Final Report Summary - NETSAT (Networked Pico-Satellite Distributed System Control)
Miniaturized satellite systems are currently gaining significant importance in the commercial space sector. Especially their potential cost-efficient utilization in large constellations and coordinated formations promises significant innovation potential for future applications of fractionated missions based on a large number of small satellites. The NetSat project addressed a variety of technical and scientific questions leading towards the technical demonstration of a distributed formation of four miniature cubesats in orbit.
Beside general technical challenges in the context of cost-effective mass production, energy efficiency, and robustness of small satellite technology, new technical solutions are necessary in order to provide the required key technology to realize a spacecraft formation within extremely limited budgets such as mass, volume and power. In particular, challenging enabling technologies concern the inter-satellite communication to enable the autonomous cooperation of individual spacecraft while precise attitude and orbit determination and control mechanisms based on mass-efficient propulsion systems are required to prevent the formation from drifting apart. Optimal control techniques close the loop to coordinate the relative motion between the satellites autonomously while new concepts for multi-satellite operations are necessary to allow efficient control of the entire formation with minimal interaction of the operators.
To enable such fractionated missions, various application scenarios have been studied and requirements for small satellite formations have been investigated. Miniature navigation sensor systems have been analysed, selected or implemented for their utilization onboard a demonstrator mission. The resulting sensor suite consisting of GNSS-receivers, high-precision gyros, magnetometers, accelerometers and novel sun sensors has been integrated into the hard- and software design of the demonstrator satellites to fuse their measurements in order to provide required navigation knowledge for formation control. Filtering and propagation methods have been developed and implemented to improve the navigation determination and prediction accuracy.
Various actuators and control algorithms for precise attitude and orbit control of individual miniature satellites have been analysed, implemented, tested and optimized. As actuator suite for the demonstrator mission a combination of energy efficient reaction wheels, magnetic torquers and miniature electric propulsion thrusters have been integrated into the hardware design. Specific embedded control software has been implemented and tested to operate on the miniature attitude and orbit determination and control hardware.
For the communication system, radio transceivers have been acquired, implemented and tested. The hard- and software interface of the ISL has been developed. The frequency coordination that is required for the operation of the communication systems of the satellites and thus the overall mission has been completed.
A concept for efficient multi-satellite operations based on remotely controlled semi-autonomous ground stations combined with autonomous planning and goal-based operations onboard the spacecraft has been elaborated and implemented in software for the ground and space segment.
Different algorithms for autonomous formation control have been designed, implemented, and evaluated based on extensive simulations using a specially developed simulation environment for satellite formations. Selected algorithms for autonomous formation control have been implemented on the satellites, for example a Model Predictive Control algorithm and a plant inversion-based approach with a reference governor is foreseen as backup. In addition, a detailed mission plan including all planned formation experiments has been created.
As a result, now at the end of the project, all components for the demonstrator mission have been selected and integrated into the overall satellite design. Almost all hardware components have been acquired. The formation and attitude control algorithms developed, have been simulated and tested and prove themselves suitable for satellite formation flying and for performing the demonstrator mission. The performance and operation of the demonstrator mission, for which additional funding could be acquired by the PI and the host institution is planned for beginning of 2020.
Beside general technical challenges in the context of cost-effective mass production, energy efficiency, and robustness of small satellite technology, new technical solutions are necessary in order to provide the required key technology to realize a spacecraft formation within extremely limited budgets such as mass, volume and power. In particular, challenging enabling technologies concern the inter-satellite communication to enable the autonomous cooperation of individual spacecraft while precise attitude and orbit determination and control mechanisms based on mass-efficient propulsion systems are required to prevent the formation from drifting apart. Optimal control techniques close the loop to coordinate the relative motion between the satellites autonomously while new concepts for multi-satellite operations are necessary to allow efficient control of the entire formation with minimal interaction of the operators.
To enable such fractionated missions, various application scenarios have been studied and requirements for small satellite formations have been investigated. Miniature navigation sensor systems have been analysed, selected or implemented for their utilization onboard a demonstrator mission. The resulting sensor suite consisting of GNSS-receivers, high-precision gyros, magnetometers, accelerometers and novel sun sensors has been integrated into the hard- and software design of the demonstrator satellites to fuse their measurements in order to provide required navigation knowledge for formation control. Filtering and propagation methods have been developed and implemented to improve the navigation determination and prediction accuracy.
Various actuators and control algorithms for precise attitude and orbit control of individual miniature satellites have been analysed, implemented, tested and optimized. As actuator suite for the demonstrator mission a combination of energy efficient reaction wheels, magnetic torquers and miniature electric propulsion thrusters have been integrated into the hardware design. Specific embedded control software has been implemented and tested to operate on the miniature attitude and orbit determination and control hardware.
For the communication system, radio transceivers have been acquired, implemented and tested. The hard- and software interface of the ISL has been developed. The frequency coordination that is required for the operation of the communication systems of the satellites and thus the overall mission has been completed.
A concept for efficient multi-satellite operations based on remotely controlled semi-autonomous ground stations combined with autonomous planning and goal-based operations onboard the spacecraft has been elaborated and implemented in software for the ground and space segment.
Different algorithms for autonomous formation control have been designed, implemented, and evaluated based on extensive simulations using a specially developed simulation environment for satellite formations. Selected algorithms for autonomous formation control have been implemented on the satellites, for example a Model Predictive Control algorithm and a plant inversion-based approach with a reference governor is foreseen as backup. In addition, a detailed mission plan including all planned formation experiments has been created.
As a result, now at the end of the project, all components for the demonstrator mission have been selected and integrated into the overall satellite design. Almost all hardware components have been acquired. The formation and attitude control algorithms developed, have been simulated and tested and prove themselves suitable for satellite formation flying and for performing the demonstrator mission. The performance and operation of the demonstrator mission, for which additional funding could be acquired by the PI and the host institution is planned for beginning of 2020.