The CHaracterising ExOPlanet Satellite (CHEOPS) is ESA's first small class mission and is a partnership between Switzerland and the ESA Science Programme, with national contributions from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden, and the United Kingdom. Launched on December 18th, 2019, with a mission lifetime of 3.5 years, CHEOPS is a follow-up mission that measures the radii of exoplanets known to transit bright host stars (Vmag 6-12). Together with the mass measurements from other instruments like ESPRESSO at ESO's Paranal site, CHEOPS provides well suitable targets for spectroscopic follow-ups with space- or ground-based observatories like the JWST or the E-ELT.

The CHEOPS Science Operations Centre (SOC) is responsible for the mission planning, the data reduction and the dissemination of science-ready data products through the CHEOPS mission archive. The small class nature of the mission places strict requirements on the SOC; the short development time and limited man power requires a high level of automation and the re-use of existing hardware and software resources. We present here the high-level architecture of the SOC software system and describe challenges and lessons learned from developing and operating the SOC of a small mission.