THE CALYPSO SPACECRAFT

Calypso is a 1U Cubesat mission conducted in cooperationwith the Aerospace Research & Engineering Systems Institute, Inc. to test systems for a translunar solar sail mission. Aphelion will fly the secondary optical communication payload and is supplying the solar panels and electrical power system for the spacecraft.

Our payload will demonstrate two key technologies that will allow low cost, purely optical satellite communication on both the uplink and downlink without the deployment of a sophisticated attitude control system.

• Directional, non-coherent visible light downlink at 4.5Mb/s
• Satellite wakeup communication uplink utilizing existing photovoltaic cells and ground-based laser transmitter

Free space optical communication techniques have been the subject of numerous investigations in recent years, with multiple missions expected to fly in the near future. Existing methods require high pointing accuracies, drastically driving up overall system cost. Recent developments in LED-based visible light communication (VLC) has convinced us that the technology has reached a critical level of maturity. On these premises, we developed a new optical communication system utilizing a VLC downlink and a high throughput, omnidirectional photovoltaic cell receiver system. Utilizing various modelling techniques and bench tests, we have demonstrated the system to be a feasible alternative to laser-based methods, opening up the path for the implementation of optical communication techniques on small spacecraft and as backup telemetry beacons.

The large surface area of the PV cells on a spacecraft provides a significant sensor area which can be utilized as an omnidirectional receiver on many solar panel layouts. Previous researchers have proposed the use of this unique asset as a backup communication system, realizing that a low cost, low power consumption uplink could be created by using the photovoltaics as a laser receiver. Such proposed systems have low data rates of around 10Kb/s, allowing them to serve as effective emergency, alternative band communication systems, but not as an operational uplink. On ground tests we have achieved data rates an order of magnitude higher than was previously demonstrated. This allows the use of the system as a primary uplink method, significantly saving on spacecraft system costs and mass budget by utilizing existing assets.