Two electronic modules from the Berlin Institute of Optical Sensor Systems are DLR's hardware contribution to ESA's CHEOPS mission. The focal plane module (FPM, left), the heart of the measuring instrument, contains the CCD detector with its electronics. In order to observe very small variations in starlight, the thermal requirements are enormous: The CCD detector and the subsequent low-noise electronics must be kept at a constant working temperature. The temperature fluctuations must not exceed one hundredth of a degree Kelvin (10 millikelvin). The Sensor Electronics Module (SEM, right) contains additional electronics to control the sensor (e.g. temperature controller, processor and software).