The main purpose of the project is to design and analyze an antenna that allows the modification of the coverage shape and the antenna pointing during the satellite lifetime, with an acceptable increase in risk, mass, and cost. The activities are focused on the antenna analyses and on the development of a Demonstration Model of the reconfigurable reflector (deformable membrane) and its mechanical actuators required for the shaping of the surface.
In order to control the shape of the surface of the reflector, the mechanical actuators shall distort the reflector active surface of few centimeters and the study shall investigate the means to monitor the surface profile by in-flight measurements using RF ground segment beacons or onboard RF/optical or mechanical devices.
Another objective of the project is the development of an optimization tool taking into account the technology of the reconfigurable reflector (design, technology and number of actuators) and the RF specifications/goals as well. The objective of using such an optimization process is to define surfaces achievable by the considered technology : flexible shell and actuator number/localization.
The main challenge of the study is the identification and definition of a flexible shell that needs to be compatible of space environment, lightweight, easily deformable, resistant to space radiation, PIM free, highly RF reflective, thermally stable and presenting appropriate mechanical properties (compromise between bending and shear stiffness). In addition, the surface accuracy required in Ku-band is extremely challenging with a limited number of actuators. In a word, the design and the definition of a new antenna product able to perform in orbit reconfiguration of the beam shape with a good level of RF performances and able to remain acceptable in terms of mass and cost constitute one of the main difficulties of the project.
The utilization of an in orbit reconfigurable antenna would allow the telecommunication operator to modify the antenna pattern at any time during the satellite lifetime and thus the mission addressed by the antenna. As a consequence, this would allow the operators the opportunity to capture new business. As a benefit for both the telecommunication operators and the space industry, this would also bring the possibility to select the initial mission of the antenna very lately in the development phase of the satellite program or even after the satellite launch.
The main advantage of mechanical reconfigurable antenna, is the good level of achieved RF performances which can be benchmarked to the ones obtained with a conventional shaped reflector antenna. This point is deemed as very important for the operators who do not want to lose performances for flexibility).
The antenna solution is a top floor dual optics Gregorian antenna with a reconfigurable main reflector composed of a flexible shell and a set of mechanical actuators. The flexible shell is designed to be subjected to large out of plane deformations., in order to meet conventional Ku-band coverage requirements. The flexible shell material exhibits high RF reflectivity, low ohmic loss and has a low PIM response making it as a suitable solution for transmit and receive applications in Ku band. The link between actuators and the bottom side of the flexible shell is done via spherical hinges on both sides of each carbon tube, whereas the flexible shell rim is free.
The reconfigurable antenna investigated within this study is composed of a reconfigurable main reflector, a set of linear actuators, an ellipsoidal sub-reflector, a Ku band feed, an antenna pointing mechanism, 4 HRM, a multiplexer used to limit the diameter and resistive torque of the electrical harness, a CFRP structure holding all the components. It can be observed that the reconfigurable technology can also be used in other antenna architecture such as a side deployable antenna with a reconfigurable sub-reflector and fixed main reflector. The actuator number and membrane layout would be in that case different but the technology would remain the same.
The study is organized in four parts :
1) The activities of the first part until BDR aims at defining the product specifications and at trading off the potential flexible shell and actuators candidates. A radiation test campaign has been done to evaluate the stability/evolution of the mechanical properties under space environment. A baseline technology has been defined for the membrane and for the actuators. The activities of the first part have been completed by a BDR.
2) The activities performed in the second part aims at evaluating the level of achievable RF performances for different number of actuators. A combined electrical-mechanical optimization software tool has been developed. A reconfigurable reflector with less than 90 actuators has been designed. Mechanical design and analysis of the reconfigurable reflector has been done. Thermal analysis has been done and the thermal control has been defined. The activities of the second part have been completed by a PDR.
3) The activities performed in the third part aim at comparing the performances obtained with a set of actuators distributed according to an hexagonal or a square lattice ( for the actuator repartition), and with different types of reflector rim. The BOL and EOL RF performances have been evaluated. Several actuator failure scenario have been evaluated and an associated recovery strategy has been defined. A preliminary definition of the actuation line has been proposed. A representative demonstration model has been defined. The activities of the third part have been completed by a CDR.
4) The activities performed in the fourth part consisted in the development of a Demonstration model (manufacturing and testing). The reflector surface shape measurement and the electrical testing of the antenna have been performed for different reflector surface shapes. An antenna PIM test has also been performed. The activities of this fourth part have been concluded by a TRB.
All the activities foreseen in the project have been successfully completed. The activities performed in this project allowed to define a multi-domain shaped reflector antenna design (RF, Mechanical, Technology), this is the first time such a method is developed and used for antenna design in TAS. Very good theoretical RF performances (Edge of coverage directivity typically -0.4dB lower than dedicated antenna) are achieved with less than 90 actuators. An advanced new flexible shell technology (biax CFRS) has been developed. The boundary conditions of the flexible shell allowing maximum reshaping amplitudes with minimum strains have been defined. The interface between control point and flexible shell has been studied and a very lightweight solution has been defined.
A demonstration model of the reconfigurable reflector has been developed, surface shape measurement as well as electrical testing have been performed for 3 different target shapes. Nonlinear mechanical analysis has been required to predict surface shape. In conclusion of the study, it is believed that , further design improvements are still necessary to reach a good correlation between surface predictions and measurements.
Reconfigurable reflector demonstration model
Further activities are still required to improve product TRL.