'Small is beautiful' in outer space

These days ''small is beautiful'' even in outer space.

Caught between federal budget reductions and start-up costs of the space shuttle, the National Aeronautics and Space Administration (NASA) is pinning the immediate future of its planetary exploration program on efforts to radically reduce mission costs.

''We have a mind-set for reduced costs now,'' says Jessie Moore, director of NASA's Earth and Planetary Exploration Division.

This represents a radical departure from the space agency's past philosophy, and one which it has found difficult to accept. Over the past decade NASA's planetary budget has steadily shrunk. Its 1983 request of $155 million is only 47 percent of its 1973 budget, and this does not take inflation into account.

But until a year ago, the agency continued to propose ever larger, more elaborate, and more expensive missions. Its last forays into the solar system, while returning spectacular pictures of, and invaluable scientific information on, such natural wonders as the rings of Saturn, also had price tags that mounted above the $500 million range. As economic conditions worsened at home, these pricey planetary projects became harder and harder to sell to Congress and the administration. The result has been to choke off the flow of new missions.

''We haven't been too successful with the high cost approach recently,'' Mr. Moore says ruefully.

Having finally accepted the inevitable, the space agency has turned to ''cost reduction'' with its characteristic technological aggressiveness. Studies are under way at a number of NASA laboratories. Guiding this effort is an advisory group called the Solar System Exploration Committee, which has been meeting regularly since last summer.

Charles Barth, director of the University of Colorado's Laboratory of Atmospheric and Space Physics, is a member of this committee. The lanky, soft-spoken scientist has been an active proponent of lower-cost planetary missions for some time.

''The reason NASA got into the big-mission syndrome goes back to the early unmanned lunar missions in the 1960s,'' Dr. Barth says. ''There were a number of failures. NASA managers learned that if you spend 'X' times more money, you get success. And politically success was far better than failure, so they began spending more dollars.'' This led to a spacecraft design philosophy that was conservative and costly. Each spacecraft was custom designed, from the ground up , to be state-of-the-art.

In addition, the scientist points out that the agency has pursued a broad-spectrum, exploratory approach which has also driven up mission costs. With only a limited number of spacecraft being launched, planetary scientists of all persuasions saw each one as a vital opportunity and lobbied strenuously for their particular experiments. As a result, more and more scientific instruments were hung on succeeding spacecraft, driving up costs and further reducing the number of missions the agency could mount.

''The net result was to mortgage the future of planetary science to a few, large missions,'' Dr. Barth says.

Now the budgetary squeeze is forcing NASA to rethink all its basic assumptions.

Along with engineers at NASA's Ames Research Center in Mountain View, Calif., Dr. Barth is looking at planetary missions which would cost $100 million or less. The Jet Propulsion Laboratory (JPL) in Pasadena is investigating methods for keeping the cost of missions to the outer solar system below $300 million.

By starting with commercial communication satellite designs, the Colorado-Ames studies have identified three Mars missions that could each be mounted for such a relatively modest sum.

One would be devoted solely to mapping water on the Red Planet's surface. This is of particular interest because the surface of Mars is cut with innumerable channels that scientists feel could only have come from running water, yet its atmosphere is far drier than the driest place on Earth.

The second probe would focus on the uppermost layers of the Martian atmosphere. The third orbiter would measure gamma rays coming from Mars and the way its surface reflects infrared light to determine the planet's mineral composition.

Dr. Barth argues that such a low-cost strategy actually embodies a number of research advantages: A steady flow of more modest missions will keep up the excitement within the scientific community and provide research opportunities for younger researchers. Missions of this sort are within the capability of European countries and Japan, so it would make collaborative efforts more likely. Going repeatedly to a planet with the same instruments would make it possible to monitor how various conditions change over time.

While the Colorado-Ames approach has been to utilize as much commercial space technology as possible, JPL engineers are exploring more exotic methods to keep down costs of outer solar system exploration.

''Basically, we are looking at deep-space missionssays Marsha Neugebauer,'' who heads up JPL's low-cost mission office. ''We want to keep the quality of the imaging (camera) system and remote sensors which we have had in past missions, but cut the cost to between $150 and $300 million.''

One key to keeping costs down, she says, is the concept of spacecraft inheritance, using the same design and components for different spacecraft. In addition, NASA is exploring the possibility of using modern computer technology to make spacecraft ''more intelligent,'' so it would take fewer people on Earth to control them as they voyage across the solar system.

The types of missions envisioned for the JPL ''Mariner Mark II''-class spacecraft include a comet rendezvous, a tour of the main asteroid belt, and probes that would pierce the atmosphere of the gas giants of Saturn, Uranus, and possibly Neptune.

Recently Solar System Exploration Committee members have become more convinced that it will be possible to have a valuable planetary program despite the current budgetary constraints.