Thom Stone

Fault tolerance in ZigBee wireless sensor networks

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 and application layers, based on the ZigBee 2007 PRO Standard, provide a convenient framework for component-based software that supports customer solutions from multiple vendors. This technology is supported by System-on-a-Chip solutions, resulting in extremely small and low-power nodes. The Wireless Connections in Space Project addresses the aerospace flight domain for both flight-critical and non-critical avionics. WSNs provide the inherent fault tolerance required for aerospace applications utilizing such technology. The team from Ames Research Center has developed techniques for assessing the fault tolerance of ZigBee WSNs challenged by radio frequency (RF) interference or WSN node failure.12

A viable COTS based wireless architecture for spacecraft avionics

Wireless communications has more to offer for spacecraft avionics than just reduced mass and space. A team at NASA Ames Research Center (ARC) is actively involved in designing and implementing wireless systems, and is part of a multi-center NASA effort to investigate wireless sensor networks (WSN) for spacecraft sponsored by the NASA Engineering and Safety Center. In this paper, we describe an implementation of ZigBee run over an IEEE 802.16.2 network architecture, and explain how this topology can be adapted to meet the rigorous challenges presented by the space environment. We present current ZigBee applications and deployments and compare ZigBee with some competing network architectures. We also present some of the wireless sensor network research and development that has been accomplished at ARC and discuss future plans. Our results show that ZigBee can meet requirements and provide the opportunity to develop a smart spacecraft infrastructure modeled on the “smart home” vision, and outline some steps that might be taken to bring this model to reality.

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.

Software architecture of sensor data distribution in planetary exploration

Data from mobile and stationary sensors will be vital in planetary surface exploration. The distribution and collection of sensor data in an ad-hoc wireless network presents unique challenges. Some of the conditions encountered in the field include: irregular terrain, mobile nodes, routing loops from clients associating with the wrong access point or repeater, network routing reconfigurations caused by moving repeaters, signal fade, and hardware failures. These conditions present the following problems: data errors, out of sequence packets, duplicate packets, and drop out periods (when the node is not connected). To mitigate the effects of these impairments, robust and reliable software architecture tolerant of communications outages must be implemented. This paper describes such a robust and reliable software infrastructure that meets the challenges of a distributed ad hoc network in a difficult environment and presents the results of actual field experiments testing the principles and exploring the underlying technology

A Lunar Communication Satellite Network Architecture Employing Internet Protocol, Laser Communication Technologies and Small Satellites

The NASA lunar exploration initiative will require a new communications infrastructure to support planned mission operations. While traditional communications support using point-to-point radio links will continue to be required, an opportunity exists to establish a fully networked communications infrastructure in parallel to support a broad range of future operations. NASA Ames Research Center, NASA Jet Propulsion Laboratory, Ball Aerospace and Cisco Systems partnered to develop a lunar communication architecture that incorporates the key technologies of the Internet Protocol, small satellites, and laser communication, along with delay tolerant networking and wireless ad hoc networking to form an adaptable, robust, end-to-end lunar communications network infrastructure. This paper presents the overall architecture and describes the component technologies.

SOAREX-8 suborbital experiments 2015 - A new paradigm for small spacecraft communication

