GOMX-3 is a CubeSat with several payloads. One of them is a software defined radio configured to read ADS-B signals sent by commercial aircraft. The idea is that a satellite can monitor aircraft over oceans and other places where there no RADAR coverage. ADB-S transmits the aircraft’s ID, its position, altitude, and intent.
The problem is that ADS-B has a short-range (about 80 nautical miles). GOMX-1 proved that the signals can be captured from orbit. GOMX-3 has more capability. The satellite has a helical antenna and an FPGA.
The people behind the satellite, GomSpace, has a complete parser for the ADS-B data beacons and [destevez] has it rolled into a GNU Radio module. There’s a good representation of captured data on a map in [destevez’s] blog post. If you want something less interactive, you can see a static map of all collected data. If you want to try your hand at picking up GOMX-3, you can hear it transmitting in the video below.