Automate Commanding the CubeSatSim to Change Configurations

[PapiSenpai]

Hello, as a beginner, I am not sure where to start. What I am trying to attempt is automating a command to change the frequency from the CubeSatSim when certain parameters determine a loss of connection. If you can provide me insight in where to start looking and how I can command the CubeSat from the ground station to change its frequency that would be greatly appreciated. I am assuming that I would have to command the modulator itself. Please help me, thank you.

[alanbjohnston]

For information on how the current Command and Control works, you should review https://github.com/alanbjohnston/CubeSatSim/wiki/Command-and-Control

The simplest command to send is DTMF, or tones sent by an HT radio. Right now, DTMF tones 1-5 and 10 and 11 are used to change modes and other commands. So you could pick another, such as tones 12 for your change frequency command. To activate it, you would transmit a 1 then a 2 then #.

The Python code that does this in in https://github.com/alanbjohnston/CubeSatSim/blob/master/dtmf_aprs_cc.py

For example, this snippet of code detects 11#:

	if ((line.find("DTMF>APDW15:t11#")) > 0):
		system("echo '\nTransmit Commands Mode!!\n'")
		mode = 'n'
		change_mode = True

So you could add some code such as:

	if ((line.find("DTMF>APDW15:t12#")) > 0):
		system("echo '\nIncrease frequency!!\n'")
		increase_frequency = True

Later in the code, you could detect this and call the script to change the frequency. Right now, the script config -F will prompt for a new frequency. Your code would need to extend this to increase the frequency by a set amount.

I hope this is helpful to you!

Alan

[PapiSenpai]

Thank you for the quick response! I will come back when I get a successful result. Another question on a similar note, is it possible to send a command to reboot the CubeSatSim and reinstall a working file that may have been tampered with by a malicious command? Ex. A malicious command sent that will be a script which will make the CubeSatSim give the wrong coordinates, or change/corrupt a file or system. I was thinking using a checksum in where it would check the integrity of files onboard the CubeSatSim and when it diverges from the original checksum, a command will be automatically sent by the ground station to replace the affected files or the OS altogether. This will be done using GNU Radio with the RTL-SDR. How would I implement a checksum? Process in mind: Configure core files onboard CubeSatSim that may be targeted with a checksum -> display in the serial monitor when a checksum is mismatched -> create a function within a GNU Radio block that will send a command when checksum is mismatched -> CubeSatSim receives command and reboots and reinstalls working files. Again, insight is greatly appreciated.

Pseudocode use of a Checksum:

while true; do
// Listen for incoming packets
packet=$(./receive_script) # custom script
// Check if packet is valid and signed
if [[ $packet == "REBOOT_CMD" ]]; then
sudo reboot
elif [[ $packet == "UPDATE_FILE" ]]; then
// write logic to fetch or accept new file and write it
fi
done