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it, you can see that the red engine covers for the other small thrusters along the side and bottom of the OMS Pod have been replaced by white covers.

Pete Conrad and crew to the rescue!

Skylab, America's first space station, was launched on May 14, 1973. It rode the last Saturn V in NASA's inventory, one which was originally intended for a canceled Moon landing. Less than a minute after launch, as the vehicle broke through the sound barrier and the zone of maximum dynamic pressure, the meteoroid shielding on the lab tore off, taking with it one of the station's two primary solar panels and jamming the other one.

As soon as Skylab reached orbit, controllers knew that something was seriously wrong. Temperatures inside the lab began to rise far outside normal ranges, eventually getting as high as 140 degrees F. There was also no power to the lab other than what was coming via the solar panels on the Apollo Telescope Mount.

I watched the launch on TV and I remember clearly the "oh no" reaction when we heard that Skylab might never be occupied because of the power and temperature problems. Pete Conrad, Commander of the first Skylab mission, and his crew of Paul Weitz and Joe Kerwin, were to have launched the next day. Their launch was scrubbed while NASA determined how to repair the station. Timing was of the essence - if NASA waited too long, the intense heat inside the lab would eventually melt the plastic and render the station uninhabitable.

In what had to be the most intensive spacecraft rescue mission ever undertaken, in less than 10 days NASA designed and built -- and trained the crew to use -- a "parasol" that could be deployed via a small airlock on the side of the station and which would bring the station's temperature back to livable levels. NASA also loaded the Apollo spacecraft with several tools that the crew could use to try to free the stuck solar panel.

The daring tactics of Conrad and crew are almost unthinkable in today's environment. Before docking with the station, Conrad maneuvered the CM close to the stuck solar panel so that Weitz, standing in the CM's open hatch, could try to cut loose the debris that held down the panel. When that didn't work, Conrad then tried to dock with Skylab. The docking mechanism refused to latch on several docking attempts. Conrad backed away and then tried again several times. Maneuvering fuel was running low, and Conrad was given one final chance to try to dock. This time he was told to continue pushing forward for 10 seconds with the CM after the probe had entered the drogue, in hopes that the pressure would cause the latches to fire. This final attempt worked; otherwise, the mission - and Skylab - would have been abandoned. Listening to this on the TV was sheer knuckle-biting tension!

Conrad and crew deployed the parasol successfully, which eventually brought the temperature inside the station down into the mid-80's. Prior to that, the crew were only able to enter the lab for a few minutes at a time without risking dehydration and heat prostration.

Finally, on June 7, 1973, Conrad and Kerwin undertook one of the most dangerous spacewalks ever attempted, to free the stuck solar panel. They worked in an area outside the station that was never meant to be serviced by astronauts, so it had no handholds or railings. They used tethers and their adapted limb pruning tool to get close to the stuck solar panel and eventually snip the metal debris that was holding it in place.

Because of the determination and skill of Conrad and his crew, the Skylab program was a complete success. The lab was occupied by three crews on and off over the next year, and America gained substantial experience in living for extended periods in space.