The bodies of missiles are made as light as possible, to minimize the thrust needed to get the payload to the target and to maximize the range. Liquid fueled missiles are made of thin sheet metal. The skins of the earliest intercontinental missiles, such as the US Atlas (1960) were so thin that they could be dented with a light touch. These missiles had to be pressurized to stand. They were just strong enough to hold the fuel, which would make them rigid enough for launch, and just strong enough to withstand the upward push of their engines. Since combustion in liquid fueled missiles takes place in the engines, the bodies have to resist only the heat of air friction. Later liquid fueled models such as the US long range Titan and its copy, the contemporary Chinese CSS-5, and indeed the entire fourth generation of Soviet missiles including the fearsome SS-18, have skins of quarter inch aluminum and are a bit tougher. Solid fueled missiles are tougher yet, typically made by miles of graphite fibers, impregnated with other carbon compounds and wrapped around clay forms until a hard tube about an inch thick is formed. These missile bodies withstand the internal high temperatures of the fuel that must burn inside them, as well as the stresses of acceleration and air friction.
The smallest ballistic missiles weigh some ten tons, and the largest hundreds of tons. Over 90% of the weight of a missile must be fuel. How much payload do they carry? The US Space Shuttle delivers some 40,000 lbs. to low earth orbit. The world’s largest rocket, the Russian Energia, delivers ten times that. Ballistic missiles used in warfare carry payloads that range from 1000 to 15,000 pounds. While it is theoretically possible to armor a missile, adding weight to the body defeats the missile’s purpose: to throw a weighty payload long and high. Neither tanks nor battleships go into space. The lightness of missile bodies has led some engineers to refer to them as flying condoms. Hence missiles are highly vulnerable. Any kind of physical hit (kinetic energy), or a relatively low amount of radiant energy, causes missiles to self destruct catastrophically.
Missile designers have even more incentive to minimize the weight of post boost vehicles (PBVs). Since these work strictly in space where there is no air friction, they typically have no skin at all to protect sensors and vital instruments. Hence PBV’s are even more delicate and vulnerable than boosters.
Warheads however are built of the toughest metal alloys available, to withstand the physical stresses of reentry and to provide initial containment of explosions. Hence they are coated with heat shields the surfaces of which gradually flake off as they are burned away by air friction as they reenter the atmosphere. Warheads stand from six to nine feet tall, and weigh from a few hundred (for the most modern nuclear weapons) to a few thousand pounds.
