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Why so huge a craft? In addition to carrying a million or more pounds of fuel, the ship must accommodate and sustain human beings for as long as three years. Just to exist in space for one day, for example, each crew member will require several pounds of oxygen, 4 lbs. of water and 3 lbs. of food. Consequently, for a crew of eight on a 900-day mission, a Mars spacecraft would have to carry as much as 40 tons of provisions alone. Any added weight would require using -- and carrying -- even more fuel, both for pulling away from the earth and launching from Mars for the return trip.
There is an alternative to a fully stocked larder: recycling, the recovery of water and oxygen from waste products. NASA has developed prototypes for reclaiming pure water from urine and wash water, and oxygen from the carbon dioxide exhaled by astronauts. For their part, the Soviets have been retrieving some of their water for years, condensing it from the exhaled, humid air in the spacecraft. But Arkadi Ushakov, of the Soviet Academy of Sciences, concedes that the recovery systems in use today cannot meet the demands of two- or three-year missions. He believes a Mars ship will have to contain its own biosphere of renewable plant and water resources.
Toward that goal, Soviet researchers are investigating natural recovery systems: plants that will not only serve as food but also, in the process of metabolizing, absorb carbon dioxide and produce oxygen. The best performers so far, Ushakov says, are traditional food plants like carrots, sugar beets and salad greens. At the Kennedy Space Center, NASA scientists are trying to develop what they call a "self-contained bioregenerative support system." It will include a chamber for growing plants; a food-processing module for extracting the maximum edible content from all plant parts; and waste management modules for capturing and recycling the solids, liquids and gases necessary to support life on a space journey.
In most of the manned Mars scenarios envisioned by NASA planners, the spacecraft would be constructed and fueled at a space station orbiting the earth at 17,500 m.p.h. Compared with blasting off from earth, considerably less fuel is needed to launch the craft from this speeding platform and boost it toward Mars at a velocity perhaps as great as 50,000 m.p.h. At that velocity, says Space Consultant and Author James Oberg, the "earth's gravity pulls on you a little, but it's like brushing your way through cobwebs." Following the path of the Hohmann ellipse,* the craft would coast in a leisurely course halfway around the sun, then begin to accelerate as it came under the gravitational sway of Mars.
To save fuel that would otherwise be used by firing retrorockets to ease the ship into orbit around Mars, the craft will be equipped with an aerobrake. This saucer-shaped structure, as large as 80 ft. in diameter, will slow the craft as it encounters the thin Martian atmosphere. A short burst from the rockets will then boost the craft just above the atmosphere and into orbit. From the orbiting craft, part of the crew will descend to the surface in a lander. After piling sand on the vehicle to shield it from the radiation that bombards the Martian surface, they will use the lander as a base for exploration.