Q. There's a lot of talk about putting up manned orbital stations. What does this mean, concretely?

A. It is very important to have scientifics tations in space. A space telescope with a mirror slightly over six and a half feet in diameter will beplaced in orbit, and there will be more and more of these.A few years ago,our group at Saclay, in collaboration with a number of other European Laboratories, orbited a telescope that revolutionized our knowledge of gamma-ray emissions by celestial objects.

Life aboard manned space stations won't be as exciting as we might suppose. It will probably be comparable to the life people lead aboard deep-sea oil rigs.

Q. What scientific interest will these stations offer?

A. Observation is much more precise beyond the atmosphere,because the sky is darker. You see many more stars and objects that are concealed by the earth's luminescence.

Q. What objects?

A. We know pretty well how stars are born because we can observe them. Two or three new stars appear in our galaxy every year. But nearly all the galaxies were born at the same time, when the universe was constituted 15 billion years ago. No new ones are thought to exist. To observe the birth of a galaxy that happened so long ago, you have to see avery long way. At present we can go back 10 to 12 billion years. We have to goa bit farther back still, and maybe catch them in the act of birth. Distant objects are necessarily very dim, so ideal conditions are needed to observe them. Orbital stations provide such conditions.

Q. Would orbital stations be choice places from which to try to communicate with extraterrestrial intelligences?

A. Not particularly through radio communication, except on certain wave lengths that are absorbed by the atmosphere. But as points of departure forexploration they'll be very useful.

Q. How far would such exploration go?

A. In 1989 the satellite Voyager II will reach Neptune after a journey of three and a half years. In addition, five probes were sent to rendezvous with Halley's comet. So exploration of the solar system is more or less under way.We've put people on the moon, sent probes to Mars and Venus, lofted satellites near the sun (within a few tens of millions of miles), and one satellite even left the solar system a few years ago. But visiting the stars is something else again. Light takes four years to reach the nearest stars, so you can see that it would take a satellite hundreds of thousands of years.

Of course, if the earth were to become over populated, we can imagine sending families in space vessels to colonize the nearest stars. But it's their great-great-great-grand children who would finally reach those stars. And they wouldn't even know where to stop.

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