The VHKL is a reusable suborbital vehicle. It is designed to reach 150,000 ft altitude and 3,000 mph. It takes off horizontally from a runway. After climbing and accelerating to burnout it glides back to earth for an unpowered horizontal landing. The VHKL is propelled by two liquid fueled rockets and one ramjet engine. The rocket engines burn hydrogen peroxide and kerosene. These propellants are supplied at high pressure by a turbopump assembly. The rockets are regeneratively cooled by oxidizer flowing through cooling channels before entering the combustion chamber. The rockets are mounted on gimbals to provide attitude control during flight outside the atmosphere.
The ramjet engine burns kerosene supplied by the same turbopumps that feed the rockets. The pump turbine is powered by high pressure steam generated by decomposing hydrogen peroxide with a catalyst. The high temperature turbine exhaust is directed into the ramjet combustion chamber where it provides the ignition source for combustion. Each turbopump assembly is a single shaft machine with a radial inflow turbine and two single intake impeller pumps. The shaft bearings are hydrostatic and use the pumped fluid as lubricant.
The VHKL is constructed of standard aerospace materials. The skin and internal structure are aluminum. The aerodynamic shape is that of a lifting fuselage. The main portion of the fuselage is separated into two internal volumes that act as the fuel and oxidizer tanks. The forward part of the fuselage is designed to provide efficient external compression for the ramjet engine at high speeds. The wings have elevon control surfaces at the trailing edge which provide pitch and roll control. The tail fins have rudder control surfaces which are used for yaw control and to provide additional yaw stability at high speeds. The control surfaces are electromechanically actuated. The landing gear configuration is tricycle type with main gear stowed in the wings near the fuselage and nose gear stored in the forward compartment. The forward compartment also houses avionics and batteries. The turbopumps are housed in the wings and the fuel and oxidizer lines are routed inside the wings as well.
The nominal trajectory for the VHKL is as follows. On the runway it accelerates under rocket thrust to takeoff speed. After takeoff it continues accelerating in level flight until it reaches a velocity enabling ramjet operation. After ramjet ignition it begins an upward turn to an optimal flight angle. It holds this flight angle until it clears the useful atmosphere. At this point the ramjet has insufficient air flow for operation and the aerodynamic control surfaces have insufficient force to control the trajectory or vehicle attitude. From here on the rocket engines provide the only thrust. The rocket engines provide pitch and roll control by thrust vector control. But the vehicle trajectory is a ballistic one now, locked in by velocity and gravity. The rockets continue to burn until fuel is depleted. Some reserve of oxidizer is kept to be used as a monopropellant for attitude control during reentry. After descending to an appropriate altitude the vehicle does a 180° turn and glides back to the takeoff location for an unpowered horizontal landing.