To design and prototype the GNC system for rendezvous and docking in Near Rectilinear Orbits (NRO) around the Moon.

The ISS Exploration Capabilities Study (IECS) is a joint study undertaken by ESA in cooperation with the 4 other ISS partners: NASA, JAXA, Rosscosmos, and CSA. In the IECS study, the human exploration programme for the period 2021-2030 is addressed. In this study it is proposed that in the first half of the 2020(s), a joint programme could start by building a Cis-Lunar Transport Habitat (CTH) vehicle. The CTH will be placed on a NRO orbit around the Moon. Safety of underlying trajectories is critical for rendezvous to human-tended infrastructure. Hence the rendezvous trajectories are designed to ensure maximum safety and in particular safe free drift (passive safe trajectories). It is therefore important to understand the relative target-chaser dynamic in the three body problem of a NRO orbit. The emphasis is placed on the relative dynamics and the guidance part of the GNC system since the rendezvous is performed in a high elliptical orbit in the Earth-Moon 3-body problem. The design of the guidance algorithms shall include passively safe trajectories as well as active collision avoidance manoeuvres. Optimal guidance and control algorithms will include all constraints to provide a feasible solution in every control loop. The guidance and control algorithms are prototyped in reliable, space-qualified processors.Tasks to accomplish the objectives are as follows:- Requirements gathering and analysis: this comprises the mission scenarios analysis and extraction of requirements. This task covers an exhaustive system analysis study about rendezvous trajectory design considering safety requirements, GNC techniques and technologies, thus arriving at requirement specifications of a reference rendezvous scenario and GNC simulation tool. This task provides a preliminary design analysis of the overall rendezvous strategy including rendezvous trajectory design down to GNC level, including the definition of the simulation tool, leading the selection of the guidance and control algorithms. This tasks also includes the collision avoidance manoeuvres, hold points, safe spheres, retreat areas, etc.- Design: the guidance and control algorithms will be designed using analysis tools to assess the performances in nominal scenario considering the uncertainties (in particular from navigation chain). It comprises the design of a non-linear simulation tool covering as well GNC performance verification, robustness and benchmarking.- Preliminary development and implementation of the algorithms: The task is related to the development of the non-linear simulation tool, and coding and integration of the selected GNC algorithm(s) into the simulation tool. This task shall cover the full development of the simulation tool and the inclusion of the algorithms. The simulation tool permits the autocoding of the algorithms for real-time testing.- Demonstration of prototype to TRL 3: This task is devoted to the testing of GNC algorithms in the simulation tool and a prototype in a PIL system. The testing shall comprise a full 6DoF closed loop simulations, including trajectory safety, GNC performances, robustness verification and validation. MonteCarlo analysis shall be performed for the most relevant parameters of the flight of the vehicles and in particular to refine requirements on the navigation specifications. Guidance, and control algorithms shall be bench marked in a real-time Processor-In-the-Loop (PIL) testbench to achieve confidence in the design. - Synthesis: It contemplates the elaboration of a set of recommendation to the Agency for future work.