regulation came very close to the experience of astronauts in the Apollo program. His characters preferred to keep the pressure of their suits just high enough for survival, but not high enough to make it difficult to move around, much like the selected design pressure range of the real Apollo A7L suits. The life support system of the suits in Have Space Suit—Will Travel was very similar to the backup Oxygen Purge System on the real Apollo Primary Life Support System, the only major difference being that the Apollo suits had a largely automatic pressure regulator, and Heinlein's suit had manual pressure regulation. One major component of modern pressure suit Primary Life Support System backpacks which he missed was the lithium hydroxide canister which absorbs carbon dioxide from the air in the suit: see rebreather. Without this, his suit's breathing apparatus would have to be open circuit and limited to approximately two hours on a filling of oxygen or air, with the time varying according to exertion and cylinder size and his body size. Another was the cooling system. He correctly recognised that overheating would be a major problem for the wearer of the suit. His cooling system was the same as the Apollo oxygen purge system: waste oxygen by letting it flow at a high rate and use it to dump heat. In practice, real suits used a water supply feeding a sublimator to provide cooling. In The Cat Who Walks Through Walls the suits are strongly influenced by experience in the space program. He correctly describes a technique for helping an injured man in a pressure suit by decompressing the suit for less than a minute. Earlier books such as Rocket Ship Galileo described horrible injuries for people decompressed for short times. In The Moon Is a Harsh Mistress Heinlein has people going onto the moon surface for about half a day in daylight and suffering from radiation exposure. In practice, overheating was the biggest risk of lunar surface operations, and cooling systems were easy to build. Perry Rhodan The front cover of the first issue of the German pulp science fiction series Perry Rhodan, published in 1961, shows a typical science-fiction open-circuit design with two large backpack cylinders instead of a modern life-support pack. Armored space suits Robert A. Heinlein's novel Starship Troopers (1959) famously featured armored power-assisted spacesuit-like battlesuits used in combat. The suits are arguably