Bernd Dachwald, Bong Wie
Solar Sail Kinetic Energy Impactor Trajectory Optimization for an Asteroid Deflection Mission
Journal of Spacecraft and Rockets, Vol. 44, No. 4, 2007, pp. 755-764
A fictional asteroid-mitigation problem created by AIAA assumes that a 200-m near-Earth asteroid, detected on 04 July 2004 and designated as 2004 WR, will impact the Earth on 14 January 2015. Adopting this example scenario, we show that solar-sail spacecraft that impact the asteroid with a very high relative velocity are a realistic near-term option for mitigating the impact threat from near-Earth asteroids. The proposed mission requires several kinetic energy impactor solar-sail spacecraft. Each kinetic energy impactor consists of a 160 x 160 m, 168-kg solar sail and a 150-kg impactor. Because of their large ΔV capability, solar sailcraft with a relatively modest characteristic acceleration of 0.5 mm/s2 can achieve an orbit that is retrograde to the target orbit within less than about 4.5 years. Before impacting 2004 WR at its perihelion of about 0.75 AU, 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 Δv 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 Earth-miss distance to a safe value. In this paper, we elaborate on a potential mission scenario and investigate trade-offs between different mission parameters; for example, characteristic acceleration, sail temperature limit, hyperbolic excess energy for interplanetary insertion, and optical solar-sail degradation.