https://discosat.dk/index.php/2022/01/groundstation-workshop/
The DISCO project will launch 3 satellites into Low Earth Orbit over the next three years. To communicate with the satellites we need to have ground stations that manage the radio communications links for telemetry and data transfer.
The DISCO project is building both fixed ground stations at the participating universities, as well as mobile ground stations that can be loaned to schools in the program.
In this workshop we cover the basics of ground station operation and building including demos and a chance to get hands on experience with a range of equipment, both mobile and fixed equipment that will be later installed at ITU.
This workshop is oriented to build an Open Source satellite tracking. First, we're going to use Python with Skyfield library and Celestrak to receive the orbit from many satellites. Second, we will use Arduino, one 180 servo motor, and a 360 servo motor to point them.
- You can use Python in your web navigator and gmail account: [Google Colab] https://colab.research.google.com/ or install it in your computer: Anaconda.
- With Arduino at the moment, the best option is installing on the computer (there is a beta online version), Arduino
You can run the code in the selected environment without issues.
Install the library:
- Google colab: pip install skyfield
- Computer: Windows/Mac/Linux Search -> Anconda pront -> pip install skyfield and pip install pyserial
Test the library:
#Library
from skyfield.api import load, wgs84
# Create a timescale and ask the current time.
ts = load.timescale()
t = ts.now()
# Load the JPL ephemeris DE421 (covers 1900-2050).
planets = load('de421.bsp')
earth, mars = planets['earth'], planets['mars']
# What's the position of Mars, viewed from Earth?
astrometric = earth.at(t).observe(mars)
ra, dec, distance = astrometric.radec()
print(ra)
print(dec)
print(distance)Get the satellites information:
#print satellites
stations_url = 'http://celestrak.com/NORAD/elements/stations.txt'
satellites = load.tle_file(stations_url)
print('Loaded', len(satellites), 'satellites')
#loop satellites
by_name = {sat.name: sat for sat in satellites}
for i in by_name:
print(i)When was the last connection to Earth from each satellite:
t = ts.now()
for i in range(0,len(satellites)):
satellite=satellites[i]
days = t - satellite.epoch
print('Satellite: ',satellite.name)
print('{:.3f} days away from epoch'.format(days))Find the time that we can track satellites in our specific location
#ITU LATITUDE AND LOGITUDE
bluffton = wgs84.latlon(+55.65, +12.59)
#days that we like to track satellites
t0 = ts.utc(2022, 3, 14)
t1 = ts.utc(2022, 3, 15)
for i in range(0,len(satellites)):
satellite=satellites[i]
t, events = satellite.find_events(bluffton, t0, t1, altitude_degrees=30.0)
for ti, event in zip(t, events):
name = ('rise above 30°', 'culminate', 'set below 30°')[event]
times=ti.utc_strftime('%Y %b %d %H:%M:%S')
aux=list(times)
hour_max=int(aux[12])
hour_min=int(aux[13])
hour=hour_max+hour_min
if(hour>8 and hour < 18):
print('Satellite: ',satellite.name)
print(ti.utc_strftime('%Y %b %d %H:%M:%S'), name)
print(ti.utc_strftime('%Y %b %d %H:%M:%S'), name)Select the satellite and receive his coordinates
# You can instead use ts.now() for the current time
t = ts.now()
satellite = by_name['AEROCUBE 12A']
geocentric = satellite.at(t)
print(geocentric.position.km)
#location
lat, lon = wgs84.latlon_of(geocentric)
print('Latitude:', lat)
print('Longitude:', lon)
difference = satellite - bluffton
topocentric = difference.at(t)
alt, az, distance = topocentric.altaz()
print('Altitude:',alt.degrees*-1)
print('Azimuth:', az.degrees)
print('Distance: {:.1f} km'.format(distance.km))To check latitude and longitud, you can check: n2yo.
To determine the COM communication, check this: Find Arduino port or Arduino support Send the azimuth and altitude to Arduino board:
import serial,time
if alt.degrees<0:
alti=int(alt.degrees*-1)
else:
alti=int(alt.degrees*-1)
azi=int(round(az.degrees,0))
message=str(azi)+":"+str(alti)Run this code just one time in your pc
import serial
ser = serial.Serial('COMX', 9600) -> COM communication before mentionedRun this section each time that you what to track another satellite.
ser.open()
ser.write(message.encode())
ser.close()If you're working on GoogleColab:
if alt.degrees<0:
alti=int(alt.degrees*-1)
else:
alti=int(alt.degrees*-1)
azi=int(round(az.degrees,0))
message=str(azi)+":"+str(alti)
print(message)Copy the message and put it in Arduino Serial monitor
After you have uploaded this sketch onto your Arduino, click on the right-most button on the toolbar in the Arduino IDE. The button is circled below. The following window will open. This window is called the Serial Monitor and it is part of the Arduino IDE software.
Install the FeedBackServo library. Add the zip library .
#include "FeedBackServo.h"
#include <Servo.h>
Servo myservo; // create servo object to control a servo
// define feedback signal pin and servo control pin
#define FEEDBACK_PIN 2
#define SERVO_PIN 3
// set feedback signal pin number
FeedBackServo servo = FeedBackServo(FEEDBACK_PIN);
int azimut=0;
int elevation=0;
void setup() {
// set servo control pin number
servo.setServoControl(SERVO_PIN);
servo.setKp(1.0);
Serial.begin(9600);
servo.rotate(0, 4);
myservo.attach(9); // attaches the servo on pin 9 to the servo object
myservo.write(0);
delay(1000);
}
void loop() {
// rotate servo to 270 and -180 degrees(with contains +-4 degrees error) each 1 second.
if(Serial.available()>0){
String data=Serial.readString();
int dot=data.indexOf(':');
String azi=data.substring(0,dot);
String ele=data.substring(dot+1);
azimut=azi.toInt();
elevation=ele.toInt();
// Serial.println(elevation);
// Serial.println(azimut);
}
myservo.write(elevation);
servo.rotate(azimut,4);
delay(1000);
}
Use the compass of your cellphone to determine the north and put the pointer in that direction before sending satellites coordinates to Arduino.
