The National Aerospace Laboratory and the National Space Development Agency of Japan have been studying a suborbital entry flight experiment. An unmanned, winged, entry vehicle would be launched using the H-II Launch vehicle and delivered on a ballistic trajectory. The entry vehicle would perform an unpowered gliding entry without orbiting the Earth and return to a predetermined landing site. This paper presnets an entry guidance algorithm proposed for the suborbital flight experiment. It employs a reference drag profile similar to that used by the Space Shuttle. The reference drag profile is adjusted during entry flight to decrease range errors or to deliver the vehicle to a desired energy state. Simple methods for adjusting the drag profile were developed instead of the analytic prediction-correction technique used for the Shuttle guidance. A trajectory control law was also developed to achieve the reference drag profile. Simulation results for various off-nominal conditions show that the guidance algorithm can precisely guide the vehicle to a desired position and fly it in an allowable flight corridor.
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