Thursday, April 21, 2011

Final Endeavour Countdown Preps Under Way

NASA is preparing to pick up the countdown to the planned April 29 launch of its penultimate shuttle flight as work on Endeavour proceeds without major problems.

Endeavour and six astronauts are scheduled to blast off from launch pad 39A at Kennedy Space Center at 3:47 p.m. April 29 -- a week from this coming Friday.

A hazardous propulsion system operation is wrapping up at the pad this morning. Helium and nitrogen gas tanks in the shuttle's Main Propulsion System as well as its Orbital Maneuvering System and Reaction Control System were filled to 80-percent levels during an operation that began late Wednesday afternoon. The tanks will be brought up to full flight pressurization on Monday.

The two-step procedure was implemented several years back as a result of industry-wide concern about Composite Overwrap Pressure Vessels, or COPVs. Safety engineers in aerospace, automotive and other industries long had thought that if these tanks failed, they would leak before they burst. However, tests showed the tanks could burst without warning.

To mitigate the risk to launch pad personnel, NASA decided to reduce the amount of time COPVs on the shuttle are at full flight pressurization. And now only essential personnel can be at the pad once the tanks are fully pressurized, which means no VIP tours within four days of launch.

The overnight operation went well. A digital gauge used to track helium bottle pressure on the shuttle's left orbital maneuvering engine failed. But it was replaced, the spare was tested, and engineers pressed on with the operation.

Aft engine compartment closeouts will pick up again today. A three-day countdown will begin next Tuesday afternoon.

Mission commander Mark Kelly and his crew will go into quarantine at Johnson Space Center tomorrow. The crew includes pilot Gregory "Box" Johnson and four mission specialists: Greg Chamitoff, Andrew "Drew" Feustel, Michael Fincke and Robert Vittori of the European Space Agency. The astronauts are due in at KSC on Tuesday afternoon.

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