The infra-red horizon sensor on board the Aureol-3 satellite

Several experiments on board the Aureol-3 satellite require precise information concerning the orientation of the spacecraft. For these experiments, an accuracy of one deg with respect to each of the three angles which determine the orientation of the spacecraft in a frame of reference linked to the earth was specified as a design goal. In order to determine the spacecraft attitude with such an accuracy under all orbital conditions, even during eclipses, it was necessary to employ, in addition to a three-axis DC magnetometer and a solar sensor, a third sensor. In fact, two more sensors were added to the payload during the implementation of the project. These two sensors include a Soviet sensor, which was derived from an already existing photometer experiment, and an infrared horizon sensor provided by the French. Details regarding the infrared sensor are discussed, taking into account the optical head, the scanning system, the electronics system, and initial results.