Interstellar Object Accessibility and Mission Design

Interstellar objects (ISOs) are fascinating and underexplored celestial objects, providing physical laboratories tounderstand the formation of our solar system and probe thecomposition and properties of material formed in exoplanetary systems. The recent Planetary Science and AstrobiologyDecadal Survey emphasized that a dedicated mission to an interstellar object would have high science value. While telescopicobservations from Earth-based observatories and telescopes canprovide valuable science, a dedicated spacecraft can acquireunique information through higher resolution optical remotesensing and physical interrogation of the target. A dedicatedspacecraft could resolve the shape, rotation properties, surfacemorphology, and composition of an asteroid-like ISO. Massspectroscopy techniques can probe the gas composition of acomet-like ISO. Using an impactor at an asteroid-like ISO couldalso reveal fresh surface material to remove any effects of spaceweathering due to long exposure to interstellar space.Because of various challenges posed by ISOs’ dynamical properties, only flyby missions can be envisioned at this time. Evenso, late detection and hyperbolic trajectories of ISOs pose major challenges to a flyby mission. Late detection times causeextremely poorly constrained ISO trajectories at the time oflaunch that need to be corrected in-flight, and hyperbolic trajectories tend to result in very high relative velocities (tens ofkm/s) between the target and the spacecraft, making navigationchallenging or impossible to include ground-in-the-loop (GITL),as is traditionally done today.Researchers at JPL and Caltech have investigated approaches todesigning successful flyby missions to ISOs. We have generatedtrajectories to a series of synthetic ISOs, simulating a groundcampaign to observe the target and resolve its state, and determining the cruise and close approach ∆V required for theencounter. Furthermore, the Caltech team developed a series ofdeep learning-driven guidance and control (G&C) algorithms toenable an accurate flyby of an ISO at velocities over 60 km/s.We assumed as an additional requirement on mission designthat the spacecraft be relatively low ∆V . This is driven bythe expectation that missions to newly discovered ISOs wouldbe best implemented using small spacecraft. The unification ofISO detection, orbit characterization, and cruise trajectory withlearning-based G&C algorithms for accurate low-∆V flybysrepresents a nearly end-to-end simulation and assessment of amission to visit an ISO. This process is simulated using JPL’sSmallSat Development Testbed, which determines the feasibilityof encountering ISOs with different initial detection and orbitcharacteristics.This paper will discuss the accessibility of and mission designto ISOs with varying characteristics, including a discussion ofstate covariance estimation over the course of cruise, handoffsfrom traditional navigation approaches to novel autonomousnavigation for fast flyby regimes, and overall recommendationsabout preparing for the future in situ exploration of thesetargets. The lessons learned also apply to the fast flyby ofother small bodies including long period comets and potentiallyhazardous asteroids, which also require tactical response withsimilar characteristics.