Telegraph: According to astronomer Dr Roger Angel, at the University of Arizona, the trillions of mirrors would have to be fired one million miles above the earth using a huge cannon with a barrel of 0.6 miles across. The gun would pack 100 times the power of conventional weapons and need an exclusion zone of several miles before being fired. Despite the obvious obstacles – including an estimated $350 trillion (£244trn) price tag for the project – Dr Angel is confident of getting the …