Communication support for future earth science space missions

Abstract

The NASA Earth Science Enterprise’s (ESE’s) vision for the future involves a scenario where all Earth observing spacecraft form a distributed network to provide real-time multi-sensor information transfer to users on the ground. This scenario will require sensors and instruments on spacecraft to become addressable nodes in a communication network. These include missions consisting of single spacecraft to multiple spacecraft flying in formation, in clusters, or in constellations. The present labor-intensive, mission-specific techniques for processing and routing data do not scale well and will become prohibitively expensive. To enable this vision, there is a critical need for advanced communications and dynamic network connectivity to provide broad coverage and intelligent-based real-time data delivery to scientists. These new missions will introduce a number of complex routing, network control, scheduling, data management and communication problems that need to be studied in detail. We introduce the current state-of-the-art in space communications for ESE, discuss potential benefits of a Uniform Space Network infrastructure and list some specific challenges in areas such as routing, transport layer and multiple access in this environment. We address issues related to extending this network in space and typical communication requirements and topologies for Earth Science missions and present a dynamic routing algorithm, MDRSH, for dynamically directing traffic from mission spacecraft to ground facilities. We present a simulation framework for studying future space missions and for testing newly developed protocols in such missions. We also present a case study for optimizing data downloads for a typical future mission scenario.

Introduction

The mission of NASA’s Earth Science Enterprise (ESE) is to understand the total Earth system and the effects of natural and human-induced changes on the global environment and to enable improved prediction of climate, weather, and natural hazards for present and future generations. The scientific goal of ESE is to observe, understand and model the Earth system and learn how it is changing, as well as the consequences for life on Earth. To achieve these goals, scientists on the ground need efficient means of accessing data collected by mission spacecraft. At the same time, it is essential to ensure fast and reliable ways of exchanging vital control information from ground facilities to spacecraft, from spacecraft to ground, or even between different mission spacecraft. Both requirements point to the necessity of a reliable and efficient mission communication support infrastructure.

ESE’s vision for the future involves a scenario where all Earth observing spacecraft form a distributed network to provide real-time multi-sensor information transfer directly to users on the ground. This scenario will require sensors and instruments on spacecraft to become addressable nodes in a communication network. These include missions consisting of single spacecraft to multiple spacecraft flying in formation, in clusters, or in constellations. The present labor-intensive, mission-specific techniques for processing and routing data do not scale well and will become prohibitively expensive. To enable this vision, there is a critical need for advanced communications and dynamic network connectivity to provide broad coverage and intelligent-based real-time data delivery to scientists. These new missions will introduce a number of complex routing, network control, scheduling, data management and communication problems that need to be studied in detail. Although there is related research and development work in wireless networking and some developments in the commercial satellite industry, no current work is addressing the unique topologies and special requirements of space-based networking.

We focus on work attempting to leverage current research in wireless and hybrid networks and deliver a state-of-the-art communication infrastructure design that can support IP-enabled spacecraft in a cost-efficient manner. Our ultimate goal would be to address the ESE mission communication requirements directly and provide solutions that will enable the simplest, most cost-effective delivery of science data when and where needed.

The structure of this paper is as follows: We introduce the current state-of-the-art in space communications for ESE, discuss potential benefits of a Uniform Space Network infrastructure and list some specific challenges in areas such as routing, transport layer and multiple access and some related work that can be applied in this case (Section 2). We define the communications characteristics of ESE missions (Section 3) and introduce a simple dynamic routing algorithm for space networks (Section 4). Finally, we discuss a simulation study for a sample case of a future mission (in this case a four-spacecraft constellation) (Section 5) and conclude with a summary and suggestions for further work.