Sample return system of OKEANOS—The solar power sail for Jupiter Trojan exploration

The Japan Aerospace Exploration Agency had planned a sample return from the Jupiter Trojans using a solar power sail in its Oversize Kite-craft for Exploration and AstroNautics in the Outer Solar system (OKEANOS) mission. Solar power sail is an extended concept of solar sail consisting of a sail membrane covered with flexible solar arrays. OKEANOS is capable of generating a large amount of power sufficient to drive high-specific-impulse ion engines in the outer solar system, thus making it possible to perform sample return from the Jupiter Trojans. Various innovative technologies are needed to realize such a challenging mission in the distant space. Specifically, OKEANOS deploys a small lander to ensure the safety and save propellant of the mother spacecraft. The lander collects samples of the asteroid, and separates them into different groups, namely, those for in-situ analysis and those for return. After completing the in-situ analysis, the lander lifts off the asteroid, docks with the mother spacecraft, and delivers the samples to the reentry capsule mounted on the mother spacecraft. The reentry capsule is designed so that it can manage the reentry speed of 15 km/s. Although OKEANOS was proposed as a Japanese large-class mission and advanced to the final selection, it was not selected because of a cost issue. However, its sample return concept is inherited by small- and massive-body explorations coming in the next generations. In this paper, we report the state-of-the-art technologies that enable sample returns from the outer solar system, which were developed through the OKEANOS mission study.