CO₂ Cold Gas Thruster

Goal

Design a 250 N cold gas thruster with a conical nozzle, sized for sea-level operation, and produce a physical model.

Sizing the nozzle

• Sized throat and exit geometry from isentropic flow relations for sea-level operation
• Calculated choked mass flow, exit velocity, and specific impulse across a 6.4 area expansion ratio
• Arrived at a specific impulse of 58 s

Choosing the contour

The contour was a trade between performance and length. An 80% Rao bell was the original path chosen, but difficulty in manufacturing meant a conical nozzle was the next best idea. As the divergent half-angle decreases, the exhaust gases become more axial and therefore produce more force, at the cost of increasing nozzle length and weight. Those costs are acceptable because manufacturing is much easier, hence the conical nozzle. I chose a 4° half-angle to maximize performance without getting too large of a nozzle.

Build

Modeled the assembly in Autodesk Fusion and printed a full-scale model in nylon 12 via SLS.