A Flexible and Autonomous Communication Subsystem for Constellations of Small-Satellites

Abstract

During the past 20 years, space communications technologies have shown limited progress in comparison to commercially available solutions on Earth. Such an evolution was not mandatory as Earth-to-Satellite (ESL) communication architecture is still conceived as a telecommand in the uplink, and telemetry and payload data on the downlink. However, communication systems designed to cope with this asymmetry are not suitable for inter-satellite (ISL) links which require a non-hierarchical and unassisted operation. In particular, ISLs can be of significant importance with the advent of small-satellite as they allow achieving common mission objectives by taking advantage of a distributed architecture. Nevertheless, since small-satellite platforms are resource-constrained, accounting with separate ESL and ISL subsystems can sometimes be prohibitive. Therefore, we envisioned the design of an autonomous and flexible communication subsystem capable of operating over a wide variety of scenarios. To this end, we present the recently developed STI-PRX-01: a CCSDS Proximity-1 protocol modem that can operate with different radio-frequency front-ends under varying communication parameters which can be autonomously negotiated upon link establishment between spacecrafts (for ISLs), or ground segment (for ESLs). Between these parameters we highlight frequency channel, modulation, datarate, error-correcting codes, transmitting power, etc. Furthermore, the chosen protocol allows for unassisted recovery of lost or corrupted frames enabling the system to efficiently operate over marginal and variable link budgets. In this paper, we describe the architecture that supports this error-recovery mechanisms and dynamic parameter negotiation to later provide an overview of the hardware of STI-PRX-01. Finally, we supply and analyze the first measurements obtained from the engineering model in order to demonstrate the benefits of this novel communication approach.