For its ancient history, you can count almost several years - when there was no war on Earth.
You can treat this as you like, but, apparently, it will be an indispensable companion of our civilization until the number of states on the planet is more than one - or until the economic and socio-political need for wars disappears in these states.
And, in general, it is not surprising that in world fiction of various levels, the plots of the fight against space aliens are quite traditional and are presented in the form of a completely barbaric, at the level of the Stone Age, with the only exception that the fight does not take place with stone axes, but more advanced weapons. Consider HG Wells' masterpiece The War of the Worlds - one of the first works of science fiction of its kind.
But seriously, how can mankind "snap back" today, if suddenly "brothers in mind" show aggression? Any combat system must solve three problems: detect the enemy, "reach" him and, finally, hit.
Up to 95% of information about the world around a person receives with the help of electromagnetic waves, mainly in the optical range. But the creation of "artificial eyes" in the optical range turned out to be the most difficult technical task, which has not been fully solved to this day. The breakthrough here was provided by active location using a laser. Today, complexes have been tested that provide orbit tracking at an altitude of 36,000 kilometers. Another thing is that their reliability is still far from ideal.
Other channels also work on Earth: hearing, smell, touch. But in space, their capabilities cannot be realized, but nothing interferes with electromagnetic waves. In the radio range, the atmosphere is also transparent. And it is not surprising that the task of detecting and tracking spacecraft was solved on the way to creating radar systems. Above horizontal early warning radars are capable of detecting targets no more than half a meter in size at a distance of about 5000 kilometers.
The diversity of our world is not limited to electromagnetic fields. There are also gravitational and torsional fields, you can try to fix something with the help of neutrinos or telepathic communication. With neutrino in general, a sore subject: how to fix it, in fact? Telepathic communication, alas, practically does not provide coordinate referencing.
If the alien ship manipulates space-time, we, in theory, can detect gravitational disturbances. But such cases can end fatally. As far as can be judged, torsion fields have the greatest prospects. Here, in any case, there is empirical confirmation, some work is underway. But how soon the installations suitable for detecting at least meteoric particles will be created is an open question.
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Thus, if the ships of the intruders appear within the geostationary orbit, if their dimensions are not less than several meters and if they do not "bend" the space, then they can be detected.
The second task is to "get" the target. For forty years it has been believed that under normal conditions an aircraft controlled by a pilot cannot escape an anti-aircraft missile. The fact is that an anti-aircraft guided missile flies in the atmosphere, and the latter, as you know, resists movement.
The engine, today, as a rule, works only on the acceleration phase of the flight. Further, the rocket flies like a blank, just controlled. And just when a reserve of speed and maneuver is needed, the rocket simply does not have enough kinetic energy …
There are two solutions to countering the alien ships. The first is to try to create flying vehicles based on new physical principles, comparable in flight characteristics to "flying saucers". Oddly enough, work in this direction is now going on in our country. Moreover, their scale is quite impressive, although the results are still far away. The second is to compensate for the quality with quantity, to use all acceptable means in the complex.
Today in anti-aircraft missiles, and in anti-satellite systems, a fragmentation warhead is used with a controlled formation of fragments, as a rule, of a given shape. For example - rods that can fly apart parallel to each other, or they can twist …
On anti-missiles, nuclear heads were out of competition, and not only to compensate for a miss. However, the X-ray flurry of a high-altitude nuclear explosion burned out the control equipment. In addition, the electromagnetic impulse of a nuclear explosion on the clock "knocked out" telecommunications on vast territories, which is unacceptable in wartime.
Military analysts have long come to an interesting conclusion: while all this "flying dish" is flying, it is too tough for us. Indeed, legends are multiplying about airplanes, even nuclear submarines, for which the attempt to attack UFOs ended fatally. But on the other hand, the aliens are believed to be physically weak. And if so, they should be taken at such and such a moment. In this regard, there is a long-term experience of partisan wars, and specially trained sabotage and counter-sabotage units. And if you believe some mouthpieces of ufology, then there are special teams prepared to capture aliens.
The 1991 American-Iraqi War was a triumph for the American military technical machine. Indeed, the huge Third World Iraqi army with 10 years of victorious combat experience was “utterly defeated” by an American group of approximately equal numbers.
Later, however, it turned out that the two tank battles that had taken place would have ended in the defeat of the Americans, if not for the timely intervention of American aviation. In addition, the Americans shot down only one of the fifty Iraqi ballistic missiles. Finally, the number of Iraqi troops was overestimated in the official American information by almost one and a half times!
If the Iraqi leadership had shown a little more courage, the Iraqi Su-24 could have done a lot … But Saddam Hussein chose the tactics of avoiding a fight …
It is not technology that is fighting, people are fighting. Technically, Earthlings are not entirely defenseless against space invasion.
And the last thing. If there really is a threat of aggression by alien "guests", anti-space defense, of course, will come in handy. But the main weapon for them and for us will be skill.