ESA GNC Conference Papers Repository

The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) of the European Space Agency was launched on 17th March 2009 with the objective of providing data for establishing a model of the Earth's gravity field with unprecedented accuracy, embarking as payloads an Electrostatic Gravity Gradiometer (EGG) and a scientific GPS receiver (SSTI). To achieve its scientific objectives, GOCE flies on a near-polar sun-synchronous orbit at an exceptionally low altitude of about 260 km. Owing to the drag environment in which GOCE is operated, the spacecraft is aerodynamically shaped and employs a unique Drag-Free Attitude and orbit Control System (DFACS). The DFACS uses an ion propulsion system and the EGG to dynamically measure and counteract the drag caused by the residual atmosphere of the Earth, maintaining the orbit and cancelling out the effects of non-gravitational perturbations on the spacecraft dynamics. After a short description of the satellite and of the scientific objectives, the paper will present the GOCE DFACS architecture and will report about the in-orbit experience with this system in over two years of commissioning and routine operations.