Conceptual Operations

What pFS should be able to do in-flight conceptually

General Aspects of pFS

The purpose of the 2019-20 TJREVERB mission is to test the usability of Iridium radio in Low Earth Orbit. Since the Iridium radio is not verified to work in LEO, another radio called the APRS radio is used as a control group. All critical messages from the ground station to the satellite are sent through the APRS radio.

Critical Messages include:

• Telemetry dumps

• Command Execution messages

• APRS echos

To test the usability of the Iridium radio, all non critical messages are sent through the Iridium radio.

Non Critical Messages include:

• Heartbeat messages

Critical Messages

• Telemetry Dumps

  • On a set interval, the satellite will send a collection of all the data it has collected through APRS

• APRS echos

  • The physical APRS radio sends automatic echo messages to the ground station. This aspect is not controlled by the flight software whatsoever

• Command Execution

  • The TJREVERB groundstation should be able to send a message to the satellite via the APRS radio, containing a message which describes a specific function the flight software should execute.

    • If the most recent telemetry data is required by the groundstation, the TJREVERB groundstation should be able to send a message via the APRS radio telling the satellite to trigger a telemetry dump regardless of the interval. The flight software should receive such a message through the APRS radio, recognize the message as a command, and follow through with the execution of that command

Non Critical Messages

• Heartbeat messages

  • On a set interval, the satellite will send a basic message(i.e 'I'M ALIVE') through the Iridium radio for the sake of using the iridium radio

Startup

This is how pFS should behave when flight-pi boots up for the first time.

1. When the flight computer(flight-pi) first boots, the computer shall run the main.py file to begin the initialization of core

2. When core is initialized, it shall read from the config and initialize all submodules regardless of order. In addition it shall initialize all other required variables.

3. After core is initialized, main.pyshall call the start() method in core which will begin the startup sequence

4. In the startup sequence, core shall call the start() method for all the submodules listed under ‘A’ submodules. Afterwards, core shall determine if it is booting up for the first time and sleep for 30 minutes if it is the first boot before initializing ‘B’ and ‘C’ submodules. If it is not the first boot, core shall ignore the 30 minute sleep period

5. After starting all submodules, core shall iterate through its processesand start all of its processes

Here is an excerpt of config/config_default.yml that outlines the startup process for core:

config/config_default.yml

core:
    modules:
        A:
            - eps
            - command_ingest
        B:
            - antenna_deployer
        C:
            - aprs
            - iridium
            - telemetry

Command Ingest

It would be helpful to read about message formatting before reading this section

1. When APRS receives a message from the ground station, it shall send the message to telemetry for processing

2. Once telemetry determines the message is of type Command, it shall send send the message to command_ingest

3. Once command_ingest encounters the message, it shall parse the message and determine the corresponding function to execute and then execute it

4. On a successful execution, command_ingest shall send a message through APRS that a command was executed successfully

5. On an unsuccessful execution, command_ingest shall send a message through APRS that a command was not executed successfully.

Dumps and Heartbeats

On a set interval, the satellite shall send data dumps and heartbeat messages to deliver data to the groundstation.

Telemetry Dump

Every hour, the satellite shall send all telemetry data collected through the aprs radio. The satellite shall purge the data collected once it has been sent to the groundstation. This dump message is flagged as a Critical Message.

Telemetry Heartbeat

Every hour, the satellite shall send a simple, "I'M ALIVE", message through the iridium radio. This heartbeat message is flagged as a Non Critical Message.

Modes

Modes