Improving Small Satellite Communications in Deep Space—A Review of the Existing Systems and Technologies With Recommendations for Improvement. Part I: Direct to Earth Links and SmallSat Telecommunications Equipment

Robotic exploration of the solar system using small satellites (SmallSats) is gaining popularity because of SmallSats' lower cost and faster development cycle compared to primary science missions. A potential obstacle for deployment of SmallSats in deep space is the limitation associated with the communications link imposed by SmallSats' frugal power and antenna size. These technical limitations constrain the range and throughput of SmallSats and may impact their navigation performance. To allow SmallSats to play a greater role in deep space science endeavors, we propose an enhanced communications architecture that will lessen the communications disparity between larger, more expensive missions and SmallSats. The objectives of the study are to define a communications architecture, in-flight and flight-to-ground, that is needed for planetary SmallSats, both standalone or in support of a larger mission; and to develop a guideline for primary spacecraft that would communicate with ride-along SmallSats. This work treats the space segment and the ground network as a whole to provide for improvements not only via investments in technology, but also via improvements in operational procedures. The study includes reviews of current communication concepts, technologies, and procedures, as well as an assessment of navigation needs, evaluation of the communication architecture performance for a range of destinations and applications, and identification of any gaps in capability. The study product is a set of recommendations to space agencies and the planetary SmallSat community. The main thrust of these recommendations is investment in technology, such as radios, antennas, protocols, and methodologies. The concepts for improving communications capability of deep space SmallSats are discussed in a series of three articles, Improving Small Satellite Communications in Deep Space. In this article, Part I, we discuss SmallSat direct-to-Earth links, as well as SmallSat communications equipment. In Part II, we discuss navigation topics, proximity links and networks, and the use of the communications channel for science observations. We present the ground network in Part III. Definitions and assumptions are provided here in Part I.