Dear Buck: what's the best way to feed astronauts?

Have you ever wondered what Buck Rogers ate while he flitted around the galaxy fighting villains? Most science fiction stories give short shrift to mundane problems such as where space travelers get food, water, and air. But these are serious problems that must be solved before humankind moves into space.

Today, United States astronauts and Soviet cosmonauts use the most primitive form of life support imaginable: They carry all their food, water, and air with them as they venture above Earth's atmosphere.

''It's amazing to realize that here we are, 20 years into the space age, and we're still using first-generation methods of life support,'' says Robert MacElroy, who oversees a $1.5 million-a-year program of the National Aeronautics and Space Administration (NASA) that explores the problems involved in growing food and recycling air, water, and wastes in space.

A study completed for NASA by Boeing Aerospace researchers earlier this year estimates just how much money more advanced life-support systems can save as orbiting space stations are established and long-term missions are initiated, developments expected within the next 25 years.

For space stations with four to 24 people, the researchers estimate that recycling all the water and air, while growing half the food, will begin paying for itself in five to 10 years. For the larger, military command post, in 15 years recycling would save about $30 million over total resupply from the ground. They reach similar conclusions for a Moon base or a mining operation in the asteroid belt. On the other hand, the researchers find that a three-year Mars mission might just as well carry its own food, although recycling air and water would be mandatory.

The problem with the current approach is weight. A person requires 11/3 pounds of food, almost 2 pounds of oxygen, and more than 6 pounds of water daily. The cost for putting a pound of anything in orbit with the space shuttle runs from $1,200 to $4,600. So the price tag on supplying each astronaut with almost 10 pounds of consumables daily begins to mount as the size of the crew and the duration of the missions increases.

At first blush, space recycling might seem fairly straightforward. On paper, it is easy to design a system where plants take up the carbon dioxide that the crew breathes out and replenish the oxygen that the people consume. Water can be separated from human and plant wastes and the residue used for fertilizer. The crew then eats the fruit and grains (or yeast and algae) that are grown. But in practice, it proves to be a very intricate problem, Dr. MacElroy stresses.

Ten years ago, the idea was to recreate an earthlike ecosystem within a space vehicle. But gradually US researchers realized that terrestrial ecosystems are too large and complex to work within the limits imposed by current technology. The Soviets, however, have a large program that still appears to be pursuing this line of research.

The current US approach is aimed at hybrid systems that seek to mechanically integrate plants with the spacecraft life-support system. Plants respond to changes in temperature, light intensity, humidity, concentrations of oxygen and carbon dioxide, but little research has been done in this area, MacElroy says. So, NASA-backed researchers are studying this in hopes of learning enough so that plants can be grown and controlled efficiently in space.

It turns out that controlling the plants may be the biggest problem. Theoretical work done by Robert Auslander at the University of California, Berkeley, suggests that this is the case. The essence of the problem is that, unlike machines, plants have a genetic program that they follow, which is poorly understood. When you're counting on them for your oxygen, you can't afford to have all your spinach plants suddenly go to seed because they think fall has arrived.

There are other issues: No one really knows how plants will respond to the lack of gravity. No one is certain either about the effect that high levels of radiation in space will have on the bacteria upon which plants depend. And there is the not entirely facetious question of how well astronauts will take to gardening and food preparation, outer-space style. Researchers have already spent a little time investigating the potential of robotics for automatically cultivating, watering, and harvesting crops.