SIPROC 3: Goddard’s Patent for a Liquid-fueled Rocket

Fellow physics guy and rocketeer extraordinaire Dr. Robert Goddard was one of the founding fathers of modern rocketry. He also saw that rockets could be used for more than just an ordinance delivery platform; rockets could be used for scientific discovery and manned spaceflight. The dawn of the 20th century was very hostile to some of these ideas, leading to misrepresentation of Goddard’s visions of space travel.

Among Goddard’s many contributions to rocketry was the invention of the liquid fueled rocket. In fact, the liquid fueled rocket was one of the first of the 214 total patents issued to him. Patent number 1,103,503, entitled “Rocket Apparatus”, describes ways of making rockets more powerful while reducing the casing mass of the rocket. The patent was issued July 14, 1914.

Goddard accomplished these efficiency-increasing feats using two technologies that form the basis of modern rocketry: a strong, small combustion chamber and liquid propellants.  At the time of Goddard’s invention, combustion chambers were one of the thickest, most robust metal parts on a rocket. All of that strength translated into significant weight, which increased as the single-stage rocket designs of the era became larger and more powerful. Thus one objective of Mr. Goddard’s invention in the ‘503 patent was “to provide means by which a large amount of propelling material may be carried and used in a rocket apparatus, while at the same time the weight of the apparatus is reduced rather than increased.” Imagine what the man could have done with carbon fiber! Instead, he devised a few different ways to successively deliver amounts of propellant to a combustion chamber that was relatively small for the size of the rocket. By successively delivering propellant instead of loading all of the propellant into one big combustion chamber, Goddard was able to significantly reduce the mass of the combustion chamber.

Goddard's cartridge rocket design. (from the '503 patent).

One way Goddard developed to reduce propulsion system mass was based on solid propellant cartridges. Functioning like a pistol, a magazine of propellant filled cartridges would be successively loaded into position above the combustion chamber and fired. When the cartridge was spent, it would be expelled like a bullet casing and another cartridge would be loaded and ignited.  This cartridge-based system obviated the need for thick-walled solid propellant motors because a series of smaller, more light weight fuel cartridges could be used.

Modern aerospace engineers are likely most interested in figure 19 of the ‘503 patent (the first picture of this post). It lays out a design for a bi-propellant liquid fueled rocket engine. The liquid-fueled rocket design had the further advantage over Goddard’s cartridge design of providing a continuous source of thrust to his relatively small combustion chamber-equipped rockets. The top tank was filled with gasoline and the second tank was filled with nitrous oxide, as the oxidizer. Interestingly, Goddard’s liquid rocket design utilized piston pumps to force the gas and oxidizer into the combustion chamber. Goddard indicates that the “force pumps” should be chosen so that the proper ratio of fuel and oxidizer is maintained.

It is interesting to note that people like Goddard went through a lot of the same trials and tribulations that modern commercial spaceflight startups experience. He toiled away on what seemed at the time to be crazy, dangerous toys. Few people could see the value of rockets besides another way of delivering bombs and entertaining wealthy clients. Some people criticized or mocked his dreams of spaceflight. Today, small commercial spaceflight companies have great difficulty finding funding, causing more than a few to fail, and many people mock spaceflight as nothing more than a temporary distraction of the super-wealthy. Goddard’s technologies were eventually integrated into some of the most amazing, inspiring devices ever developed. Hopefully, the legacy of the emerging commercial spaceflight industry will be just as bright.

Happy creating!