IN THE LATE 1980s Edward Teller, the father of the hydrogen bomb, and Lowell Wood, an astrophysicist, proposed a seemingly bizarre scheme to defend America against missile attack. The “Brilliant Pebbles” system envisaged thousands of small satellites in low-Earth orbit, each housing heat-seeking missiles to take out incoming Soviet nukes long before they released their warheads. The idea faded, not least because the technology seemed distant. Now Donald Trump is resuscitating it.