Great cinema springs from often improbable and unsolvable situations. So it is with the scenario where the astronomers discover and interdict an asteroid on course to strike earth.
The physics of deflecting an object are monumental. And no space vehicles are currently on the shelf that are designed to perform such a mission. Explosive (nuclear) warheads are not found on any scientific spacecraft, nor are acquisition and maneuver capabilities built into current spacecraft with the exception of ground based counter-ICBM systems. ICBMs are ballistic missiles made for attacking earth based targets. Neither hardware nor software (guidance) exists that would enable a succeful attack on an asteroid moving many thousands of miles per hour.
Hitting an asteroid with a warhead is similar in difficulty to shooting a bullet in flight using another bullet from a gun pointed in the opposite direction. Direction, speed, and angle of approach are all variables that would have to be factored into any successful interception equation. These problems are highly complex and problematic.
Our opinion: if an asteroid approaches earth on a collision course look for a few spectacular “interception” launches, and look for them all to fail. The asteroid is going to go where the asteroid is going to go, and there won't be much at all we can do about it.
Intercept plans include the following:
The idea is pretty simple: if we see an asteroid on an impact trajectory with earth, our best option is to change the orbit so it doesn't hit us. While we could attempt to blow it up, that would leave a ton of debris that could still fall down to earth.
ESA's plan is more of diversion. By impacting the incoming asteroid with enough advance time, the orbit can be changed, without any collateral damage.
The biggest problem with the idea is how much of an impact do you need? Scientists aren't exactly sure.
The space agency says that if the asteroid still appears to be threatening Earth by 2013, it will start work on a mission to visit Apophis with a probe in 2019. This would be followed by an attempt to deflect the asteroid some time between 2024 and 2028.
It also estimates that planning and executing a deflection mission would only take seven years from start to finish, rather then the 12 suggested by the B612 Foundation. This would make it unnecessary to mark the asteroid with a transponder before 2021, when a decision on deflection would have to be made, because by then scientists should have a far more accurate idea of the path Apophis is going to take.
The Deep Impact mission would serve as a model for the deflection attempt mission, although presumably the impactor would be considerably more massive than Deep Impact's 300kg chunk of copper.
How fast do asteroids travel?
433 Eros:Found in the main asteroid belt, this odd-shaped near-earth asteroid has an average orbital velocity of 24.360 kilometers per second. With a size twice that of Manhattan island, the asteroid was first discovered by Gustav Witt on August 13, 1898. It is the first asteroid to have been visited by a NASA spacecraft, Near Earth Asteroid Rendezvous Shoemaker. The spacecraft landed on Eros’ surface on February 12, 2001.
Ceres: The largest object that orbits in between Mars and Jupiter in the asteroid belt, Ceres has an average orbital speed of 17.822 kilometers per second. It was discovered in 1801 by the Italian monk and astronomer Giuseppe Piazzi. In 2006, Ceres was classified as a dwarf planet.
951 Gaspra: With an average orbital velocity of 19.88 kilometers per second, Gaspra orbits in the main asteroid belt. It was the first asteroid to have been closely approached by the Galileo spacecraft on October 29 1991.