  DESTINY+ is an upcoming JAXA Epsilon medium-class mission to fly by the
Geminids meteor shower parent body (3200) Phaethon. It will be the world's
first spacecraft to escape from a near-geostationary transfer orbit into deep
space using a low-thrust propulsion system. In doing so, DESTINY+ will
demonstrate a number of technologies that include a highly efficient ion engine
system, lightweight solar array panels, and advanced asteroid flyby observation
instruments. These demonstrations will pave the way for JAXA's envisioned
low-cost, high-frequency space exploration plans. Following the Phaethon flyby
observation, DESTINY+ will visit additional asteroids as its extended mission.
The mission design is divided into three phases: a spiral-shaped apogee-raising
phase, a multi-lunar-flyby phase to escape Earth, and an interplanetary and
asteroids flyby phase. The main challenges include the optimization of the
many-revolution low-thrust spiral phase under operational constraints; the
design of a multi-lunar-flyby sequence in a multi-body environment; and the
design of multiple asteroid flybys connected via Earth gravity assists. This
paper shows a novel, practical approach to tackle these complex problems, and
presents feasible solutions found within the mass budget and mission
constraints. Among them, the baseline solution is shown and discussed in depth;
DESTINY+ will spend two years raising its apogee with ion engines, followed by
four lunar gravity assists, and a flyby of asteroids (3200) Phaethon and
(155140) 2005 UD. Finally, the flight operations plan for the spiral phase and
the asteroid flyby phase are presented in detail.
