Colonization of the outer Solar System is subject to only 0.01 rem a day. When NASA carried out a study called "HOPE" (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the Solar System, the target chosen was Callisto. It might be possible to build a surface base that would produce fuel for further exploration of the Solar System. The Keck Observatory announced in 2006 that the binary Jupiter trojan 617 Patroclus, and possibly many other Jupiter trojans, are likely composed of water ice, with a layer of dust. This suggests that mining water and other volatiles in this region and transporting them
Gravity assist orbital inclinations from 0° to 74°. The "Rosetta" probe, launched in March 2004, used four gravity assist maneuvers (including one just 250 km from the surface of Mars) to accelerate throughout the inner Solar System - enabling it to match the velocity of the 67P/Churyumov–Gerasimenko comet at their rendezvous point in August 2014. NASA's Parker Solar Probe mission, launched in 2018, will use multiple gravity assists at Venus to remove the Earth's angular momentum from the orbit, in order to drop down to a distance of 8.5 solar radii (5.9 Gm) from the Sun. Parker Solar Probe's mission will be