ProtoSat to Ground Station Over-the-Air Testing
Author: Alexander Doknjas
A critical test to perform before launch of satellite is an end-to-end Over-The-Air (OTA) test to confirm the link works all the way from the mission control software to the satellite with the ground station and free space in between. The FlatSat (satellite bus electronics connected to a ground control PC for firmware development and testing) has a RF link which includes a ground segment transceiver, variable attenuators, and circulator. This allows developers to run tests on FlatSat as if the link between FlatSat and the ground control PC was over the air. This extremely useful for testing everything on both the space and ground side on a day-to-day basis.
However, the full ground station is quite a bit more complex than this simplified model and the end-to-end test is required to ensure that we did not miss anything, specifically with the link between the ground control software and ground station. Ideally this test would be performed over a significant distance to simulate an actual link with the fully completed ground station and the flight unit before launch. However, we integrated the satellite back in June, so we have to use the prototype satellite (ProtoSat). This is one of the main functions of ProtoSat, it includes a flight electronics stack up (antenna, radio, computer, and power system) inside the satellite structure with solar panels, so the satellite side of link is as close to the actual flight unit as possible. Successful completion of this test validates that the link between the satellite and the ground actually works and increases everyone’s confidence in the ground control software and ground station.
On September 2022-09-19 we successfully completed this test. We were able to perform this test after integration of the flight unit because FlatSat gave us enough confidence that there would be no issues on the satellite side of the link. We demonstrated a ping-ack over the air, followed by a payload operation and data downlink. Next we ran our full suite of automated tests for ProtoSat, the same tests we ran after vibration testing to confirm everything was still working, but completely over the air and with the ground station. Everything performed well and it ran just as FlatSat does with its wired RF link.
Levente Checking the Power Levels on the Ground Station
The test did not use the ground station antennas, it used everything up to the antennas, but because the antennas are not yet mounted on the tower, we swapped in a handheld (tripod mounted) antenna for the test. Due to the satellite transmitter swamping the ground station receiver, we had to move the satellite inside and behind a few walls before the link was attenuated enough to get reliable communications.