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REACTION SPHERES | ARTICLE


REDUCED-WEIGHT REACTION SPHERE MAKES WAY FOR


Extra Satellite Payload Leopoldo Rossini, CSEM, Switzerland


When launching satellites to orbit, every gram of payload is extremely valuable.


Depending on the orbit and the launcher, an estimated cost is about 15,000 euros per


kilogram. With this in mind, researchers at CSEM, the Swiss Center for Electronics and Microtechnology, are working on ways to minimise the weight of satellite attitude control systems. Here, a single multi-axis


reaction sphere is proposed to replace four conventional single-axis reaction wheels. Its geometry and electromagnetic design are quite complex, and only with the help of COMSOL Multiphysics are they able to


examine various configurations of magnets to find the one that works best.


<< Figure 1: Geometry of the 3D motor on a magnetic bearing for the reaction sphere; in the ideal


case eight permanent magnets for the rotor (whose fields today we


approximate instead using a mosaic of 728 cylindrical magnets) and 20 coils for the stator. >>


system engineering, micro electronics and communication technologies. With headquarters in Neuchâtel, it has some 400 employees in Switzerland.


F


Until Now: Multiple Reaction Wheels In conventional 3-axis stabilised spacecrafts, three reaction wheels are arranged along the three axes, with a fourth wheel for optimisation and redundancy; they are normally employed to implement attitude control systems with the required accuracy and without using fuel to fire jets. This attitude control allows the satellite to be pointed towards an object in the sky, towards a particular location on earth or to stabilise the satellite by compensating for disturbances it might encounter.


>> Continued on page 30 29 | commercial micro manufacturing international Vol 7 No.2


ounded in 1984, by grouping three former watch-industry research laboratories, CSEM is now a private applied research and development centre specialising in micro technology,


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