CR3BP-Based Reachability Analysis for the Comet Interceptor Mission

Comet Interceptor is ESA’s Fast-Class mission within the Cosmic Vision Programme, aiming to perform the first-ever flyby of a dynamically new comet, entering the inner Solar System for the first time. Unlike previously visited comets, which had already undergone multiple perihelion passages, such pristine targets are expected to have experienced minimal alteration since their formation in the outermost regions of the Solar System, making them of high scientific interest. Comet Interceptor will be launched into a parking-orbit around the Sun-Earth Lagrangian L2 point, where it will remain on standby until the detection of a suitable long-period comet. As such comets are usually discovered only when entering the inner Solar System, the mission cannot rely on pre-optimized trajectories to a specific target. Instead, the key design challenge lies in characterizing and maximizing mission accessibility, i.e. understanding how the accessible region and the fraction of reachable candidate targets vary with available ΔV budget, time of flight, and parking orbit configuration. This paper proposes a Sun-Earth Circular Restricted Three-Body Problem-based framework to quantify the accessible region from the Lagrangian L2 parking orbit. Intercept trajectories are defined as two-impulse transfers, exploiting the unstable invariant manifolds of halo orbits for low-cost departure, followed by a Lambert arc to the interception point along the comet trajectory. The reachable region is first characterized in the synodic ecliptic frame for a representative parking orbit and a realistic maximum time of flight constraint, allowing mission accessibility to be quantified as a function of ΔV budget. This is completed by an analysis of feasible transfers departing from different parking orbit on a list of historical long-period comets. The results highlight a strong dependence of reachable regions on both the ΔV and time of flight. The initial parking orbit, does not impact the global behavior ΔV as a function of time of flight, however, the initial energy contained in the orbit, characterized by the Jacobi Constant, shifts the location of the minimum within this space, with higher energy levels (lower Jacobi Constants) implying both a lower ΔV and a shorter time of flight.