Recovery Module - Rowan-Rocketry/SRAD-Avionics GitHub Wiki

Cyber-Physical System Description

1. Sensing

The recovery module is equipped with a pressure sensor and an accelerometer to monitor key flight parameters. The pressure sensor measures the altitude, providing data on the rocket's height above ground level. The accelerometer tracks the rocket's acceleration, giving insights into its speed and dynamic motion during flight.

2. Computing

The onboard microcontroller processes data from the pressure sensor and accelerometer to compute critical flight metrics such as apogee (the highest point in the rocket's trajectory) and current altitude. Post-flight, this data is transmitted to the ground station via the radio module for detailed analysis and recovery operations.

3. Actuating

The recovery module is composed of two separate systems which will operate at various points of the launch lifecycle. These systems include pyro and valve. Based on the rocket's apogee mainly when the velocity is less than 0, the recovery module will trigger the valve which will operate the compressed air canisters to execute critical flight operations, for separating from the drogue to main frame. This separation is triggered at a specific point during flight to ensure safe deployment and recovery of the rocket. When the altitude is less than or equal to 1500 ft pyro will trigger and electric match for its first separation stage. At less than or equal to 1000 ft the pyro will trigger its secondary event to work on separation of the main frame from the payload. NOTE: the minimum pressure of the valve to be used is 116 psi. The minimum value of the compressed air that can be released is 800 psi.

4. Communicating

The recovery module uses UART communication to send data to the radio module and vice-versa for computing. The valve module utilizes UART (Universal Asynchronous Receiver-Transmitter) communication to exchange data with the radio module. Initially, a CAN (Controller Area Network) interface was considered, but UART was chosen for its simplicity and sufficiency for the current application. The decision to use UART was driven by the reduced complexity of the system after consolidating various modules. While CAN is preferable for systems with multiple nodes requiring robust communication, UART is well-suited for simpler, two-to-three-device setups, facilitating straightforward communication between components.

5. Circuit Description

The system includes a 1/4 Inch NPT 2mm Orifice Nitrous Oxide Solenoid Valve, repurposed to operate with compressed air instead of nitrous oxide. Unlike the rest of the modules that operate at 3.3V or 3.7V, the valve portion of the recovery board requires 20W/12V power. To accommodate this, a separate 12V lithium-ion battery is included for the valve module. This approach was chosen over using a buck-boost converter, which would have stepped up the system voltage from 3.3V to 12V. The choice was influenced by the high thermal conditions inside the rocket during flight, which could lead to instability in a converter circuit, causing power cycling and potential system failure. Will be using the STM32H503 microcontroller with the LQFP (quad flat package) to be able to tolerate heat changes.