Gravity Field and Steady-State Ocean Circulation Explorer

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The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) is an ESA satellite to be launched in summer of 2008. Its main payload is the Electrostatic Gravity Gradiometer (EGG) to measure the gravity field of Earth.

Its arrow shape and fins help keep the satellite stable as it flies through the wisps of air still present at an altitude of 260km. The low orbit and high accuracy of 1 mGal will improved the known accuracy of the geoid to 1-2 cm at a spatial resolution better than 100 km^[1]. To increase resolution, the satellite will fly in an unusually low orbit; an electric engine will make up drag losses to compensate for the residual drag losses.

GOCE data will have many uses, probing hazardous volcanic regions and bringing new insight into ocean behaviour.

The latter, in particular, is a major driver for the mission.

By combining the gravity data with information about sea-surface height gathered by other spacecraft, scientists will be able to track the direction and speed of geostrophic ocean currents.

GOCE will be launched from the Plesetsk Cosmodrome in northern Russia with a Rockot vehicle. The Rockot is a modified SS-19 intercontinental ballistic missile that was decommissioned after the Strategic Arms Reduction Treaty. The launcher uses the two lower liquid fuel stages of the original SS-19 and is equipped with a third stage developed for precise orbit injection. GOCE will be launched into a Sunsynchronous dawn-dusk orbit with an inclination of 96.70˚ and an ascending node at 6:00. Separation from the launcher will be at 295 km. The satellite’s orbit will then decay over a period of 45 days to an operational altitude, currently planned at 270 km. During this time, the spacecraft will be commissioned and the electrical propulsion system will be checked for reliability in attitude control.^[2]