Christopher P. Bridges

Characterising Wireless Sensor Motes for Space Applications

This paper is concerned with application of standard wireless COTS protocols to space. Suitability of commercially available wireless sensor mote kits for communication inside and between satellites is investigated. Spacecraft applications of motes are being considered and a set of requirements are identified. Selected mote kits are tested under various scenarios complying with spacecraft testing procedures. The paper details the results of the carried out functional, EMC/I, vibration, thermal and radiation tests.

Development of a Satellite Sensor Network for Future Space Missions

Future spacecraft are envisioned as autonomous, miniature, intelligent and massively distributed systems. At the Surrey Space Centre, a research project is currently under investigation, which aims to develop a picosatellite sensor network using the CubeSat platform. The proposed satellite sensor network will be used to demonstrate technology advances in space, including modified IEEE 802.11 wireless standard for inter-satellite links (ISL), distributed computing for computationally intensive onboard signal processing, and reconfigurable system-on-a-chip (SoC) design.

Space-based wireless sensor networks: Design issues

This paper is concerned with a satellite sensor network, which applies the concept of terrestrial wireless sensor networks to space. 1,2 Constellation design and enabling technologies for picosatellite constellations such as distributed computing and intersatellite communication are discussed. The research, carried out at the Surrey Space Centre, is aimed at space weather missions in low Earth orbit (LEO). Distributed satellite system scenarios based on the flower constellation set are introduced. Communication issues of a space based wireless sensor network (SB-WSN) in reference to the Open Systems Interconnection (OSI) networking scheme are discussed. A system-on-a-chip computing platform and agent middleware for SB-WSNs are presented. The system-on-a-chip architecture centred around the LEON3 soft processor core is aimed at efficient hardware support of collaborative processing in SB-WSNs, providing a number of intellectual property cores such as a hardware accelerated Wi-Fi MAC and transceiver core and a Java co-processor. A new configurable intersatellite communications module for picosatellites is outlined.

Agent computing applications in distributed satellite systems

Space and satellite systems are considered to be the most extreme environment to design for and are fraught with engineering difficulty. Performance metrics such as fault tolerance, reliability, pre-determinism and heritage are still high of the list of requirements for all missions. But with the advent of modern day electronics, greater computing capability and networking technologies have enabled research into distributed satellite systems, where multiple spacecraft work collaboratively to perform a mission. Leveraging from these technologies, a satellite can be considered one of many nodes in an autonomous system. This paper proposes the use of an Agent based computing platform to solve orbit dynamics problems leading to a highly mobile and decentralized system. The latest Agent platforms are compared and possible Agent applications are presented; specifically, distributed image compression and a novel topology reconfiguration scheme.

STRaND-2: Visual inspection, proximity operations & nanosatellite docking

The Surrey Training Research and Nanosatellite Demonstrator (STRaND) programme has been success in identifying and creating a leading low-cost nanosatellite programme with advanced attitude and orbit control system (AOCS) and experimental computing platforms based on smart-phone technologies. The next demonstration capabilities, that provide a challenging mission to the existing STRaND platform, is to perform visual inspection, proximity operations and nanosatellite docking. Visual inspection is to be performed using a COTS LIDAR system to estimate range and pose under 100 m. Proximity operations are controlled using a comprehensive guidance, navigation and control (GNC) loop in a polar form of the Hills Clohessy Wiltshire (HCW) frame including J2 perturbations. And finally, nanosatellite docking is performed at under 30 cm using a series of tuned magnetic coils. This paper will document the initial experiments and calculations used to qualify LIDAR components, size the mission thrust and tank requirements, and air cushion table demonstrations of the docking mechanism.

Distributed Computing in Reconfigurable Picosatellite Networks

This paper presents the results of a research project, which aims to develop enabling technologies for future distributed space architectures based on flexible, reconfigurable, evolvable, and intelligent multi-spacecraft sensing networks. One important goal of the project is to propose a distributed computing platform over wireless inter-satellite links. The paper discusses initial results on the application of distributed computing technologies to future networked constellations of picosatellites.

