Storm in a Teacup: The Physics of Everyday Life(11)

In Europe, rocket post only really happened because of one man: Gerhard Zucker. A few inventors at that time were tinkering with rockets, but Zucker led the field in dogged persistence and unfailing optimism in the face of continual discouragement. This young German was obsessed by rockets, and since the military weren’t interested in what he was doing he looked to the civilian world for an excuse to continue. Sending mail by rocket sounded to him like something the world was crying out for—fast, capable of crossing the sea, and covered in the glitter of novelty. The Germans tolerated his early (unsuccessful) experiments and then decided they’d had enough, so Zucker went to the UK. There he found friends and support in the stamp-collecting community, who liked the idea of a new kind of novelty stamp to go with a new kind of novelty mail delivery system. Things were looking up. After a small-scale test in Hampshire, Zucker was sent up to Scotland in July 1934 to test sending his mail rocket between two islands, Scarp and Harris.

Zucker’s rocket wasn’t particularly sophisticated. The main body of it was a large metal cylinder about a yard long. Inside, a narrow copper tube with a nozzle at its back end was filled with packed powder explosive. The space in between the inner tube and outer cylinder was filled with letters, and there was a pointy nose on the front with a spring in it, presumably to help soften the landing. Rather sweetly, on his diagram of the setup, the thin layer between the explosive and the highly flammable letters is labeled “asbestos packing round cartridge, to prevent damage to mails.” The rocket was laid down on its side on a slanted trestle, pointed upward and sideways. At the moment of launch, a battery would ignite the explosive, and the burning would produce vast quantities of hot, high-pressure gas. The gas molecules, now moving at high speed, would bounce off the inside of the front end of the rocket, driving it forward, but there would be no equivalent push at the back end—gas would just escape through the nozzle to the atmosphere. This imbalance in pushing could drive the rocket forward very quickly. The explosive burn would continue for a few seconds, enough to push the rocket high into the air and over the channel between the islands. There didn’t seem to be too much concern about how and where it would land, but that was one reason for trying it out in a very remote part of Scotland surrounded by sea.

Zucker collected 1,200 letters to send as part of the trial, each adorned with a special stamp that said “Western Isles Rocket Post.” He packed as many as would fit inside his rocket and set up the trestle, watched by a bemused crowd of locals and an early BBC-TV camera. The moment had come.

When the launch button was pressed, the battery ignited the explosive. The rapid burning generated the expected mixture of hot gases inside the copper tube, and the energetic molecules hammered on the front of the rocket, shoving it up the trestle at high speed. But after only a couple of seconds, there was a loud, dull thud and the rocket disappeared behind a plume of smoke. As the smoke cleared, hundreds of letters could be seen fluttering to the ground. The asbestos had done its job, but the rocket hadn’t. Hot, high-pressure gas is hard to control, and the energetic molecules had broken the casing. Zucker blamed the explosive cartridge, and set about collecting the letters and preparing for a second trial.

A few days later, 793 surviving letters from the first rocket and also 142 new ones were packed into a second rocket. This one was launched from the other island, Harris, back toward Scarp. But Zucker was out of luck. The second rocket also exploded on the launch pad, this time with an even louder bang. The surviving letters were collected up again and sent to their recipients by the conventional mail system, with singed edges as souvenirs. The trial was abandoned. For the next few years, Zucker stubbornly carried on, always convinced that next time, it would work. But it never did,# at least not for mail. Zucker pushed hard against the unknown, and it’s only hindsight that tells us that it wasn’t the right time or the right place or the right idea. If it had been all three, we’d hail him as a genius. But small-scale rocketry was just too unreliable and fiddly to deliver messages better and faster than motorized transport and the telegraph. In a way he was right: Using hot, high-pressure gases as a propellant has enormous potential to get things from A to B. But it was others who took the principle, found a suitable application, and solved the practical problems until it became a success. Rocket development became the preserve of the military, with the German V1 and V2 rockets used in the Second World War showing the way, and civilian space programs taking over after that.

These days, we are all familiar with images of giant rockets carrying huge cargoes of people and equipment to the International Space Station, or taking satellites into orbit. Rockets can seem frighteningly powerful, and the modern control systems that now make them safe and reliable are a huge human achievement. But the basic mechanism behind every Saturn V rocket, every Soyuz and Arianne and Falcon 9 that has ever flown, is the same as it was for Gerhard Zucker’s primitive mail rocket. If you make enough hot, high-pressure gas quickly enough, you can make use of the huge cumulative force that comes from billions of individual molecules bumping into things. The flight pressure in the first stage of a Soyuz rocket is about sixty times greater than atmospheric pressure, so the push is sixty times stronger than the normal push of the air. But it’s exactly the same type of push: just molecules bumping into things. Vast quantities of them colliding often enough and fast enough can send a man to the Moon. Never underestimate things that are too small to see!