Chris Bowlby explores the shifting balance between two visions of outer space - as a place of harmony and as a zone of growing international tension. We may think war in space is a scenario dreamed up by Hollywood. But the world's top military minds now believe future wars will be fought both on Earth - and above it. Chris visits an arms sales fair, and hears how space now affects everything from how armies move, to how nuclear deterrence works. Could crucial satellites he hacked in an act of aggression, might space debris trigger a war? Why is China taking space security so seriously? And can the international cooperation which put astronaut Tim Peake into space survive?

Producer: Chris Bowlby

Editor: Hugh Levinson.