2017.B.2.5. High Density Cold Gas Jet Propulsion System for Interplanetary Probes


Junichiro Kawaguchi (1)

  1. Patchedconics LLC, Japan




Propulsion, Thruster, Low Cost, Safe


Contemporary small satellites trend seeks even for interplanetary miniaturized probes. One of the biggest problem for those small satellites on high altitude orbits and interplanetary flight is in the propulsion system aboard. There is no geomagnetic field and torquers are useless for those applications.

However, in order to handle desaturation of wheels and also to reorient the angular momentum, those spacecraft need to carry thrusters aboard inevitably. The simplest way is equipping the spacecraft with cold gas containers. This realizes cold gas propulsion system. However, the amount of gas carried is very much limited. And orbital maneuver is hardly possible.

This difficulty is overcome by introducing liquid propellant containers with vaporization mechanism for the liquid propellant. It is sometimes referred to as liquid-gas equilibrium thruster. This sounds very easy and implemented with no difficulty. Unfortunately, it is not realized as easy as expected. Even a fraction of vapor is extracted outside for thrusting, gas pressure and temperature go down and re-condensation occurs quickly making the vapor back into mist again. This results in water jet and performance is significantly degraded. Especially continuous thrusting is hardly possible.

So, the problem here is how to have un-saturated dry gas from liquid propellant aboard. When liquid is just heated up, boiling starts and the liquid tends to consist of a lot of vapor bubbles. Vapor bubbles have very low heat conductivity and heating it up is inefficient and takes a lot of time.

The propulsion system of ours vaporizes the liquid through super-criticality. This process maintains high heat conductivity and produces dry gas efficiently. The process is usually used in power plants on the ground, and nothing special as long as high pressure pump is usable. However, such pump is not available on spacecraft, especially on small satellites. JAXA devised a new device, what we call, Charger that pressurizes liquid with no electric power consumption only with heat exchanger for phase transition. This device and process make the dry gas production continuously, in efficient way.

This scheme carries liquid in equilibrium state and the resulted propellant container keeps burst factor of four (4) before the heat exchanger is on, once on orbit. So, even secondary payload satellites can carry propulsion system while complying with the launch pad regulations. This is a bi-product benefit by using this scheme.


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