Friday, May 29, 2009

Keeping the rain and critters out

The spate of rain showers and thunderstorms we have been enduring here in the Washington DC area this past month makes me think of weather-proofing. In particular, I am reminded of the challenge of keeping rain, insects, and other critters out of the many external apertures in the Space Shuttle in times when it is exposed to the elements.

This is not a trivial problem in an area with such abundant fauna as coastal Florida. Whilst on the launchpad, the Shuttle has been attacked by woodpeckers, necessitating a return to the Vehicle Assembly Building to repair the External Tank's insulation. A bat clung tenaciously to the External Tank during a recent launch.

The device shown above is a ground cover for the one of the 'Aft 3' vernier motors that form part of the Space Shuttle Reaction Control System (RCS). The RCS is comprised of the relatively small engines that fire to help the Space Shuttle make small attitude and translation changes in space. Once the Space Shuttle is back on the ground, the servicing crews place covers like this one over all of the exposed engine openings.

This cover is about 13 inches in diameter and it is about 15 inches deep. Once the cover is placed over the engine aperture, the technician pushes to the side the lever that's in the center of the cover (as seen at left in the illustration). Moving this lever causes the end of the shaft (the black rubberized part shown near the center of this picture) to expand and firmly clamp within the throat of the vernier engine. (I don't know about you, but I get excited just writing about it!) Anyway, this locks the cover firmly into place over the engine. The cover is removed once the Shuttle is inside the Orbiter Processing Facility. It is eventually replaced by a paper covering which burns off or ruptures when the Shuttle launches.

The illustration below shows Discovery being towed out of the Orbiter Processing Facility en route to the Vehicle Assembly Building. Near the base of the tail I have drawn in an arrow pointing to the Aft 3 vernier motors at the top of the Orbital Maneuvering System (OMS) Pod. If you click on the photo to enlarge it, you can see that the red engine covers for the other small thrusters along the side and bottom of the OMS Pod have been replaced by white covers.

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