  Near Earth Asteroids have a possibility of impacting with the Earth and
always have a thread on the Earth. This paper proposes a way of changing the
trajectory of the asteroid to avoid the impaction. Solar sail evolving in a
H-reversal trajectory is utilized for asteroid deflection. Firstly, the
dynamics of solar sail and the characteristics of the H-reversal trajectory are
analyzed. Then, the attitude of the solar sail is optimized to guide the sail
to impact with the object asteroid along a H-reversal trajectory. The impact
velocity depends on two important parameters: the minimum solar distance along
the trajectory and lightness number. A larger lightness number and a smaller
solar distance lead to a higher impact velocity. Finally, the deflection
capability of a solar sail impacting with the asteroid along the H-reversal is
discussed. The results show that a 10 kg solar sail with a lead-time of one
year can move Apophis out of a 600-m keyhole area in 2029 to eliminate the
possibility of its resonant return in 2036.
