By Michael Collins

Grove Weidenfeld. 307 pp. $22.50

IN EARLIER books (Carrying the Fire, Liftoff), Michael Collins has looked back at the events leading up to and following the historic lunar manned missions. Now, in a work that looks forward to the human exploration of Mars, he confirms that he is perhaps the most thoughtful and certainly the most articulate of all the astronaut-writers.

The work is in two parts: First, background is provided on the planet Mars, and on the physical, physiological, political and psychological factors that will constrain a first human mission to it; second, a detailed fictionalized description is offered of the initial mission. That description is provided in the form of a story, but the events described are all possible, and many are inevitable.

Collins begins by proposing his own preferred mission: Leave Earth in June 2004, performing a Venus swing-by on the way to Mars; land on Mars in May 2005 for a two-month stay; and return to Earth by April 2006. In a series of concise and clearly written chapters, Collins then spells out the main variables: basic facts about Mars and the orbital mechanics needed to reach it; estimated mission costs (he thinks everybody has so far been too optimistic); dangers, both physical and psychological; life support systems (messy -- "Life support may indeed be the 'long pole in the tent' -- the term NASA people give to the one item holding up the whole show"); propulsion systems (chemical rockets, unless you want to wait a long time for that first mission); analogies with other confined human environments (Antarctica and submarines); and the Soviets' experience, in both habitat design and in long-term space living.

It is easy to question some of the mission details, or the design and background assumptions. For example, I have never seen, in even the most pessimistic projections, a world population estimated at 12 billion by the year 2005. The proposed launch date for the Mars mission, 2004, is at odds with the slow pace of development of the U.S. space station, and with Collins's proposed use of such a station as the testing ground for elements of the mission. The full recycling requirement for both solid and liquid wastes seems to me to be asking for trouble (which, in the fictionalized recounting of events, duly occurs). And the projected two-month stay on the surface of Mars, after the 20-month out-and-back travel time and the huge project expense, looks unsatisfyingly short (but other recent studies are even worse; the Ride Report suggests only 10 to 20 days on the surface of Mars).

However, these are no more than quibbles. Collins's central thesis is unaffected by them. That thesis is stated only at the very end of the book: "For a variety of reasons the space program has bogged down since 1969 . . . it is time to get moving again."

He sees a human mission to Mars as the best way to get moving. Who can disagree? Certainly not the Mars Underground, a loosely coordinated group of individuals who set human exploration of Mars as a high-priority item in the affairs of the United States and the world. However, a deeper reading of this fascinating book should give them cause for concern. Collins suggests reasons for pessimism, if not outright despair, at the inability of the United States in general and NASA in particular to do the necessary job. Again and again, almost as a subliminal subtext to the enthusiastic main development, his reservations and questions about the direction taken by today's U.S. space program appear. "NASA has been presented with four views of the future . . . Mars features prominently in all of them . . . But to all, and to any outsider who asks, NASA steadfastly replies that it needs space station Freedom . . . The shuttle and the space station don't leave much room in the NASA budget for anything else . . . {NASA} has been studying the design {of Freedom} intensively for half a dozen years . . . Freedom has become an albatross around NASA's neck rather than a talisman of future success."

At the same time, Collins's admiration and respect for Soviet resolve and accomplishment in space are clear: "The Soviet Union is a space-faring nation second to none, and has had its sights fixed on Mars for a long time."

Putting all this together, it is easy to read a message from this book that is never explicitly stated: The first human Mars mission may have no Americans on board, unless we find a way to take part in a joint U.S./U.S.S.R. or a multi-nation project.

When I reached the last pages I thought to myself, "Here is first-rate thinking and planning on how to send humans to Mars; but if and when a U.S. Mars project is given the green light and a working budget, NASA will start from scratch. It will take two years and five billion dollars to rediscover what Collins and others have already done."

I didn't like my own reaction; but if enough other people have it, the chances of a U.S. Mars mission by 2004, or even by 2014, don't look good.

Charles Sheffield is a past president of the American Astronautical Society.