THE CAPTURE OF ASTEROIDS and Transport of Asteroid Materials to Earth

摘要

Recently there has been much discussion on the capture and mining of asteroids. While the technology might be years away, in this paper we will discuss an energy-efficient method of transporting a small asteroid, or materials gathered from asteroids, to Earth. In particular, the paper will concentrate on one of the nearest and largest asteroids - 8 Flora in the Flora family. Generally, asteroids are located 2-3 AU (astronomical units) from Earth, and in transporting materials from asteroids to Earth, an energy equivalent of the gravitational potential energy difference GM_☉(1/r~(-1)_E-1/r~(-1)_A) must be dissipated, where τ_A ≈ 2 → 3 AU are respectively the distances of the Earth and the asteroid from the Sun. This amount of potential energy is a sizeable fraction of the orbital kinetic energy of the Earth around the Sun, and with the Earth's orbital speed at around 29 km/s, the amount of energy to be dissipated is considerable. In this paper we propose to use the planet Mars as a medium to remove much of the gravitational energy difference through gravity-assisted deceleration ("gravity braking"). To achieve this aim, it is necessary to launch the payload in the reverse direction of the asteroid with a certain velocity; in the case of 8 Flora, this launch velocity is around 3 km/s. The deceleration could be achieved by non-rocket powered ejection platforms on 8 Flora. The landing velocity on Earth is about 3 km/s over the escape velocity of the Earth (11.2 km/s). It is also proposed to separate a pair of contact asteroid binaries by using impulse propulsion, and to propel one component of the separated asteroids to pass by Mars to receive gravity-assisted deceleration to reach the Earth, or to become captured by the Earth or the Moon. The feasibility of this ambitious project will be discussed.