THETHERS AS FAR MISSION DESCENT-RETURN TOOLS

摘要

Space tethers are investigated as possible future reusable competitive-cost tools for non-gasdynamic descent, landing, takeoff and return from target celestial bodies. The Moon, Mars and a distant planet satellite like Titan are first taken into account as sample mission objectives. The investigation is focused on the mechanical usefulness of the system in comparison with the heavy duty mass expelling energy requirements of equivalent gasdynamic propulsion systems. The two potential categories are (a) the free tether release and return systems and (b) two fixed-points elevator systems. The first one is a further development of the already proposed partial descent system from the Earth ISS adapted to be maneuvered from a robot, remotely flying unmanned spacecraft, up to a complete descent. The second type is an extraterrestrial extension of the proposed Earth based space elevator system and is numerically investigated. Specific deployment techniques prove fitting descent on target bodies with and without an atmosphere. For the case of the Earth, Moon, Europa and similar planetary satellites a free deployment mode is proposed, considering the feasibility of Lunar based, manned deployment maneuvers as solutions of the future. A number of hard technical requirements still remain to be investigated and solutions found, regarding for instance the control of errors in correlation with system dynamics. It proves that, for some of the sample missions analyzed and particularly for the Moon, Europa and Rhea the tethered systems are nevertheless more likely to reach a convenient exploitation stage than the future Earth based space elevator system. This is due to the negligible atmosphere and the low gravity of these moons. It is supposed that the manufacturing technology of light strings will properly mature.