Aug. 7, 1998 CHAMPAIGN, Ill. -- Small ball bearings, slung from orbiting centrifuges, could one day be used to boost satellites into higher orbits, launch spacecraft to distant planets, or slow satellites and returning space probes for safe re-entry into the atmosphere, say researchers at the University of Illinois.
"Centrifugal relays are rotors that progressively accelerate reaction mass to higher velocities," said Clifford Singer, professor of nuclear engineering and director of the university's Program in Arms Control, Disarmament and International Security. "In this case, the reaction mass consists of thousands of reusable ball bearings. This avoids the use of bulky on-board engines and massive fuel storage."
In operation, ferromagnetic balls would be thrown from the primary centrifuge and caught by a second centrifuge mounted on the payload. Coils would adjust the velocity of the balls, which would transfer momentum to the payload while being reflected back to the rotor. To further increase the velocity, additional relays could be inserted between the primary launcher and the payload.
"Using centrifugal relays to accelerate payloads at high velocity is becoming an attractive alternative to chemical propulsion systems," Singer said. "With chemical propulsion, the reaction mass increases exponentially with the final velocity. With centrifugally launched ball bearings, however, all the reaction mass is recovered, thereby avoiding this exponential growth."
Singer, aeronautical and astronautical engineering professor Lawrence Bergman and graduate student Malika Ouzidane recently studied the system kinetics and dynamics of centrifugal relays. They also devised a guidance system that meets the demanding accuracy constraints such a spaceborne launch system would require.
"Accurately aiming and tracking the miniature projectiles over a launch path extending up to 10 kilometers will be difficult, but not impossible," Singer said. "We have to monitor and control both the velocity and the direction of the rapidly moving balls so they encounter the appropriate guide tracks on the spinning rotors at just the right time and location."
Precise position and timing measurements could be obtained as the balls interrupt two sets of laser beams directed upon fine-scale photodiode arrays, Singer said. Accurate aiming could be accomplished by energizing electromagnetic deflection coils, which would adjust the speed and direction of the balls.
"What really matters is not the absolute aiming of the projectile stream, but the dispersion in projectile velocities," Singer said. "Controlling the dispersion is a much more manageable task than the actual aiming of the projectile stream."
The centrifugal relay concept is unique in that all components of the system would operate at ambient temperature without any chemically reactive or corrosive materials, Singer said. "This could make it particularly attractive in the long run for reusable spaceborne transportation systems."
The researchers described their centrifugal relay system in the July issue of Acta Astronautica.
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