Abstract: In near-Earth asteroid defense missions, the kinetic impact method is currently the primary approach for on-orbit deflection of target asteroids. Centered on the impactor, such missions aim to alter the asteroid's orbit through momentum exchange, and the impactor is used to accomplish orbital transfer, proximity approach, terminal guidance, and high-speed kinetic impact. This paper completes mission analysis by considering mission constraints, including asteroid characteristics, impact effects, orbit design, and navigation configuration, and proposes three key overall design points for the impactor: full-chain precision control, high-reliability design, and autonomous mission design. The main error sources affecting impact precision are identified, qualitative sensitivity analysis is conducted for key error sources, and error control suggestions are provided. A hierarchical high-reliability design approach is proposed based on measures such as secondary impact design, product or functional heterogeneous backup, and fault isolation. Terminal guidance autonomous handover and reverse handover designs are introduced to enhance the impactor’s autonomous mission capability, providing a reference for the engineering design of impactors in near-Earth asteroid defense missions.