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    The danger of asteroid strikes

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    MOSCOW. (Yury Zaitsev for RIA Novosti) - Colonel General Vladimir Popovkin, commander of the Russian Space Force, told a news conference that the national satellite cluster lacked a spacecraft capable of preventing an asteroid strike.

    He said that chances of such a collision were infinitely small, and that it was inexpedient to spend huge sums on neutralizing this unlikely threat. But it seems that the general may be underestimating the scale of the asteroid threat.

    Over the last few decades there has been a great deal of debate about the level of danger posed by impacts from asteroids and comets. It appears that the world needs to take the threat of asteroid strikes a lot more seriously. Astronomers have already spotted about 800 asteroids, solid rocky celestial bodies, with a diameter of over 1,000 m moving along circumsolar elliptical orbits. However, there may be as many as 2,000 large asteroids, and some 135,000 rocks with a diameter of 100 m and more.

    It should be noted that asteroid orbits are unstable and tend to change under the influence of gravitational fields of terrestrial-group planets, Mercury, Venus, Earth and Mars. An asteroid, which flashed past our planet at a distance of 5 million km in November 1996, returned in September 2004 and flew by just 1.5 million km from the Earth's surface. In March 1989, a 300m asteroid crossed the terrestrial orbit and missed the Earth by just six hours. Astronomers spotted the rock only when it was receding into space.

    An asteroid measuring over 1,000 m in diameter is potentially capable of destroying human civilization. Chances of a major asteroid impact in the 21st century are a mere 0.0002%, while there is a 2% probability of the Earth colliding with a 100m asteroid before 2100. The blast would equal to 100 Mtons in trinitrotoluol equivalent and kill millions of people if it hits a vast industrial region with many hazardous enterprises. Scientists are quite alarmed because they register additional asteroids buzzing the Earth. Spaceguard Survey, an international service responsible for detecting and tracking potentially dangerous space objects, has now been established.

    Russia established the Space Shield Foundation (SSF) east of the Urals. The organization involved scientists from the Snezhinsk (Chelyabinsk-70) nuclear center and the Makeev State Rocket Center (Miass). The foundation eventually set up subsidiaries in Novosibirsk and Korolev, outside Moscow. The Planetary Defense Center, which was established in Russia three years ago, comprises the best defense-industry facilities, aerospace enterprises, in the first place, as well as academic and sectoral research.

    Scientists say that the best way to cope with the asteroid problem is to register and observe all potentially dangerous space objects. However, it is not enough to spot an asteroid because most of them have unstable orbits; consequently, such asteroids may disappear later on. Every terrestrial hemisphere must therefore have three or four telescopes with primary mirrors 4-5 m in diameter for observing asteroids round the clock. Such observations would make it possible to catalog asteroids with a diameter of less than 1,000 m. Many observatories, Russian observatories included, are now working on the asteroid catalog. Scientists claim that it would become possible to warn about impending asteroid strikes 80 to 100 years in advance if 90% of asteroids are registered, and in case of regular observations. But long-term asteroid protection is still in the realm of science fiction.

    There are two scenarios for shielding this planet from a dangerous space object. First, any "hostile" object can be shattered in deep space, before it reaches the Earth. Second, its orbit can be changed, so that the asteroid steers clear of our planet. Some scientists believe that a nuclear device could be detonated on the asteroid's surface or in direct proximity to it. Consequently, it would become possible either to shatter that asteroid, whose fragments may still threaten the Earth. On the other hand, a nuclear explosion near the asteroid would heat up one of its sides and vaporize large segments. The resulting explosion would change the asteroid's flight path. Technically speaking, a powerful nuclear explosion can change the orbit of the asteroid several months before it impacts the planet.

    Russian scientists suggest using the kinetic energy of asteroids in order to destroy them. This can be accomplished by creating an artificial dust cloud in the asteroid's path. That cloud's particles would interact with the asteroid surface and gouge craters. The dangerous object would finally disintegrate because the mass of crater particles would be directly proportional to the kinetic energy of colliding bodies. The United States demonstrated this effective method on July 4, 2005, when part of the Deep Impact spacecraft, a copper ball, 65 cm in diameter and weighing 140 kg, hit the comet Tempel 1 with a radius of 3 km and carved a 200m crater.

    It would be much harder to build a catapult with the help of robots on the asteroid's surface for launching rocks into space and reversing the asteroid's trajectory. A jet engine on the asteroid's surface could change its flight path. Still there are some problems because the spacecraft would have trouble maneuvering near the asteroid and placing the jet engine on its surface. Another method suggests using laser or solar beams to heat up a small asteroid-surface section and to propel it in the required direction. But it would be hard to deliver a laser unit or a mirror-lens to the asteroid and to ensure the required attitude control for a long time. An asteroid patrol would prove quite expensive; consequently, it would be expedient to streamline its elements during current space programs, which is being done at present. The Deep Impact project shows that scientists are working in the right direction.

    Russia's Lavochkin NPO has suggested the demonstration project Space Patrol for perfecting various asteroid-protection methods and systems. A small spacecraft with a mass of just 200 kg, now being developed within this project's framework, would act as navigator or pilot and could lift off atop converted ballistic missiles such as the Strela and the Rokot.

    The European Space Agency is now working on its Don Quijote mission aiming to check the possibility of deflecting a dangerous asteroid (once it has been spotted). A Russian Soyuz-Fregat launch vehicle would launch the Sancho and Hidalgo spacecraft, due to reach the asteroid with an interval of six to seven months. The Sancho would be the first to arrive at its destination, revolving around the asteroid. The Hidalgo would eventually slam into it at 10 km/s. The Sancho would then inspect the damaged asteroid and assess its changed trajectory. The unlucky asteroid is to be selected in 2007. The Sancho and Hidalgo are scheduled to lift off in 2010-2015.

    Yury Zaitsev is an expert of the Space Research Institute, Russian Academy of Sciences.

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