Abstract
SpaceWire is a point-to-point bit shipping protocol for high-speed data communication links and networks providing equipment compatibility and seamless component reusability. It has found great application in many space missions reducing the development cost, offering architectural flexibility, and improving reliability. This chapter delves into the standard describing the SpaceWire, focusing on the lower levels that play a key role in the electromagnetic behavior of the system and concern cable assemblies, shielding, bonding, and grounding. Findings regarding emissions affecting spacecraft components are presented as well as other EMC issues that have an impact on the system performance. Recent developments on the modelling of the cable of the system with a focus on radiated emissions of SpW systems are also presented and discussed.
TopIntroduction
SpaceWire is a standard for high-speed data communication links and networks primarily intended for use on spacecraft systems. SpaceWire was initially defined in the European Cooperation for Space Standardization (ECSS) standard ECSS-E50-12A in 2003. The SpaceWire standard was authored by Steve Parkes, the University of Dundee with contributions from many individuals within the SpaceWire Working Group from the European Space Agency (ESA), European Space Industry, Academia, and NASA. It was replaced by ECSS-E-ST-50-12C (ECSS Secretariat, 2008) to ensure the standard was following the new ECSS numbering system. There are no actual technical content differences between ECSS-E-50-12A and ECSS-ST-E-50-12C and any information relating to the ‘old’ ECSS-E-50-12A is still applicable to newer ECSS-ST-E-50-12C (“ECSS-E50-12A vs ECSS-E-ST-50-12C, what's the difference? | STAR-Dundee”, 2017; “SpaceWire - The Standard”, 2017).
The Standard specifies the physical interconnection media and data communication protocols to enable the reliable transmission of data at high‐speeds, between 2 Mb/s and 400 Mb/s, among units. SpaceWire links are full‐duplex, point‐to‐point, and serial data communication links. Since the SpaceWire standard was first published by the European Cooperation for Space Standardization, it has been adopted by ESA, National Aeronautics and Space Administration (NASA), Japan Aerospace Exploration Agency (JAXA), and Roscosmos State Corporation for Space Activities (ROSCOSMOS) for many missions and is being widely used on scientific, Earth observation, commercial and other spacecraft. Gaia, ExoMars, Bepi-Colombo, GOES-R, Lunar Reconnaissance Orbiter, ASTRO-H, and James Webb Space Telescope are among high-profile missions which use SpaceWire (Parkes, 2012).
The increasing need for spacecraft on‐board data handling applications slowly led to the development of SpaceWire technology. The Standard provides a formal basis for the exploitation of SpaceWire in a wide range of on‐board processing systems. For example, the integration and testing of complex on‐board subsystems with ground support equipment connecting directly into the onboard data‐handling subsystem. SpaceWire aims to offer equipment compatibility and reusability for components and subsystems. This means directly connecting a component made for one subsystem to another and operating without issues and readily use systems in one mission that were developed for another mission, thus reducing the cost of development, offering architectural flexibility, improving reliability, and most importantly increasing the amount of scientific work that can be achieved within a limited budget (ECSS Secretariat, 2008).
Since the publication of the ECSS-E-ST-50-12C standard (ECSS Secretariat, 2008), the engineering and scientific community have applied the guidelines that it dictates in many missions. Experience of practical applications highlighted the best practices as well as common problems. Different applications called for different designs, some of them were hard to implement while maintaining conformity with the standard. This fact led the European Cooperation for Space Standardization in 2012 to start the long process of updating the Standard including the experience of the past and the needs of the future. Working Group ECSS-E-ST-50-12C Rev.1 WG prepared Revision 1 of the standard (ECSS Secretariat, 2019), an effort concluded in May 2019 with the publication of the revised standard. The revision is an effort to overcome many of the earlier versions’ shortcomings and limitations. Additionally, since the Standard’s publication in 2008, the ESCC Detail Specification No. 3902/003 was updated and ESCC Detail Specification No. 3902/004 was published. Revision 1 of ECSS-E-ST-50-12C is expected to reflect these changes in the normative framework.
Taking into consideration the widespread use of the SpaceWire, personnel active in the space mission field is bound to come across some implementation of a system incorporating SpaceWire. The main objective of the chapter is to discuss the SpaceWire standard ECSS-E-ST-50-12C with regard to Electromagnetic Compatibility and Immunity issues. The authors aim to highlight the levels of the standard that define the electromagnetic compatibility (EMC) behavior of the system. This can be beneficial for the engineer or scientist either from a system modelling or a radiated emissions measurement standpoint. Students interested in space missions can also benefit from the concentrated information found in this chapter. Additionally, the chapter has been enhanced with various recent modelling methodologies focusing on different perspectives of the system which are also presented and discussed.
Key Terms in this Chapter
AWG: American wire gauge.
SpaceWire: A standard that specifies the physical interconnection media and data communication protocols to enable the reliable sending of data at high-speed (between 2 Mb/s and 400 Mb/s) from one unit to another. SpaceWire links are full-duplex, point-to-point, and serial data communication links.
Electromagnetic Compatibility (EMC): The ability of a system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment.
Jitter: Random errors in the timing of a signal.
Skew: Difference in time between the edges of two signals which should ideally be concurrent.
Electromagnetic Immunity: The ability of a system to maintain its proper functionality under exposure to various sources of electromagnetic disturbance.
Lay-Length: Number of twists per length unit expressed as the length between one complete turn of a single end in the cable.
Data Strobe Encoding (D-S): encoding scheme in which a sequence of data bits and clock is encoded as the original Data bit sequence, together with another bit sequence (Strobe) which changes state whenever the Data bit sequence does not. The clock can be recovered by performing the XOR function on the Data and Strobe.
Shielding: A method for the mitigation of electromagnetic disturbances which is based on the concept of creating an electrically continuous enclosure around the under-protection structure, mainly by the use of conductive materials.