The First Liquid Fuel Rocket

March 17."The first flight with a rocket using liquid propellants was made yesterday at Aunt Effie's farm in Auburn. . . .It looked almost magical as it rose, without any appreciably greater noise or flame, as if it said, "I've been here long enough; I think I'll be going somewhere else, if you don't mind." . . .Some of the surprising things were the absence of smoke, the lack of very loud roar, and the smallness of the flame."

from Dr. Goddard's Diary

BACKGROUND

For hundreds of years man lived with the deficiencies of the solid, gunpowder type rocket developed by the Chinese in the 13th century. So too, for a while, did Dr. Robert H. Goddard, the New England physics professor and American rocket pioneer. As early as 1909, however, Goddard considered the idea of a liquid fuel rocket utilizing hydrogen and oxygen. In his studies he recognized that solid fuels produced a lower exhaust velocity than could be obtained by the use of liquid fuels. After 17 years of theoretical and experimental work, Dr. Goddard finally achieved flight of a liquid fueled rocket on March 16, 1926. The manner in which that rocket worked is described here.

TECHNICAL PROBLEMS

A liquid fuel requires a continuous source of oxidizer to be able to burn at a rate capable of producing the rocket thrust desired. A means for combining the fuel and the oxidizer at the proper rates in the combustion chamber had to be developed. The high pressures created by combustion required that the fuel and oxidizer be injected into the chamber under even higher pressure.

NOVEL USE OF LOX

After a number of design attempts, Dr. Goddard finally chose gasoline as the fuel and liquid oxygen (lox) as the oxidizer. Below - 297 degrees F. oxygen is a liquid at atmospheric pressures. At higher temperatures it vaporizes, and produces tremendous pressures in closed containers. Dr. Goddard used the pressure of this gas to push both liquids simultaneously from their tanks, through separate pipes, to the combustion chamber where they mixed and burned. To speed the vaporizing of the lox, he applied heat with an alcohol burner.

Figure 1 points out the 1926 rocket's main features.

MECHANICAL INGENUITY

There was a pipe connection for the pressurizing gas between the lox tank and the gasoline tank. Safety required that neither liquid should pass through this pipe and mix with the other before entering the combustion chamber. Figure 1 shows the cork floats Dr. Goddard used to minimize sloshing of liquid into the pipe, but still allow gas to flow. Once the rocket left the ground, this gas pressure would be the only means for pumping fuel and oxidizer. Before launch, however, it was necessary to pressurize the system from an oxygen cylinder located about 30 feet from the rocket. Heavy rubber tubing fed the oxygen into the rocket's pressure line. As the rocket began to rise, this hose had to be pulled free. The resulting opening was rigged with a flap check value to slam shut and prevent loss of pressure.

The combustion chamber was equipped with an igniter system containing match heads and black gunpowder to provide the starting fire for ignition of the lox and gasoline when they were forced into the combustion chamber (Figure 2).

THE LAUNCH

Only a few steps were necessary in the countdown and launch. First, an assistant using a blowtorch on a long pole reached up and heated the igniter casing until the enclosed match heads caught fire and ignited the black powder. He then closed the pressure relief vent on the lox tank (Fig. 3) and quickly lighted the alcohol soaked cotton in the burner. Next, Dr. Goddard piped oxygen from the cylinder to the propellant tanks at 90 pounds per square inch pressure. This forced gasoline and lox to the combustion chamber, where the igniter was still burning. With a loud roar, the rocket motor fired. When the rocket motor's thrust exceeded the weight, it rose a few inches from the ground, tethered only by the hose. With a long rope, Dr. Goddard pulled a hinged rod that yanked the hose away, and the rocket was free to fly (Fig. I ). The swing of this rod also unseated a spring loaded valve (Fig. 3), allowing lox to drip into the heated chamber surrounding the lox tank. Here the lox flashed into vapor, and the resulting gas pressure fed the liquids to the combustion chamber.
Figure 3 - Liquid Oxygen Tank

THE FLIGHT
After 21/2 seconds of flight, the fuel was expended, the roar ceased abruptly, and the rocket fell to earth 184 feet away. It had reached an estimated speed of 60 miles per hour and the height of 41 feet. This was the world's first liquid fuel rocket flight, an event considered comparable in its significance to the Wright Brothers' achievement of manned flight at Kitty Hawk.

"It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow."
-Dr. Robert H. Goddard