Encyclopedia Astronautica
1973.05.14 - Skylab 1

First and only US space station to date. Project began life as Apollo Orbital Workshop - outfitting of an S-IVB stage with docking adapter with equipment launched by several subsequent S-1B launches. Curtailment of the Apollo moon landings meant that surplus Saturn V's were available, so the pre-equipped, five times heavier, and much more capable Skylab resulted.

An unexpected telemetry indication of meteoroid shield deployment and solar array wing 2 beam fairing separation was received 1 minute and 3 seconds after liftoff. However, all other systems of the OWS appeared normal, and the OWS was inserted into a near-circular Earth orbit of approximately 435 km altitude. The payload shroud was jettisoned, and the ATM with its solar array was deployed as planned during the first orbit. Deployment of the Workshop solar array and the meteoroid shield was not successful. In fact the xternal solar/meteoroid shield had ripped off 63 seconds into ascent, tearing away one solar panel wing and debris jamming the remaining panel. Without shield temperatures soared in station. Repairs by crews led to virtually all mission objectives being met.

Following the final manned phase of the Skylab mission, ground controllers performed some engineering tests of certain Skylab systems--tests that ground personnel were reluctant to do while men were aboard. Results from these tests helped to determine causes of failures during the mission and to obtain data on long term degradation of space systems.

Upon completion of the engineering tests, Skylab was positioned into a stable attitude and systems were shut down. It was expected that Skylab would remain in orbit eight to ten years. It was to have been visited by an early shuttle mission, reboosted into a higher orbit, and used by space shuttle crews. But delays in the first flight of the shuttle made this impossible.

On July 11, 1979, Skylab disintegrated when it re-entered the earth's atmosphere after a worldwide scare over its pending crash. The debris stretched from the south-east Indian Ocean into Western Australia.

Later evaluation of the available data indicated that the following sequence of events and failures occurred:

- Time from Liftoff (hr:min:sec) Event .
- 0:01:02.9 Meteoroid shield tension strap 2 separated.
- 0:01:03 Meteoroid shield tension strap 1 and 3 separated.
- 0:01:03 Solar array system wing 2 beam fairing separated.
- 0:01:30 Meteoroid shield temperatures went off-scale.
- 0:01:30 Partial deployment of meteoroid shield was indicated.
- 0:10:00

Thermal measurements on wing 2 solar array panels ranged from 345 K (161°F) to 389 K (240°F), rather than the expected temperature of about 300 K (80°F). Wing 1 temperatures remained normal. 0:55:55.9 Wing 1 beam fairing separated. Solar array wing 1 was released, but there were indications that the wing had not fully deployed. Wing 2 was inoperative or had encountered structural failure. Temperature excursions in the OWS showed that the meteoroid shield was not affecting the temperatures as intended. The remainder of the planned Workshop system activation and deployment functions occurred as scheduled with transfer of attitude control from the instrument unit to the OWS approximately 41/2 hours after liftoff. The OWS was maneuvered into a solar inertial attitude, with the plane of the solar arrays normal to the Sun for maximum electric power generation. The OWS area temperature then rose above operating limits. The Workshop was subsequently pitched up toward the Sun at 13 hours into the flight to reduce the solar incidence angle on the OWS area. This attitude further reduced the power generation capability which had already been severely limited by the loss of the Workshop solar array wing 2 and the failure of wing 1 to deploy. A continuing adjustment of attitude was necessary to keep the power and temperature within acceptable limits. Constraints to maintain adequate heat in other critical areas of the Workshop and to optimize the operation of the attitude control system in an off-nominal mode added further complications. This delicate balance continued for approximately 10 days. The electrical power available from the ATM solar array was further reduced by the requirement to cycle certain power regulator modules on and off to prevent the overheating caused by unplanned vehicle attitudes. Although considerably below the total design capability of approximately 8500 watts, the power was sufficient for the critical loads. Many components and systems were turned off or were cycled as required to remain within the power generation capability. The high internal temperatures that were reached in the Workshop could have caused outgassing of some materials which would have been hazardous to the crew. Therefore, before crew arrival, the habitation area was depressurized and repressurized four times with nitrogen to purge the outgassing products. The final repressurization was with the proper oxygen/nitrogen mixture for the crew. Maneuvering into and out of the various thermal control attitudes and maintaining attitude hold and control during several docking attempts caused a much larger use of the Workshop thruster propellant than predicted. Sufficient propellant remained, however, for the three manned missions.

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