The ESA Comet Interceptor Mission

Comet Interceptor (Comet-I) is the first Fast track development mission (F1) in ESA’s Cosmic Vision 2015-2025 Programme, selected in June 2019. The mission aims to perform multi-point observations to characterize a yet-to-be-identified comet. All space missions to comets so far have visited short-period comets (SPCs). Comet Interceptor will, for the first time, target a long-period comet (LPC), ideally a dynamically new one  (DNC) or even an Interstellar Object (IO).

The mission will investigate the processes of planetesimal formation by evaluating which of the phenomena observed by previous missions, particularly during the rendezvous of Rosetta with Comet 67P, are primordial and which have developed during the many perihelion passages of those SPCs. Specifically, the objectives of Comet Interceptor are:

1) Comet Nucleus Science - What is the surface composition, shape, morphology, and structure of the target object?

2) Comet Environment Science - What is the composition of the coma, its connection to the nucleus (activity) and the nature of its interaction with the solar wind?”

The mission consists of a main spacecraft (S/C A) and two small probes (B1 and B2). The space segment is under ESA’s responsibility, with OHB Italia as prime contractor and Probe B2 developed by SENER Spain. The scientific instruments for S/C A and Probe B2 are developed by nationally funded consortia, while Probe B1 is provided by the Japan Aerospace Exploration Agency (JAXA). A comprehensive suite of instruments is distributed among the S/C A and the probes providing full coverage to the European cometary science community to address the scientific objectives of the mission.

The spacecraft and the probes are expected to be integrated, tested and ready for flight by mid 2028. Few months later, the Comet-I will be launched on Ariane 64 from Kourou in a double launch configuration, together with a co-passenger on the upper position of the dual launch structure. Following separation from the launch vehicle, Comet-I will use its own propulsion system to reach a waiting orbit at the Sun-Earth Lagrangian point L2 (SEL2). After a waiting phase at SEL2 limited to up to 4 years and used to select the actual target object, Comet-I will then initiate a transfer phase which could last up to 2 years.

The final fly-by at relative velocities ranging between 10 and 70 km/s represent a single-shot science opportunity for the mission. Therefore, and from the concept of operations viewpoint, the approach and encounter are critical mission phases.  The approach phase will start 60 days before the closest approach (CA) to the comet and with the ground-based navigation aided using the S/C A on-board navigation cameras. In the last 3 days, in order to ensure each spacecraft’s nominal fly-by geometry within the required dispersion error a series of targeting manoeuvres will be executed which will conclude with the release of the two probes (42h and 20h before CA respectively for B1 and B2) and the initialisation of the S/C A autonomous tracking and control functions (13 h before CA). These functions will guide the S/C A autonomously (with no ground intervention) during the fly-by phase with sufficient control authority and agility to react to dust impacts, as well as to the navigation challenges given the uncertainty in target size and activity.

Throughout the encounter phase, the Probes B1 and B2 will relay their scientific data back to the S/C A via the inter-satellite link (S-band) for as long as possible. Following the encounter, the SC-A will downlink to Earth (X-band) the data acquired during the fly-by. This concept of operations enables a combination of a lower risk and guaranteed baseline science return from the more distant spacecraft with higher-risk but high-gain sampling of the inner coma by the releasable probes, which may not necessarily need to survive the encounter for ensuring mission success.

This presentation describes the Comet-I mission design and reports on the overall concept of operations  highlighting the main system level capabilities  to cope with an unknown target that provides an innovative mission concept to enable wider planetary exploration.