Hiroto Saito, Pale Blue Inc.
Yuichi Nakagawa, Pale Blue Inc.
Daiki Tomita, Pale Blue Inc.
Jun Asakawa, Pale Blue Inc.
Hiroto Saito, Proposal for a Fully Integrated 1U Ion Thruster Using Water as Propellant, Pale Blue Inc.
Space development in the private sector is flourishing, especially in the low-Earth orbit constellation market with small to medium-sized satellites weighing less than several hundred kilograms. Generally, satellites orbiting in low Earth orbit are subject to atmospheric drag and other disturbances, causing their orbits to shift with time. Orbit correction is essential to make observations at the same point on the earth and to operate the satellites without disrupting the formation between satellites. In addition to orbit maneuvering, there is an international demand to avoid space debris by reducing the altitude of satellites at the end of their operations, and an increasing number of satellites are equipped with propulsion systems to answer these emerging needs.
The small electric propulsion systems currently on the market have two major characteristics. One is the use of alternative propellants rather than relying on Hydrazine or other traditional propellants, and the other is that the entire propulsion system is compact and fully integrated. The former has the advantage of simplifying complex processes, such as safety screening and filling at the launch site. The latter not only facilitates rapid and simple integration into satellites, but also provides scalability and flexibly to meet a wide range of needs through the clustering of multiple units. In particular, propulsion units of about 1U in size are often found.
While indium and iodine propellant types are already widely used as 1U electric propulsion systems, we have now developed a 1U ion thruster “PBI” that uses water as the propellant. The details of the PBI are described below.
Performance
The PBI has a thrust of 0.35 mN, a total impulse of 7000 Ns, and a power of 60 W. All components, including the tank, are contained within a 98 mm x 98 mm x 106 mm envelope. A notable feature is the large total impulse for a 1U propulsion system, which means that it can provide a larger ΔV to the satellite. Physically, the total impulse is determined by the propellant loading mass and specific impulse. We achieved this performance by expanding the tank volume, downsizing the components, and by enhancing the specific impulse by focusing on improving the thruster head during development.
Electrical interface
The supply voltage is 24V-34V and the communication format is RS422. The power supply and communication interface is a 9-pin MDM connector, resulting in a simple “plug and play” system.
Software interface
The software interface is highly automated so that thrust generation can be performed with simple commands. Specifically, after power-on, the internal modes are “Standby,” “System Check Out,” “Warm-up,” “Pre-Thrusting Ignition,” and “Thrusting”. Standby” is a standby state, ‘Warm-up’ is a mode to raise the propulsion unit temperature to the level required to generate thrust, Pre-Thrusting Ignition” is a mode to generate plasma, and ‘Thrusting’ is a mode to accelerate the generated plasma to generate thrust.
Additionally, a “System Check Out” mode is provided for diagnosing the health of the propulsion system and to verify that there are no anomalies before the propulsion system is put into operation. The user can operate the PBI by transitioning between these modes with simple commands.
Temperature Interface
The tanks are designed to be freeze-resistant. The ability to generate thrust at relatively low temperatures is a benefit of the high vapor pressure of water. This means that the user saves time and power by not having to heat the propellant to high temperature by “Warm-up”.
Radiation Environment
To reduce costs and increase scalability, PBI uses COTS products for ICs. Since the radiation resistance of these ICs is not guaranteed by IC manufacturers, PBI uses only ICs that have been subjected to tests that check for the resistance of the ICs to TIDs and SEEs. These tests include a detailed screening process where the ICs are subjected to gamma irradiation or particle irradiation using an accelerator.
Ground test
Injection tests are conducted in a vacuum chamber in a fully integrated configuration. Ion beam measurements and other tests are being conducted to evaluate specifications.
The above is a complete description of the newly developed PBI, which is scheduled for space demonstration in 2025, with plans to conduct in-orbit thrust measurement and other experiments.