Abstract: The invention provides a momentum wheel energy storage device for a spacecraft or satellite. The device has six wheels whose axes of rotation are parallel to edges of a tetrahedron. It thus provides redundancy which makes it possible simultaneously to store energy and to generate an arbitrary net angular momentum, even in the event of one of the wheels failing. The failure of one wheel can be accommodated without degrading operation, with energy storage being optimal regardless of the angular momentum to be generated. The failure of two wheels can be accommodated but operation may then be in degraded mode. The invention makes it possible to limit the number of momentum wheels used in a device that can accommodate failures.

Abstract: A reversible electric device M is connected in an H bridge with a first side formed by first top and bottom switches and a second side formed by second top and bottom switches. The current Im flowing in the device from the first side to the second side is determined cyclically with a given constant switching frequency. The difference .DELTA. is determined between Im and an instantaneous set point current. Each cycle is divided with a ratio R into a first part and a second part. R is determined and for each part a set point setting for the switches (diagonal mode or freewheel mode) is chosen according to the sign .DELTA., the sign of the set point current (or of Im) and the value of a preselected correlation law relating to .DELTA. the mean value of the voltage that can be applied to the device during each cycle.