Montage of our solar system

Miniature spacecraft about the size of coffee can could be launched by electromagnetic launchers to conduct dozens of different space exploration missions, according to an engineer at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Ross M. Jones of JPL's spacecraft systems engineering section said that Earth-orbiting electromagnetic launchers, or railguns, being developed for the U.S. Strategic Defense Initiative Office (SDIO), would be useful in launching very small, low-cost scientific probes to various destinations in the solar system. Jones discussed the proposal in paper presented today at the American Institute of Aeronautics and Astronautics' Aerospace Sciences Conference held in Reno, Nev.

Electromagnetic launchers are being developed by the U.S. military for use both on the ground and in space. Instead of using explosive power to propel projectile, electromagnetic guns and launchers generate brief but powerful electrical pulses that in turn produce strong electromagnetic forces that accelerate projectiles to extremely high velocities.

By taking advantage of the small-scale construction possible with microelectronics, and by limiting the science objectives of mission, spacecraft weighing about three pounds could be launched by Earth-orbiting railguns on trajectories toward the Sun, planets, asteroids, comets or interplanetary space.

"Instead of one large, expensive spacecraft launched every few years," said Jones, NASA "could launch many, perhaps 10 to 50 identical, small, relatively inexpensive spacecraft per year." He estimates that such spacecraft could be developed at fraction of the cost of today's sophisticated, multi-instrument spacecraft, which cost from $300 million to $800 million.

Small spacecraft would call for an entirely different approach to space science compared to current practice, Jones added, "but not so different from what was practiced at the beginning of the space age" 30 years ago when probes weighing less than 50 pounds were the norm.

Drawbacks to miniature spacecraft, such as limited space for instruments, would be offset by advantages such as the speed with which their highly focused missions could be accomplished. For example, Jones estimates that l-kilogram (2.2-pound) spacecraft launched by an orbiting railgun would achieve an exit velocity of about 10 kilometers per second (about six miles per second), giving the probe enough velocity to travel about 750 million miles (about the distance between Earth's and Saturn's orbits) in two years.

(As comparison, the one-ton Voyager 2 spacecraft, launched by Titan-Centaur rocket from Cape Canaveral, Fla., took more than four years to travel to Saturn, and that relatively speedy travel time was possible only because of gravity boost from Voyager's flyby of Jupiter. No current U.S. launch vehicles are capable of sending spacecraft that distance without gravity-assist flyby of another planet.)

NASA's most recent planetary spacecraft launch was Pioneer Venus in 1978. Due to delays caused in the Space Shuttle program following the Challenger accident, the next planetary project, the Magellan mission to Venus, won't be launched until April 1989 at the earliest.

If his concept is shown to be feasible and ultimately applied, Ross said, "it will open an entirely new avenue for the achievement of space science objectives.

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