Abstract
The paper presents the development of a fully-safe, automatic rendezvous strategy between a passive vehicle and an active one orbiting around the Earth–Moon L2 Lagrangian point. This is one of the critical phases of future missions to permanently return to the Moon, which are of interest to the majority of space organizations. The first step in the study is the derivation of a suitable full 6-DOF relative motion model in the Local Vertical Local Horizontal reference frame, most suitable for the design of the guidance. The main dynamic model is approximated using both the elliptic and circular three-body motion, due to the contribution of Earth and Moon gravity. A rather detailed set of sensors and actuator dynamics was also implemented in order to ensure the reliability of the guidance algorithms. The selection of guidance and control is presented, and evaluated using a sample scenario as described by ESA’s HERACLES program. The safety, in particular the passive safety, concept is introduced and different techniques to guarantee it are discussed that exploit the ideas of stable and unstable manifolds to intrinsically guarantee some properties at each hold-point, in which the rendezvous trajectory is divided. Finally, the rendezvous dynamics are validated using available Ephemeris models in order to verify the validity of the results and their limitations for future more detailed design.
Highlights
The paper presents some of the dynamics models and potential guidance algorithms usable for the preliminary assessment of a rendezvous between an unmanned vehicle ascending from the Moon, and a permanent manned/unmanned service station located in a collinear Lagrangian point orbit of the Earth–Moon system
The paper presents a comprehensive preliminary analysis of the dynamics and control issues arising in a rendezvous mission between an active vehicle departing from lunar orbit to a target station located in an Near Rectilinear Halo Orbit (NRHO) L2 orbit
The accuracy of the model was improved with the inclusion of sensors and actuators models, and guidance algorithms were selected in order to verify the reliability of the GNC loop
Summary
The paper presents some of the dynamics models and potential guidance algorithms usable for the preliminary assessment of a rendezvous between an unmanned vehicle ascending from the Moon, and a permanent manned/unmanned service station located in a collinear Lagrangian point orbit of the Earth–Moon system. The Heracles project was initially planned with the objective of delivering Moon samples to Earth on NASA’s Orion spacecraft as early as its fourth or fifth mission. The initial project was set up to be integrated with NASA’s plan to return to the Moon, and to build a permanent station (Gateway) in cislunar orbit. When the ascent module carrying the sample container arrives, the Gateway’s robotic arm will capture it and berth it with the outpost’s airlock for unpacking and transfer of the container to Orion and subsequent unmanned flights to Earth and later on with returning astronauts
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