## Proving the slingshot effect causes less speed for a space shuttle

When a rocket approaches a planet from the front of it's orbit such as in the bottom drawing shown in the link <http://img156.imageshack.us/img156/724/slingshotph4.jpg>, the gravitationally assisted manoeuvre or slingshot affect will cause the shuttle's final velocity to be less than the initial velocity, which makes logical sense. However, I can't however seem to prove through using the law of the conservation of momentum that the final velocity of the shuttle will be less than the initial velocity.