Towards an Agent Computing Platform for Distributed Computing on Satellites

Todays mobile devices and countless other embedded devices now aim to use networking technologies utilizing the latest electronics and software to provide new functions. Distributed satellite systems, seen to be analogous to mobile ad hoc networks (MANET), perform new mission functions with high mobility and intermittent connectivity that make satellite network management and operations difficult. New drivers and requirements are outlined for node and network levels in any given topology requiring real-time client-server or peer-to-peer (P2P) networking applications. To meet these requirements a novel agent computing platform (ACP) is proposed utilizing technologies from the multi-processor and agent middleware fields for real-time Java networking and mobile ad hoc network-based distributed computing applications at a minimal overhead to existing systems. The Java optimised processor (JOP) is investigated and embedded into an existing LEON3-based system-on-a-chip (SoC) design to provide a new fault-tolerant, parallel processing, and network functionalities. Agent middleware is discussed and compared for porting to the new dual processor design with a new middleware instance manager thread to enable software resets at runtime on the Java processor without halting the processor. After verification these two technologies are combined and discussed in depth to highlight key technological problems of this real-time ACP implementation.

Real-time agent middleware experiments on java-based processors towards distributed satellite systems

Distributed satellite systems are large research topics, spanning many fields such as communications, networking schemes, high performance computing, and distributed operations.12 DARPAs F6 fractionated spacecraft mission is a prime example, culminating in the launch of technology demonstration satellites for autonomous and rapidly configurable satellite architectures. Recent developments at Surrey Space Centre have included the development of a Java enabled system-on-a-chip solution towards running homogenous agents and middleware software configurations.

Software Defined Radio (SDR) architecture to support multi-satellite communications

Software Defined Radio (SDR) is a key area to realise new software implementations for adaptive and reconfigurable communication systems without changing any hardware device or feature. A review on efficient use of limited bandwidth and increasing distributed satellite missions can lead to the need for a generic yet configurable communication platform that can handle multiple signals from multiple satellites with various modulation techniques, data rates and frequency bands that must be compatible to typical small satellite requirements. SDR is beneficial for space applications as it can provide the flexibility and re-configurability and this is driven by fast development times, new found heritage, reduced cost, and low mass Commercial Off-The-Shelf (COTS) components. The implementation of a combined System-On-Chip (SoC) and SDR communication platform enables additional reduction in cost as well as mass. This paper proposes a SDR architecture in which Field Programmable Gate Array (FPGA) System-on-Chip (SoC) is paired with a Radio Frequency (RF) programmable transceiver SoC to solve back-end and front-end re-configurability challenges respectively. The test-bed is aimed at implementing the signal processing software functions in both the dual-core ARM processors and associated FPGA fabric. The distribution of the functions between the FPGA fabric and dual-processor is based on profiling experiments using signal processing blocks, implemented on the development platform, in order to identify where bottlenecks exist. This paper discusses further the results from the new multi-signal / multi-satellite pipeline architecture and the subsequent bandwidth, data rate and processing requirements. Aspects of implementing and testing signal processing chains needed for CubeSat Telecommand, Telemetry and Control (TT&C) are presented together with initial results. Thus the proposed technology not only contributes for a lightweight and portable ground station but also for an on-board satellite transceiver.

A multicellular architecture towards low-cost satellite reliability

A new class of low-cost satellites has the potential to reduce the cost of traditional space-based services. Unfortunately, to date, low-cost satellites have proven to suffer from poor reliability. While traditional techniques for increasing reliability are well known to satellite developers, these techniques are poorly suited for implementation on low-cost satellites due to intrinsic budgetary, mass and volume constraints. This research proposes that alternative techniques for increasing system reliability can be derived by studying biological organisms, which have proven their robustness by inhabiting even the harshest locations on earth. Both unicellular and multicellular organisms are examined. The result is a conceptual system architecture, based on initially identical, reconfigurable hardware blocks, or artificial cells, and a decentralized task management strategy. This multicellular architecture is described in detail. Finally, preliminary details of a planned implementation are given. This implementation aims to demonstrate that a significant portion of traditional satellite avionics can be replaced by the proposed artificial cells.