The MiDES Earth sensor is designed to provide horizon position information in two mutually orthogonal axes (X and Y) which form a plane that is normal to nadir. This is accomplished utilizing one assembly that contains two optical heads that view the Earth and share common electronic signal processing circuitry and a common mechanical chopper.
The performance of the MiDES G is achieved through the use of a multi pixel detector array of 16 discrete pixels in each of the two hybrid detector assemblies. The radiant contrast needed to produce a voltage output from the pyroelectric detectors is achieved through the use of a chopper mechanism that causes the radiant energy falling on the detector to alternate between the energy emitted from the scene and from the chopper. The chopper temperature is much higher than the scene (space and Earth) thus producing a large output voltage at all times.