ELSA - the European Levitated Spherical Actuator is a small size collaborative FP7 project, that is addressing research to support space science and exploration.
The ELSA project has the goal of improving European capacity to independently manufacture commercial and scientific satellites by bringing a new actuator for attitude and orbit control systems to a higher level of maturity. This goal is in line with ESA’s technology strategy and long term plan.
The consortium of the project consists of 7 partners from Switzerland, Spain, Belgium and Poland: Centre Suisse d' Electronique et de Microtechnique (project coordinator), maxon motor, SENER, Société Anonyme Belge de Constructions Aéronautiques (SABCA), RedShift, Centrum Badań Kosmicznych Polskiej Akademii Nauk (CBK PAN) and Foundation for Space Development (FSDSA).
ELSA 2nd Progress Meeting took place in CBK PAN,Warsaw on 24 January 2013. The following items were discussed: electro-mechanical design, tests to be done using dedicated test benches, control and power electronic design.
Static Force and Torque Measurements
Some of the latest achievements in the development of the dynamic model of a magnetically levitated reaction-sphere system were presented on 32nd Dynamics Days Europe in Gothenburg, Sweden, September 2-7, 2012.
The reaction sphere is a magnetic bearing spherical actuator consisting of an 8-pole permanent magnetospherical rotor that can be accelerated about any axis. Inertial attitude control systems used in spacecrafts, traditionally consist of one to four reaction wheels (RW) or control-moment gyroscopes (CMG).
In practice, for three-axis attitude stabilization, four or five wheels are common for optimization and redundancy purposes. In principle, the attitude of a satellite can be changed by the reaction to the acceleration of the appropriate wheel. Another traditional approach is to use a control-momentum gyro consisting of a rapidly rotating wheel held by gimbals. In the frame of ELSA project, the use of a single reaction sphere held in position by magnetic levitation is being developed as an alternative to the current approach. The sphere can be accelerated in any direction by a three-dimensional motor. Because of its unparalleled symmetry, a hollow sphere constantly delivers maximum inertia independently of its current rotation axis. However, in opposition to its potential usefulness, control procedures that are applied to the reaction sphere require appropriate investigation of stability and dynamics of the whole system, which is nonlinear and includes a wide range of phenomena, such as interaction between rotating permanent magnets and coils in stator, sticking forces, and generation of eddy currents.
The reaction sphere concept was also presented on the Project Meeting in ESTEC in 2012.