While the flight of Discovery on STS-116 was another testament to NASA’s improvements in the reduction of debris threats on ascent, the orbiter did suffer a debris strike during the December 9 ride uphill.
Interestingly, the hit on her TPS (Thermal Protection System) wasn’t from foam liberating from the External Tank (ET), but from insulation from the left Solid Rocket Booster (SRB).
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Full Late Inspection Presentation. Unreleased ascent images used for NASA evaluations. Video of booster debris striking Discovery. Several related TPS evaluation presentations – all available on L2.
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Importantly, the resulting damage was more cosmetic, as opposed to being a serious concern, but evaluations are continuing on how a 6 inch piece of booster managed to fly off and hit the belly of Discovery.
‘At 124.8 sec MET, the Left-hand SRB camera captured video of debris striking Orbiter TPS in the vicinity of the LH2 umbilical (~30 ft. forward of BSMs). The debris size is estimated at 2 inch x 6 inch +/- 1 inch,’ noted a NASA memo acquired by this site.
‘It appears to originate from the LSRB aft BSM following BSM ignition. Debris may be BTA closeout insulation around the BSM nozzle, which normally releases during re-entry.’
An unreleased video of the debris strike, also acquired by this site, clearly shows the large chunk of debris rising up and striking Discovery at the time of SRB separation, before bouncing back off the orbiter.
The area of impact, sources claim, is seen in the images (click pictures for larger screenshots) gained from the International Space Station (ISS) during Discovery’s RPM (Rbar Pitch Maneuver) underneath the orbital outpost.
Those images showed impacts to tiles around the Port (left) ET door, specifically to one tile that suffered the most visible damage at the location Xo 1359 Yo-110 Zo267. However, the 1.2 inch tile did not lose its ability to withstand the heat of re-entry, as noted by NASA’s initial analysis.
‘Available ET Door RPM photos have been reviewed by the imagery team. No evidence of off nominal thermal barrier protrusions. No evidence of off-nominal steps. No evidence of paint stripe visible.’
Overall, the mission was another success for the goal of reducing debris strikes of concern, and more so for eliminating the danger of foam liberation from the ET. The only notable shedding was observed from the opposite side of the tank (and thus held no threat of hitting Discovery).
That foam loss was seen missing from the LH2/Intertank closeout flange, noted in images from the Johnson Space Center (JSC) Science and Analysis Group.
Such have been the improvements in reducing damage to the orbiter’s heat shield, these impacts are now highlighted by the huge depth of data that is now available to NASA, whereas in the early flights of the shuttle, such damage would be commonplace.
This can be seen through the huge bonus of the OBSS (Orbiter Boom Sensor System) inspections, which check for damage after ascent, and prior to re-entry – classed as ‘Late Inspections.’
‘All Late Mission Inspection LDRI Imagery has been evaluated. A total of 89 Regions of Interest (ROIs) were identified during the evaluation. 35 ROIs were subsequently found in the Baseline or determined to be Image Artifacts. 46 ROIs were determined to be Benign. Benign is defined as not exceeding damage criteria and not exhibiting damage characteristics
‘8 ROIs were classified as Unresolved and required additional evaluation by the PRT. The LESS PRT reviewed all of the Unresolved ROIs, in addition to all ROIs corresponding to Port Wing Panels 19 through 22. None of these ROIs exhibited damage characteristics
‘Port wing tip evaluation. 8 of the 89 ROIs were reported on Port Panels 19 through 22. 6 of these were not identified in the FD2 imagery and determined to be benign. None exhibited any damage characteristics or exceeded damage criteria
‘Following Late Mission Inspection the LESS has been deemed safe for re-entry.’
Some of those vast array of images highlight areas that are hardly noticeable, even through the close ups. While benign, the ability NASA now has in checking the orbiter’s TPS is staggering and practically guarantees no damage will be missed on post Columbia missions.
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