NASA working another strange event seen on STS-116’s boosters

by Chris Bergin

Following the confirmation that a small piece of SRB (Solid Rocket Booster) insulation managed to apparently defy the laws of physics by travelling up the stack and strike the belly of Discovery, another strange event – which is still under investigation – has been noted by NASA managers in post STS-116 evaluations.

Super high resolution video of STS-116’s “Thermal Curtain Stabilization” shows what appears to be a large amount of flapping at the aft end of the left SRB, which continues to cause confusion as to exactly what was being observed.

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The 100mb STS-116 Thermal Curtain Stabilization Video. IS&AG Presentation on the TCS evaluations. PRCB Presentations (ATK) on Booster incidents. SRB Bible (vast amount of presnetations on the SRBs – unavailable anywhere else on the net). ASRM Booster Presentation by MSFC video (130mb). PRCB Presentations on STS-117 SRB modification following STS-116 debris strike – all available to download on L2.

While it needs to be stated that there are no notes of concerns or constraints relating to STS-117, the improving abilities of tracking the shuttle through the ascent stage is providing increased insights into the powered first stage of the ride uphill.

Although such super hi res video was set up to watch out for debris events, the ability to observe all items related to flight has proved extremely useful with this incident, which was initially thought to be the thermal blankets – that are literally laced together around the nozzle to protect the systems in the aft skirt – flapping during ascent, as per normal.

However, the video has been the subject of an extended evaluation process, that involved nearly all of the vast imagery resources available to NASA.

Just last week, Shuttle manager Wayne Hale wrote in a Shuttle Standup/Integration report that ‘there is a continuing question about SRB curtain imagery. Imagery group, S&MA, SE&I, and SRB met to review and analyze the video. There are a few actions being worked, but are getting closer to being able to say that the environments have been adequately captured in the SRB certification.’

Soon after, IS&AG – a highly specialised imagery analysis group, sent their evaluations to NASA in the form of a 13 page presentation – called ‘Comparing the dimensions of the flapping material to the Thermal Curtain Viton-coated nylon moisture barrier,’ noting their findings from NASA’s 100mb version of the video that focused in on the left SRB during what appears to be the roll program.

‘It was suggested that the flapping material seen below the left SRB skirt on STS-116 was too large to be the Viton-coated nylon moisture barrier and therefore, it must be smoke,’ opened the presentation. ‘Our measurements do not support this. The largest visible section of the material appears to be 78 percent of the possible length and 63 percent of the possible surface area of a single section of moisture barrier.’

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Following pages of image analysis and notes, the conclusions failed to be specific on what exactly was being observed in the video, but believes it is certainly not smoke or an optical illusion.

‘The flapping material looks to be attached inside the outer ring of the thermal curtain and it appears darker, possibly less reflective, which indicates that it is a different material,’ added the presentation.

‘One piece of the flapping material appears to have a largest dimension which is at least 35 inches and a surface area of at least 532 in2. This is only 78 percent of the possible length and 63 percent of the possible surface area of a single section of moisture barrier which is at most 44.7 inches long and 840 in2.

‘The sheet could be smaller because it is partially burned away or it could be completely intact, but appear smaller because it is curled and never imaged fully face-on. This inner material also appears to be less reflective than the outer material and so, it is consistent with being the nylon moisture barrier.’

The other strange event was also related to the left SRB, but is not linked to the thermal curtain, was a debris strike which hit the orbiter, after originating from the aft of the booster. NASA’s Program Requirements Control Board (PRCB) ordered a modification – within existing certification – to the Solid Rocket Boosters (SRB), following the incident during STS-116’s launch.

The debris, which was insulation flying off the aft of the left SRB, impacting on Discovery, was ‘greater than defined allowable (0.0002 lbm)’ – and work was carried out in the Vehicle Assembly Building (VAB) to trim the area which shed the material on Atlantis’ boosters ahead of STS-117.

‘During a video review we saw that there was some insulation that came off the little separation rockets that did in fact fly up and hit the shuttle on the tiles,’ said Hale. ‘This was a surprise to us.

‘We’re going about four times the speed of sound, these little booster rockets are located some 30 feet lower, aft, down wind of the shuttle, and for a piece of insulation to come off sideways and travel upwards of 30 feet against a mach four air stream is just a little surprising.

‘Clearly there’s something happening in that rear atmosphere that we need to understand better, (but (we) have made some alterations for this flight (STS-117) and trimmed the insulation back.

‘This is just another example of the very complicated things that happen. This wasn’t a run-of-the-mill problem, this was a little more interesting, but it’s a good example of what we deal with on every flight.’

In regards to the boosters, such information is likely to be of great use to the on-going design process with the shuttle’s replacement, Ares I – which will utilize a SRB for first stage flight.

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