Its objective is to determine the size of known extrasolar planets, which will allow the estimation of their mass, density, composition and their formation.

Few exoplanets to date have highly accurate measures for both mass and radius, limiting the ability to study the variety in bulk density that would provide clues as to what materials they are made of and their formation history.

The defocused mirror distributes the light of the star over many pixels of the detector, making the measurements of starlight more precise.

[11] A sunshield mounted on the platform protects the radiator and detector housing against the Sun, and it also features solar panels for the electrical power subsystem.

[11] The control system is 3-axis stabilized, but nadir locked, ensuring that one of the spacecraft axes is always pointing towards the Earth.

During each orbit, the spacecraft will slowly rotate around the telescope line-of-sight to keep the focal plane radiator oriented towards cold space, enabling passive cooling of the detector.

The CCD is mounted in the focal plane of the telescope, and will be passively cooled to 233 K (−40 °C), with a thermal stability of 10 mK.

The plaques, prepared by a team at the Bern University of Applied Sciences were unveiled in a dedicated ceremony at RUAG on 27 August 2018.

[29] The main goal of CHEOPS is the accurate measurement of the size (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' density and thus their approximate composition, such as whether they are gaseous or rocky.

CHEOPS is 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).

[7] CHEOPS measures photometric signals with a precision limited by stellar photon noise of 150 ppm/min for a 9th magnitude star.

Another part of the GTO programme includes exploration of multi-systems and search of additional planets in those systems, for example using the transit-timing-variation (TTV) method.

Researchers can submit proposals for observations with CHEOPS through an annual Announcements of Opportunity (AO) Program.

[34] The approved AO-1 projects include observations of the hot jupiters HD 17156 b, Kelt-22A b,[35] warm jupiter K2-139b,[36] multi systems GJ 9827, K2-138, the exoplanet DS Tuc Ab,[37] 55 Cancri e (likely GTO),[38][39] WASP-189 b[40] and other exoplanet science related observations, such as planets around rapidly-rotating stars, planet material around white dwarfs and searching for transiting exocomets around 5 Vulpeculae.

The full transit of v2 Lupi d was observed for the first time with CHEOPS, potentially aiding any future searches for exomoons around this planet.