More than 200 spacecraft have successfully explored about 100 extraterrestrial bodies, including all planets and their major satellites. In-situ observations and return-sample analyses revealed the orbital parameters and compositional distributions of solar system bodies, which are essential to discuss possible utilization of space materials. At an early stage of the future in-situ resource utilization (ISRU), the availability of volatiles, including water on asteroids and putative ice on the Moon, becomes a primary issue, especially for their utilization as propellants. Autonomous transportation systems between solar bodies would then be supported by such volatile materials obtained on small bodies. Infrastructures, including bases, could be developed with materials excavated from appropriate bodies and transferred through such a system. Extensive utilization of space resources on Earth may happen but not in the near future.