So far, only two balloons have flown outside of Earth. In 1985, the Soviet Union dropped two simple ones into the atmosphere of Venus during the Vega missions. These were highly successful, returning atmospheric data for several hours. Scientists have been planning to send balloons to Mars for decades, but none have even reached the flight approval stage. The first Martian balloon would probably be similar in size and capabilities to its Venusian counterparts. It would be a simple helium sphere with no sophisticated navigational capabilities. A small instrument package, powered by a battery, would send data to an overhead orbiter. The balloon would carry atmospheric sensors and a small CCD camera.