This paper presents the first trial of a flight demonstration experiment using a direct-injection gas-hybrid rocket (DIGHR) system, with glycidyl azide polymer (GAP) as the solid fuel and nitrous oxide (N₂O) as the oxidizer. In this work, the combustion characteristics of the DIGHR system were studied. GAP is a high-energy material with characteristics such as self-decomposition, high density, and high heat of formation. N₂O has high vapor pressure. Therefore, the system does not need to use additional pressurized gas to oxidize the combustion chamber. Consequently, the DIGHR system is characterized by a high-density specific impulse that enables the development of a small thruster system. In this study, a 400 N thrust class DIGHR was developed to use in the flight demonstration and a ground test was conducted before the flight test. The performance of a DIGHR system using gaseous oxygen (GOX) was previously reported, in which all of the experiments confirmed smooth ignition and stable combustion. In addition, the efficiency of the characteristic velocity (C*) decreased to approximately 85% in comparison to a system using GAP/GOX. One reason for this is that the motor sizes were different. The second reason is the use of liquid N₂O as an oxidizer. However, these experimental results support the use of a small rocket at an altitude of 100 m. Therefore, a GAP/N₂O flight motor was designed and developed for a small hybrid rocket. The DIGHR was launched from the ground to the sea and the experiment was successfully performed.

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