  Context. The close approach of the near-Earth asteroid (99942) Apophis to
Earth in 2029 will provide a unique opportunity to examine how the physical
properties of the asteroid could be changed due to the Earth's gravitational
perturbation. As a result, the Republic of Korea is planning a rendezvous
mission to Apophis. Aims. Our aim was to use photometric data from the
apparitions in 2020-2021 to refine the shape model and spin state of Apophis.
Methods. Using thirty-six 1 to 2-m class ground-based telescopes and the
Transiting Exoplanet Survey Satellite, we performed a photometric observation
campaign throughout the 2020-2021 apparition. The convex shape model and spin
state were refined using the light-curve inversion method. Results. According
to our best-fit model, Apophis is rotating in a short axis mode with rotation
and precession periods of 264.178 hours and 27.38547 hours, respectively. The
angular momentum vector orientation of Apophis was found as (275$^\circ$,
-85$^\circ$) in the ecliptic coordinate system. The ratio of the dynamic
moments of inertia of this asteroid was fitted to $I_a:I_b:I_c=0.64:0.97:1$,
which corresponds to an elongated prolate ellipsoid. These findings regarding
the spin state and shape model could be used to not only design the space
mission scenario but also investigate the impact of the Earth's tidal force
during close encounters.
