Propulsion system for controlling the orbit of a satellite in earth orbit having an angular momentum accumulation capacity, and for generating torque assisting the control of the angular momentum, said satellite being driven at a travelling speed tangential to the earth orbit, the propulsion system comprising: - a propulsion unit capable of delivering a force along an axis F having a component perpendicular to the orbit, and a motorised mechanism (52; 52b; 52c; 52d) connected, on the one hand, to the propulsion unit and capable of being connected, on the other hand, to a structure of the satellite, the motorised mechanism (52; 52b; 52c) comprising: - a first motorised link (L1; L1b) capable of being connected to the structure of the satellite and configured to allow rotation about an axis substantially perpendicular both to a parallel axis V of the speed of the satellite and to the axis F; - a first rigid offset arm; - a second motorised link (L2; L2b) configured to allow rotation about an axis substantially perpendicular both to the axis V and to the axis F; the first motorised link (L1; L1b), the first rigid offset arm and the second motorised link being connected and positioned in series from the first motorised link (L1; L1b) to the second motorised link (L2; L2b); the first motorised link or the second motorised link being configured to allow rotation about an axis substantially parallel to the axis V; the propulsion system being characterised in that: - the motorised mechanism has three degrees of rotational freedom, with two of the three degrees of freedom being mutually parallel and separated by the first rigid offset arm; and - the motorised mechanism (52; 52b; 52c) is configured to move the propulsion unit along the axis V and to orient the propulsion unit in order to be able to control: - a component of the force along the axis V, for controlling the orbit; - an amplitude and a torque direction in a plane perpendicular to the axis F, for controlling the angular momentum. - a propulsion unit capable of delivering a force along an axis F having a component perpendicular to the orbit, and a motorised mechanism (52; 52b; 52c; 52d) connected, on the one hand, to the propulsion unit and capable of being connected, on the other hand, to a structure of the satellite, - a first motorised link (L1; L1b) capable of being connected to the structure of the satellite and configured to allow rotation about an axis substantially perpendicular both to a parallel axis V of the speed of the satellite and to the axis F; - a first rigid offset arm; - a second motorised link (L2; L2b) configured to allow rotation about an axis substantially perpendicular both to the axis V and to the axis F; - the motorised mechanism has three degrees of rotational freedom, with two of the three degrees of freedom being mutually parallel and separated by the first rigid offset arm; and - the motorised mechanism (52; 52b; 52c) is configured to move the propulsion unit along the axis V and to orient the propulsion unit in order to be able to control: - a component of the force along the axis V, for controlling the orbit; - an amplitude and a torque direction in a plane perpendicular to the axis F, for controlling the angular momentum.