Preliminary trajectory design of implementing the asteroid rendezvous and impact in a single launch

This paper presents the preliminary design of single-launch rendezvous and impact trajectories targeting asteroid 2015 XF261, one of the potential candidates for China's first Near-Earth Asteroid Defense Mission. The mission is planning to involve launching an observer for long-term escort operations and an impactor for high-velocity collision with the target asteroid using one rocket. First, based on initial mission requirements, the gravity-assist sequences for the observer and impactor are optimized under simplified models and constraints. Considering the single-launch condition, the selection of the launch orbit is discussed, with results showing that a large elliptical orbit offers advantages over a direct escape orbit for the two spacecraft. Then, to tradeoff their distinct requirements in terms of escape velocity magnitude and direction, impulse maneuvers are designed at varying positions and velocity increment magnitudes during the geocentric segments. The high-precision dynamical model is then employed to determine the final rendezvous and impact trajectories. The optimal velocity increments are 1.59 km/s and 0.14 km/s for the observer and impactor, respectively. Additionally, three alternative trajectory designs are proposed, incorporating an extra flyby of either the target or the asteroid 99942 Apophis, as well as utilizing a distant retrograde orbit around Earth.