Large Space Structures (LSS) are required for the advancement of modern space activities and represent a challenging research topic. In particular, large space antennas are a key technology for communications and Earth Observation (EO). However, in-orbit disturbances affecting the deployed configuration can deteriorate the accuracy of the communications system. Perturbations originated by on board sources (e.g. thrusters jetting, fuel sloshing) and thermal deformation can be transmitted from the satellite platform to the flexible supporting frame of the antenna and to the reflector. Furthermore, their elastic dynamics is coupled with the spacecraft rigid body motion and the choice of a suitable integrated control strategy is crucial to avoid the complete failure of the mission caused by instability phenomena. As the performance requirements of these systems become more and more demanding, their elastic dynamics starts to be a serious concern using traditional control systems. In this research, an intelligent adaptive structure concept is investigated. The in-orbit dynamics of a satellite equipped with large flexible appendages will be studied considering orbital perturbations, thermal solicitations and attitude control commands. The flexible structure will be configured with a network of distributed smart materials actuators and sensors guided by a controller to actively modify the response of the system. The active elements are embedded within truss elements, one of the most widespread passive structural solution in the space field. As for that, this control approach can be suitable to different types of space antennas (i.e. mesh reflectors, SAR-like panels, long mast concepts). After an optimization procedure to assess the best placement and authority of devices, different strategies will be implemented to coordinate the simultaneous action of the actuators devices, react to a variety of disturbances and ensure the mission requirements are fulfilled.
The opportunity to investigate in-depth the design of an advanced integrated control system for large antenna-structures spacecraft could produce a cutting-edge technology to push forward the current state-of-the-art. This research would improve scientific knowledge of a field long engaged by space agencies and industries, tuning the up-to-date findings to a meaningful (not merely academic) test case. Moreover, the need to meet the high accuracy standards could require a renewal in the use of PZT devices for space applications and enhancement of the current technological equipment, with positive effects on future years operations.
The expected impact of this project is presented below:
- The distributed control will make the structure stiffer in active control manner, rather than by implementing more mass or material with a higher Young modulus. In this perspective, the development of an actuated smart network devoted to control large antennas truss-like supports in space conditions is a new concept and can produce innovative solutions for satellite sensor pointing as well as control actuation;
- The approach will be focussed on realizing an advanced integrated control of the system, i.e. the orbiting spacecraft will be viewed in full to simultaneously consider both the attitude control of the rigid platform and the vibration damping of flexible appendages. This will lead to a progress of control design techniques for flexible orbiting satellite with respect to the actual state-of-the-art;
- The research will take another step toward space validation of piezo-electric devices, contributing to making it a proven viable technology to improve future European space missions. Indeed, the control strategy lend itself to be applied to different types of structures: beam like structures where the material is light and with low stiffness in the form of tubes and rods, large parabolic antennas with an underlying reflector supporting structures, large truss structures, as part of larger infrastructures as space stations;
- The concept is also partially applied to non-space sectors, as aviation, automotive and other industries. This reality guarantees an established heritage to achieve a fruitful extension to space field too. Indeed, regarding civil engineering, stack piezo material are investigated for seismic isolation and health monitoring of structures. The solution is studied to realize intelligent suspension systems. Piezoelectric devices can also be used to build smart wings and blades for airplanes and helicopters;
- The new technology could help in finding a new solution for more accurate future satellite scientific instruments implementation, for instance, optical payloads mounted at the end of a very long mast requiring high dimensional stability;
- With the development of computer software, co-simulation has been widely applied to the design of the controller system by using multi-software platforms. The researcher could create an in-house open-source code to be interfaced with most diffused commercial simulations software to perform accurate and precise multibody analysis involving piezoelectric elements. This code could remain at other researchers' disposal and be useful for more than this study purposes;
- To perform experimental tests at the university facilities additional hardware/software will be required. This procurement will entail an improvement of already existing equipment, available for future students to complete their thesis or laboratory activities.