Leaking valve won’t delay tanking test

by Chris Bergin

A small hydrogen leak found in a flow control valve won’t delay Thursday’s crucial Tanking Test – where 500,000 gallons of propellant will be piped into Discovery’s External Tank (ET).

The valve – only used during the loading of the Liquid hydrogen – is located in the inside of the aft fuselage near the T-0 interface. It will be fixed after this week’s test for launch.

The leak, classed as 6.6 SCMS – when it should register less than 6.0 SCMS, was detected as preparations began for the Tanking Test at the weekend. Replacement values are no longer manufactured, meaning the existing value will have parts repaired on site. 
Such is the nature and importance of how the re-designed ET holds up during the test, a serious failure will see Discovery rolled-back to the Vehicle Assembly Building (VAB), ending the opportunity for a May 15 to June 3rd launch window. However, such an event is highly unlikely.
With the valve sent for repair after the Tanking Test, it is unclear if this will eat up more time into the proposed launch window – something that will become clearer when Shuttle Manager Bill Parsons addresses the launch date after the Test. Currently, Discovery is still potentially on target for meeting the latter part of the window that lasts until June 3. Failing that, the Orbiter will move to a July launch window – starting July 12 to 31, the window currently reserved for Atlantis’ STS-121.
Atlantis’ progress continues to support Discovery’s ability to launch, with her twin Solid Rocket Boosters (SRBs) already stacked in the VAB for STS-121 – the importance of which is any potential need for Atlantis to launch ahead of schedule on STS-300, a rescue mission requirement should there be a critical failure with Discovery on orbit.
Atlantis’ ET will be stacked with the SRBs on the Mobile Launch Platform (MLP) on April 23.
Endeavour is still well over a year away from joining the fleet on operations, meaning Discovery will back Atlantis up as her rescue ship (designated STS-301) before and during processing for STS-116, the third mission since the loss of Columbia, with a launch date targeted as February 9, 2006.

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