Modern Information Approaches and Technology in Autonomous Control Systems of Perspective Aerospace Vehicles

MEMS (Micro-Electro-Mechanical-System) technology involves micro-mechanics, micro-electronics and micro-optics. In the last few years, MEMS technology has leaded to the development of a number of low-cost, miniaturised devised (sensors and actuators on a single chip) for space, thus making feasible low cost space missions based on the use of microsatellites (<50kg) and nanosatellites (<10kg). In the framework of the “New Millennium Program” NASA is studying a number of projects for interplanetary missions based on the use of microsatellites and nanosatellites. Also in Europe, ESA (European Space Agency) has identified MEMS technology has one of the guidelines for future space systems. Among several issues, one related to the development of micro-sensors and micro-actuators for satellite guidance, navigation and control has been identified. It is expected that the evolution of micro-electronics and micro-mechanics will lead to miniaturisation of components and entire subsystems, with the result of reducing space mission complexity and cost. Micro-technology makes feasible competitive space missions with microsatellites: a number of scientific and technology demonstration missions based on the use of small satellites have been already flown by universities and space agencies. Recently a number of studies have been presented in international symposia to fly several microsatellite/nanosatellites in formation for a variety of applications. In the future the use of small satellites will be more and more frequent, thanks to the evolution in miniaturisation of components and devices. One of the most demanding requirements of a modern space system is operational autonomy. Concerning guidance, navigation and control, autonomy means having on board appropriate sensors and actuators, sophisticated navigation and control algorithms (which account also for failures) and adequate computational resources. In addition to component size reduction, modern technology offers the possibility of having on-board large computational resources, thus making possible also complex and heavy navigation and control algorithms to be executed. For instance, it is possible to have on board large star catalogues, thus making possible to perform initial attitude acquisition (from “lost-in-space” condition) also by star sensors. Among various solutions for navigation and control of Earth-orbiting satellites, the ones based on the use of modern star sensors, miniaturised accelerometers and gyros and magnetic sensors and actuators are the most challenging. In fact, MEMS technology has leaded to the development of miniaturised inertial sensors of low cost and high performance. In addition, thanks to MOS and CMOS technologies, it is now possible to have high-performance star sensors based on the use of CCD and APS (Active Pixel Sensor). Due to their low-cost and reliability, magnetic devices (magnetometers and magnetic actuators) are very attractive for navigation and control of microsatellites. Usually, magnetic sensors and actuators are used in conjunction with other devices for satellite attitude determination and control. On the contrary, magnetic-only navigation and control is very attractive since it could drastically reduce the cost and mass of the guidance, navigation and control subsystem, but pose a number of problems. For instance, the use of only magnetic actuation poses the problem that the resulting system is under-actuated. In fact, magnetic control can be realised only in the direction perpendicular to the magnetic field. In addition, microsatellite volume and power constraints usually push toward the use of magnetic-core actuators, which introduce magnetic hysteresys and non-linearity in the control, thus reducing the achievable accuracy. Finally, magnetic-only navigation requires the implementation of heavy filtering algorithms to get adequate accuracy. In this framework, the proposed research aims at identifying a possible architecture of an autonomous navigation and attitude control system for microsatellites. In particular, the system architecture will be defined considering state-of-art, competitive solutions for components (sensors, actuators, electronics, on-board computers) and innovative solutions for navigation and control, such as the use of a magnetic-only system. The system main parameters (mass, volume, power consumption, accuracy) will be defined by means of analytical models describing, under simplified assumptions, the satellite dynamics and control. The analytical models will consider critical aspects, such as adopted magnetic field model, magnetic hysteresys and non-linearity, adopted error models for sensors and actuators. The system effectiveness for satellite navigation and attitude control will be tested by ad-hoc developed simulation programs, which integrate the satellite orbital and attitude dynamics with the operations of the on-board sensors and actuators. Project results The project, conducted in co-operation with the Russian party, will last two years and the result will be the definition of the architecture of an autonomous navigation and attitude control system for microsatellites. A preliminary system design will be performed. In particular, system critical components will be defined: sensor and actuator typology, navigation and control algorithms. Finally, a system numerical simulation will be carried out.