Habitability

The first two major priorities of Skylab were space medicine and solar phys­ics. The third was habitability. How was a space station to be designed so that humans could live and work in it effectively?

Engineers had been designing spacecraft for human operability since the Mercury program, but they hadn’t yet made a methodical study of the sub­ject. Skylab was their opportunity because of its generous weight and vol­ume available and its long missions. The opportunity was recognized and taken.

Two experiments were submitted and approved. The first was M487, hab­itability/ crew quarters, the purpose of which was “to measure, evaluate and report habitability features of the crew quarters and work areas of Skylab in engineering terms useful to the design of future manned spacecraft.” Its lit­tle brother was M516, crew activities/maintenance study, designed “to eval­uate Skylab man-machine relationships by gathering data concerning the

crew’s capability to perform work in the zero-g environment on long dura­* * 3?

tion missions.

Plans for gathering data were made, prominently including crew voice reports and questionnaires, film and video, and measurements of how long tasks took to accomplish. Tools were provided to measure light, sound, air movement, temperatures, and forces. Procedures were tested during the smeat simulation and improved. The engineering approach suited the crews, who recognized the importance of the effort and were glad to furnish their evaluations and opinions. The experiment was continued into design. Many different types of restraints, handholds, equipment tethers, and even door openings were provided, so that the crews could show and tell which worked and which didn’t.

It’s been said by some observers that the astronauts were constantly com­plaining about Skylab systems and accommodations. Actually, they were doing their jobs. They thought it more important to describe inefficiencies and suggest solutions than to praise successes, although there was plenty of the latter, especially postflight. And the human-factors engineers behind the experiments, ably led by Bob Bond, knew how quickly memories fade and wanted the evaluations during the missions, not after. So there was a lot of air-to-ground communication on how things worked and how to make them work better.

The results, gathered over the ensuing two years into “Skylab Experience Bulletins,” filled seventeen volumes.

Two very important, unanticipated observations were made about the crews’ bodies: first, they became taller by one to two inches; second, they adopt­ed a characteristic “zero-G posture,” flexed at knees, hips, and neck. These two facts greatly affected the way the people fit into space suits and at work­stations of all sorts and led to some important recommendations for future spacecraft. One was “No Chairs!” The body doesn’t want to flex into a chair; it’s uncomfortable and unnecessary. (On the space shuttle, chairs are used for launch and entry and stowed in orbit.) Don’t make an individual crouch at a workstation by putting key instruments below his or her eye level; it’s not feasible to slump. Without gravity to help, bending over to tie your shoes is harder. And size the space suits and clothing with some extra length. Future engineers would look with interest and amusement at the photo of the fifth percentile girl beside the ninety-fifth percentile guy, and spend some extra time designing one workstation that will fit either.

If chairs are no good, how can you restrain a person to do a task? Foot restraints are the answer, and the best ones give a firm purchase that allows both hands to be occupied with the task. More casual restraints were ok for one-handed tasks.

There was quite a bit of debate before flight about whether people would feel more comfortable in a work space that looked like an Earthly room with floors and ceilings and all the signs oriented the same way, or whether in zero-G they could operate nicely on walls and ceilings, allowing space to be more effectively utilized. The answer to both questions was “yes.” The report says: “The Skylab crewmen were able to operate equipment easily from any orientation. They quickly established their own coordinate sys­tem in which the location of their feet signified ‘down.’” But the one-grav­ity architecture of the ows crew compartment was preferred to the put-it – anywhere radial arrangement in the mda. The latter was a bit disorienting when you entered it; it was ok once you’d reached your workstation. With­in a workstation everything had to be oriented to the same “up.”

Improvements were suggested in the overall layout of Skylab too. “Don’t ever put the airlock in the middle again,” was a good example. Having the airlock right on the main pathway between the systems center in the mda and the work and living center in the workshop meant that nothing could be stowed in the airlock lest it impede traffic. It also meant that if the air­lock hatch wouldn’t close after a spacewalk, the workshop became unin­habitable and the mission was over.

This work, combined with systems evaluation, resulted in a very thor­ough set of design criteria for future spacecraft, especially permanent space stations. It had some impact on Shuttle design, although Shuttle was already well into its design process when the Skylab results were promulgated in 1975. It had considerable impact on the European Spacelab module in whose development several Skylab astronauts participated. And it significantly assisted the Russians in the design of Mir, although no Americans were invited to take part directly in that space station’s initial design. Later, of course, NASA astronauts would live and work with their Russian counter­parts aboard Mir.

In the eighties the Skylab human-factors lessons and several other sources

were combined into one massive habitability design book, NASA Standard 3000. It was used in the design of Space Station Freedom and its successor, iss. What other lessons from Skylab were not learned by the designers of iss is material for another book.