Asteroid and comet collisions have become a popular topic in the 1990s. Public awareness of the potential for a collision with a rogue asteroid or a comet was raised because of several recent occurrences that were all highly publicised. Many things have contributed to a more collective and political awareness of the dangers of asteroid collisions: from the Alvarez’ team promotion of the “dinosaur extinction by impact”, the reports of a “near miss” by 1889 FC asteroid, the Jovian impact of SL-9.that could be watched on TV in real time, to the premature announcement that the Asteroid 1997XF11 was on a collision course with Earth in 2028. Clearly, the movies Armageddon and Deep Impact have also contributed to capturing the imagination and the concern of the general public. As early as 1990 the U.S. House of Representatives, in its NASA Multiyear Authorization Act stated in part:
The Committee believes that it is imperative that the detection rate of Earth-orbit-crossing asteroids must be increased substantially, and that the means to destroy or alter the orbits of asteroids when they threaten collision should be defined and agreed upon internationally.
Spacewatch is the name of a group at the University of Arizona/s Lunar and Planetary Laboratory (LPL)
The primary goal of this group is
.... the study of statistics of comets and asteroids in order to investigate the collisional evolution of the solar system’ the discovery of target asteroids for space missions, such as Clementine, whose aim is the exploration and the protection the Earth from asteroid impact.
The Spacewatch program was the result of action taken by Congress in the US that asked for national workshops in 1990. The astronomer and asteroid expert, Tom Gehrels, of the University of Arizona, started systematically looking for asteroids using a special telescope, using the newly developed CCD’s (charge-coupled devices) which are superior to photographic emulsions.
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spin and tumble so that it would be impossible to attach a sail. The second one, however, seems possible. They showed that a sail of 0.5 km in diameter could deflect an asteroid up to 2 km in size, assuming continuous operation for a year. The reflective material would only have a mass of about one ton. Already in 1967 there were groups of scientists concerned about a possible asteroid collision with the Earth. At MIT a group of engineering students was given the problem of diverting the asteroid Icarus, which was imagined to be on a collision course with Earth. The conclusion of the students was that the asteroid could be diverted by using a Saturn V heavy-lift capability (then available for the Apollo program) and six 100 megaton hydrogen bombs. The scenario was based on the assumption that there was only about a year left before impact, and that meant high velocity changes were required.