"Bluestar: The First Think Tank in Space" is a beautiful, almost unbelievable object -- a great sphere of water illuminated all around by holographic images, surrounded by a transparent oval shield and a ring of zero-gravity work places, the whole huge thing set in geosynchronous orbit about 23,000 miles above the United States.

Paintings and a model of it are on view at the Octagon Museum in a somewhat overambitiously titled exhibition, "Ideas Above Earth: Space Architecture." Besides the Bluestar project, conceived by architect Doug Michels, the show includes photographs of contemporary space stations, a scale model of a playroom for children in space by artist Tom Ashcraft, and entries by Washington, D.C., and Oklahoma City sixth-graders in a competition to design a learning station in space.

Part of Bluestar's allure is visual. It looks like a great facetless jewel, a startling cabochon glowing against the limitless dark. And part of the appeal is conceptual: the impossible dream and the mundane reality of inhabiting space joined with peaceful intent "to nurture the growth of non-earthbound ideas," as critic Michael Sorkin writes in an introduction to the show.

Would it work? Well, who knows? Clearly it would take huge amounts of money and an organization chart that would dwarf those of all earthly think tanks combined. One can't help wondering about the possibilities of giant accidents or what effect zero gravity would have on office politics -- obviously earthbound thoughts. Still, there is excitement in the very idea of getting architects and artists to work on the issue. Why leave it all to the engineers (or, much worse, to the generals)?

Michels, a senior designer in the Washington office of Hellmuth, Obata & Kassabaum (HOK), took the trouble (on a recent Loeb Fellowship from the Harvard Graduate School of Design) to base Bluestar on plausible technology. The image originally came to him in 1978 after he had seen a NASA film on the behavior of liquids in space: They can be stretched unbelievably or molded almost like clay, and can be held in place with ultrasonic beams. Hence his notion of a ball of water 250 feet in diameter floating inside a tough, transparent membrane of "spaceglass" (a clear titanium alloy that has not yet been invented).

The architect had done a lot of work with dolphins -- he once designed a prototype laboratory boat to study them in their habitat -- and so it seemed natural to him to use their superior sonar in his watersphere. The idea is that the dolphins would on command activate a supercomputer in the center of the sphere to generate holographic images (three-dimensional laser "pictures") of, say, the planet Earth on the surface of the sphere. These could be studied by scientists from their weightless perches in the outer ring of laboratories.

Among the immediately applicable results of Michels' research are the prototype laboratories designed fully in the round. "Why should we be designing spaces with floors and ceilings for places where there is no difference between up and down?" he asks with reason. His seriousness is leavened by playfulness, thank goodness. After work, with the computers turned off, Bluestar residents could go for swims with the dolphins.

"My inspiration is architecture," Michels says. "There is so much history in architecture on Earth today, it seems that if it hasn't been done before somewhere, it isn't worth doing."

The drawings and models by the grade school pupils are the results of an admirable educational effort sponsored by NASA and the American Institute of Architects. The exhibition was supported by a grant from HOK, the firm that designed the Air and Space Museum. It continues through Aug. 17.