Usage of light emitting diodes for small satellites tracking, early identification after launch and light-based communication

With the increasing number of cluster and mega-constellation launches, there is a urgent need for new spacecraft tracking techniques during all the mission phases, from in-orbit deployment to disposal. In this framework, the usage of Light Emitting Diodes (LEDs) on the spacecraft external surfaces can provide significant improvements to the small satellites early identification after launch in large clusters and for orbit and attitude determination. When applying the conventional RF-based identification to large cluster launches, strong uncertainties on the identity of small satellites of the same cluster remain even months after the launch. The implementation of LEDs can provide immediate recognition after deployment, if assigning specific flashing patterns to each satellite, as for aircraft recognition in trafficked airfields. The implementation of LEDs can also improve the precision achievable by optical orbit determination, making the satellites traceable throughout the eclipse phase. Any optical observatory can acquire the satellite LEDs flashes, thus with a great improvement of the spacecraft optical traceability and of the achieved precision in orbit and attitude determination. The LED-based orbit determination is focused on the celestial coordinates acquisition with respect to the background stellar field. Attitude reconstruction is possible when implementing LEDs, executing different flashing patterns, on different surfaces of the spacecraft. The improvement of orbit determination could help to augment the situational awareness for the small satellites population, as well as performing less and more accurate collision avoidance manoeuvres. The attitude determination can be applicable both for an improved trajectory estimation at low altitudes, when heavily influenced by drag force, and for planning future Active Debris Removal (ADR) missions. As example of LEDs in-orbit applications, the LEDSAT CubeSat, conceived by Sapienza University of Rome and by the University of Michigan, is equipping LEDs on all its external faces. The CubeSat is part of the Italian Space Agency (ASI) IKUNS Programme, it has been selected for the second edition of the ESA Fly Your Satellite! Programme, and it will be launched in 2020. This paper will describe the solutions offered by the implementation of LEDs on the external surfaces of small satellites for early recognition after deployment in large clusters and orbit and attitude determination. All the improvements offered by the LEDs in the framework of orbital debris mitigation, improved orbit determination and clusters early identification will be presented. Finally, an example of LED-based operations will be presented with an overview of the LEDSAT CubeSat mission.