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August 28, 2011

Capturing Near Earth Objects

Arxiv -Capturing Near Earth Objects (22 pages)

Technology Review -
A particularly good candidate is a 10-meter object called 2008EA9 which will pass within a million kilometres or so of Earth in 2049. 2008EA9 has a very similar orbital velocity as Earth's. Baoyin and co calculate that it could be fired into Earth orbit by changing its velocity by 410 metres per second. That's tiny.

This nudge should place the asteroid in an orbit at about twice the distance of the Moon. From there it can be studied and mined

Recently, Near Earth Objects (NEOs) have been attracting great attention, and thousands of NEOs have been found to date. This paper examines the NEOs' orbital dynamics using the framework of an accurate solar system model and a Sun-Earth-NEO three-body system when the NEOs are close to Earth to search for NEOs with low-energy orbits. It is possible for such an NEO to be temporarily captured by Earth; its orbit would thereby be changed and it would become an Earth-orbiting object after a small increase in its velocity. From the point of view of the Sun-Earth-NEO restricted three-body system, it is possible for an NEO whose Jacobian constant is slightly lower than C1 and higher than C3 to be temporarily captured by Earth. When such an NEO approaches Earth, it is possible to change its orbit energy to close up the zero velocity surface of the three-body system at point L1 and make the NEO become a small satellite of the Earth. Some such NEOs were found; the best example only required a 410 meter per second increase in velocity.



In order to capture a near Earth object, there are several alternatives. These alternatives were broadly classified as “impulsive” if they acted nearly instantaneously, or “slow push” if they acted over an extended period of time (NASA 2006). The impulsive techniques generally included conventional explosive, kinetic impactor and nuclear explosive. And the slow push techniques included Enhanced Yarkovsky effect, focused solar, gravity tractor, mass driver, pulsed laser and space tug. Considering the required impulsive velocity increment is not so small and the diameter of NEOs is relatively large, there are two impulsive capture methods available, kinetic impactor and nuclear explosion, but they are never tested or applied. Among them, the nuclear explosion method may not be proper one for the mentioned small NEO, because the nuclear explosion can release a very large amount of energy, the result may be a fragmentation of the target NEO. So the kinetic impactor is often considered as a better maneuver means especially for the NEOs smaller than 50 meters in diameter.

Kinetic impact: A space probe or a specially designed projectile which will hit an NEO at a very high velocity, and therefore deliver an impulse that will change the orbit of the NEO. The relative velocity between the impactor and the NEO depends on the orbit of the impactor, the limited payload capacity of the available launch systems, and the application of new technology. For example, the relative velocity can reach 60 km per second by utilizing solar sailing.

The effective momentum changes for kinetic impact are calculated to range from about
5X10^7 to 2X10^10 kg-meter per second.

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