Initial flight operations of the miniature propulsion system I-COUPS (Ion Thruster and COld-gas Thruster Unified Propulsion System) are presented with problems found in space and its countermeasures for them. The I-COUPS was developed by the University of Tokyo and installed on a 70 kg space probe, PROCYON as main propulsion system to verify propulsive capability of the first micropropulsion in deep space. The PROCYON was successfully launched on December 3rd, 2014 and inserted into an orbit around the Sun. The PROYON project team started flight operation on the interplanetary orbit. Up to today, the cold-gas thrusters have successfully conducted unloading maneuvers since the launch. The ion thruster overcame several problems and achieved 223 hours operation with the averaged thrust of 346 μN. The I-COUPS will become the first electric propulsion and reaction control system operated on a small space probe (<100 kg) on an interplanetary orbit.

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This paper presents the development of a thrust stand to enable direct measurement of thrust and specific impulse for a CubeSat propulsion system during firing. The thrust stand is an inverted pendulum and incorporates a mass balance for direct in situ mass measurement. The proposed calibration procedure allows precise performance characterization and achieves a resolution of 80 μN thrust and 0.01 g mass loss, by taking into account the drift of the thrust-stand zero caused by propellant consumption. The performance of a water micro-resistojet propulsion system for CubeSats was directly characterized as a proof of concept of the thrust stand. Continuous profiles of thrust, specific impulse, and mass consumption were acquired under various conditions in a single firing test. A thrust from 1 mN to 10 mN and a specific impulse from 45 s to 100 s with a maximum measurement uncertainty of ±15.3% were measured for the throat Reynolds number in the range 100–400.

In this study, a water resistojet propulsion system, named AQUARIUS, is proposed and the breadboard model (BBM) test results and the engineering model (EM) design are described. AQUARIUS will be on-boarded the SLS EM-1 CubeSat: EQUULEUS, which is scheduled to be launch in 2019. AQUARIUS uses a storable, safe and non-toxic propellant: water, which allows for the design of all propulsion system below 100 kPa, reduction of dry mass ratio and simplification of feed line routing using soft tubes. AQUARIUS consists of three components as follows: a tank, a vaporization chamber and thruster head. BBM of the vaporization chamber, and the thruster head were designed and tested. The evaporation rate required heat and thrust performance were evaluated. Based on the BBM test results, the engineering model of AQUARIUS was designed.

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