Hybrid Fuels and the Candlestick Rocket

In their search for new rocket fuels, scientists have tried many unusual materials. A recent discovery, however, is one of the most ordinary materials imaginable: candle wax. Scientists figured out a way to make candle wax—or paraffin-burn fast enough to serve as rocket fuel. Unlike the candles on a birthday cake, however, this paraffin burns in the presence of pure oxygen gas. This causes it to burn much hotter and faster.

One of the exciting things about this discovery is that paraffin rocket fuel would be much simpler and safer to work with than the toxic, explosive fuels. An ordinary household candle can be safely carved, melted, and molded. If free from artificial colors or perfumes, it can even be chewed on. In contrast, solid-fuel rockets use materials in which the fuel and oxidizer are mixed together before being packed into the rocket. So the fuel is ready to explode—an unsafe material to work with, as well as environmentally unfriendly.

When ordinary solid fuels burn, they produce many noxious chemicals. When it rains, these compounds find their way into lakes and soils where they can harm plant and animal life. Paraffin, in contrast, burns cleanly. The only gases left behind are water vapor and carbon dioxide.

The other advantage to hybrid fuels such as paraffin—where a solid fuel is combined with a liquid oxidizer—is that they allow for controllable rockets. They can be turned on and off just by turning on and off the flow of oxidizer. Their thrust can be throttled the same way.

Many other unusual rockets are either on the drawing board or are being tested. Some of these are based on existing principles and materials, while others have to wait for the development of future technologies—which may or may not come to pass. Either way, the rockets of this century will look as primitive and quaint to future space explorers as Fourth of July skyrockets look to us now.

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