Space shuttle Atlantis is ready for its second trip into orbit on a mission that anticipates the space station. Astronauts Sherwood C. Spring and Jerry L. Ross are prepared to simulate the construction and repair of space station structures during two grueling, six-hour ``space walks.''
Standardized struts, beams, and connecting nodes -- which fit together like elements of a space age Tinker Toy set -- are on board Atlantis, now poised at the Kennedy Space Center's launch complex 39-A for a scheduled liftoff at 7:29 p.m. EST Tuesday. With the help of Mary L. Cleave, who will operate Alantis's mechanical arm, astronauts Spring and Ross will use the elements to build a 45-foot-long truss and an upside-down tetrahedron structure, each with a mass of several hundred pounds. They will assem ble and disassemble these structures several times; do simulated repair work on the truss; and maneuver the tetrahedron to help planners evaluate the efficiency of humans and of work methods in space construction.
``This is probably the most ambitious, or at least the most energetic, EVA [ExtraVehicular Activity] that we have attempted so far,'' says Ross.
Spacecraft commander Brewster H. Shaw Jr., shuttle pilot Bryan D. O'Connor, and their five-member crew have other tasks during this seven-day mission. First, they have what astronaut Shaw calls ``the bread-and-butter'' work of launching three communications satellites for paying customers. Then they have a variety of experiment and photography assignments. These include photographing Ethiopia and Somalia in Africa with a very-large-format Linhof camera. They hope to bring back detailed geological pictur es which will help experts locate possible underground and surface sources of water in those thirsty lands.
While the NASA professionals are busy with simulated space station work and other duties, representatives of two shuttle customers will carry out experiments for their employers.
Rudolfo Neri Vela -- the first Mexican to go into space -- is accompanying his country's second Morelos communications satellite. He has four experiments involving growth and nutrition of certain food plants, bacterial growth, and human adaptation to weightlessness. He also is to photograph Mexico, especially those parts affected by the recent earthquake.
Veteran commercial astronaut Charles Walker of McDonnell Douglas Corporation is going up again with his company's electrophoresis experiment -- with which he plans to develop a commercial method for separating a hormone in very pure form from a mixture of proteins.
Ortho Pharmaceuticals, which had been McDonnell Douglas's partner, has withdrawn from the venture. However, Mr. Walker says his company is going ahead with the project and expects to sign up a new partner shortly. He explains that ``we . . . still are very positive and certain that it [space] is the only place where you can produce [this high-value hormone product] in a truly pure and economical form.''
This time, Walker is taking along a liter (about a quart) of raw material to produce some of the product for Food and Drug Administration drug-acceptance tests. Next year, his company expects to orbit a prototype production unit in a shuttle cargo bay, with 24 times the experimental unit's capacity.
If Atlantis's mission lasts for the full seven days now planned, the winged spacecraft should land at Edwards Air Force Base in California Dec. 3 at 6:23 p.m. EST during orbit 110.
Mission planners had hoped to land at the Kennedy Space Center in Florida. But flight director John Cox says that modifications to the nose wheel steering mechanism, needed for safe maneuvering on Kennedy's restricted landing strip, could not be completed in time.