The Systems Integration team is responsible for the structure of the rocket, ensuring the various subsystem components fit together, and ensuring flight stability. The team must closely track the size and mass of the different components, as well as be aware of special requirements imposed upon the system. These include adding a fiberglass section for the avionics package to communicate, accounting for the shock loading of the parachute opening, and ensuring the structure can handle the thrust produced by the propulsion system throughout the burn.
Above is the general configuration of the rocket, which is important for analyzing flight stability. CPSS’ new Kronheim rocket is 14.9 feet tall and 8.715 inches in diameter. The propulsion system must be located at the bottom of the rocket, and takes up the majority of the rocket’s volume. The flight computer must be located near the top as it is used for deployment of the drogue and main parachutes. Using OpenRocket, a size for the fins to ensure flight stability was determined.
Previous CPSS rockets required an aluminum or wood fin can to support the fins. For Kronheim, a new method has been developed to support the fins. It uses a composite honeycomb structure for the fins themselves, and is bonded to the surface of the body tube using Hysol and additional composite materials. This process has significantly reduced the mass of the lower structure, as well as simplified assembly of the hybrid propulsion system into the rocket.
The body tube contains all of the rocket’s components, and creates a smooth surface for flight aerodynamics. To manufacture the body tubes, we spread epoxy over large areas of carbon fiber or fiberglass material, then wrap the material around a mandrel and compress it with packing tape. The significant loads the body tube must handle are the thrust, which produces a compressive force throughout acceleration, and the tensile shock loading during parachute deployment. The shock loading was determined to be the greater load, so the number of composite layers in the structure, particularly at the joints, were determined based on the expected loading during main parachute deployment.
There have been two test flight rockets which tested flight avionics, recovery, and structure of the Kronheim rocket. The major structural component that failed during the tests were the fins, which upon their controlled landing, broke, resulting in the fins not being ready for use again. In order to prevent this failure in the future, and enable body tubes with fins to be reused, the structural capabilities of the fin materials were determined in a 4 point bend test in the Cal Poly Aerospace Structural Engineering Lab.