Kraken of the Sky (KotS) is a hybrid rocket developed for participation in the 2022 Spaceport America Cup (SAC), 30,000 ft SRAD (Student Researched And Designed) liquid/hybrid engine category. Building on the success of last year's rocket (SotS), design of KotS focused on mass reduction and engine improvements. KotS is powered by the Kismet hybrid SRAD engine.
Diameter: 6"
Length: 202"
Motor Classification: O
Wet Mass: 155 lbs
Fuel: Hydroxyl-Terminated Polybutadiene
Oxidizer: Nitrous Oxide
Two Stage Reefing Parachute"
Full Chute Diameter: 148.8"
The team developed a payload this year that assessed the radiation shielding properties of various experimental materials including boron-nitride nanotubes (BNNTs) and metal oxide composites. These materials are theorized to be lighter and better at shielding radiation than traditional solutions using lead, steel, or concrete. This experiment was housed in a 3U CubeSat and was operated using an independent electrical system that measured the amount of radiation passing through the rocket and the materials during flight and ground operation.
The recovery system onboard KotS uses a reefing two-stage recovery system consisting of a small pilot parachute and a control-line reefed main parachute. A carbon dioxide canister-based separation mechanism deploys the recovery system at apogee, at which point the pilot parachute pulls the reefed parachute out of its bag. At 1500 ft AGL, pyrocutters actuated by electric matches disreef the full parachute. The system is housed inside the nosecone and a fiberglass tube directly below.
KotS is equipped with two COTS (Commercial Off-the-Shelf) altimeters for recovery deployment. A PerfectFlite StratoLoggerCF and a Featherweight Raven3 were used for increased reliability. Each altimeter is powered by a 9V battery and is armed immediately prior to launch. The deployment system includes dual redundancy, with two carbon dioxide ejectors, two pyrotechnic cutters, and both altimeters being capable of independently deploying the parachute.
KotS has a network of 11 custom PCBs spread throughout the rocket that handle everything from arming pyrotechnics and actuating valves to collecting and transmitting sensor data during flight. The PCBs communicate over a CAN bus which is notable for its property of being masterless; any board can fail without bringing down the rest of the system. KotS features a live telemetry system built around the RFD900x 1W 900 MHz transceiver, allowing critical sensor data such as the rocket’s altitude and location to be streamed to the ground during flight.
Because of the possibility of going supersonic, a Von Kármán nosecone with a 4:1 fineness ratio, built from fiberglass was selected for KotS. Two mold halves were formed with foam on a CNC router, and then joined during the layup to form the complete nosecone shape. The nosecone was post-cured at 50 °C for 6 hours, to protect against the hot desert temperatures.
KotS's oxidizer tank holds its propellant, nitrous oxide, and must also control its pressure while filling. It is built from 6061-T6 aluminium alloy and is 80" long, with a 6" outer diameter and 3/16" wall thickness. Twenty-four 1/4"-28 bolts join the bulkheads to the tube at each end with redundant Buna-N o-rings, resulting in a minimum safety factor of 2.4, based on a maximum operating pressure of 1000 psi.
The combustion chamber houses the injector, solid fuel, and nozzle. The chamber is insulated with a 1/8" thick G11 fiberglass tube, and has a 5" outer diameter. It has been hydrostatically tested to 1.5x the maximum expected operating pressure at 700 psi. Kismet burns a solid mixture of 90% HTPB and 10% powdered aluminium by mass. A pseudo-finocyl grain geometry achieved through investment casting is used for the fuel. Once the injector valve opens, nitrous oxide flows through the system into the combustion chamber. The propellants combust and resulting exhaust gases leave the nozzle, providing the rocket with thrust.
KotS uses a carbon fibre fin can holding 3 trapezoidal carbon fiber fins. Carbon fiber was chosen for its high specific stiffness and low mass. The fins were cut on a CNC router and bonded to the tube with a high shear strength epoxy. 3 tip-to-tip layups were done on top of the fins with structural carbon fibre plies to add strength.
A complete report of this project, including descriptions of onboard and ground support systems, engineering drawings of all rocket components, and a complete set of assembly and launch procedures for KotS can be downloaded here.
