Crucial ET Design Certification Review passed

by Chris Bergin

NASA managers met on Wednesday to pour over the latest wind tunnel results, ahead of a crucial PRCB (Program Requirements Control Board) meeting on Thursday.

A large number of documents have been collated as part of the External Tank Design Certification Review – which was a potential showstopper for Discovery’s STS-121 mission, currently set to launch next month. The review was passed on Wednesday.

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Last week saw Shuttle managers negotiate one major hurdle with the passing of the Debris Verification Review (DVR), despite protests from the Marshall Space Flight Center (MSFC) who wanted further modifications made to the ice/frost ramps on the External Tank (ET).

While the other major modification that has been made to the ETs – the removal of the PAL ramp – has also passed previous reviews, the certification process has now moved on to the affects the modifications will have on the aerodynamics of the tank’s structure during ascent.

Early wind tunnel computer simulations showed some ‘poke outs’ on the changes seen with the aerodynamics around the tank at ‘max Q’ – the time the shuttle is under the stress of maximum dynamic pressure during the ride uphill, at the time of SRB (Solid Rocket Booster) separation and when encountering strong wind sheer.

The reasons the modified tank is being scrutinised is to ensure that the cable tray, LOX feedline and pressure lines can handle the stresses of a launch without the protection of the now-removed PAL ramp. Early results have been positive, according to Shuttle manager Wayne Hale.

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‘We are going to the External Tank Design Certification Review, and at that time we will find out from the structural analysis whether all of the aerodynamic changes have resulted in a situation where the structure will still hold together,’ said Hale.

‘Our preliminary (results) are good, but we are going to find out the final story on Wednesday at that review.

‘Then on the 16/17th of June will we have the Flight Readiness Review (FRR) as the final management review for the preparations of the flight STS-121.’

Wednesday’s review will help collate the agency wide presentations that will be presented to the PRCB on Thursday, at a meeting that will round up most of the certification process to allow STS-121 to press ahead with its July launch.

In addition to the External Tank Design Certification Review,  those presentations will include:

Johnson Space Center (JSC) Verification of limitations for the ET TPS (Thermal Protection System) presentation from MSFC. Actions from STS-121 Debris Verification Review (DVR) to review all major non-standard repairs on ET-118 and ET-119. JSC ‘prior to STS-121 FRR’ LOX feedline fairing – as a separate debris source in the rollup risk matrix, plus hazard report for bi-pod closeout foam and IFR modification decision.

Meanwhile, ET-118 – set to fly with Atlantis on STS-115 (STS-300) begun its journey from New Orleans, for an arrival at KSC around June 10. The tank is set to undergo a 30 day long ECO (Engine Cut Off) sensor swapout at KSC and is currently a long way behind its scheduled launch processing flow.

Full coverage of the aforemented meetings and reviews are on L2.

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