Microsatellite constellation geolocates RF signals

Space Flight Laboratory (SFL) has launched three formation-flying HawkEye 360 Pathfinder 15-kilogram, 20 x 27 x 44-centimeter microsatellites designed to detect and geolocate radio frequency (RF) signals.

Hawkeye 360 Pathfinder satellite trio flies in formation, seeking RF signals from Earth. (Image: UTIAS Space Flight Laboratory)

The target signals emanate from VHF radios, maritime radar systems, automatic identification system (AIS) beacons, very small aperture terminal (VSAT) communication systems and emergency beacons. HawkEye 360 applies advanced RF analytics to the data to assess suspicious vessel activity, survey communication frequency interference and direct search-and-rescue.

Precise formation flying is critical, as the relative position of each satellite must be known to accurately geolocate transmission sources. The satellites carry space-qualified GPS receivers and high-performance attitude control systems to keep them stable in orbit.

Flying in formation, two or all three satellites may receive the same transmission when it originates from their common footprint. The signal’s different times of arrival at each satellite and their different apparent center frequencies (Doppler) will enable onboard comparison of time-of-arrival and frequency-of-arrival measurements to then calculate the transmitter’s position.

The onboard GPS receivers provide precise estimates for the position and velocity of the receivers, information required for multilateration. The satellites further synchronize their clocks using GPS receivers, which also stabilize the phase-locked loops governing the tuning frequency in the RF tuners.

The satellites were built by Deep Space Industries of San Jose, California, and University of Toronto, Institute for Aerospace Studies/Space Flight Laboratory (UTIAS/SFL). They were launched in December 2018 into low-Earth orbit.