Solar Sail Trajectory Optimization for Intercepting, Impacting, and Deflecting Near-Earth Asteroids

Abstract

A fictional asteroid mitigation problem posed by AIAA assumes that a 200m nearEarth asteroid (NEA), detected on 04 July 2004 and designated as 2004WR, will impact the Earth on 14 January 2015. Adopting this exemplary scenario, we show that solar sail spacecraft that impact the asteroid with very high velocity are a realistic near-term option for mitigating the impact threat from NEAs. The proposed mission requires several Kinetic Energy Interceptor (KEI) solar sail spacecraft. Each sailcraft consists of a 160m × 160m, 168 kg solar sail and a 150 kg impactor. Because of their large ∆V-capability, solar sailcraft with a characteristic acceleration of 0.5mm/s can achieve an orbit that is retrograde to the target orbit within less than about 4.5 years. Prior to impacting 2004WR at its perihelion of about 0.75AU, each impactor is to be separated from its solar sail. With a relative impact velocity of about 81 km/s, each impactor will cause a conservatively estimated ∆v of about 0.35 cm/s in the trajectory of the target asteroid, largely due to the impulsive effect of material ejected from the newly formed crater. The deflection caused by a single impactor will increase the Earth-miss distance by about 0.7 Earth radii. Several sailcraft will therefore be required for consecutive impacts to increase the total Earthmiss distance to a safe value. In this paper, we elaborate a potential mission scenario and investigate trade-offs between different mission parameters, e.g. characteristic acceleration, sail temperature limit, hyperbolic excess energy for interplanetary insertion, and optical solar sail degradation.