Saturday, May 19, 2012

Skylab reboost concept art

After the Skylab 4 crew returned to Earth in February 1974, NASA had no further plans for the space station and shut down its systems. Prior to undocking, the crew had used the engine of their Apollo spacecraft to nudge Skylab into a higher orbit, roughly 440 km above the Earth. However, even at this height, the Earth’s atmosphere is dense enough to exert significant drag on a satellite. A period of increased solar activity in the 1970s made this situation worse for Skylab. This activity caused the density of the atmosphere at Skylab’s altitude to increase, and therefore the drag on the station to increase in proportion.

Based on measurements taken during the Skylab missions, NASA predicted that the station would remain in orbit another nine years, re-entering Earth’s atmosphere sometime in 1983.

Doomed if left where it was, the station still represented a valuable collection of resources in orbit: air, water, and shelter that NASA had already  paid to carry up there. By 1977, with the Space Shuttle program well underway, NASA planners recognised an opportunity to save the station for refurbishment and reuse. With orbital flights of the shuttle scheduled to begin in mid 1979, NASA contracted Martin Marietta Corporation (today, absorbed into Lockheed Martin) to develop a booster that could be carried to Skylab by a space shuttle and used to raise Skylab’s orbit out of imminent danger, as illustrated in this piece of concept art:

Here’s a close-up of the booster module itself, designated the Teleoperator Retrieval System (TRS):

It’s docked to the main port of Skylab’s Multiple Docking Adapter (MDA). The square plate visible at the centre of the cluster of engines carries an attachment point to allow the shuttle’s robot arm (Remote Manipulator System — RMS) to grasp the module and manœuver it into position. Note also that Skylab’s main solar array has been re-folded into its launch position (it’s the long, flat, rectangular structure along the side of the station with the words “United States” barely legible along it). I presume this was to keep the station’s centre of mass as close as possible to the TRS’s line of thrust during the boost, as well as to minimise stresses on the array—although the solar panels on the Apollo Telescope Mount (ATM) are still fully deployed.

Safe in its new orbit, Skylab would then be ready for renovations and expansions to keep it in useful service perhaps as far as 1989. Alternatively, NASA also considered the possibility of using the TRS to de-orbit Skylab in a safe, controlled manner, far away from human populations (Skylab’s orbit carried it over around 90% of the world’s people).

However, none of this was to be. Solar activity through the 1970s remained higher than predicted, and by April 1979, it was clear that Skylab would not last longer than a few more months. It was also clear that the Space Shuttle was nowhere near ready: ongoing problems and delays with its revolutionary new heat shield and engines postponed the first orbital flight past the end of the year.

On 11 July 1979, Skylab’s orbit decayed and brought the station down in an uncontrolled1 re-entry over the Indian Ocean and Western Australia.

On 12 April 1981, the first space shuttle flew.

Incidentally, I’d love to know the name of the artist who did the original painting. If you know, please leave me a note!

1 Well, almost uncontrolled. As the station crossed the east coast of North America, headed  south-east on what was almost certainly to be its final orbit, ground controllers fired the station’s thrusters to set it tumbling in its orbit. This tumble was intended to maximise the atmospheric drag and bring Skylab down as quickly as possible, hopefully somewhere in the South Atlantic or Indian Ocean and before it re-appeared over the Pacific North-West of the United States.

Copyright information: The print in my collection was formerly held by a newspaper archive. It is a black-and-white version of NASA image S78-23631. As a work of the US federal government, this image is in the public domain.

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