Omnidirectional Optical Communicator

Abstract

We are developing an inter-satellite omnidirectional optical communicator (ISOC) that will enable cross-link communications between spacecraft at Gbps data rates over distances of up to thousands of kilometers in free space. The ISOC will allow superfast cross-links and will be a technology enabler for swarms and formation flying spacecraft. The ISOC under development features a truncated dodecahedron geometry that can hold an array of fast photodiode detectors and gimbal-less MEMS scanning mirrors. The main goals of the ISOC development include: 1) full sky coverage, 2) Gbps data rates and 3) the ability to maintain multiple simultaneous links. We have developed two omnidirectional communicator prototypes capable of full-duplex operation. We are using advanced single-mode laser diodes operating at 850 nm capable of producing hundreds of milliwatts of laser radiation. We are also employing MEMS-based beam steering mirrors, and fast PIN photodiodes to achieve long-range communications. The ultimate goal of the project is to achieve full duplex operation at 1 Gbps data rates over 200 km and slightly lower data rates at longer distances. In this paper we describe the overall ISOC architecture and present the design tradeoffs for gigabit data-rate operation. We also present preliminary NRZ On-Off Keying communications simulation results obtained using our optical link budget model. The ISOC is ideally suited for crosslink communications among small spacecraft, especially for those forming a swarm and/or a constellation. Small spacecraft furnished with ISOC communications systems, should be able to communicate at gigabit per second rates over long distances. This data rate enhancement can allow real-time, global science measurements and/or ultra-high fidelity observations from tens or hundreds of Earth-orbiting satellites, or permit high-bandwidth, direct-to-earth communications for planetary missions.