MPDT Rocket Engine

We created a low-cost version of a MPDT and included a swirl ring, a part used in the field of plasma cutting to increase accuracy. We tested this idea in an MPDT using the following procedure. 

1. Placed a sacrificial wire between the electrodes for discharge initiation.
2. Positioned a low-friction cart with a vertical plate facing the nozzle for thrust measurement.
3. Set the flow rate for argon entering the nozzle.
4. Manually pulled the switch to complete the circuit and release the capacitor's stored energy.

The pulse vaporized the sacrificial wire, allowing propellant ionization to create thrust. For three tests, the cart mass, initial capacitor voltage, and argon flow rate were constant. Detectable thrust was produced by each pulse. 

Shown below. The capacitor, switch, test track, and camera can also be seen.

We successfully designed and built a low-cost version of a MPDT which included a system to test a swirl ring within the copper anode. We sourced an argon gas canister and gas flow system and incorporated them into the apparatus. We created a high-voltage and high-current switch from tungsten electrodes with a physical actuation and clamping mechanism.

During the testing of our low-cost MPDT, we compared cart movement when the swirl ring was used to the corresponding movement when it wasn't used, and found that the swirl ring increased the thrust significantly. This supported our hypothesis on targeted flow improving efficiency.

We also recorded the change in capacitor voltage. The lowest final voltage was 45 volts – far from 0 volts – and suggested that argon could not maintain the arc between the electrodes, i.e., ionized particles were ejected faster than new ones formed. This evidence supports, but does not confirm, the hypothesis that as flow rate increases, efficiency increases.

For the next iteration, we hope to use a better gas delivery system to match the flow rate to the current. Including a hall-effect sensor to measure current would also allow us to compare thrust to our predicted value from the Maecker formula. 

This project was extremely gratifying. It pushed us to learn at the outer edges of our knowledge, presented a tough a technical challenge, and was an inspiring peek into what students can accomplish on a budget.