Kepler space telescope. Computer artwork of NASA's Kepler telescope leaving Earth orbit. The Kepler Mission is designed to discover Earth-like planets orbiting other stars. Kepler's 0.95-metre diameter photometer will scan 100,000 stars in the Milky Way for evidence of Earth-sized terrestrial planets that transit the star's path. The mission was launched in March 2009, and will orbit the Sun for at least 3.5 years. The mission is named in honour of German astronomer Johannes Kepler.