Return to Flight under major review

by Chris Bergin

Shuttle Discovery’s Return to Flight mission STS-114 looks set to be delayed until at least July – following a review of the Engine Cut Out (ECO) sensor fault.

The fault was found during the Tanking Test. A meeting is set for 7pm GMT Thursday on the plan of action, although sources claim the Shuttle will be rolled back to the VAB.

Around 10 days ago, United Space Alliance workers installed extra work platforms around the aft engine compartment on Discovery, in order to search for a double sensor fault noted from the Tanking Test that was carried out to test the redesigned External Tank (ET).
Despite the test being classed as a success – which it was for the most part – two Engine Cut Out (ECO) sensors failed during and after the propellant loading.
Evaluation of the sensors found nothing amiss, leading to the replacement of the avionics box on Discovery so that further testing on the ECO sensors could be performed. This testing now appears to have led to a concern large enough that the Stack will be rolled back into the Vehicle Assembly Building (VAB) next week. A de-stack is not believed to be necessary.
According to one source said a the time, the signature of the problem indicates that the fault is in the sensor box or the wiring, with as much as possible replaced. It was also noted that some connectors can not be de-mated to test because the retest of the connector would require closing the ET umbilical doors, which is not possible with the vehicle stacked. However, as of today, a de-stack was not understood to be a requirement.

A second fault has also been mentioned – although at time of publishing it has not been identified or noted if the fault is with the Orbiter or the ET.
Added to the issues surrounding STS-114 is the Debris Verification Review. A log was entered last night:
“NTD (NASA Test Director) reports that the launch director Mike Leinbauch wants S0024 to be delayed for at least 24 hours because of high level discussions going on with the NASA administrator (Mike Griffin) about the ET debris verification review.
“A debris mitigation report was presented today and the administrator had some questions he wants answered related to this. The answers to these questions could have a major impact on the overall vehicle flow, hence hyper(golic) load(ing) is being delayed until the situation firms up.”
A hydraulic fluid leak also occurred on the launch pad – which saw fluid being blow on to the left OMS Pod Thermal Protection System (TPS) blankets.
While most of the fluid was removed, the remaining residue had a potential to burn during assent – given the heat created by the Solid Rocket Boosters (SRBs). This would have led to a visible flame on launch, although it was determined that this would not have harmed the Orbiter and would have been blown out as the Shuttle accelerated.
It is understood that loading of hydrazine into the APUs and HPUs may now happen at the weekend to allow for a hot fire test of the systems, before rolling back the Stack into the VAB.
While Debris Reviews continue, engineers will be able to look at items such as a partial LOX line bellows heater modifications, troubleshoot the ECO’s without a de-stack, and await procedure for when they expect the new launch date to be named by NASA managers.  
Updated throughout…

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