How to divert an asteroid from collision path with earth

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

02 October 2022

This week, the National Aeronautics and Space Administration (NASA) of the USA carried out a test on the how to divert an asteroid (space rock) from its natural path. The mission started in late November last year when the 610kg spacecraft was launched and directed towards its target. The ten-month journey took it to a distance of over 11 million kilometres from Earth.

The target object for the test was small moonlet rock measuring about 170 metres that orbits a larger asteroid that is 730m in size. The moonlet weighs about 5 million tonnes and had an orbital period was 11 hours and 55 minutes before the collision.

Striking such an object with a 600-kg spacecraft would of course make a very small change in its motion. However, before the collision, the impactor was moving at 6.6km/s (22,376km/h) and the moonlet at just 0.6264km/h. Therefore, after colliding, the moonlet was slowed down measurably. Its orbital period changed by 15 minutes from 11h:55m to 11h:40m.

This might appear too small but, if this was an object headed on a head-on collision with earth, a small nudge like this would be enough to save the planet. This because a small change in direction becomes a very big over a long distance.

Suppose there is a space rock that is 11 million km away and on a head-on collision course with earth. By how much would we need to change its direction in order to save the planet? Earth is 6,400km from the centre to the surface and, from such a great distance, this radius makes an angle of 0.03 degrees. This is how much we would need to change the direction of the asteroid in order to save our planet.

 But that might not be enough since we also very many man-made satellites orbiting the earth. These satellites support our civilisation and without them we would be thrown back to the stone-age: imagine life without GPS!

The farthest of these satellites are about 35,000km away and so, we may want to deflect the space rock by, say, 50,000km. From a distance of 11 million km, 50,000km makes an angle of about one-quarter of a degree. This is still small enough to achieve, but the key to the success of such a mission is early detection of the threat. We need to be able to detect it from a few hundreds of millions of kilometres away.