MMOD hit on Atlantis was from another vehicle

by Chris Bergin

The MMOD (micrometeoroid/orbiting debris) debris strike on Atlantis during STS-115 was actually a piece of circuit board from a previously launched vehicle, new NASA information has revealed.

The debris, which would have likely been from “an exploded upper stage,” sources note, hit one of Atlantis’ radiator panels at a super high velocity, punching through in what was the second largest on-orbit debris strike in Shuttle history.

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The area in which the debris impacted on Atlantis was fortunate, just missing a Freon-22 coolant plumbing in the panel – which would have caused an emergency to be called, and the immediate order to land Atlantis.

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 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.

The debris strike on STS-115 could have also caused a potentially serious problem if the impact had been on areas of the orbiter such as the Chin Panel.

Also an area of concern was the fact the hole in the starboard panel was discovered after Atlantis had landed, not on orbit. However, if it had hit a critical area of the orbiter TPS (Thermal Protection System) – it would have been spotted via the OBSS (Orbiter Boom Sensor System) inspections carried on the final days of STS-115.

At the time information confirming the debris strike was exclusively revealed by this site back in early October, a NASA integration report acquired by this site’s L2 section noted: ‘Radiator panel on STS-115 took MMOD hit. ‘0.108 inch diameter at entry point. One-half inch thick honeycomb damaged.

‘If hit were on RCC, it would have penetrated, but criticality of resulting damage is not known.’

United Space Alliance engineers have since ‘plugged’ the hole in Atlantis’ panel, but evaluations have continued, with the purpose of understanding the strike, and to recommend any potential action that can be taken to protect orbiters from such events.

While those recommendations are believed to be in-works, MMOD hits are common and have occurred throughout the lifetime of the Shuttle program, with no serious outcomes. However, the result of what actually hit Atlantis has been revealed.

‘Evaluated the material from hole on STS-115 radiator. The composition was consistent with that of a circuit board,’ noted Steve Hawley, KA/Astromaterials Research and Exploration Science, in a memo acquired by this site confirming the debris was not from Atlantis herself.

Also noted as interesting by sources is that ‘circuit board material is not all that dense,’ which leaves open questions about such types of orbital debris from the same source, which also contain such items as screws, brackets and metal casing, which would potentially cause a lot more damage during an MMOD event.

Meanwhile, processing Atlantis towards her STS-117 mission next year – including her LON-317 rescue mission support requirement for Discovery – is going well.

Major processing work is concentrated on orbiter power system testing in work, plus R&R work on Fuel Cell 1.

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