In 2015 NASA plans to launch a payload to 280 Km altitude on a sounding rocket from the Wallops Flight Facility. This payload will contain several novel technologies that work together to demonstrate methodologies for space sample return missions and for nanosatellite communications in general. The payload will deploy and test an Exo-Brake, which slows the payload aerodynamically, providing eventual de-orbit and recovery of future ISS samples through a Small Payload Quick Return project. In addition, this flight addresses future Mars mission entry technology, space-to-space communications using the Iridium Short Messaging Service (SMS), GPS tracking, and wireless sensors using the ZigBee protocol. SOAREX-8 is being assembled and tested at Ames Research Center (ARC) and the NASA Engineering and Safety Center (NESC) is funding sensor and communications work. Open source Arduino technology and software are used for system control. The ZigBee modules used are XBee units that connect analog sensors for temperature, air pressure and acceleration measurement wirelessly to the payload telemetry system. Our team is developing methods for power distribution and module mounting, along with software for sensor integration, data assembly and downlink. We have demonstrated relaying telemetry to the ground using the Iridium satellite constellation on a previous flight, but the upcoming flight will be the first time we integrate useful flight test data from a ZigBee wireless sensor network. Wireless sensor data will measure the aerodynamic efficacy of the Exo-Brake permitting further onorbit flight tests of improved designs. The Exo-Brake is 5 m2 in area and will be stored in a container and deployed during ascent once the payload is jettisoned from the launch vehicle. We intend to further refine the hardware and continue testing on balloon launches, future sounding rocket flights and on nanosatellite missions. The use of standards-based and opensource hardware/software has allowed for this project to be completed with a very modest budget and a challenging schedule. There is a wealth of hardware and software available for both the Arduino platform and the XBee, all low-cost or open-source. Along with the Exo-Brake hardware and deployment discussion, this paper will describe in detail the system architecture emphasizing the successful use of opensource hardware and software to minimize effort and cost. Testing procedures, radio frequency interference (RFI) mitigation, success criteria and expected results will also be discussed. The use of Iridium short messaging capability for space-to-space links, standards-based wireless sensor networks, and other innovative communications technology are also presented.

IP telephony for interplanetary exploration

Voice over IP (VoIP), using techniques developed for telephony, is a natural method for providing voice services for planetary explorers. Providing the ability to make telephone calls over the Internet, VoIP can replace radiofrequency communications in remote environments that are not serviced by a conventional telephone system. VoIP can provide better quality voice than either analog radio or conventional phone. As another benefit, VoIP enables the integration of voice and data applications, thus eliminating the need for separate frequency management and antenna systems. This paper provide an overview of IP telephony and wireless LAN concepts and examine VoIP applicability for planetary exploration. The use of VoIP at the Mars Desert Research Station (MDRS) be evaluated. Benefits be highlighted and additional features that would be desirable to incorporate with VoIP be discussed. The paper conclude with a discussion of VoIP studies that be conducted by the NREN group in the future.

The successful PhoneSat wifi experiment on the Soarex-8 flight

On the 7th July 2015 at 06:15 AM EDT a Terrier/Black Brant sounding rocket left the Earth from the Mid-Atlantic Regional Spaceport on Wallops Island in Virginia. On its 10-minute sojourn across the sky and into the sea it carried the 8th Sub-Orbital Aerodynamic Reentry Experiment (Soarex-8) payload. A description of some of the experimental elements on this payload were presented in last years paper. The elements described (the exobrake, ZigBee wireless sensor net, and Iridium short message communications) were all successful. Another Soarex-8 experiment is described herein: the successful demonstration of point-to-point IEEE 802.11 (wifi) communications from space. We believe this set a new distance record for wifi as well as being the highest wifi-to-ground link, transmitting from the edge of space. Soarex-8 reached an apogee of 334 km (206 mi). During the flight we sent low frame rate video to a ground station at NASA Wallops Flight Facility from payload ejection until loss-of-signal when Soarex-8 passed over the horizon. The Soarex-8 team did not intend to achieve records in this endeavor. We were attempting to establish a very low cost method to downlink high speed data from small spacecraft. We will repeat this experiment as part of a future small spacecraft launch from the International Space Station in the near future. We will then send low frame rate video from orbit. This paper presents the methodology, process and interfaces of the long haul wifi experiment. We discuss an innovative space camera designed at NASA Ames Research Center (ARC) and the camera/wifi interface. We describe the onboard system, power requirements, hardware specifications, interface to the rest of the Soarex-8 payload and hardware integration. Flight software was written to circumvent the handshaking requirement of wifi links and deal with the image stream from the camera. We describe the ground system including the software and how we were able to use existing antenna at Wallops to track and downlink the wifi signal. Finally we present our plans for future orbital and suborbital flights.