CHEOPS will be a small spacecraft with a total launch mass of approximately 250 kg. The baseline is to use a standard small satellite platform with some modifications. The spacecraft design was consolidated during the Phase A/B1 study, and Airbus Defence and Space - ECE (CASA) was selected as the platform provider.
CHEOPS has one instrument – a photometer with a single CCD, operating mainly in the visible, that is at the focal plane of an on-axis Ritchey-Chrétien telescope of 32cm diameter (clear aperture diameter of 30cm). All platform requirements are aimed at supporting the functionality of the payload and its ultrahigh photometric precision. The main implications for the platform are related to pointing capabilities and the thermal environment for the payload.
The instrument and telescope will be mounted on a stiff optical bench, which defines the interface to the platform, and will be thermally decoupled. A sunshield mounted on the platform will protect the focal plane radiator and detector housing from solar illumination and also carry solar panels for the power subsystem. When stowed for launch, the satellite will measure about 1.5 m × 1.4 m × 1.5 m.