In order to power a rocket to several thousand feet, I needed a rocket motor of some sort. After scrounging the internet for designs, I landed on Richard Nakka’s website, which outlines his adventures in experimental rocketry.

One of the designs really stood out to me was the A-100M rocket motor, which was a simple solid rocket motor design made out of metal, which could be reused over and over by casting the propellant. The propellant of choice for Nakka was a mixture of Potassium Nitrate and sugar/sugar substitutes, which appealed to me because it seemed to be relatively safe (loads of research has been done on them) as well as easily accessible.

A-100M Rocket Motor Diagram. Taken from Richard Nakka's website.

A-100M Rocket Motor Diagram. Taken from Richard Nakka’s website.

 

I created the first prototype mostly out of aluminum using a lathe. I had hoped that the thicker aluminum parts would help with heat dissipation and counteract the lower melting temperature. However, the end result didn’t last, and I will need to remake this motor out of carbon steel.

Closeup of the nozzle which melted during the motor's first firing. A nozzle made out of steel will be needed.

Closeup of the nozzle which melted during the motor’s first firing. A nozzle made out of steel will be needed.

In addition to the motor, I also made a “test-stand” which can interface with my Rocket Control Board. The test stand can precisely measure the weight exerted on it by the rocket motor, and these values can be logged by the control board onto an SD card. When these values are integrated, the impulse of the motor can be determined. The impulse and burn characteristics of a motor can then be used in a rocket simulation software like OpenRocket, where the data can be used to optimize the rocket for the highest apogee.

During the casting process, the wooden ram-rod I used got stuck inside the fuel. I decided to light the failed casting off in the motor anyways, where it melted and destroyed part of the nozzle. I will remake this motor out of steel so that it can better survive the temperature. The instant the nozzle melts through is caught on this video: