Detection of objects on LEO using signals of opportunity

Recently more attention has been paid to the space debris orbiting the Earth. Until 5 July 2016, the United States Strategic Command tracked a total of 17 729 artificial objects including 1419 operational satellites[1]. Information about the current position of these objects should be taken into consideration while planning space missions. There are various solutions to cope with the problem considered. The main objective was to design a low-cost system that would detect objects which do not emit their own signal and can cause collision with spacecrafts. The reception system is based on Doppler detection. One of the methods of gathering information about space objects which are changing their position relatively to the Earth is using the continuous wave reflection. The reflected outgoing sinusoidal wave is Doppler-shifted to higher or lower frequency according to whether it has a line of sight velocity towards or away from the receiver. It is also common to use this method for meteor detection. In this project we use signal emitted by the Graves Radar. Graves is a French radar-based space surveillance system which transmitter is located in the east of France and generates continuous wave with a frequency 143,05 MHz. In order to receive the reflected signal we built the passive radar which works on frequency similar to Graves. It is located 15 km to the south of Warsaw centre, thanks to its position it is possible to avoid radio noise coming from the city. Our construction includes directional antenna designed for 144 MHz and FUNcube Dongle Pro+. The FUNcube Dongle Pro+ is a software-defined radio (SDR) covering all broadcast andamateur radio bands from 150 kHz to 1,9 GHz. We use Orbitron as a software. Orbitron is an application related to satellite tracking. We can predict what kind of data will we receive from our construction by verifying it in application. Our first tests of the system were performed on objects with a well known trajectory and velocity. Also a correlation with data from two-line element set (TLE) was made. TLE is a data format encoding a list of orbital elements of an Earth-orbiting object for a given point in time. Results show spectrogram of a signal reflected from satellite with a Doppler shift that fits our expectations. The flying object generated a Doppler shift of about 10 kHz below the carrier frequency. Although the first data come from objects with a large size and mass above 1 ton, in further observations we expect to receive reflection from satellites which mass is less than 10 kg.