CROWN/Apophis Mission

The close encounter of asteroid (99942) Apophis with Earth on 2029 April 13 represents a once-in-thousands-of-years opportunity to study the effects of tidal interaction from a planet on the evolution of an asteroid. We propose to use the CROWN technology pathfinder spacecraft to perform a flyby exploration of Apophis. CROWN is a mission concept for a space-based asteroid survey that will deploy a constellation of spacecraft in a Venus-like heliocentric orbit to substantially improve the searching and tracking efficiencies for near-Earth asteroids (NEAs). A technology pathfinder mission is planned to send a spacecraft to the Sun-Earth L1 halo orbit to demonstrate the technical readiness of a space-based survey telescope for NEAs and to gain experience for the design and operations of the CROWN mission. The pathfinder spacecraft will be launched to L1 halo orbit, testing the space-based NEA survey, and waiting for Apophis to arrive. While in L1, the camera is expected to detect Apophis over 100 days before it encounters Earth, and will gather photometric data of the asteroid.  The spacecraft will then drift out of the halo orbit to perform a flyby of Apophis on April 16 at 10:45 UT, about 2.5 days after its Earth encounter. The scientific goals of the CROWN/Apophis mission are to measure the basic properties of Apophis and search for the signatures of the tidal interaction with Earth during the encounter. The pathfinder spacecraft is equipped with a panchromatic visible camera and a visible-near-infrared spectrometer. It will also carry a cubesat to be separated before the flyby to perform intersatellite ranging and Doppler measurements during the flyby to detect the gravitational field of Apophis for a mass estimate. Such measurements, if successful, will be the first mass measurement of a sub-km-sized asteroid from a flyby, and will demonstrate such a technology that can be widely used in future NEA flybys for science explorations and resource utilization reconnaissance. The panchromatic camera will continuously collect images of Apophis during the flyby and is expected to reach sub-meter resolution near the closest approach. The spectrometer will also continuously collect data during the flyby. With the observations and intersatellite ranging and Doppler measurements, we expect to measure the density and probably density distribution of Apophis, determine surface composition, constrain the rotational status of Apophis before and after the encounter, and observe potential mass movement on the surface of Apophis during the Earth encounter. A dust detector is also under consideration to search for potential dust activity of Apophis and the interaction with the terrestrial magnetosphere during the Earth encounter. The CROWN/Apophis mission is expected to contribute to the coordinated effort from around the globe to study Apophis in the 2029 opportunity, and to demonstrate the capability of performing fast-response reconnaissance of potential hazardous asteroids in the future.