Skoden

Skoden is a liquid rocket that has been designed with a simple philosophy: keep it small, simple, and easy to integrate. Liquid rockets are complex enough; why reinvent the wheel? These goals in turn have made it affordable, accessible, and power dense for its size.

The airframe is only 5” in diameter and cut from 0.125” thickness 6061-T6 tubes. To keep the fuel and oxidizer tanks as short as possible and fit comfortably in our 105” long airframe, we used concentric tanks. NOS sits on the outer ring with ETH in the central tube. This compact design has allowed us to maintain a proper stability margin and fineness ratio with a total dry and wet mass of 17 and 28kg respectively. This is a rocket that can be transported in the back of a sedan and built on-site.

To ensure the reliability of these pressurized systems, all GD&T studies came from proper research and documentation from HalfCat Rocketry, NASA, Parker O-Ring Guides, and other industry leaders. Surface roughness, geometric tolerances, bulkhead design, and more has been done with extensive safety margins dictated by empirical experience. What does this lead to? Trust in the drawings we send out to be machined without extensive fears of boil-off, leakage, bolt tear-out, or god-forbid catastrophic failure.

The airframe is highly integrated and rigid. By using the outer tank as a body tube of the rocket itself, it is very strong, with the remaining vehicle length covered by fiberglass tubing. DFM and DFA reduced the part count of both the engine and airframe, leading to a goal of assembly in under 1 hour, and the only manufacturing that takes place is 3D Printing and CNC machining, with the latter outsourced overseas.

The Skoden rocket’s avionics and communication architecture is designed to ensure robust telemetry, command, and control throughout the mission, leveraging a combination of long-range wireless protocols and onboard automated controllers. The telemetry and transmission system relies on a LoRaWAN communication architecture operating on RF channels, facilitating a reliable link between the onboard systems and Ground Support Equipment. This setup is critical for real-time monitoring of the vehicle's state, including pressure, temperature, and battery telemetry, during both pre-flight fill procedures and flight operations.

An on-board custom Flight Controller employs a robust sensor suite that feeds data to the GSE team, allowing for dynamic monitoring of NOS mass, ETH levels, and system pressures. Safety is further bolstered by integrating 3-way ball valves for all fluids, actuated by remote servos. This includes control of CO2 lines that pressurize the integrated valves above the Injector. In the event of any anomalies, the fluids can be remotely dumped, and as a further redundant safety mechanism, there is a fitting above the Nitrous tank that bleeds pressure slowly over time. Even if all valves fail, the rocket can be safely depressurized with the ingredient of time.

The Avionics system is tasked with initiating the dual-deploy recovery sequence at the appropriate apogee. This system is all OTS, with trusted components from Eggtimer and Blue Raven. These systems track the rocket's position and allow for proper initiation of the recovery sequence as well as post-flight data analysis. We have thus performed countless 3-sigma Monte Carlo simulations of the landing zone, mapping flight and descent trajectories in OpenRocket and RocketPy. With high-fidelity weather data from networks of balloons far into the atmosphere, and redundant LoraWAN and HAM radio communication channels, we can have assurance in successful recovery of Skoden, ready for the next launch.

Skoden's propulsion system is a liquid bipropellant engine using NOS and ETH, designed within a 5" geometric envelope. The engine targets 3.96 kN max thrust with an average of 3.51 kN, generating a total impulse of 22,166 Ns over a 7-second burn. Nominal propellant flow is 1.439 kg/s of nitrous and 0.340 kg/s of ethanol, giving an O/F ratio of 4.235 and a characteristic length of 0.55m, with a 3.328" chamber diameter.

At the heart of the engine is a 45-element Coaxial Shear Injector. Machined as a single piece from 6061-T6, it features 304 stainless steel hypodermic needles bonded in place with DP420 Epoxy. Nitrous is distributed to the elements through an annular manifold that ejects concentrically around the ethanol stream. Upon collision, these streams atomize within our engine chamber and are ignited with an Estes motor.

The combustion chamber is a single machined block of Phenolic Ablative sandwiched between the Injector faceplate and a machined boattail container. A machined piece then radially constrains it and acts as an air insulator between the engine chamber and fincan. This design was enabled by DFA, allowing us to swap ablative engine chambers across launches and ensure affordable, quick turnaround with a single disposable component replaceable by removing 8 bolts.

Our final design iteration was to 3D print the fincan from 6061-T6. This was a bold move pushed by thermal simulations that showed our fincan, planned to be nylon-composite, climbing above working temperatures. We originally had this concentrically fixed around a thin-walled engine chamber, to have 6061-T6 fins epoxied into the nylon, but replaced all these components with one component. This is what advanced manufacturing is all about!