MAY DAY 1989. A Soviet robot spacecraft hovers just 160 feet from Phobos, one of the two small Martian moons. Suddenly, brilliant flashes from a laser stab the moonlet's surface. Vaporized material escapes Phobos's feeble gravity and drifts toward the waiting spacecraft's sensors. Meanwhile, a small probe sent from the robot explorer hops about like a mechanical frog metering surface composition.
Back on Earth, Soviet scientists and their collaborators from more than a dozen countries -- including perhaps the United States -- eagerly await the first on-site analysis ever made of one of the legendary moons of Mars.
This imaginative mission, which the Soviets have already announced, ``is the next step'' in an exploration which ``is moving toward human flights to Mars,'' notes Louis Friedman, executive director of the Planetary Society. That, he says, ``is probably where space flight is taking us.''
``Humans to Mars: Why not?,'' NASA Administrator James M. Beggs asks rhetorically. Both he and Dr. Friedman reflect a renewed interest in this often dreamed-of adventure. Time right to consider trip
Neither they nor many other specialists suggest that spaceflight has reached a stage where planners could lay out such an expedition today. But they explain that the time is ripe to consider seriously a long-term commitment to manned Mars exploration -- preferably as an international enterprise. Setting this as a goal would strongly influence what the US, the Soviet Union, and other interested nations do in space over the next two decades.
If such nations were serious about going to Mars early in the next century, they would have to consider the steps needed to get there. There are major questions of human health, life support, and engineering design to be answered before undertaking what would be a 2- to 3-year mission. This means planning the design and activities of such facilities as the US space station so as to get the needed answers.
The National Aeronautics and Space Administration (NASA) expects to have that station on orbit by 1992. So the design work is going on now. Likewise, planetologists need to know more about Mars and its space environment before they can help lay out a program for human exploration. As Dr. Friedman notes, the Soviet Phobos mission is just the sort of reconnaissance needed.
There seems little thought among Mars enthusiasts that any one nation should make the journey largely on its own.
Looking ahead to permanent Mars settlements, Mr. Beggs observes that this ``epochal step to a planet which will become the first self-sufficient home [beyond earth] for human beings should be a cooperative international effort. . . . It should not be -- and I believe it will not be -- done unilaterally by any one country.''
Apollo-Soyuz cosmonuats Aleksey Leonov and Valeri Kubasov attended the Steps to Mars symposium held recently at the National Academy of Sciences by the American Institute of Aeronautics and Astronautics and the Planetary Society. They also stressed cooperation. General Leonov cautiously noted that proposals for joint missions are matters for governments to decide. Yet, citing the spaceflight experience the US and Soviet programs are gaining, he said that such experience should belong to all mankind. His
Apollo-Soyuz partner Kubasov noted the many unmanned joint missions in which the USSR has participated. ``We believe all countries only gain by such contact,'' he said.
There is, however, a great deal of technology to be developed and much to be learned about living in space before the world is ready to reach out for Mars. Indeed, all preliminary thinking about manned Mars missions starts with the assumption that permanent space stations have already been established and are part of the working infrastructure of global commerce.
John Niehoff of Science Applications International Corporation in Chicago says that, given this assumption, a study he made for the Planetary Society suggests that an initial Mars mission would cost about $25 billion to $30 billion in today's costs. For comparison, he quotes estimates made at the NASA Marshall Space Flight Center in Huntsville, Ala., that suggest it would cost $20 billion to $25 billion in inflation-adjusted dollars to launch a single Apollo moon flight. Peak funding for a $30-billion M ars mission, spread over several years, would be about $5 billion in the most expensive year, Mr. Niehoff says. Shared internationally, this should be a manageable expense. Mission studies beginning
It's hard to predict in any detail just what a Mars flight would involve. American mission studies have only just begun again, having been abandoned when the Apollo program wound down. Soviet studies probably are no more advanced, according to Friedman, who has reviewed the Soviet Mars program.
