GAINS Flight Software

University of Colorado Boulder

Ann and H.J. Smead Dept. of Aerospace Engineering

Fall 2022 / Spring 2023 - Senior Design Project - ASEN 4018 / 4028

Bennett Grow, Addison Woodard, Jason Popich, Kaylie Rick, Derek Popich, Cannon Palmer, Tucker Peyok, Ben McHugh, Alfredo Restrepo, Alexander Pichler, Ross White, and Brian Trybus

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Project GAINS aims to determine near real-time position and velocity estimation of a CubeSat beyond GEO with relatively low power and size while maintaining a high level of accuracy with the help of intermittent ground station updates. Clohessy-Wiltshire (CW) dynamics predict the state of the satellite/inertial navigation system (INS) by determining the deviations of the INS from a nominal circular orbit. During periods of ground contact aquisition, the external ground software sends state updates treated as truth data into the INS. During satellite thrusting in periods of loss of contact, an accelerometer measures thrust. Accelerations, ground software state updates, and CW dynamics are incorperated into a Kalman Filter (KF) to produce a final estimate.

The code in this repository falls into three main categories:

1. Matlab code to develop a Kalman Filter utilizing the Clohessy-Wiltshire equations of motion to determine the position and velocity of a satellites in a lunar orbit.

2. C/C++ code to implement the CW KF on a Teensy 4.1 microcontroller.

3. Analysis of physical testing of the Teensy implementation. Analysis completed in Matlab.

Folder Descriptions

1. _Archive - Largely depricated early files from experimentation
2. Figures - Relevant images depicting the results from the KF development and testing analysis.
3. GAINS_FSW - Main flight software. C/C++ CW KF implementation for a Teensy 4.1 microcontroller.
4. Integration Methods - Exporation of numerical integration methods using continous differentiatable sample data.
5. Kalman Filter - Matlab development of the Kalman Filter
6. Testing - CNC - Analysis of testing of the KF on the Teensy using data from moving the INS in a circle on a CNC mill to simulate forces from a thrusting satellite.
7. Testing - Temperature and Bias Calibration - Analysis of static heating and cooling the INS to determine calibration parameters to remove bias and scale factor from the accelerometer signals in the FSW.

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Flight Software

Prerequisites

• Microsoft VSCode
• PlatformIO extension for VSCode
• GAINS PCB with Teensy 4.1
• Ethernet cable
• Micro-USB cable
• Internet Router
• Ability to set static IP adresses on the router

Flight Software Initialization

1. Click on the PlatformIO button on the left hand side of VSCode
2. Under the Quick Access menu, select PIO Home > Open
3. Select Open Project
4. Open the GAINS_FSW directory
5. The PlatformIO extension should initialize
6. Connect the Micro-USB port on the Teensy 4.1 to the computer running VSCode/PIO
7. Connect the both the computer and the ethernet port on the GAINS PCB to the same router/LAN
8. Ensure the Teensy is recognized by the computer
   1. Navigate to PIO Home
   2. Select the Devices tab on the left
   3. Under Serial, click the Refresh button and ensure the Teensy is listed (likely "COM#")
9. Click the Upload button (symbol: rightwards arrow) on the bottom left of VSCode
10. Once program compilation and upload is complete, click the Serial Monitor button (symbol: electrical plug) on the bottom left of VSCode
11. The Serial Monitor should open. After a few seconds the MAC address and other information should be displayed.
12. Assign the Teensy a static IP address on the network using the MAC address
13. Configure the correct IP addresses and ports in the main.cpp file under the src.
14. Complete steps 9-11 again. The Ground Software should now be recieving packets.

Library Information

• The main C++ file is under GAINS_FSW/src/main.cpp
• NativeEthernet is used for external communications: GAINS_FSW/lib/NativeEthernet
• CControl is used for linear algebra: GAINS_FSW/lib/CControl
• SDFat is used for writing data to a microSD card using the reader on the Teensy 4.1: GAINS_FSW/lib/SDFat
• GAINS original files are under GAINS_FSW/lib/GAINS
  • ccsd implements the CCSD Space Packet Protocol to encode/decode packets to/from the ground software
  • GAINSEthernet wraps the NativeEthernet library and the CCSD packet encoding to provide one interface for GAINS to communicate over ethernet
  • kf handles all of the Kalman Filtering operations. See the Matlab scripts under Kalman Filter for understanding. Boolean CW_or_K configures usage of Clohessy-Wiltshire or kinematic dynamics
  • operations contains some helper functions for linear algebra and KF execution
  • SDRW handles SD card memory operations
  • sensor handles reading and processing data from the accelerometer