How do objects in space travel?
An orbit is the perfect balance between a satellite's forward momentum or inertia and the pull of gravity on it. If either of these are changed, the orbit will fail, and the satellite will either crash down onto the object it is orbiting or spin off into space.
This rendering shows what it would look like if a large body collided with Earth at about 40,000 m.p.h. Many scientists believe an impact like this was responsible for the death of the dinosaurs and many other species of life 65,000,000 years ago. From NASA's Asteroid Comet Impact Hazards Gallery Page, http://impact.arc.nasa.gov/gallery/index.html Painting by Donald E. Davis.
Here are some ways an orbit could fail:
What is an orbit?
What causes an orbit to happen?
Is there gravity in space?
What is a satellite?
Once a ship is in orbit, do we have to do anything to keep it there?
How can a spaceship leave orbit?
How does speed affect an orbit?
What is mass?
What are different kinds of orbits?
What is retroburning? What is aerobraking?