Asked by: Tony Hersh, Newbury
They don’t! The main asteroid belt is actually much less populated than is often depicted in the movies. It has a volume of about 50 trillion trillion cubic kilometres (which would take about 35 million Suns to fill!).
Astronomers estimate the number of asteroids larger than about 1km in size in the main asteroid belt is about 80,000. This means that, on average, the distance between large asteroids is about 17 million km. Even if we include estimates for the number of smaller asteroids in the main belt we still find that the average distance between asteroids is millions of times the size of a typical spacecraft.
Outside the main asteroid belt the average distance between potentially hazardous objects is millions of times greater still. So, the chances of an accidental collision are actually extremely small. Hence, mission planners don’t need to take any steps to avoid asteroids and meteoroids.