According to Niehoff, mission designers have to balance three critical factors -- round-trip time, staying time at Mars, and the fuel energy required. The traditional approach, which needs the least fuel, is to head for Mars when it is in conjunction on the opposite side of the Sun from Earth. This involves a nine-month trip out to the planet, more than a year and a half at Mars, and a six- to nine-month return. Niehoff observes that, while this may save fuel, staying that long at Mars would be daunting . Twin spaceships
There are faster ways to do it. For example, two space ships could be launched 30 days apart. When the first one reached Mars, the crew would descend to the planet's surface in a transfer vehicle. Thirty days later, it would rendezvous with the second ship, which would then continue on in its solar orbit until it had come back to Earth. The advantage of such a scheme is that the heavy mother ship does not have to slow down and park in a Martian orbit and then be relaunched toward Earth. Niehoff sa ys this plan saves fuel, shortens mission time, and is compatible with current technology.
These and other mission profiles being studied assume there are no unusual human needs that would be costly to meet. In particular, they do not provide for artificial gravity or heavy shielding against cosmic radiation. Yet these two measures may turn out to be necessities, explains John Billingham, chief of the life sciences division at the NASA Ames Research Center.
American and Soviet experience shows that weightlessness produces a 10 percent bone loss for for every eight months in space. There are losses of blood volume and muscle protein as well. No one yet knows whether these losses continue indefinitely or eventually level off in space, Dr. Billingham says. No one knows how serious the central nervous system adaptation to weightless, as evidenced by the frequent astronaut-cosmonaut ``space sickness,'' may be. If there is a critical biomedical danger that canno t be countered by exercise, diet, or medication, then artificial gravity will have to be provided, Billingham says.
That could be awkward and expensive. The only known practical way to do it is to spin the spacecraft to create a centrifugal force. The crew could only cope with very slow rotation, say one to two revolutions a minute. That, Billingham says, would require a large radius to simulate a significant fraction of Earth gravity. The ship might wind up as a dumbbell-like structure with two capsules at the ends of a long connecting tube. This would be a much more costly and more difficult design than usually is contemplated. Danger from cosmic rays
Also, he notes that little is known about the danger from cosmic rays and solar protons. If these are more harmful than anticipated, heavier and more costly shielding than is usually considered may be needed.
Joseph Loftus, assistant director for plans at the NASA Johnson Space Center adds that communications problems dictate much more sophisticated technology on a Mars ship than was needed to go to the moon. Radio signals, which travel at the speed of light, would take up to 30 minutes to reach the spaceship. And communications blackouts would occur when the ship is hidden by the sun. These phenomena make it essential that crew and spaceship be much more autonomous than they have ever been. Real-time monito ring by Earth-based controllers who can quickly radio warnings and new procedures to the crew will not be possible.
Mr. Loftus urges that the US space station complex be used as a test bed to develop such technology. This would also be a good place to develop closed-loop systems for recycling water, oxygen, and other essential materials and to experiment with space gardens for growing food, as the Soviets have been doing with their Salyut station. Why go in the first place?
But why go to Mars anyway? Several planetologists raise this question rhetorically and answer it with variations of essentially the same theme. The basic reason, as they see it, is a combination of the manifest destiny of mankind to expand outward into the solar system and of getting to know another planet well enough to gain new insights into our own earthly home.
Harold Masursky of the US Geological Survey notes, for example, that Mars, like Earth, has had a succession of ice ages. These are reflected in the different ages of water-cut channels seen on the Martian surface. If the channels and the glaciations they represent can be dated and compared with Earth's glacial epochs, they might shed light on the ice-age mechanism.
``Perhaps what we can do is to compare the long history of glaciations and deglaciations on Mars with those on the Earth and see if they match,'' Dr. Masursky explains. ``If they match, it's probably variations in the solar output. If they don't match at all, then it says the heat engine of the two planets is what causes glaciation and deglaciation and we have to look for individual mechanisms.''
Then there is the profound question of why there is life on Earth and, perhaps, not on Mars. If there is indeed no Martian life, this presents a ``remarkable'' scientific opportunity, says Cornell University astronomer Carl Sagan. ``Mars is the planet with the closest environment to the Earth in all the solar system and life is on one and not on the other,'' he explains. ``How come? It's the classic situation of the experiment and the control. There are enormously good scientific reasons to go to Mars.' '
But he and others admit that this in itself is insufficient reason to make the journey. Basically, says NASA's Beggs, we should go to Mars to further human development: ``Why not go to Mars to use human judgement, human ability, and human intelligence to explore an exciting new world?''
Roger Bonnet, director of space sciences for the European Space Agency, says that his agency would start to raise money for a Mars mission if this were set as an international goal. Man will land on Mars, he says, adding that it is as inevitable as building the space station.