Two-coordinate pointing and tracking system for an infrared Fouriertransform spectrometer

Abstract

We describe a 1-inch aperture pointing system realized with a rope transmission driven by geared stepper motors for operation at the surface of Mars. The system is intended to serve in the Fourier-transform spectrometer to observe both the sun through the atmosphere and the thermal emission of the atmosphere. The scanner covers a full 2π field of view (the upper hemisphere). The accuracy of 0.1 mrad (~21 arcsec) for the sun tracking is achieved using an automatic control system with an IR array sensor (32x32) in the loop. The optics of the pointing system consists of three flat mirrors and a germanium inlet window. The mass of the subsystem does not exceed 0.8 kg. The design accounts for the necessity of dust protection in the Martian environment. The effect of a finite accuracy of the pointing and tracking on the instrument signal to noise ratio is modeled.