A Precursor for a Crewed Mission to Near-Earth Asteroids: the SESAME Concept

摘要

A crewed mission to Near-Earth Asteroids (NEAs) would maximize the quality and the amount of returned information regarding scientific, technological, mitigation or resource utilization purposes. To effectively prepare such a mission, a robotic precursor should visit the asteroid target(s) to ensure its relevance and safety. This study describes the architecture, trajectory and system design of a precursor mission. Using low-thrust propulsion for multi-rendezvous approaches to Near-Earth Asteroids (NEAs), this mission named SESAME (Spacecraft for Evaluation of Suitability of Asteroids for Manned Exploration) is the first multi-targets precursor mission towards NEAs. A comparison of the lists of accessible targets for human spaceflight with the trajectories from the 5~(th) Global Trajectory Optimization Competition (GTOC5) is presented. GTOC5 trajectories are highly optimized, low thrust trajectories reaching multiple (up to 18) NEAs. However, the low correlation between the lists makes them unusable for a precursor mission and a new trajectory was computed. The outcome was a trajectory with a departure in 2023 reaching seven asteroids in less than 10 years (all in the top 25 of the Near-Earth Object Human Space Flight Accessible Targets Study (NHATS)). To comply with this trajectory, the final design focused on payload, propulsion, communication and power subsystems resulted in a precursor spacecraft reaching the first five targets of the trajectory: 2001 QJ142, 2000 SG344, 2009 OS5, 2007 YF and 1999 AO10. SESAME carries five 27.6 kg landers each having a short term observation function and a long term beacon function to guide the future crew. The spacecraft is powered by two 17 m~2 solar arrays and its propulsion system consists of three RIT-22 ion engines (one redundant). It uses Ka-band for the downlink communication to Earth. The total fuel mass of 576 kg consists of 451 kg of xenon for the ion propulsion and 125 kg of bi-propellant for the attitude control thrusters. The total launch mass is 1571 kg, well within the capabilities of current launchers. Finally, the results of a sensitivity analysis of the design evaluating the impact of changes in the ?V required for the maneuvers at each target, in the power supply and in the dry mass are presented. SESAME represents a feasible spacecraft capable of reaching five of the most promising NEAs in less than seven years, with an average of five months of operation at each target.