Three astronauts now orbiting on board space shuttle Atlantis are about to become the first construction crew in space. Using two sets of interchangable parts, which fit together like giant Tinker Toy units, mission specialists Sherwood C. (Woody) Spring and Jerry L. Ross are to practice techniques for building what NASA space-station planners call the ``framework for the future.'' They will do this during two physically demanding, six-hour space walks (extra-vehicular activities, or EVAs) Saturday and Monday. Some of the time, mission specialist Mary L. Cleave will help them by manipulating the spacecraft's mechanical a rm while either astronauts Spring or Ross is mounted on it.
The National Aeronautics and Space Administration (NASA) now is looking at detailed schemes for building the space station it hopes to have on orbit by 1992. A key element in that planning is to develop efficient techniques for putting together the station's structure under the weightless conditions of space.
Spring and Ross will try out some of the techniques they've been practicing underwater in a mock-up of the shuttle's cargo bay. With water supporting their weight so that they can float freely, this is the closest they can come on Earth to the zero-gravity environment of orbital flight. Now scientists and engineers who designed the construction experiments want to see how tests on orbit compare to what they've learned with these simulations.
The astronauts have two sets of ``Tinker Toys'' with which to work. They're called EASE (Experimental Assembly of Structures and EVA) and ACCESS (Assembly Concept for Construction of Erectable Space Structures). These awkward acronyms refer to equipment that, actually, is designed to minimize any awkwardness in assembling the structures.
Each set consists of standardized struts or beams and nodes into which the ends of the struts easily fit. Locking sleeves slide down to secure a joint once a beam end is fitted into a node socket.
EASE has six 12-foot-long, 64-pound beams and four nodes, which join to form a tetrahedron or pyramid-shaped structure.
ACCESS has 93 one-inch-diameter aluminum tubular struts and 33 nodes. These connect to form modular cubes, or cells, 4.5 feet square. The astronauts will build 10 of these cells and link them together in a long truss. This 45-foot tower, rising into space from Atlantis's cargo bay, has a mass of several hundred pounds.
The equipment is stowed on a work platform that is mounted cross-wise in the shuttle's 15-foot wide cargo bay. It has work stations with foot restraints, where the astronauts can stand, and a set of three guide rails, which form a vertical framework within which the astronauts assemble the ACCESS modules and link them together.
As of this writing, the astronauts are scheduled to carry out basic assembly/disassembly experiments with EASE/ACCESS Saturday. The essential difference between the two experiments is that Spring and Ross are firmly held by foot restraints when they build ACCESS but one of them floats freely in assembling the EASE tetrahedron.
Monday, the flight plan calls for the astronauts to try simulated repairs on the ACCESS truss in which they remove and replace parts of it. They will manhandle the structures to see how efficiently they can maneuver bulky, massive units in space. And they will put two of the EASE 12-foot beams together to form a long pipe -- similar to a heat pipe that may remove waste heat from a space station. Experimenters want to see how well the astronauts can handle such a unit.
Flight director John Cox calls this a pair of ``very agressive'' EVAs. Ross says they probably are ``the most ambitious or, at least, the most energetic'' EVAs NASA has yet attempted.
However, David Akin of the Massachusetts Institute of Technology, principal investigator for EASE, says that the underwater simulations show people can adapt quickly to these tasks. He notes that, for the free-floating assembly of EASE, after 15 or 20 hours ``there's an instinctive adaptation to the weightless environment so that you would do a task in the manner that the counter rotation of your body would put you into the position you needed to be in for your next task.'' He adds, ``It's not something
you that you think about. You just learn instinctively how to do it.''