Atlantis suffered major MMOD hit

by Chris Bergin

Shuttle orbiter Atlantis was hit by a MMOD (micrometeoroid/orbiting debris) event during STS-115, which NASA is describing as the “second largest hit” in the history of the Shuttle program.

While the debris hit a starboard radiator panel on the cargo bay doors, NASA are concerned, given the size of the MMOD, which they claim was large enough to have penetrated – possibly critically – Atlantis’ heatshield.

**Full Orbiter Standup Status Reports, STS-116 Flight Plan and over 200mb of 116 mission presentations available on L2**
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MMOD hits are common for Shuttle missions, but are usually too small to be of any concern. This event, however, raises questions, especially when it is currently unclear if the damage was spotted on orbit.

‘Radiator panel on STS-115 took MMOD hit. This is first or second largest hit in history of SSP (Space Shuttle Program), noted a NASA report, updated today, and acquired by this site. ‘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.’

NASA is investigating how serious the damage to the RCC (Reinforced Carbon Carbon) panels – located along the leading edge of each wing – would have been, with sources reporting that previous MMOD hits to RCC panels are being used for analysis.

While the very nature of a penetrating hit to RCC panels brings back haunting memories of the damage sustained by Columbia on STS-107, it needs to be stated that there is a huge difference between a MMOD hit and the large chunk of foam that caused the fatal damage to Columbia.

What would have been a concern is the potential of a near miss on the MMOD hitting any of the Freon-22 coolant plumbing in the radiator panel. This could have caused 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.

Meanwhile, NASA has updated the status of both Atlantis and Discovery’s processing flows, with both orbiters remaining in the red for their respective upcoming missions.

Last week, NASA moved Discovery’s STS-116 up a week to a NET (No Earlier Than) December 7 launch target, but she remains behind schedule in orbiter processing for that date. Atlantis is also behind schedule with processing for both her next mission (STS-117) and LON (Launch On Need) STS-317 support for Discovery. NASA is hoping to mitigate the red timelines by pulling workers off Endeavour.

While Discovery is classed as red, it would appear that NASA is optimistic of picking up the timeline with the flow, as they aim to mate Discovery with ET-123 and her twin SRBs (Solid Rocket Boosters) on November 1.

‘OV-103 (Discovery) is still red overall,’ noted an acquired report. ‘They will track to 11/3 rollover date in support of 12/7 launch date. Completed APU connect . Over next couple of weeks, will repair RH ET door. Will pick up on landing gear function. Will do final hydraulics this week.

‘TPS processing effort proceeding well, with 32 cavities remaining. Will pick up some of the forward and aft final closeouts this week. Checkout of ET-123 in support of STS-116 going well. Scheduled to mate tank on 10/13, which will support orbiter mate date of 11/1.

Atlantis’ processing – also in the red – is going through a couple of major flow milestones, although the status of Atlantis’ External Tank (ET-124) is still one of the critical factors to her LON target.

‘OV-104 is red overall,’ noted the same report. ‘Completed SSME removal. Big activity this week is preparation for ball valve cavity drain, which is scheduled to start second shift. Chin panel removal will pick up today to support nose cap repair, which is scheduled later in the flow. They will pick up FRCS functional and continue TPS inspection (TPS is 76% complete).

‘ET-124 – this is next tank. Moved to Building 420 (at Michoud) this weekend. This is tank’s final processing spot as wind up all RTF (Return to Flight) mods. Will set up scaffolding and should finish putting pads on tank in one day.

‘Critical path for tank runs thru bipod installation, which is off to a good start. ECO Sensors R&R complete. Harnesses being fabricated in background and remainder of TPS activities will move forward. After complete setup, will be move forward with suite of other TPS mods (e.g., drip lip, hydrogen PAL ramp DC&R, cable trays and longerons).

‘ET-117 – this is next tank following ET-124. Vertical in Cell A. Good progress, including flange, longeron and ECO sensor mods. No issues.’

Among other issues noted on the excellent report – which gives full run downs of the current status of the orbiters, work is continuing on a Speedbrake issue that was spotted with Atlantis, while on Discovery, work is going well on her right hand ET door – which is being repaired.

‘Much good work on ET door problem by people around the US. On Friday, removed qualification unit from ET door setup at JSC (Johnson Space Center). On Sunday, aft bellcrank from qualification unit determined to be good.

‘Forward bellcrank from qualification unit has more dings, so more work will be needed to consider it a good replacement unit. Pushrods, torque tube and damaged bellcrank from vehicle will be sent (for testing) to determine reusability status of hardware.

‘Ground Operations have good access in the vehicle. Logistics is working on making a new part, and should be able to complete it by 10/20.’

Image credit: CollectSPACE

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