Efficient Electric Spacecraft Propulsion

Abstract

A propulsion system for spacecraft is based on an electric engine that expels propellant to achieve thrust. The propellant is first ionized to generate a plasma. Plasma particles are selectively accelerated via a pulsed laser that accelerates predominantly the electrons in the plasma. The electrons are expelled first, forming a space charge that acts as a virtual cathode to accelerate the positive ions. Interactions between the laser beam and plasma electrons are predominantly through the ponderomotive force.

What is claimed is: 
     
         1 . An apparatus for imparting thrust to a spacecraft, the apparatus comprising:
 a plasma generator operable to generate a plasma comprising generated ions;   a containment vessel operable to contain the plasma;   a power supply operable to generate voltage;   a first outlet within the containment vessel;   a second outlet within the containment vessel;   a first electrode positioned adjacent to the first outlet, coupled to the power supply, and orientated such that an electric field generated by the first electrode causes electrons to move preferentially with respect to the first outlet such that some of the electrons escape from the containment vessel through the first outlet; and   a second electrode positioned adjacent to the second outlet, coupled to the power supply, and oriented such that an electric field generated by the second electrode causes the generated ions to move preferentially with respect to the second outlet such that some of the generated ions escape from the containment vessel through the second outlet.   
     
     
         2 . The apparatus of  claim 1 , wherein the electrons that escape the containment vessel through the first outlet form a virtual cathode outside the containment vessel such that the virtual cathode generates an electric field causing some of the generated ions to escape the containment vessel through the second outlet. 
     
     
         3 . The apparatus of  claim 1 , wherein a constant charge is maintained with respect to the first electrode. 
     
     
         4 . The apparatus of of  claim 1 , wherein a constant charge is maintained with respect to the second electrode. 
     
     
         5 . The apparatus of  claim 1 , wherein controlled operation of the plasma generator varies a magnitude of thrust imparted to the spacecraft. 
     
     
         6 . The apparatus of  claim 1 , wherein controlled operation of the first electrode and the second electrode varies a magnitude of thrust imparted to the spacecraft. 
     
     
         7 . The apparatus of  claim 1 , wherein controlled operation of the plasma generator varies a duration of thrust imparted to the spacecraft. 
     
     
         8 . The apparatus of  claim 1 , wherein controlled operation of the first electrode and the second electrode varies a duration of thrust imparted to the spacecraft. 
     
     
         9 . A method for imparting thrust to a spacecraft, the method comprising:
 generating a plasma, the plasma comprising generated ions;   containing the plasma within a confined volume of space;   providing a first electrode associated with a first outlet, the first electrode oriented to generate an electric field causing electrons within the confined volume of space to move preferentially with respect to the first outlet such that some of the electrons escape from the confined volume of space through the first outlet;   providing a second electrode associated with a second outlet, the second electrode oriented to generate an electric field causing the generated ions within the confined volume of space to move preferentially with respect to the second outlet such that some of the generated ions escape from the confined volume of space through the second outlet;   coupling a power supply to the first electrode and to the second electrode; and   controlling the first electrode and the second electrode to vary thrust imparted to the spacecraft.   
     
     
         10 . The method of  claim 9 , wherein the electrons that escape from the confined volume of space through the first outlet form a virtual cathode outside the confined volume of space such that the virtual cathode generates an electric field causing some of the generated ions to escape from the confined volume of space through the second outlet. 
     
     
         11 . The method of  claim 9 , wherein a constant charge is maintained with respect to the first electrode. 
     
     
         12 . The method of  claim 9 , wherein a constant charge is maintained with respect to the second electrode. 
     
     
         13 . The method of  claim 9 , further comprising controlling the generation of plasma to vary thrust imparted to the spacecraft.