolant loop to be shut down and declared ‘failed’. This would have forced an immediate landing on the earliest US landing opportunity.

On STS-109, a small piece of debris was lodged stuck in Columbia’s coolant loop 2 and restricted the flow of Freon-22 in that coolant loop. The amount of Freon-22 in the coolant loop was slightly below the flight rule red-limit, but after exhaustive analysis by the engineers on the ground, they decided to press on with the mission.

As of right now, the MMOD impact appears to have missed vital systems on Endeavour, given an impact relating to the coolant loops would have resulted in controllers on the ground immediately noticing a change in orbiter data. Further news will follow as it arrives.

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Meanwhile, Endeavour is enjoying a smooth processing flow, as she heads into preparations for her next mission, STS-123, set to launch in February 2008.

‘TPS (Thermal Protection System) roll-in inspections are 30 percent complete,’ added processing information. ‘Identified 65 cavities so far, 46 of which are new BRI tiles. Plan this week is to remove SpaceHab, start thermography on RCCs and nose cap; this will lead to hyper deservicing Friday.

‘Pyro Interrupt Box installation was completed 3rd shift Friday. Payload Bay Door strongback installation was completed Friday. SSME (Space Shuttle Main Engine) Pneumatics system validation and defoaming were worked over the weekend; all are complete and good.’

Those post flight processing milestones also included the removal of the damaged TPS, caused when a piece of foam liberated off one of the LO2 feedline brackets on ET-117, 58 seconds into ascent.


‘On tile damage site on OV-105 (Endeavour), team completed 3-D laser scans, and they will compare to 3-D imagery taken on orbit,’ noted the Orbiter Project notes on Monday. ‘Believe (engineers have) removed – or are about to remove – the tiles and ship to KSC M&P lab. Forensics data gathering will begin, including looking for chemical residue constituency inside cavities.

‘Removal of two damaged tiles was accomplished; samples were taken to satisfy the forensics CHIT; current testing was rescheduled for today.

Mitigation efforts on the foam liberation potential on these brackets for the next flight, STS-120 with Discovery, are on track, with a team from the Michoud Assembly Facility (MAF) working on re-building four of the five brackets on ET-120, which had all of its foam removed over the weekend. A full report – based expansive reports in L2 – will follow this week.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.


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