Exploration of Jupiter reach Europa after a 6.5 year cruise. The spacecraft would fly by the moon 32 times to minimize radiation damage. Because of the possibility of subsurface liquid oceans on Jupiter's moons Europa, Ganymede and Callisto, there has been great interest in studying the icy moons in detail. Funding difficulties have delayed progress. The "Europa Orbiter" was a planned NASA mission to Europa, which was canceled in 2002. Its main objectives included determining the presence or absence of a subsurface ocean and identifying candidate sites for future lander missions. NASA's "JIMO" ("Jupiter Icy Moons Orbiter"), which was canceled in 2005, and
Colonization of Mars missions, as the "Apollo" missions to the Moon were not planned to be sites of a permanent base. Colonization requires the establishment of permanent habitats that have potential for self-expansion and self-sustenance. Two early proposals for building habitats on Mars are the Mars Direct and the Semi-Direct concepts, advocated by Robert Zubrin. As of 2019, SpaceX owner Elon Musk is funding and developing a series of Mars-bound cargo flights with the BFR rocket and spaceship system as early as 2022, followed by the first crewed flight to Mars on the next launch window in 2024. During the first phase, the