Directing light for thermal and power applications in space

Abstract

Solar collectors can provide power for electricity, thermal propulsion, and material processing (e.g., mining asteroids). In one aspect, a rocket propulsion system is configured to produce thrust for a spacecraft and includes: one or more optical elements configured to receive solar energy. The optical elements include: a first window configured to allow energy to enter the rocket propulsion system and form a concentrated energy beam, and a second window positioned to allow the concentrated energy beam to pass to the heat exchanger. The second window is spaced away from the first window to form a pressurized plenum chamber therebetween. The system further includes: a heat exchanger configured to receive the energy and use it to heat and pressurize a propulsion gas, and a rocket nozzle configured to expel the pressurized propulsion gas.

What is claimed is: 
     
         1 . A rocket propulsion system configured to produce thrust for a spacecraft, the system comprising:
 one or more optical elements configured to receive solar energy, the optical elements comprising:
 a first window configured to allow energy to enter the rocket propulsion system and form a concentrated energy beam; and 
 a second window positioned to allow the concentrated energy beam to pass to the heat exchanger, the second window spaced away from the first window to form a pressurized plenum chamber therebetween; 
   a heat exchanger configured to receive the energy and use it to heat and pressurize a propulsion gas; and   a rocket nozzle configured to expel the pressurized propulsion gas.   
     
     
         2 . The system of  claim 1 , wherein the first window is configured to function as a pressure window of the pressurized plenum chamber and further comprises one or more curved surfaces configured to provide a controlled amount of focusing of the energy. 
     
     
         3 . The system of  claim 2 , wherein the controlled amount of focusing is selected to limit the concentration of the energy to temperatures within safe operating limits of system components. 
     
     
         4 . The system of  claim 1 , further comprising a plenum injector tube configured to inject the propulsion gas into the pressurized plenum chamber. 
     
     
         5 . The system of  claim 4 , wherein the second window comprises an array of holes that allow the propulsion gas to flow out of the plenum chamber into a pressure chamber containing the heat exchanger and toward the rocket nozzle. 
     
     
         6 . The system of  claim 5 , wherein the array of holes is configured such that the propulsion gas flows through the holes to form a protective gas barrier within a defined distance of an output surface of the second window. 
     
     
         7 . The system of  claim 5 , wherein the plenum injector tube is configured to introduce the propulsion gas into the plenum chamber prior to heating such that the gas:
 cools the plenum chamber;   cools at least one surface of the first and second windows; and   removes contaminants from at least one surface of the first and second windows.   
     
     
         8 . The system of  claim 7 , wherein one or more surfaces of the first and second windows are coated with anti-reflection coatings. 
     
     
         9 . The system of  claim 4 , further comprising a second injector tube, configured to inject a stream of propulsion gas directly into the pressure chamber. 
     
     
         10 . The system of  claim 9 , wherein at least one of the plenum injector tube and the second injector tube is configured to receive and inject a mixture of molecules derived from an asteroid mining process. 
     
     
         11 . The system of  claim 1 , wherein the heat exchanger is formed of a porous solid material configured to allow the flow of the propellant gas through the heat exchanger. 
     
     
         12 . The system of  claim 11 , wherein the heat exchanger has an internal surface area having a size sufficient to transfer heat energy from the heat exchanger to propellant gas via heat conduction in order to produce the thrust for the spacecraft. 
     
     
         13 . A method of manufacturing a spacecraft, comprising:
 positioning a first window toward an outer face of a spacecraft such that it can receive solar energy;   aligning a second window with the first window such that the second window is spaced toward an interior of the spacecraft, forming a plenum chamber therebetween;   configuring the first and second windows to focus an energy beam onto a heat exchanger;   positioning a conduit for propulsion gas to flow into the plenum chamber;   positioning the heat exchanger to receive the concentrated beam such that it heats and pressurizes propulsion gas located adjacent or within the heat exchanger; and   providing a nozzle configured to expel the heated and pressurized propulsion gas after it is pressurized by the heat exchanger.   
     
     
         14 . The method of  claim 13 , further comprising configuring the first window to maintain pressure within the plenum chamber. 
     
     
         15 . The method of  claim 14 , further comprising providing for focusing of the energy beam using a curved surface on at least one of the first and second windows. 
     
     
         16 . The method of  claim 15 , wherein the curved surface is configured to limit concentration of the beam to temperatures within safe operating limits of the heat exchanger. 
     
     
         17 . The method of  claim 15 , wherein the second window comprises an array of holes configured to allow propulsion gas to flow from the plenum chamber into a pressure chamber containing the heat exchanger. 
     
     
         18 . The method of  claim 17 , wherein one or more surfaces of the first window are coated with anti-reflection coatings. 
     
     
         19 . The method of  claim 18 , wherein the array of holes are configured to allow propulsion gas to form a protective barrier at a second window surface that faces the pressure chamber. 
     
     
         20 . The method of  claim 18 , wherein the array of holes is positioned and configured to facilitate cooling the first and second windows using the propulsion gas. 
     
     
         21 . The method of  claim 20 , wherein the conduit is configured to introduce into the plenum chamber a propulsion gas comprising a mixture of molecules derived from asteroid mining processes, and the array of array of holes is configured to facilitate removal of contaminants from at least one surface of the first and second windows. 
     
     
         22 . The method of  claim 13 , wherein the heat exchanger is formed of a porous material configured to allow the flow of the first propellant gas therethrough, and the porous material provides sufficient surface area for heat energy transfer to the propellant gas to produce the thrust for the spacecraft. 
     
     
         23 . The method of  claim 13 , further comprising configuring a second injector tube to inject a stream of propulsion gas directly into the pressure chamber.