CRIST Sol Orbiters (Cargo and Resources In-System Transports) are hollow, potato-shaped interplanetary spacecraft powered by solar sails and used to ferry supplies between Earth and Mars. They orbit around the sun, and are loaded up by a tether swinging the materials into orbit behind the CRIST and a reel pulling it in. Offloading was accomplished by "a powerful ion beam which would pound the offloading material with a steady stream of ion particles." Presumably this means that the supplies were launched out of the CRISTs and fell towards the planet, and their descent was slowed to safe speeds by said ion beams. Five CRISTs were made throughout history.