IF an American flag is going to be planted on Mars by the year 2019, as President Bush recommended on May 11, it's likely to be a robot rather than a human that will do the planting. ``Thirty years from now, I believe man will stand on another planet,'' Mr. Bush told a commencement gathering at Texas A&I University, Kingsville, Texas, in an evocation of President Kennedy's famous challenge to land a man on the moon during the decade of the '60s. ``I believe that before Apollo celebrates the 50th anniversary of its landing on the moon, the American flag should be planted on Mars.''
However, it is becoming increasingly doubtful that any human will ever step on the surface of the red planet - or any other extraterrestrial body except the moon.
The irony is that the space-age technology that is making exploration of the solar system possible is also making humans obsolete as the explorers. Astronauts and auto workers alike are being elbowed aside by the same competitor: the computer.
By the time even the Russians and Americans working together could get a crew of astronauts to Mars, computers will be as much advanced beyond today's models as the space shuttle is beyond the Wright brothers' flyer.
These incredible computers of the future, which are being developed today mostly under military sponsorship, have compelling advantages over human explorers: They don't have to be fed, they don't need their own atmosphere, and they can cope with the psychological stress of prolonged isolation in space. Best of all, they work cheap - a lot cheaper than the $500 billion price tag that NASA has put on the manned Mars mission.
But can the computers do the job? They certainly couldn't during the Apollo days, when the astronauts had to fly their spacecraft back from the moon manually because the total vocabulary of their on-board computers was only 39,000 words. Today's personal computers have the equivalent of 30 million words of memory and sell for about $1,000.
The friction between manned and unmanned space projects has been endemic since President Eisenhower created NASA in 1958. The scientific value of the unmanned projects has had to be weighed against the publicity value of the more glamorous manned missions. While it's true, as one astronaut remarked, that ``nobody gives a ticker tape parade for a computer,'' it's also true that flags aren't lowered to half staff after the loss of a Mariner or Voyager unmanned spacecraft, as they were after the Challenger tragedy.
In less than 50 years the information processing power at the microchip level has grown exponentially, from one function per transistor in 1947 to 64 million in today's state-of-the-art memory chips.
Dr. Robert Noyce, the inventor of the integrated circuit, estimated in 1983 that the US semiconductor industry produced the equivalent of 100 trillion functions at a cost of a hundredth of a cent per function. ``That number, 100 trillion, is equal to the number of the synapses in the human brain,'' he noted. ``If we were to continue to approximately double the number of elements produced each year by the semiconductor industry we would have produced the number in all human brains by about the year 2020.''
There is no end in sight to this trend. As today's silicon-based electronics is superseded by more powerful materials such as gallium-arsenide - and later by photonics, in which photons rather than electrons process information even more efficiently - computers rivaling the human brain will become commonplace.
This kind of machine intelligence embodied in robot-like devices is going to transform a lot of human activities, not just space exploration. The Pentagon is developing what is known as a ``pilot's associate'' to take over the routine functions of flying a fighter aircraft and permit the pilot to concentrate on performing his mission. The University of Michigan's Transportation Research Institute is applying this technology to ``intelligent vehicles'' and ``intelligent highways'' that will make even the act of driving obsolete.
Although this may be hard to swallow for former Navy pilot George Bush, the evidence is becoming clear that automated systems can function better in such hazardous environments as the battlefields on Earth and the void of space - and do it at a fraction of the cost and risk to human life.
There is already a precedent for one space-age technology superseding another: fiber optics. These tiny strands of glass, a tenth the diameter of a human hair, have grabbed away much of the point-to-point data traffic from communications satellites. Other technologies will undoubtedly follow.
If there is no performance or cost advantage of sending humans to Mars, why do it at all? A popular notion among some space enthusiasts is that it would be the perfect way to cement improving Soviet-American relations. However, the two countries could just as well pool their technological capabilities (American computers, Russian rockets) to do a first-class unmanned exploration of Mars and use the rest of the $500 billion to clean up the environment of this planet.
Humans may never take that first step on Mars, but they will be ably represented by a race of fearless and diligent robots that can plant the flags of all the world's nations.