Kiba V. D., Mitikov U. A., Timoshenko Zh. I.
Oles Honchar Dnipropetrovsk National University
PROTECTING THE EARTH FROM COMETS AND ASTEROIDS
I believe that before we start discussing ways to protect the earth from large comets and asteroids, the discussion should focus on the more «simple» problems – and it’s really a great danger of collision with the Earth by comets or asteroids? Speaking the language of mathematics, it is about finding the probability of intersection of the Earth orbits and the comet almost at one point. Intuitively, it seems that this probability should be extremely small, but what is the quantitative assessment of this smallness. To answer the question sufficiently it’s enough to take into account that the observations of about 200 long-period comets it is known that about 5 comets per year cross the Earth’s orbital plane. For collision it’s necessary that the trajectory to be at least one of these comets crossed with the position of the Earth, or rather would have passed through the area of a circle 1/4 Earth’s surface area. Calculations show that the probability of such an event, as expected, extremely low is about one event in 50–100 million years. But the geological age of the Earth is close to 4.5 billion years. So, during this time the Earth’s surface has been fallen at least a few dozen comets. And when you consider that every year, astronomers still open 3–5 new comets, the comet factor becomes one of the most important elements of the earth’s history. This conclusion is supported by observations of the moon craters, most of which was formed under the influence of comets, asteroids and meteorites.
But even if the probability of a comet or asteroid collision with Earth is so small, we should still be able to prevent these collisions. I want to list the methods which prevent collisions and tell you about them.
The first way is a nuclear explosive device. Undermining a nuclear device over, on or under the surface of the asteroid is a potential threat for this reflection. The analysis methods of the deviation threats conducted by NASA in 2007, stated: that according to various estimates, radiation implosion (nuclear explosions) is in 10–100 times more effective than non-nuclear alternatives analyzed in this study. Other techniques, which made superficial or deep nuclear explosion, may be more effective, but they have a significant risk of destruction of near-Earth object at the wreckage. They also have greater situational and operational risks.
The second way is a kinetic ram. Sending a huge object, like a spacecraft or other near-Earth object, as a battering ram. The analysis methods of the deviation threats conducted by NASA in 2007 stated that: non-nuclear kinetic ram is the most elaborated approach. It may be used in some cases, particularly against small NEO, consisting of a solid.
The third method is a gravitational tug of an asteroid. Slow shifting of the asteroid over time. Small constant thrust and accumulates sufficiently to reject with the alleged diversion. The analysis methods of the deviation threats conducted by NASA in 2007, stated: Towing equipment – the most expensive, have the lowest level of technical readiness, and their ability to repel threatening objects will not be greatly restricted only if there will be sufficient time during many years and decades.
The fourth way is an ion beam. It lies in the fact that it uses ionic engines with low divergence towards asteroid located near the vehicle. Kinetic energy transmitted through the ions that reach the surface of the asteroid, create a weak but persistent force capable to reject asteroid, as in the case of the gravitational tug, only by using a lighter ship.
The fifth way is the help of ordinary rocket engines. If the near-Earth object set ordinary rocket engines, they will also give a permanent condition that may lead to a change in the flight path.
In my opinion, the most effective way is undermining a nuclear device near the asteroid. Because it is not always possible to see in advance the asteroid approaching Earth because it can be aperiodic, i. e. move unclosed trajectories (parabolic or hyperbolic). And so it is difficult to determine the mass and the material from which the object is to be able to use kinetic ram. Method of detonating a nuclear device does not require much time to prepare, so you can quickly use it and destroy the space object that can reach the ground within one or two days.