CGT - Build

Project Overview

This cold gas thruster used CO2 gas to produce almost 10lbs of thrust for a period of about 10 seconds. The thruster was mainly used to verify one of my design calculators and observe the effects of rapid expansion of CO2 through a nozzle. 

Design

The design for the thruster used equations from Rocket Propulsion Elements and NASA SP 125. A few of the igniter's characteristics are given below:

Chamber pressure: 800 - 850 psi         Chamber temperature: 25 C            Exit Mach: 3.16

Thrust: 20 lbf  (designed)           Theoretical ISP: 66s                Expansion Ratio: 6.53

The body of the thruster was designed with safety and ease-of-use in mind. the geometry made it easy for me to fit a clamp over it on my test stand, tap the hole on the back of the thruster, and made it easy to manufacture. 

It should also be noted that the design of this nozzle took a slightly different approach than previous projects. With the requirement of 20lbf of thrust, I needed a way to check the mass flow of my nozzle while also comparing its throat area and thrust. The ability to play with these parameters and see the direct result on other variables was helpful in that it minimized the throat area as much as possible, while also maintaining as much of the mass flow as possible.

I created several designs and graphed their characteristics: 

Manufacturing

The thruster was made primarily using a lathe. Machined out of aluminum 6061, this thruster was machined by Xometry and tapped by hand once it arrived. Since the nozzle was designed to work at such high pressures, it was ultimately decided that a metal nozzle would eliminate all risk of the nozzle bursting (for example, if it was made of resin or PLA). 

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Initial nozzle CAD