But according to rocket scientists at the China Academy of Launch Vehicle Technology (CALT), slamming a nuclear warhead directly into the side of a space rock is a rookie mistake. A proposed planetary defense strategy suggests carving a crater into an incoming asteroid and detonating a nuclear warhead inside it. First, a heavy metal penetrator slams into the targeted asteroid, gouging out a crater up to 30 meters deep (98.4 feet). Seconds later, a second spacecraft lowers a 3-megaton nuclear warhead directly into the newly carved cavity and detonates it from the inside out. For a massive 1-kilometer asteroid, burying a 3-megaton charge 30 meters deep altered its velocity by 30 centimeters per second (0.98 feet per second).