2017-18 Kronheim

This year’s rocket was 7th iteration hybrid motor named Kronheim using solid hydroxyl-terminated polybutadiene (HTPB) fuel and liquid nitrous oxide oxidizer pressurized by nitrogen gas.


The Manufacturing team is in charge of building all of our necessary rocket components and providing them on time. Manufacturing largely occurs in the Cal Poly Machine Shops located in the hangar and Mustang 60. Much of the Propulsion system is machined from aluminum by our manufacturing team.

Injector Manufacturing Pictures:
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CPSS puts significant resources into the design and development of rocket motors. Our Propulsion Team handles the engineering, manufacturing, and testing of these motors. With a dedicated and hard working team, CPSS has the capability to build ever-improving rocket motors to reach our lofty goals.

Test Fire Remote Testing SetupOur remote testing setup in Cal Poly’s on-site Propulsion Laboratory allows us to safely test our high-powered rocket motors. Safe operations is a critical goal of CPSS and test procedures are closely followed during every test fire to ensure no members are ever injured.

Test Stand This test stand gives us the capability to test our smaller hybrid rocket motors conveniently in the Propulsion Lab on campus. It has been used since HM-4 was first tested, and provides us with the data necessary to improve our hybrid motors. We have data acquisition systems set up to measure thrust, oxidizer and pressurant tank weight, and oxidizer and pressurant pressures at key points of the system.

Fuel Production The fuel production team is responsible for assuring that our fuel grains are consistent and perform optimally.

mixing vats

The mixing vat (left) and vacuum chamber (right) ensure that we get consistent fuel grains every time. The vacuum chamber is used to quickly vacuum the air from the mixing vat after mixing HTPB. The vat is then connected straight to the vacuum pump, where it is brought down to just a few mmHg to vacuum out any additional bubbles.


The shake table, designed by Alec Bluhm and manufactured by Kevin Chouinard, is a newly added component to our fuel production process. A motor runs at a high rpm on a vibrationally-isolated from the ground platform, which shakes all the bubbles in the fuel grain to the top, thus providing a more solid fuel grain. Thanks to the shake table, our fuel grains have less instability-adding bubbles and provides more consistent thrust.

The Recovery team is in charge of safe return of our rockets. They design, manufacture and test a recovery system that can safely return all portions of our rocket to the ground at the speeds required by competition rules.


In the 2017-18 year, the main parachute was 14.77 feet large and the drogue parachute was 3.48 feet. The drogue deploys at apogee and descends at 100 feet per second, and the main deploys at 1100 feet for a landing speed of 23 feet per second. Both of these parachutes are elliptical design, and deployment occurs with an algorithm that reads pressure compared to the launch altitude. Sewing, packing and safely deploying such a large parachute is a significant challenge and as of February 2, 2018 the recovery system was certified flight-ready by the Test Rocket team.

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Separator One of the main components of the recovery system is the separator that safely splits the rocket in half and lets the parachutes deploy. The separator consists of two cylinders of metal connected by a ring of FFFF black powder charge.

Testing Ensuring the parachute works is key to any recovery system.

Parachute Testing on the Field

No system will be considered flight-ready in the FAR 1030 rocket without going through rigorous testing. The Test Rocket team is responsible for building and launching rockets to support the other subsystem teams and certify hardware and software that cannot be tested on the ground.

Test Rocket

🅱️ronheim launched February 3, 2018 and was successful. It tested the recovery subsystem, avionics subsystem (particularly in-flight telemetry and radar tracking), and systems integration subsystem. Nose cone pressure data was planned but software was not ready. Assembly was quick and only took about an hour between arrival and launch. There was damage to the fins upon landing as expected but otherwise no problems.

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Check for team updates here.

Systems Integration

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.

Rocket Layout Below 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.


Tail Fins 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.

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Body Tube 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.

Tube body manufacturing

Testing 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.

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Fin bend test 2


The Avionics team is responsible for flight control, telemetry and tracking our rocket as it flies, as well as the payload unit. They are responsible for ensuring that data is gathered and the system is reliable and safe. In CPSS, we design and assemble our own circuit boards entirely in-house to control our rockets.

UpBoard X R1 UpBoard is our completely in-house developed board to control the various components of our rocket system.

UpBoard X R1 improves upon its predecessors with a faster processor, a more robust power system, and onboard memory. It is extremely versatile and can interface with a wide range of other systems, such as the XBee radio board shown below.

Ground Support

The ground support team is responsible for maintaining the trailer and acquiring data from the rocket. They also build our test equipment and gather the data from tests. The trailer contains several major elements; the most prominent is the launch rail, standing at about 40ft tall when upright. The plumbing systems for the nitrous oxide and nitrogen are also on the trailer, as well as the flight data acquisition system, both of which are used for test fires.

Left: Getting the trailer ready for a test fire.
Right: Showing off the trailer at Open House Club Showcase (with half the launch rail).