ELSA (European Levitated Spherical Actuator)

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 ESAs technology strategy and long term plan. Support for initial development activities for this innovative actuator technology was provided within the framework of ESAs GSTP program.

An Attitude Control System (ACS) traditionally requires a minimum of three reaction wheels (in practice, four wheels are common because the system can be better optimized and the extra wheel allows for failure recovery). Hence, the orientation of the satellite can be changed by accelerating the appropriate wheel. Another traditional approach is to use a control moment gyro consisting of a rapidly rotating wheel held by gimbals. Applying torques on the gimbals joints changes the satellite orientation.

ELSA concept consists of a levitated sphere that can be accelerated about any axis producing a resultant torque in any direction. This system aims at replacing the three (or four) traditional reaction wheels or control moment gyroscopes commonly used in satellites and spacecrafts.
It provides many upgrades and benefits:

  • It reduces the mass and power supply allocated to the attitude and navigation unit;
  • The mass and power saved can be allocated to the payload;
  • It offersperformance gain;
  • It provides more momentum for a given system mass in comparison with the current inertial subsystems;

It improves the system reliability as no mechanical bearings are present and allows more flexible mission planning.