Session
Poster Session 2
Location
Salt Palace Convention Center, Salt Lake City, UT
Abstract
Failure of the communication subsystem has been responsible for approximately 20% of small satellite mission failures over the period between 2000 and 2019. Insufficient system-level integration and testing has been cited as one reason why corrective actions weren’t taken before launch to prevent such failures. Here, we introduce a relatively inexpensive GTEM-cell-based dynamic channel emulator that will permit designers of CubeSats operating at frequencies up to 20 GHz to evaluate their spacecraft’s communications over multiple simulated passes with the spacecraft in as close to over-the-air flight condition as possible, including fully deployed antennas. Using this over-the-air channel emulator allows the designer to confirm that the communications subsystem will function correctly while experiencing: 1) path loss and Doppler shift, 2) random fading due to satellite motion or rain fading, and/or 3) noise, interference, or scintillation, as applicable, that perfectly matches what would be experienced during actual satellite passes.
Our dynamic channel emulator comprises a controller, a pair of channel emulators that operate on the uplink and downlink, respectively, a diplexer, and a GTEM cell into which the satellite is placed. The compact size and relatively low cost of a GTEM cell are significant advantages compared to a full-size anechoic chamber or an open area test site. The ground station transmitter and receiver are disconnected from the ground station antennas and transmitter power amplifier and connected to the uplink and downlink channel emulators. The instantaneous attenuation and Doppler shift on the uplink and downlink are set by a pair of channel emulators of our own design that are driven by standard orbit propagation software (free space path loss and Doppler shift) augmented our own channel models (excess fading due to high frequency signal propagation through hydrometeors and spacecraft tumbling). A fixed attenuator emulates the minimum path loss on the link while a programmable attenuator accounts for excess fading associated with increases in distance, polarization mismatch, or the presence of hydrometeors along the path. An SSB modulator implemented using a software defined radio implements the Doppler shift associated with orbital motion as the satellite approaches and then recedes from the Earth station. A circulator directs signals from the satellite in the GTEM cell into the downlink path, and signals from the uplink path into the satellite in the GTEM cell. It also isolates the uplink and downlink chains from each other.
Tests conducted using our dynamic channel emulator can confirm that the communications subsystem will function correctly under ultra-realistic channel conditions, and significantly lower the risk of communications subsystem failure. The basic system can be upgraded to allow simultaneous testing of: 1) the GNSS subsystem by applying simulated GNSS signals that account for the position, speed, and orientation of the CubeSat with respect to the simulated constellation, and 2) the CubeSat’s electrical power system by illuminating the solar cells using a solar simulator. If the standard radio frequency absorber is replaced with closed cell foam, suitable fans and air filters are installed, and appropriate cleaning protocols followed, the GTEM cell can be upgraded to provide an ISO 8 clean room environment and used for flight model testing.
Document Type
Event
A Dynamic Wireless Channel Emulator for Realistic CubeSat Testing
Salt Palace Convention Center, Salt Lake City, UT
Failure of the communication subsystem has been responsible for approximately 20% of small satellite mission failures over the period between 2000 and 2019. Insufficient system-level integration and testing has been cited as one reason why corrective actions weren’t taken before launch to prevent such failures. Here, we introduce a relatively inexpensive GTEM-cell-based dynamic channel emulator that will permit designers of CubeSats operating at frequencies up to 20 GHz to evaluate their spacecraft’s communications over multiple simulated passes with the spacecraft in as close to over-the-air flight condition as possible, including fully deployed antennas. Using this over-the-air channel emulator allows the designer to confirm that the communications subsystem will function correctly while experiencing: 1) path loss and Doppler shift, 2) random fading due to satellite motion or rain fading, and/or 3) noise, interference, or scintillation, as applicable, that perfectly matches what would be experienced during actual satellite passes.
Our dynamic channel emulator comprises a controller, a pair of channel emulators that operate on the uplink and downlink, respectively, a diplexer, and a GTEM cell into which the satellite is placed. The compact size and relatively low cost of a GTEM cell are significant advantages compared to a full-size anechoic chamber or an open area test site. The ground station transmitter and receiver are disconnected from the ground station antennas and transmitter power amplifier and connected to the uplink and downlink channel emulators. The instantaneous attenuation and Doppler shift on the uplink and downlink are set by a pair of channel emulators of our own design that are driven by standard orbit propagation software (free space path loss and Doppler shift) augmented our own channel models (excess fading due to high frequency signal propagation through hydrometeors and spacecraft tumbling). A fixed attenuator emulates the minimum path loss on the link while a programmable attenuator accounts for excess fading associated with increases in distance, polarization mismatch, or the presence of hydrometeors along the path. An SSB modulator implemented using a software defined radio implements the Doppler shift associated with orbital motion as the satellite approaches and then recedes from the Earth station. A circulator directs signals from the satellite in the GTEM cell into the downlink path, and signals from the uplink path into the satellite in the GTEM cell. It also isolates the uplink and downlink chains from each other.
Tests conducted using our dynamic channel emulator can confirm that the communications subsystem will function correctly under ultra-realistic channel conditions, and significantly lower the risk of communications subsystem failure. The basic system can be upgraded to allow simultaneous testing of: 1) the GNSS subsystem by applying simulated GNSS signals that account for the position, speed, and orientation of the CubeSat with respect to the simulated constellation, and 2) the CubeSat’s electrical power system by illuminating the solar cells using a solar simulator. If the standard radio frequency absorber is replaced with closed cell foam, suitable fans and air filters are installed, and appropriate cleaning protocols followed, the GTEM cell can be upgraded to provide an ISO 8 clean room environment and used for flight model testing.
