Slated for launch in 2017, the mission aims to bring an optical Ritchey–Chrétien telescope with an aperture of 30 cm, mounted on a standard small satellite platform, into a Sun-synchronous orbit of about 800 kilometres (500 mi) altitude. For the planned mission duration of 3.5 years, CHEOPS is to examine known transiting exoplanets orbiting bright and nearby stars.
The main goal of CHEOPS will be to accurately measure the radii of the exoplanets for which ground-based spectroscopic surveys have already provided mass estimates. Knowing both the mass and the size of the exoplanets will allow scientists to determine the planets' approximate composition, such as whether they are gaseous or rocky. CHEOPS will be the most efficient instrument to search for shallow transits and to determine accurate radii for known exoplanets in the super-Earth to Neptune mass range (1-6 Earth radius).
CHEOPS will measure photometric signals with a precision limited by stellar photon noise of 150 ppm/min for a 9th magnitude star. This corresponds to the transit of an Earth-sized planet orbiting a star of 0.9 Rsun in 60 days detected with a S/Ntransit >10 (100 ppm transit depth). For example, an Earth-size transit toward a G star creates an 80 ppm depth.
The spacecraft is to be powered by solar panels that are part of the Sun shield. They will provide 60 W continuous power for instrument operations and allow for at least a 1.2 GBit/day data downlink capacity.