The integration and test of a 5-N hydrazine propulsion system

As a payload of a sounding rocket mission, this research designed a 5-N hydrazine propulsion system and tested it at high altitude environment. In this system, none of the component used was space-qualified. A piston-type tank was used for propellant storage, a pyrotechnical valve was used to replace the latch valve, single-coil solenoid valves were used as thruster valves. The self-designed hydrazine thruster was equipped with a single-tube radial-type injector and a conical C-D nozzle with an expansion ratio of 81. Two different sizes of Shell 405 catalyst (14-18 meshes and 20-25 meshes) were packed and separated by porous plates connected to a supporting spring in the reactor. The amount of packed catalyst achieved proper hydrazine dissociation with ammonia dissociation near 0.5 in the exhaust at the design hydrazine inlet flow rate (2.1 g/sec). The system had passed a series of environmental tests including thermal, vibration, shock, EMI, and vacuum tests, and produced an vacuum (-2 torrs) thrust of 4.69 N at hydrazine flow rate of 1.97 g/sec, where the chamber pressure was 13.7 bar, and the specific impulse (Isp), characteristic velocity (C^*) and thrust coefficient (C_f) were evaluated to be 242.8 sec, 1246.2 m/sec and 1.91, respectively. In pulse operations, the system produced stable impulses of 1.18±0.12 TV-sec for 250 ms pulse duration and 2.07±0.15 N-sec for 500 ms pulse duration measured in 15-bit cycles. Noticeable pressure oscillations (~30Hz) of a low-amplitude stage followed by a high-amplitude stage in the reactor were observed during hot firing of the system. Analyses revealed that the pressure oscillation was inevitably from the violent catalytic hydrazine dissociation reactions. With an isolation orifice to prevent the pressure wave propagating to the feed line, the pressure oscillation can be effectively suppressed. In addition, the spring of the catalyst supporting assembly was also shown to be an effective damper to the pressure oscillation. By analysis, the second-stage high-amplitude oscillation was induced by the dysfunction of the spring damper for the thermal expansion of the reactor chamber and the catalysts.