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

As a payload of Sounding Rocket VI mission of NSPO in Taiwan, this research designed a 5-N hydrazine propulsion system and tested it at high altitude environment. As budget was concerned, none of the components used in the system was space-qualified. In the system, 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 nozzle with expansion ratio of 81. Two different sizes of Shell 405 catalyst (14∼18 mesh and 20∼25 mesh) were packed in the cylindrical chamber, where catalysts were separated and supported by porous plates connected to a spring to keep the density of the packed catalyst constant. The size of the nozzle throat was chosen to produce a chamber pressure of -14.3 bars. With the above designs, the system was ensured to achieve proper ammonia dissociation as well as the specific impulse. Temperatures and pressures in the reactors as well as in the feed lines were monitored during system performance tests. Before launch, the system had passed a series of environmental tests including thermal, vibration, shock, EMI, and vacuum tests. At the operation closed to the design point, the system produced an averaged vacuum (∼2 torrs) thrust of 4.69N with a chamber pressure of 13.7 bar and hydrazine flow rate of 1.97 g/sec. The specific impulse (Isp), characteristic velocity (C^*) and thrust coefficient (C_f) were evaluated to be 242.8sec, 1246.2m/sec and 1.91, respectively. In pulse operations, the system produced stable impulses of 1.18+0.12 N- sec and 2.07+0.15 N- sec measured in 15-bit cycles for 250ms and 500ms pulse durations, respectively. During the hot-firing operation of the system, noticeable pressure oscillations (∼30Hz) in the reactor with a low-amplitude stage followed by a high-amplitude stage were observed. The analyses revealed that the pressure oscillation was inevitably originated from the violent catalytic dissociation reaction and the two-stage oscillation was caused by thermal expansion effect coupled with an inappropriate design of catalyst supporting assembly. With an isolation orifice to prevent the pressure wave propagating to the feed line, and with a proper design of the catalyst supporting assembly to damp the local pressure surge, the pressure oscillation can be effectively suppressed.