Question: How big of an impact do forces have on your spacecrafts?

Neil Bowles answered on 17 Mar 2014:

Hmmm, do you mean micrometeorites (not much, except for possible damage) or more generally? In space things keep going the same direction until an external force, like the gravitation pull of a planet pulls them in a different direction. An impact with some space debris would also do this, but one that is big enough to change the spacecraft’s direction would probably destroy it, or at least very badly damage it.

We can use these to our advantage – the Cassini spacecraft in orbit around Saturn at the moment enters the giant moon Titan once per orbit, and uses Titan’s gravity to gently alter its orbit allowing us to visit many of Saturn’s moons without using much fuel.

Very small forces can actually cause large changes in the direction a spacecraft travels if they are left acting unchecked for long enough. For example, sunlight actually has a very small force associated with it (radiation pressure, one of the things that pushes a comet’s tail away from the Sun) and over time this can start to push a spacecraft around, requiring us to correct for it using small thrusters or ‘reaction wheels’ – spinning wheels that spin to counter act the force pushing on it.