A rotor assembly for deployment within a momentum control device for a spacecraft, the rotor assembly comprising: a rotor; a rotor shaft having a first end and a second end, and mounted on the first end to the rotor; a first sensor assembly comprising an encoder, coupled to the rotor shaft and a stationary portion of housing for the rotor assembly providing (i) a first rotor shaft rotational position (RSRP) data, and (ii) an associated frequency of rotation; a magnet coupled to the second end of the rotor shaft, the magnet oriented to produce an output magnetic flux that uniquely identifies an angular position of the rotor shaft; a second sensor assembly (214, 218, 220; 302, 304) coupled to the second end of the rotor shaft and comprising a stationary cylindrical housing partially surrounding the magnet, the housing enclosed on a first side and open on a second side, and having a sensor element disposed within the housing on an inner surface of the first side, the second sensor assembly thereby configured to substantially confine a closed magnetic flux loop generated by the magnet, wherein the sensor element senses magnetic flux output of the magnet and the sensor assembly thereby uniquely identifies an angular position associated with the rotor shaft and provides therefrom a second RSRP data and a second frequency of rotation, and a controller coupled to the first source of RSRP data and the second source of RSRP data and configured to (i) receive the first RSRP data and the second RSRP data, and (ii) generate final RSRP data therefrom, wherein the final RSRP data comprises one from the set including (a) only RSRP data from the second sensor assembly, and (b) only RSRP data from the second sensor assembly when a frequency of rotation of the rotor shaft is below a predetermined rotational speed. a rotor; a rotor shaft having a first end and a second end, and mounted on the first end to the rotor; a first sensor assembly comprising an encoder, coupled to the rotor shaft and a stationary portion of housing for the rotor assembly providing (i) a first rotor shaft rotational position (RSRP) data, and (ii) an associated frequency of rotation; a magnet coupled to the second end of the rotor shaft, the magnet oriented to produce an output magnetic flux that uniquely identifies an angular position of the rotor shaft; a second sensor assembly (214, 218, 220; 302, 304) coupled to the second end of the rotor shaft and comprising a stationary cylindrical housing partially surrounding the magnet, the housing enclosed on a first side and open on a second side, and having a sensor element disposed within the housing on an inner surface of the first side, the second sensor assembly thereby configured to substantially confine a closed magnetic flux loop generated by the magnet, wherein the sensor element senses magnetic flux output of the magnet and the sensor assembly thereby uniquely identifies an angular position associated with the rotor shaft and provides therefrom a second RSRP data and a second frequency of rotation, and a controller coupled to the first source of RSRP data and the second source of RSRP data and configured to (i) receive the first RSRP data and the second RSRP data, and (ii) generate final RSRP data therefrom, wherein the final RSRP data comprises one from the set including (a) only RSRP data from the second sensor assembly, and (b) only RSRP data from the second sensor assembly when a frequency of rotation of the rotor shaft is below a predetermined rotational speed.