I signed up for this course a few months ago and it started today. You can find out all the details at Design & Make Your Own Solid Rocket Motors. I flew into Denver yesterday, rented a car, and drove to Caspar, Wyoming to attend this class. After dodging a tornado, driving through a hail storm, and siting antelope; I arrived. So let’s start with the Rocket Motor Design Class – Day One.
The course is taught by U.S. Rocket legend, John Wickman. He worked on the Space Shuttle Solid Rocket Booster re-design after the Challenger accident. Other assignments include analysis on the MX, Minuteman, and Polaris missile programs. He decided to start this course as he saw a need in the amateur rocketry community for a source of information that was based upon good science.
The class size for this course is limited as it is a hands-on course. For this session there are two students attending class. Another person from the Czech Republic was supposed to attend, but he had to cancel. Besides your humble author, the other student is a chemist and amateur rocket enthusiast from Andrews Air Force Base.
To start the morning, John takes the class through the basic physics of rocket flight. He then applies these principles to the key variables in the design of rocket engines. Liquid-fueled rockets and hybrid (liquid oxidizer and solid fuel) rockets are described. There are advantages and disadvantages to each approach. But the focus of this course is solid rocket motors.
Solid Rocket Motors
After a delicious lunch provided by CP Technologies, he turned our attention to the topic of this course, solid propellant rocket motors. We received his book, and two DVDs. One with videos from the course and the other with the software he created to design motors.
Using this software, the students developed the basic configuration, propellant amounts, and and expected pressure curves for the type of motor assigned to them. In my case it is progressive. This means the pressure starts at a set value and climbs as the propellant is expended.
My final calculations determined that my propellant cartridges will need to be 3 7/8 inches long and that there will be four of them.
John describes static testing goals and procedures. During this portion of the class he shows quite a few videos of static testing failures. Very enjoyable. A description of the equipment needed is explained and sources given. Thrust is not the only measurement goal. Other data are chamber pressure, video looking for structural failures, temperature measurements, and after-firing forensic dissection of the rocket motor body.
The cool thing about this course is that each student designs, builds, and test fires a solid rocket motor. The first step on day one is to create a rocket nozzle. We are using Durham’s Water Putty for this application. This was done on the first day of the course as the material used needs a few days to dry and harden.
Once this has dried, the drain end was masked off with duct tape. The putty was mixed and spooned into the bottom half of the coupler. You will notice an irregular gray object in the middle of the putty in the next picture. That is a piece of graphite that will be drilled out to the required nozzle diameter. Graphite will resist the rocket motor exhaust better than just the putty.