Patent Number: 062696297
Section: description

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION In the sole figure, propellant modules 1 are schematically illustrated for generating thrust in particular directions, depending upon their orientations. Each module includes a segment of an ordinary coaxial cable 2, having a "TEFLON" copolymer spacer or core 3 positioned between outer semi-rigid cylindrical conductor 4 and inner conductor 6, in the well known configuration. Each cable segment is connected across an associated secondary winding 7 of voltage step-up transformer 8 via a switch 9, as shown. Primary winding 11 of the transformer is coupled to energy storage capacitor 12 via switch 13. The storage capacitor 12 may be charged up by voltage source 14 via adjustable resistor 16. Assume the uppermost propellant module is to produce thrust at a particular time. This is effected by closing switch 9, charging capacitor 12, and thereafter closing switch 13. Rapid discharge of energy previously stored in the energy storage capacitor occurs in microseconds across the selected coaxial cable segment, which produces vaporization of the spacer copolymer 3, to in turn produce a single thrusting impulse. The thrust is created by the ablated material accelerating out through a combination of electro-thermal and self-field electromagnetic forces. A high voltage pulse of at least 1000 volts, is thus generated by capacitor 12 and the secondary transformer winding and is applied to coaxial cable components 4 and 6, acting as electrodes. Switch control circuit 15 of the thruster control means 20 is coupled to the switches as indicated, and thus is used to selectively apply the high voltage impulses to selected propellant modules. These modules are oriented in various directions to control positioning and acceleration of the space crafts in desired directions as is well known to those skilled in the art. Alternatively, a single or a multitude of the modules can be oriented in one direction to provide primary, or bit transfer, propulsion for small spacecraft. This arrangement results in a light weight, low cost thruster comprising several propellant modules 1 and the thruster control apparatus shown. Coaxial cables can also be beneficially used to connect the secondary windings of the transformer to the separated propellant modules. These coaxial cables together with the cable segments in the modules also beneficially reduce EMI or electromagnetic radiation. Optionally, this arrangement can use propellants other than coaxial cable segments, but in any case, the aforesaid undesirable spark plug igniters are eliminated by the described arrangement. Good results were attained by the application of pulses to the modules 1 using conventional coaxial cable segments in the 1800-3000 volt range. The cables contained conventional "TEFLON" tetrafluoroethylene copolymer spacer material therein. As mentioned above, changing the capacitor discharge frequency and thus the frequency of the resulting pulse train applied across the coax components can also be used to change the degree of thrust. This could be effected by altering the setting of adjustable resistor 16 to change the RC time constant, since switch 13 is only closed after full charge-up. Numerous variations of the foregoing arrangement will be obvious to workers skilled in the art, and thus the scope of the invention is to be limited solely to the terms of the following claims and art recognized equivalents. For example, the switches could be mechanical, as indicated, or be of the solid state variety. Voltage step up circuitry could be provided other than the transformer illustrated. Such circuitry, well known to those skilled in the electrical arts, include Marx bank capacitor stacking, or Blumlein inductive stacking. Alternatively, the voltage step-up can be eliminated by simply charging the capacitor to a higher initial voltage. In the ideal case, voltage step-up is sufficient to allow for charging directly from the spacecraft power bus to eliminate the need for a separate power processing unit to charge the capacitor to voltages higher than the spacecraft power bus. The ablated propellant could comprise electrically conductive propellants described in a copending patent application of Gregory Spangers, rather than the insulating material found in commercially available RF coaxial cables. Cable variations include employing a cable with a thick outer shell which would remain after the ablation of the propellant and the inner conductor, or a thin outer shell which would ablate with the propellant. Another alternative could involve micro-machining a cylindrical spring surrounding the inner conductor and biased against the back end of the cylindrical propellant to feed it to the front as it is ablated without any loss of the inner and outer electrode conductors.