Cold gas thrusters are a very simple and reliable form of thruster that operate only by spraying a compressed gas, without any chemical reaction.

What are the most common, performant, or otherwise notable propellants used by cold gas thrusters? What advantages and disadvantages do they present over other cold gas thruster propellants?


2 Answers 2


Here's a nice overview document which covers some common propellant choices for cold gas thrusters.

Nitrogen is probably the most popular choice for cold gas thrusters — readily available and practically inert.

Hydrogen and helium can produce better specific impulse (but lower thrust due to their low density), but are more complicated to handle.

Carbon dioxide produces less specific impulse than nitrogen, and is an asphyxiant in smaller amounts than nitrogen, albeit still relatively safe to work with.

  • 1
    $\begingroup$ CO2 is dangerous at a few percent above normal atmospheric content; N2 less so. Technically both are asphyxiants. I’ll edit to clarify. $\endgroup$ Dec 16, 2018 at 14:01
  • $\begingroup$ CO2 is really dangerous at a few percent only with prolonged exposure, leading to acidosis over many minutes to hours - meaning it's slightly toxic. Its asphyxiant properties (displacing oxygen in air) are similar to nitrogen - but being heavier than air it can concentrate in low places creating dangerous pockets, although very cold nitrogen freshly boiled off from LN2 will do so too. $\endgroup$
    – SF.
    Dec 16, 2018 at 22:03
  • $\begingroup$ @SF. acidosis saved these two: youtu.be/8qEsqjJAY-k?t=95 ;-) $\endgroup$
    – uhoh
    Dec 17, 2018 at 4:15
  • $\begingroup$ Gravity Probe B used the natural boil off of helium from its large cryogenic system. There were 8 pairs of opposed thrusters and after cooling various parts of the probe the flow of helium could be balanaced between the thrusters of each pair, to create tiny, vibration free, very accurately controlable net thrusts and torques. $\endgroup$ Dec 18, 2018 at 11:32

Designing a cold gas propulsion system is much more complex than just selecting the "right" gas. Nitrogen is popular for many reasons but my guess is that one of the reasons is its high availability and low cost.

The design criteria for such a system are varied, for example, let's assume that allowed mass of the propulsion system is limited, this mass is highly affected by the thickness of the tank, the thickness of the tank is affected by the gas pressure that related to the selected gas.

Another issue is that fact some gas might turn into a liquid while being under pressure. This might create some undesired sloshing phenomena that have an effect on the satellite attitude control system.

I recommend you read the following article: "Cold Gas Propulsion System Conceptual Design for the SAMSON NanoSatellite" where the authors describe the entire design process of a cold gas propulsion system.


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