Kepler Space Telescope
Kepler has been on a quest to find possible terrestrial and habitable exoplanets. NASA’s tenth discovery mission has been surveying our part of the Milky way since its launch in 2009. Kepler aims to explore and observe the structure and diversity of planetary systems, but after four years and 150,000 monitored stars it lost the second of four reaction wheels. This mission failure called for the K2 mission, which enabled the telescope to operate again by using the pressure of sunlight to hold its gaze steady.