Rapid Response to Long Period Comets and Interstellar Objects using SmallSat Architecture

Once in about each decade, a large, pristine Oort Cloud Comet (OCC) completes a ~million-year journey to the inner solar system, bringing with it a fossil record of the solar system's formation. These dynamic comets contain preserved, pristine volatiles from their accretional environment at the edge of the protoplanetary disk. OCCs appear with little notice, necessitating a rapid response approach to conduct a close-encounter mission. A mission to encounter an OCC was previously thought to be impossible or unaffordable due to the large launch energies required to encounter these bodies, the technical capability required to encounter the OCC at extremely high velocities, and, especially, the short duration between discovery of the target and latest possible launch date. We present a SmallSat mission architecture concept, Xenia - named for the Greek tradition of welcoming far-away guests, that would encounter C/2017 K2, henceforth K2, a “great” comet discovered in 2017 that will cross the ecliptic in December 2022 around 2.3 AU from the Sun and 2.1 AU from Earth. This is the first time that an OCC has been detected more than five years before its perihelion in the inner solar system. Xenia would consist of two 75 kg spacecraft equipped with a small payload suite to conduct a pathfinding mission - the first ever flyby of an OCC. Xenia would require a dedicated launch vehicle to achieve a launch energy exceeding 57 km
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/s
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in order to encounter the comet at the ecliptic after a short six-month cruise. The spacecraft would feature state-of-the-art technology to deal with the limited spacecraft resources and challenging observation conditions, including a very fast flyby and constrained data return. The synergy between increasingly capable SmallSat technology, miniaturization of science instrumentation, and next-generation Earth-based telescopes that may detect OCCs up to 10 years prior to perihelion makes now the opportune time to devise plans for future missions to OCCs. Although Xenia is feasible with current or near-future technologies, there is no current programmatic path to conduct a rapid response mission. The prescribed cadence of NASA' mission calls, such as the Small Innovative Missions for PLanetary Exploration (SIMPLEx) and the mandate of that program to use a ride-share makes rapid response prohibitive. The SIMPLEx low cost-cap (as of 2018) is also likely too low for a mission of this class. With small modifications to the SIMPLEx call or with the introduction of a new type of announcement of opportunity (AO), a SmallSat mission to visit an OCC would become feasible. If flight system designs or flight hardware is readily available before the next object is discovered, a mission is surely achievable. This paper outlines the Xenia mission concept and lessons learned. We also provide recommendations for future work in rapid response, which is relevant to Planetary Defense and interstellar object exploration, as well. With NASA revisions to AO structures and dedicated technology maturation, Xenia or a similar concept could tease out the secrets of the next “great” OCC that visits the inner solar system.