PY4 is a joint CMU / NASA Ames Small Spacecraft Constellation.

General mission webpage: to be announced

[!TIP] You can manually parse PY4 beacons with this simple web app: https://maholli.github.io/PY4_gs/

Receiving & decoding PY4 beacon packets

Each of the four PY4 spacecraft transmit a LoRa modulated beacon packet every 30 seconds.

PY4 Beacon modulation parameters

Hardware

This repo supports only RPI-based stations for now.

Python Dependencies

General python packages

# uncomment below if you have trouble with pip. Adjust python version accordingly.
# sudo rm /usr/lib/python3.12/EXTERNALLY-MANAGED
pip install --upgrade paho-mqtt==1.6.1
pip install msgpack numpy

Setting up CircuitPython (if not done already)

sudo apt update && sudo apt upgrade -y
sudo apt-get update && sudo apt-get upgrade -y
sudo apt-get install -y python3-pip ; sudo apt install --upgrade python3-setuptools
sudo raspi-config nonint do_i2c 0
sudo raspi-config nonint do_spi 0
sudo raspi-config nonint do_serial_hw 0
sudo raspi-config nonint do_ssh 0
sudo raspi-config nonint do_camera 0
sudo raspi-config nonint disable_raspi_config_at_boot 0
sudo apt-get install -y i2c-tools libgpiod-dev python3-libgpiod
pip3 install --upgrade RPi.GPIO ; pip3 install --upgrade adafruit-blinka

RX Operation

There are two options for RX operation:

1. py4_rx.py logs all packets to a file.
2. py4_rx_mqtt.py logs all packets to a file + attempts to send each packet to the PY4 mqtt server.

If your groundstation has internet access, please consider running py4_rx_mqtt.py (no additional setup required) to help us keep track of beacon packets over time. A public grafana dashboard will be available to view historic data.

Default radio config is an unmodified Adafruit LoRa Bonnet connected to the RPI. See rpi_radio_helpers.py to adjust pin assignments or LoRa parameters.

To start the script:

cd PY_gs/rx_only && python3 py4_rx_mqtt.py

By default, the ground station will parse and print a formatted version of each beacon. To disable this, comment out the PARSE_AND_PRINT_BEACONS line of the respective script.

Testing your RX station

It can be helpful to test your RX ground station without relying on a satellite pass. Below is a 60-byte packet exactly as it would be stored in the radio's FIFO buffer upon successful beacon reception.

# python bytes format
b'IL\x00\x00\x05\x00\x00\x00\x808mI\xf3\x11R\x00\n@\t\x00\x00\x00\xb1\x00R\x01\xa4\x00\x01\t\x00Q\xfe\xb5\xfe\xdd\xff\x02\x00\x1f\x00\x18\xc6\x00x\x00H\x01\x98\x04\x13\x0e\xd8\x00\x00\x00\x00\x00\x00I'

If you transmit the above packet from a second rfm9x radio setup while your RX station is running, you should see a parsed beacon message output in the terminal of your RX station running the python script.

NOTE: if you're using a CircuitPython library (pycubed_rfm9x.py, adafruit_rfm9x.py, etc...) to transmit the dummy packet, the library automatically inserts a 4-byte RadioHead header to the front of the data payload. Therefore, to transmit the above 60-byte payload you will need to trim the first 4 bytes off the dummy packet as well as set the destination and node bytes of the radio object as shown below. RadioHead header format: [TO] [FROM] [MSG ID] [FLAGS] ([MSG ID] and [FLAGS] will always be 0 in a beacon packet)

#!/usr/bin/python3

import time,busio,board
from digitalio import DigitalInOut, Pull
import pycubed_rfm9x

# radio1 - STOCK ADAFRUIT BONNET https://www.adafruit.com/product/4074
CS1    = DigitalInOut(board.CE1)
RESET1 = DigitalInOut(board.D25)
IRQ1   = DigitalInOut(board.D22)

# set pins before radio init
CS1.switch_to_output(value=True)
RESET1.switch_to_output(value=True)
IRQ1.pull=Pull.DOWN

cfg = {
    'r1b':(1,7,62500,1),  # default radio1 beacon config (CRC,SF,BW,LDRO) symb=2ms
}

# dummy 60-byte beacon packet to send
dummy_packet = b'IL\x00\x00\x05\x00\x00\x00\x808mI\xf3\x11R\x00\n@\t\x00\x00\x00\xb1\x00R\x01\xa4\x00\x01\t\x00Q\xfe\xb5\xfe\xdd\xff\x02\x00\x1f\x00\x18\xc6\x00x\x00H\x01\x98\x04\x13\x0e\xd8\x00\x00\x00\x00\x00\x00I'

spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)
radio1=pycubed_rfm9x.RFM9x(spi, CS1, RESET1, 915.6, code_rate=8, baudrate=5_000_000)
radio1.dio0 = IRQ1
radio1.node = dummy_packet[1]
radio1.ack_delay= 0.2
radio1.ack_wait = 2
radio1.set_params(cfg['r1b']) # default CRC True, SF7, BW62500
radio1.listen()

# set the node id to the one used in the packet
# set the destination byte and transmit the packet
radio1.send(dummy_packet[4:],
    # set the 4-byte RadioHead header from the first four bytes of the dummy packet
    destination=dummy_packet[0],node=dummy_packet[1],identifier=dummy_packet[2],flags=dummy_packet[3],
    keep_listening=True)