Patent Number: 
Section: claims

1. A combined cycle propulsion system for an aerodynamic vehicle, comprising: a propellant store housed in the vehicle for storing a fuel therein;  a nuclear-based thermal rocket (NTR) coupled to said propellant store, said NTR burning said fuel and producing a hydrogen exhaust stream whereby a thrust force is applied to the vehicle so that the vehicle is propelled through the air; and  means for selectively introducing an uncompressed flow of the air surrounding the vehicle into said exhaust stream at speeds of the vehicle up to approximately Mach 6 , and for stopping said flow of air when a specified combination of speed of the vehicle and altitude of the vehicle is achieved, said specified combination being defined by a speed of the vehicle of approximately Mach 6 and an altitude of the vehicle of approximately 40 kilometers. 2. A system as in  claim 1  wherein said fuel is a hydrogen-based fuel. claim 1 3. A method of propelling an aerodynamic vehicle into space, comprising the steps of: providing an aerodynamic vehicle with a nuclear-based thermal rocket (NTR) propulsion system capable of producing a hydrogen exhaust, wherein a thrust force is applied to the vehicle;  operating said NTR propulsion system starting at a static at-launch condition of the vehicle and all during flight of the vehicle through the air;  introducing a flow of uncompressed air into said hydrogen exhaust to augment said thrust force at speeds of the vehicle up to approximately Mach 6;  adjusting said flow of uncompressed air into said pure hydrogen exhaust based on the speed and altitude of the vehicle; and  stopping said flow of uncompressed air when a specified combination of speed of the vehicle and altitude of the vehicle is achieved, said specified combination being defined by a speed of the vehicle of approximately Mach 6 and an altitude of the vehicle of approximately 40 kilometers. 4. A method according to  claim 3  wherein said step of adjusting comprises the step of reducing the mass of said flow of uncompressed air as the speed and altitude of the vehicle increase. claim 3 5. A combined cycle propulsion system for an aerodynamic vehicle, comprising: a propellant store housed in the vehicle for storing a fuel therein;  a nuclear-based thermal rocket (NTR) coupled to said propellant store to receive said fuel therefrom at a static at-launch condition of the vehicle and throughout flight of the vehicle, said NTR burning said fuel at said static at-launch condition and continuously throughout flight of the vehicle to produce a hydrogen exhaust stream whereby a thrust force is applied to the vehicle so that the vehicle is propelled through the air; and  means for selectively introducing an uncompressed flow of the air surrounding the vehicle into said exhaust stream at speeds of the vehicle up to approximately Mach 6, and for stopping said flow of air when a specified combination of speed of the vehicle and altitude of the vehicle is achieved, said specified combination being defined by a speed of the vehicle of approximately Mach 6 and an altitude of the vehicle of approximately 40 kilometers. 6. A system as in  claim 5  wherein said fuel is a hydrogen-based fuel. claim 5