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Welcome to the wiki for the Rowan Rocketry SRAD Avionics System!

Philosophy

Our design philosophy draws heavy inspiration from the Unix Philosophy, with our fundamental principles being modularity and specialization. Our reasoning for this technique is as follows:

1. Things Break

The mantra, "move fast and break things" is the engineering equivalent of learning through failure and past experience. While it is a great technique, it does have the side effect of creating broken parts.

Another way of interpreting "move fast and break things" is in a more literal sense. After all, we are building a rocket, and the internal components will be subject to harsh conditions, including moving fast.

In the past year, our COTS avionics boards have been through hell. We started off the 2023-24 season strong, blowing out the main voltage regulator on our TeleMega by plugging in a bad battery. During the year, we had to attach SMA connectors to boards that had their pads ripped off. Finally, on the same day at Spaceport America Cup 2024, the scorching New Mexico heat loosened some solder connections, causing us to lose the USB port on both flight computers on board the rocket.

By making a more modular system, we are mitigating the costs of component-level failures. For example, if we damage an SMA connector, it would be much easier to replace a small radio module than it would be to replace an entire flight computer.

2. Engineering is Hard

No matter the specific discipline, engineering is always an iterative process. That is to say, no design is ever fully right on the first try. Unfortunately in the case of embedded electronics design, there isn't really a great way of knowing if the boards you ordered are going to work until they are manufactured and shipped to you. This makes hardware design a particularly slow process with little to no immediate feedback.

Additionally, engineering is hard. At least its not rocket sci-. Anyway, engineering is hard, and things are not going to work on the first try, and probably not on the second try either. By breaking the design down into simplified modular components, the slow, iterative process can be made much faster. Additionally, since each module becomes inherently simpler through this approach, both the chances and the cost of failure are reduced.

3. Rocketry is Expensive

One of the ESRA volunteers at Spaceport America Cup 2024 put it best, "high-power rocketry is one of the most expensive hobbies."

Sure we flew on a budget under $5k last year, but we had the benefit of having flight computers in inventory from past seasons. Avionics are expensive, man. A COTS tracker will easily set you back a few hundred bucks, and tracker-less flight computers aren't particularly cheap either.

Yes, building an SRAD avionics system will not be a cheap process. However, small modules are more affordable than large circuit boards. Since PCB manufacturing costs jump seven fold when one dimension becomes larger than 100mm, it is important that the individual boards are small. This pricing scheme also means that it costs the same amount (not including shipping) to make seven different orders for 100mm by 100mm boards as it does to place one order for one type of 101mm by 100mm board.

Hardware Overview

The modular avionics system is comprised of several circuit boards that interface with each other over controller area network (CAN) bus. While the mother board has several responsibilities, each of the daughter boards has a single responsibility. By implementing this topology, most of the fragile components (gps antenna, radio SMA connector) and parts that should be easily swapped out.

Some of the boards that we plan to develop include:

  1. The Motherboard
    • Battery
    • USB C port for charging and data
    • STM32H503RBT6 microcontroller
    • Pressure sensor
    • Accelerometer
    • 128 MBit flash memory
    • Terminating CAN transceiver
  2. The GPS/GNSS Board
    • GPS transceiver
    • GPS antenna
    • Possibly another microcontroller for configuring the GPS transceiver
  3. LoRa Radio Board
    • SMA connector
    • LoRa transceiver
    • CAN transceiver
  4. APRS Radio Board
    • SMA connector
    • APRS transceiver
    • CAN transceiver
  5. Recovery Controller (Black Powder)
    • Two pyro charge connectors (drogue and main)
    • CAN transceiver
    • Two pyro charge controllers (drogue and main)
  6. Recovery Controller (Compressed Air)
    • Two valve connectors
    • CAN transceiver
    • Two valve controllers
    • 12 valve valve power supply