"I recognized a long time ago [the need], and I began, as soon as I could, to carry out researches with liquid propellants, which had several times the heat energy of powder."
The American rocket pioneer Robert H. Goddard was probably the first man in the world to experiment with liquid rocket propellants. His initial experiments, begun in 1915, used solid propellants, which were simple to work with and inexpensive. But, in 1921, he switched to liquids. Theoretically, they possessed far greater energy content than solids and promised superior performance.
Goddard realized that the combustion of liquid propellants in an engine could be controlled by valves opening or closing, thereby regulating the flow of fuel. In contrast, once a solid-fuel rocket ignited, it could not be throttled down or shut off — it burned until the fuel was exhausted. (Today, there are devices that cut off the burning when desired.) In both solid and liquid propellants, an "oxidizer" is needed — a substance that contains oxygen for the fuel to burn. In solid propellants, such as gunpowder, the fuel and oxidizer are mixed together. In liquid fuel systems, the oxidizer and fuel are separate substances, each contained in its own tank. They must be brought together and then ignited for combustion. Together, the fuel and oxidizer are called the "propellant."
Goddard chose liquid oxygen for his oxidizer and ordinary gasoline for fuel. But this choice of oxidizer posed a serious problem. As a liquid, oxygen is extremely cold, -183°C (-297°F). But Goddard benefited from a prior invention. In 1872 the Scottish chemist James Dewar invented a special container that maintains the temperature of either very hot or very cold liquids. This container, now called a Dewar flask, is usually a double-layer glass bottle, the narrow space between the walls a near vacuum to prevent the transmission of heat. In addition, the inner and outer walls have a silver or other reflective coating to reflect thermal energy. The ordinary Thermos® bottle works on the same principle.
The device shown here is one of the original small Dewar flasks probably used by Goddard during his experiments in 1923 and 1924. Later, as his rockets grew in size and became more sophisticated, he used much larger liquid oxygen containers. A Dewar flask is extremely fragile — this one is made of hand-blown glass. For this reason, and the fact that liquid oxygen makes the outer wall of the flask intensely cold, the manufacturer provided thick felt padding (that seen here is original) to protect and handle the flask.
Goddard needed to transport the fuel for his experiments and flights so built his own carrier made out of wood. The flask fits easily between the slats, the lips resting on the slats and preventing the flask from falling out. Goddard made the carrier with handles at each end, enabling two people to carry the delicate flask. The Dewar flask and homemade carrier seem very crude by our standards, but they worked.
Today, our increased understanding of cryogenics (the behavior of very cold substances) has enhanced our ability to handle and work with extremely cold liquids. The J-2 rocket engines of the second and third stages of the Saturn V and the Shuttle main engine used liquid hydrogen, which, at -259°C (-434°F) is far colder than liquid oxygen. These advances highlight the daunting challenges that confronted Goddard as he experimented with rocket technology. The Dewar flask was one small part of years-long work to fulfill his dream of reaching space.
Mrs. Robert Goddard, who witnessed many of her husband's rocket test activities, donated the flask and carrier to the Museum in 1959.