A Message Transfer Service for Space Applications

Spacecraft applications that interact with on-board sensors, effectors, and major components have traditionally used private interfaces which are tightly bound to the interface details of the data links connecting these sub-systems. The latest spacecraft, which often include several powerful processors running real time operating systems, highspeed on-board networks, and intelligent peripherals, can support a more layered networked environment. Use of standard interfaces and networked elements is expected to yield reusable software and hardware components. Within CCSDS Panel 1K we have been developing such on-board interface standards. This paper will present a Message Transfer Service that defines a common API for use within a single spacecraft or among spacecraft flying in a constellation. CCSDS PANEL 1K INTRODUCTION The Consultative Committee on Space Data Systems (CCSDS) is an international volunteer organization of space agencies and industrial associates interested in mutually developing standard data handling techniques to support space research, including space science and applications. It has, over the years, published a series of standard recommendations for space communications, starting with physical layer modulation and coding, and including link layer and reliable data delivery over near Earth and Deep Space communication distances. See http://ccsds.org for details of the entire program and standards suite. Recent efforts have been focussed on providing Internet-like connectivity for mission operating in deep space and on providing multi-point connectivity among in-situ elements and spacecraft flying in constellations or other formations. Since missions are becoming increasingly interdependent, with one agency’s rover using another’s orbiting spacecraft to communicate to Earth through even a third agency’s ground station, interoperability and cross-support, the foundations of CCSDS agreements over the years, have become even more important. CCSDS Panel 1K is specifically focused on defining standard interfaces that are suitable for use on board spacecraft. The context of the Spacecraft Onboard Interface (SOIF) is the communications bus (network) onboard the spacecraft, and the elements connected to such busses [SOIF]. It does not necessarily include ground, spacelink, or special onboard interfaces where they are required, but instead seeks to define interface approaches to meet the broadest set of common instrument, sensor, and affector requirements. The scope includes all types of devices from large instruments to small engineering sensors like a temperature sensor, and all types of spacecraft, from micro and small to large and/or manned, from LEO to deep space. See Figure 1, SOIF Context. The intent of SOIF is to define several levels of interfaces, which can be adopted, as desired, by compliant missions. These interface standards, at the physical, network, and applications layers provide services that permit device and application level portability, and thus promote reuse, risk reduction, and cost savings. Where many current missions develop applications that interact with devices directly at the data link layer, SOIF recommends use of a “convergence layer” that isolates applications from the vagaries of individual data links. This permits ∗ This work was performed at and under the direction of the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration. Copyright © 2002 by the California Institute of Technology. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Released to AIAA to publish in all forms