This is a best-practice time-limit adopted by the world's space agencies for the removal of their equipment from orbit once it has completed its mission.

BBC: Space debris collisions expected to rise

The Orion capsule, which is intended to carry at least four astronauts into Earth orbit and beyond, has completed its preliminary design review, or PDR.

BBC: Spaceship passes critical review

It completed the first commercial flight in October and is vying for a contract for manned flights into orbit alongside Boeing and Sierra Nevada.

CNN: 'Fireflies' to scope out space rocks for mining