Patent Number: 
Section: description

Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. Thermal solar rocket 10 is generally comprised of a solar energy receiver 12 that is formed from a thermal energy storage section 14 and a direct gain section 16, a solar concentrator 18, means 20 for selectively directing solar energy to either the thermal energy storage section 12 or the direct gain section 14, and a propulsion nozzle 22. Thermal energy storage sections are generally known but will be described for the sake of clarity. Thermal energy storage section 14 is a container with insulation material 24 provided in the walls. The walls define a cavity in the container. Thermal energy storage material 26 provided in the cavity is typically formed from graphite rods clad in rhenium. The thermal energy storage section is in fluid communication with the direct gain section 16 via piping 34. The direct gain section 16 is comprised of refractory metal tubes (typically rhenium) and is positioned adjacent means 20. The metal tubes are provided with channels through which the gaseous propellant flows. The gaseous propellant is heated as it flows through the channels. Insulation material 24 is also provided around the direct gain section 16. The direct gain section is in fluid communication with the propulsion nozzle 22 via piping 28. As seen in the drawings, a gap is left in the insulation material 24 around the direct gain section 16 to allow the solar energy from the solar concentrator into the direct gain section 16 and the thermal energy storage section 14. The solar concentrator 18 collects and focuses solar rays into the solar energy receiver 12. Solar concentrators are generally known and may have a parabolic shape or may be formed from a refractive or fresnel lens. A secondary solar concentrator 38 may be provided in the insulation gap on the direct gain section to further focus the solar rays. The secondary solar concentrator would result in a reduction of the accuracy requirements of the solar concentrator 18. In the preferred embodiment of FIGS. 1 and 2, means 20 for selectively directing solar energy to either the thermal energy storage section 14 or the direct gain section 16 is provided in the form of a movable wall of insulation material 24. In the first open position seen in FIG. 1, the solar rays from the concentrator 18 are directed into the thermal energy storage section 14 for heating the storage material 26. In the second closed position seen in FIG. 2, the solar rays from the concentrator 18 are blocked by the insulation and thus heat the direct gain section 16. A propellant supply tank 30 contains a suitable gaseous propellant such as hydrogen. The tank is in fluid communication with the thermal energy storage section via piping 32 for selectively supplying propellant to the solar energy receiver during the propulsion phase by means of a valve 36 in piping 32. Operation is generally as follows. In the thermal energy collection and storage phase of the orbital period, means 20 is held in the first open position seen in FIG. 1. Solar rays are indicated by the lines striking the solar concentrator 18. The arrows indicate the reflected solar rays. This allows the solar rays from the concentrator to heat the thermal energy storage section 14 to a temperature of approximately two thousand four hundred degrees Kelvin (for a rhenium/graphite cavity). Once the maximum temperature is achieved, means 20 is moved to the second closed position seen in FIG. 2. In this position, the solar rays from the concentrator 18 heat the direct gain section to at least three thousand degrees Kelvin. During the propulsion phase, propellant is released into the thermal energy storage section 14 where it is heated to approximately the temperature of this section. The heated propellant then flows into the direct gain section via piping 34 where it is further heated to approximately the temperature of this section. The heated propellant then flows through piping 28 to the propulsion nozzle where it produces thrust. FIGS. 3 and 4 illustrate an alternate embodiment of the invention where the means for selectively directing solar energy to either the thermal energy storage section 12 or the direct gain section 14 is provided in the form of relative rotation between the solar concentrator and the solar energy receiver. In this embodiment, the thermal energy storage section is provided with one or more apertures in the wall for receiving the solar rays. As indicated above, a secondary solar concentrator 38 may be provided in the aperture to reduce the aperture size. Also, the direct gain section 16 is not positioned around the aperture in the walls of the thermal energy storage section 14. The relative rotation may be in the form of rotating either the solar energy receiver 12 or the solar concentrator 18. In the first position seen in FIG. 3 the solar rays and energy are directed into the thermal energy storage section 14 for solar energy collection and storage. In the second position seen in FIG. 4 the solar rays are directed to the direct gain section 16 for heating thereof during the propulsion phase. Propellant is supplied from propellant supply 30 to the thermal energy storage section 14 via piping 32 where the propellant is pre-heated. The propellant then flows to the direct gain section 16 via piping 34 where it is heated to the propulsion temperature and then to the propellant nozzle 22 via piping 28 for producing thrust. Although means 20 is illustrated as a rotating or butterfly valve in FIGS. 1 and 2, other types of mechanical switches might be used. The insulation could slide in and out, or a rotating design with windows could be used. Another option would be to use a radiative gap insulation (multi-foil insulation) and fill the gap with gas to xe2x80x9copenxe2x80x9d the heat flow and pump out the gas to xe2x80x9cclosexe2x80x9d the heat flow. The thermal energy storage and direct gain sections could be made from a variety of materials. The thermal energy storage material must have a high specific heat and must be compatible with hydrogen. Two material combinations are typically used in these designs, graphite with a rhenium coating/cladding or boron nitride with a tungsten coating/cladding. However, other material combinations are possible. The direct gain section is preferably made of rhenium. However other refractory metals are possible. Highly conductive composite materials may also be used if they can be made compatible with hydrogen and can contain the pressure loads of the propellant. The invention provides the advantage of achieving the high performance of a direct gain rocket (i.e., high propellant temperatures) using small collectors/concentrators like a thermal energy storage rocket. This enables the rocket to use existing collector technology to achieve performance that otherwise would be decades away. The specific impulse of such a system is two to four times that of a conventional chemical rocket and thus can deliver significantly greater payloads to orbit from any launch vehicle. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.