Assuming an asteroid is on an imminent collision course with Earth, there are a number of ways we might prevent it. The asteroid could be slowed down, sped up, or by slightly changing its trajectory just enough so that it does not intersect with Earth’s orbit when and where Earth happens to be.
Humanity faces a variety of natural disasters on a daily basis. Volcanoes, earthquakes, hurricanes, and tornadoes claim the lives of roughly 60,000 people every year. And a major disaster – such as a supervolcano eruption – could threaten the continued existence of mankind altogether.
NASA is by far the most well-funded, well-developed space agency on the planet. Even as its budget -- relative to total U.S. tax income -- has continually been reduced over the decades since the Apollo era, NASA still receives several times the funding of its largest international competitors.
There are hundreds of satellites, 8,000 tons of junk and more than 500,000 pieces of debris that are tracked as they circle the planet. This orbital debris and the speeds at which it travels increases the potential danger to both manned and unmanned space vehicles due to the increased potential for collision-related damage.