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Sun Devil Rocketry: Liquid Propulsion Research

Sun Devil Rocketry:

Sun Devil Rocketry, Arizona State University's oldest rocketry student organization, helps prepare students to become leaders in aerospace through meaningful projects, interactions, and experiences. Our members have the opportunity to explore and make contributions to solid, liquid, and hybrid rocket propulsion research and development. In addition, our members design, manufacture, and launch high-power rockets for competitive and experimental purposes. Our award-winning outreach program exposes hundreds of K-12 students to rocketry each year. Contact us to learn more about how you can become better prepared for industry and graduate school through applied projects.

Liquid Propulsion Research:

With the recent successes of commercial spaceflight, university students have become increasingly interested in acquiring the skills and know-how to better contribute to the development of liquid propulsion systems in industry and academia. However, no program at ASU currently exists to provide the type of hands-on education that fully exposes students to the intricacies of liquid propulsion systems. To create such an industry-relevant and educational environment, the liquid propulsion team set out in fall of 2019 to design, manufacture, and test a liquid rocket engine from the ground up.

Efforts to build the liquid engine have been organized into four areas. These are project management, engine development, ground support equipment, and testing operations. Technical development is coordinated with three subteams, namely propulsion, avionics, and structures. While the propulsion subteam is mainly involved in engine development, the avionics and structures subteam are mostly responsible for the integration of associated infrastructure.

Combustion Chamber and Injector Assembly

Propellant Feed System Plumbing and Instrumentation Diagram (P&ID)

Liquid Propulsion Avionics:

Due to the complexities inherent in the propellant feed systems of liquid propulsion systems, Sun Devil Rocketry’s liquid engine project requires a semi-autonomous avionics system that can execute engine sequences with precise timing, wirelessly communicate with a ground station command and control computer, record and log sensor data, and manage electronic power systems such as ignition circuitry, solenoid drivers, and servo motor actuators. To accomplish this, the Sun Devil Rocketry Avionics team has designed a number of PCBs that are designed specifically for use in propulsion systems. These include an engine controller, valve controller, a ground station unit, a photogate valve-calibration sensor, and a pressure transducer differential output amplifier.

Liquid Engine Controller:

The Liquids Engine Controller PCB is the main embedded processor of SDR's Liquid Engine. The Controller is equipped with an STM32 ARM Cortex M7 processor and 4Mb of external flash for data logging. The board includes a micro-SD card jack for easy access to the logged data. The board includes many power sources for flexible use of the controller during testing and normal operation. These include a 12V power jack, a USB Type B connector, and female header pins which are regulated down to 5V and 3.3V with a buck converter and linear regulator power supply. The board includes a UART to USB transceiver for easy PC interfacing. The screw terminals on the board connect to the ignition wires, consisting of an ignition e-match and two continuity wires. The board supplies 2A to the ignition e-match using a power MOSFET, and the continuity wires provide feedback to the controller on the status of the solid propellant slug and main propellant ignition statuses. Additionally, the board includes a reset button and several LEDs for visual indication of the power and firmware status of the controller.

Liquid Engine Controller CAD

Future revisions of the board will include an RGB status LED, a wireless transceiver for communicating with the ground station computer, a thermocouple amplifier, and connectors for attaching pressure transducers.

Valve Controller:

The liquid engine's valve controller (L0005) contains the processor responsible for managing valve actuation commands issued by the liquid engine controller (L0002). The board contains opto-isolated solid state relays for solenoid actuation and a pulse width modulation interface for issuing stepper motor commands that initiate actuation of the liquid engine's main propellant valves. The board contains an NXP ARM Cortex-M4 microcontroller for processing, programmed using a J-Link with a 20-pin IDC cable connection. The board is powered from the 5V buck converter on L0002, which is also used to power the photogate sensors used for valve position calibration. In order to allow the controller to know the true actuation state of the solenoids even in the event of a power failure, the board contains an AC power supply monitoring circuit which produces an indication signal read by the MCU when AC power is available for solenoid actuation.

Valve Controller CAD

Photogate:

The photogate board functions as an optical sensor for calibrating the absolute position of stepper motors upon controller startup (L0005). The photogate is mounted on the stepper motor adjacent to the motor shaft, which is coupled to the stem of a ball-valve used as the main propellant valve in SDR's liquid engine. The photogate uses an infrared LED to produce an optical signal on the infrared-sensitive phototransistor surface. The board has a characteristic U-shape that allows a small standoff strut on the motor coupler to block the optical path of the sensor when the valve reaches the closed position.

Photogate CAD

Instrumentation Amplifier:

The instrumentation amplifier IC uses an adjustable gain differential amplifier with buffered inputs to amplify the readings from an analog sensor using a wheatstone bridge such as a load cell or pressure transducer. The amplifier supply voltage was chosen to match that of the pressure transducers it is intended to be used with.

Instrumentation Amplifier CAD

Ground Station Computer:

The ground station computer allows Sun Devil Rocketry engineers to remotely interface with the engine hardware. The computer consists of a Raspberry Pi with an external wireless interface that issues commands to the liquid engine controller. The computer runs a GUI program that is developed entirely by the Sun Devil Rocketry Avionics team, which provides visualization of the current engine state and allows the test operations engineer to send commands to the engine controller.