 In 1981 , a proposal for an asteroid mission was submitted to the European Space Agency ( ESA ) . Named the <unk> Gravity Optical and Radar Analysis ( <unk> ) , this spacecraft was to launch some time in 1990 – 1994 and perform two flybys of large asteroids . The preferred target for this mission was Vesta . <unk> would reach the asteroid belt either by a gravitational <unk> trajectory past Mars or by means of a small ion engine . However , the proposal was refused by ESA . A joint NASA – ESA asteroid mission was then drawn up for a Multiple <unk> Orbiter with Solar Electric <unk> ( <unk> ) , with one of the mission <unk> including an orbit of Vesta . NASA indicated they were not interested in an asteroid mission . Instead , ESA set up a technological study of a spacecraft with an ion drive . Other missions to the asteroid belt were proposed in the 1980s by France , Germany , Italy , and the United States , but none were approved . Exploration of Ceres by fly @-@ by and impacting <unk> was the second main target of the second plan of the <unk> Soviet Vesta mission , developed in cooperation with European countries for realisation in 1991 – 1994 but canceled due to the Soviet Union disbanding . 
