Beginning this September, with the ninth scheduled mission of the space shuttle, ''non-astronauts'' will get a taste of life with zero gravity and dinner from plastic pouches.
''They call us non-astronauts because we're not selected by NASA [the National Aeronautics and Space Administration] or trained in the systems of the shuttle,'' says Byron Lichtenberg, the first American scheduled to fly as a shuttle payload specialist.
Along with West German physicist Ulf Merbold - the other payload specialist slated to make the flight - their mission will be to boldly go where only trained astronauts have gone before, as overseers for scientific tests aboard the first Spacelab.
In the past, there were two distinct groups in the shuttle crew: the pilots who sat in the driver's seats, and the mission specialists who tended the shuttle's computer systems. With the advent of the Spacelab, however, there's need for full-time researchers, able to focus on performing experiments and recording data.
The $1 billion Spacelab, which looks a bit like a huge barrel tipped on its side, was built by the European Space Agency. The self-contained minilaboratory tucks into the shuttle's cargo bay and connects by a passageway to the orbiter's living area.
''We're the eyes and ears for the scientists back on Earth - their surrogates ,'' says Dr. Lichtenberg, a biomedical engineer from the Massachusetts Institute of Technology, who sees the coming mission as a key step toward lofting a permanent space station separate from the shuttle.
Lichtenberg and his German counterpart, with help from the mission specialists, will conduct more than 70 experiments - from growing silicon crystals to zapping the Earth's atmosphere with electron beams. In many of the experiments, having along scientists skilled in lab techniques is essential, since a slip of the hand can be crucial.
''But some experiments are automatic and self-contained,'' says Lichtenberg. ''We don't have to do anything except flip a switch at the beginning of the mission and let them run for nine days.''
Because of delays in the shuttle program, the payload specialists have already trained for more than four years. In the future, NASA officials say they intend to pare down preparation to ''a matter of months.'' Scientists are expected to return to their jobs in universities or private businesses after the mission.
But while the first shuttle-bound scientists gear up for its stint in space, observers say they're helping to speed a subtle change in the image of astronauts. Space travel - once the domain of heroes - is becoming a more common experience.
''The emphasis has also shifted away from the need for physical capabilities and flying ability to something a little more flexible,'' says Charles Lewis, NASA's crew training coordinator for the mission. That doesn't mean the standards for payload specialists are lower, he adds, just different factors highlighted.
Candidates are expected to have at least five years of hands-on experience in the lab and graduate degrees - if not doctorates - in their specialty.
The Europeans put together a list of qualified applicants, while American researchers with experiments riding the Spacelab were each allowed to nominate two candidates. NASA then picked four from these two pools. The two scientists not scheduled to fly in September will monitor the mission from the ground and act as backup crew members.
The only difficulty, it seems, has been agreeing on what these scientists-in-orbit should be called. Some insiders balk at the term ''non-astronauts.''
''I always avoid calling them non-astronauts, because by the time they fly, they'll be considered astronauts according to most people's definition,'' says NASA's Lewis, who prefers to lump them under the somewhat unromantic heading of ''noncareer astronauts.''
Whatever label finally sticks, one thing seems certain: the number of space travelers of all discriptions seems likely to grow in the future. Indeed, a NASA task force is now working on a plan to take passengers into space by the late 1980s.