t color photo thumbtacked to the wall, above the TV set, and
the shelf of dog-eared technical books. It showed a fragile, pearly
ring, almost diaphanous, hanging tilted against spatial blackness and
pinpoint stars. Its hub was a cylindrical spindle, with radial guys of
fine, stainless steel wire. It was like the earliest ideas about a space
station, yet it was also different. To many--Frank Nelsen and Paul
Hendricks certainly included--such devices had as much beauty as a yacht
under full sail had ever had for anybody.

Old Paul smirked with pleasure. "It's a shame, ain't it, Frank--calling
a pretty thing like that a 'bubb'--it's an ugly word. Or even a 'space
bubble.' Technical talk gets kind of cheap."

"I don't mind," Frank Nelsen answered. "Our first one, here, could look
just as nice--inflated, and riding free against the stars."

He touched the crinkly material, draped across its wooden support.

"It _will_," the old man promised. "Funny--not so long ago people
thought that space ships would have to be really rigid--all metal. So
how did they turn out? Made of stellene, mostly--an improved form of
polyethylene--almost the same stuff as a weather balloon."

"A few millimeters thick, light, perfectly flexible when deflated,"
Nelsen added. "Cut out and cement your bubb together in any shape you
choose. Fold it up firmly, like a parachute--it makes a small package
that can be carried up into orbit in a blastoff rocket with the best
efficiency. There, attached flasks of breathable atmosphere fill it out
in a minute. Eight pounds pressure makes it fairly solid in a vacuum.
So, behold--you've got breathing and living room, inside. There's nylon
cording for increased strength--as in an automobile tire--though not
nearly as much. There's a silicone gum between the thin double layers,
to seal possible meteor punctures. A darkening lead-salt impregnation in
the otherwise transparent stellene cuts radiation entry below the danger
level, and filters the glare and the hard ultra-violet out of the
sunshine. So there you are, all set up."

"Rig your hub and guy wires," old Paul carried on, cheerfully. "Attach
your sun-powered ionic drive, set up your air-restorer, spin your
vehicle for centrifuge-gravity, and you're ready to move--out of orbit."

They laughed, because getting into space wasn't as easy as they made it
sound. The bubbs, one of the basic inventions that made interplanetary
travel possible, were, for all their