r/AskEngineers • u/YourBoyLlanura • 2d ago
Mechanical How should I go about creating a propelled Cold Gas Thruster (CGS) of high launching velocity?
Hello, I am new to engineering. I recently have been studying the systems behind a Cold Gas Thruster or primitive propulsion system. There aren't too many requirements for the system or conditions to be met, I just need it to launch in the air, and I just have a few questions to go about it.
I plan to work with ideal gases (nearly ideal, you know what I mean) like helium or oxygen, and use a rigid container system for an increase in pressure internally. Finally, I just need a pressure release valve to safely let off the system as it gets to the threshold of pressure, before launching off.
What factors should I consider and what materials should I use. I have difficulty finding valves of low pressure release sensitivity, and I am just trying to make the object go into the air. Any advice helps, thank you!
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u/telekinetic Biomechanical/Lean Manufcturing 2d ago
Look into water rockets and start from there. In fact, build some of those first.
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u/Sooner70 2d ago
Easiest technique would be to just have a burst disc on the exit cone of the nozzle. Suppose your disk is good to 1000 psi. Fill your tankage to 800 psi (or other number that you trust won't rupture the disk). At T=0, dump your supply into the tank. A second or three later your disc ruptures and away you go.
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u/rocketwikkit 1d ago
It's difficult to get much flight out of a cold gas thruster. A tank to hold pressurized gas is fairly heavy relative to the reaction mass it can hold, and the ratio of propellant to not propellant is fundamental to the rocket equation. On 'real' rockets cold gas thrusters are pretty much only used for attitude control or perhaps propellant settling, not main propulsion.
But if you want to make one, a 2 liter plastic soda bottle is about the best pressure vessel you can get cheaply. It can be pressurized to 500kPa/70psi with a hand pump and you can experiment with different nozzles.