The Comet Interceptor Mission

In 2019, Comet Interceptor was selected by the European Space Agency, ESA, as the first in its new class of Fast (F) projects, with the Japanese space agency, JAXA, making a major contribution to the mission. The mission's primary science goal is to characterise for the first time, a yet-to-be-discovered long-period comet, preferably dynamically new, or an interstellar object. An encounter with a comet approaching the Sun for the first time will provide valuable data to complement that gathered by all previous comet missions, which all visited more evolved short period comets. The spacecraft will be launched in 2029 to the Sun-Earth L2 Lagrange Point. This relatively stable location allows a rapid response to the appearance of a suitable target comet, which will need to cross the ecliptic plane in an annulus that contains Earth's orbit. A suitable new comet will be searched for from Earth using powerful facilities such as the Vera Rubin Observatory, with known short period comets acting as backup targets. The spacecraft could encounter an interstellar object if one is found on a suitable trajectory. The spacecraft must cope with a wide range of target activity levels, flyby speeds, and encounter geometries. This flexibility has significant impacts on its solar power input, thermal design, and dust shielding that can cope with dust impacts. Comet Interceptor comprises a main spacecraft and two smaller probes, one provided by ESA, the other by JAXA, which will be released by the main spacecraft on approach. This primary spacecraft will act as the communication point for the whole constellation, and will be targeted to pass outside the most hazardous region of the inner coma, making remote and in situ observations on the comet's sunward side, whilst the two probes will venture closer to the nucleus. Planned measurements of the target include its surface composition, shape, and structure, its dust environment, and the gas coma's composition. A unique, multi-point 'snapshot' of the comet- solar wind interaction region will be obtained, complementing single spacecraft observations at other comets. We shall describe the science drivers, planned observations, and the mission's instrument complement, to be provided by consortia of institutions in Europe and Japan. Team members are listed at www.cometinterceptor.space