Bracket Ice concern constraint removed

by Chris Bergin

Three sources have confirmed that the “launch constraint” of ice debris issues relating to the LOX Feedline Brackets have been removed from STS-114.

The removal of the constraint came in the form of an e-mail – following wind tunnel tests that confirmed the ‘liberation’ of ice that built up on the brackets did not occur.

A Lox Feedline Bracket Ice Mitigation – Tiger Team – was tasked with finding a solution to ice and frost build up on the External Tank – specifically on the six areas relating to the brackets along the length of the feedline.

While testing was on-going at Marshall Space Flight Center’s Hot Gas Facility in Alabama on two test articles – a “No-Purge Bag” and “Inflatable Surrounds” – wind tunnel testing was also implemented to see just how serious the Ice Debris potentially would be to the Orbiter during assent.

The first issue of note was the reduction of the potential ice debris strikes from the bracket areas, as testing failed on all occasions to liberate ice – even under hundreds of different simulated scenarios and aerodynamic load pressures.

Ice Debris testing will continue up to the final Debris Verification Review, which is due to be presented on Friday.

As with many new modifications, designed to eradicate a concern raised, the solution is not always just simply a cure – sometimes even becoming a potential cause of a new concern. The no-purge bag solution was reviewed to be one of those cases.

The review noted that the removal technique required calling on a “Special Red Team” using lanyards to pull the bags off the bracket areas prior to launch. This not only proved to be a hazardous job, but was also reviewed to be a potential cause of damage to the foam that encompasses the External Tank – when the bags were ‘pulled off’.

Any loosening of foam on the External Tank could then become a threat in itself when the Shuttle reached Mach speeds on assent, the review noted.

While optimism is rising that a Return to Flight launch is very much on target for a launch in the July 13-31 window, the next week will prove to be highly important for NASA and United Space Alliance workers and managers alike.

The all-important Flight Readiness Review (FRR) is set for June 29, which will go some way to pre-empting the launch date decision that NASA administrator Mike Griffin will make the following day.

Although issues remain, all signs are pointing towards the launch flow moving towards a conclusion in the July window – finally, after a two and a half year wait, leading to the Return to Flight of the Space Shuttle fleet.

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