In 2011, after the retirement of the space shuttle, NASA announced its intentions to invest money into developing three technologies vital to deep space exploration. The "must-have technologies" include a deep space atomic clock, a large solar sail and a more advanced laser communications system to improve communication, navigation, and propulsion in future missions.[1] In June 2013, NASA announced the selection of eight American astronauts that will begin to train for future deep space missions beyond low Earth orbit. NASA intends that these eight astronauts to train for future Mars or asteroid travel.[2]