One of the more popular Earth sensors in use today is produced by NEC. These sensors are mounted on the earth facing deck of the satellite and are used to measure Roll and Pitch errors. This earth sensor uses inferred detectors to sense the Earth and measure the duration of its presence in the field of view. Two inferred detectors are mounted in a fixed location in the earth sensor and an oscillating mirror is used to reflect light in the inferred spectrum into the detector.

Detector locations are offset to produce north and south scans that are compared to calculate pointing errors in the roll axis , used for control of north/south pointing.  East/west error in the pitch axis is calculated by comparing the measure start of the scan to a center reference and center reference to the end of scan to produce east/west pointing errors.

While operating in the Normal mode on this sensor the oscillating mirror travels plus and minus approximately 15 degrees of its center point. For course measurements the mirror travels can be commanded to Wide scan mode widening the scan range to plus and minus 30 degrees, used during contingency operations and during initial acquisition of the earth.

Earth sensor Roll and Pitch error signals are acted on by the ACS subsystem to maintain pointing accuracy.