Wireless Space Plug-and-Play Architecture (SPA-Z)

Space Plug-and-Play Architecture (SPA), defined by the Air Force Research Laboratory, is a new standard for spacecraft component interconnections (AIAA-S-133-x-2013) providing new capability for managing intelligent components. Wireless Sensor Networks (WSN) based on the IEEE 802.15.4 Personal Area Network standard are finding increasing use in the home automation and emerging smart energy markets. The network protocol and application layers can be based on the ZigBee standard as defined by the ZigBee Alliance, providing a framework for component-based software that supports solutions from multiple vendors. SPA and ZigBee create selfconfiguring ad-hoc networks, but differ in their approach. SPA focuses on self-configuring components using wired interconnects while ZigBee forms self-configuring wireless networks. The optimal combination of SPA with ZigBee technology can bring the advantages of both methods to next-generation spacecraft by using self-configuring wireless networks for data and intelligent components with universal SPA-compliant interfaces. Mesh-enabled WSNs provide inherent fault tolerance and SPA provides dynamic fault management leading to low-power, low-cost ancillary sensing solutions for spacecraft. Self-configuring architectures are the key for supporting a large number of sensors in dynamic configurations, allowing intelligent response for fault tolerant networks. Plug-and-Play for sensor networks could be defined as the capability for application software to query any sensor module connected to the ad-hoc dynamic network using module resident information defining the sensors characteristics. The embedding of sensor information into each Wireless Sensor Module (WSM) allows identifying each sensor unambiguously and accurately in terms of function and status, without the use of any configuration database. The IEEE 1451 Smart Transducer Interface Standard defines Transducer Electronic Datasheets (TEDS) containing key information regarding sensor characteristics such as name, description, serial number and calibration information. SPA defines an extensible format called xTEDS using XML embedded meta-information for sensor management enabling software to identify the sensor and interpret the sensor data stream without reference to any external information. The application software is able to read the status of each sensor module, responding in real-time to changes of WSN configuration and provide the appropriate response for maintaining overall sensor system function, even when sensor modules fail or the network is reconfigured. Temporal integrity of sensor data delivery is ensured by the use of a global network clock and embedding timestamps into each measurement result accurate to one millisecond. SPA provides high-level mechanisms for self-configuration and integration with other spacecraft components and can significantly improve interoperability. The architecture and technical feasibility for creating wireless fault-tolerant sensor networks is presented through integration of SPA, IEEE 1451 and ZigBee into the proposed SPA-Z architecture. SPA provides the broad framework, the IEEE 1451 standards provide templates for TEDS and sensor management and ZigBee provides effective wireless network management. The approach is to tailor these multiple standards into a viable architecture. The result conforms to multiple standards, enables deterministic response and provides a capable publish/subscribe interface to application software. Our proposed software architecture for intelligent sensor management using the SPA standard will be discussed in the context of the specific tradeoffs required for effective use. Two examples are presented, the first highlights SPA-Z advantages for reconfigurable payloads and the second describes the development of a SPA compliant WSN.