Today we almost take for granted one of the key technologies that makes spaceflight possible: the liquid propellant rocket engine. Exactly a century ago today, famed American rocket pioneer, Robert H. Goddard, filed a patent application for the liquid propellant rocket whose invention he is probably best known for today. Goddard first wrote in his research journal about the possibility of using liquid propellants for a rocket in 1909 while he was a physics instructor at the Worcester Polytechnic Institute. His calculations had shown that a rocket engine burning liquid hydrogen and liquid oxygen as propellants, for example, could increase the efficiency of rocket engines far beyond what was possible with the conventional powder rockets that had been in use for centuries up until that point in time.

In the fall of 1909, Goddard entered the graduate program at Clark University and received his PhD in physics in 1911. After graduating, he stayed at Clark University as an honorary fellow in physics for a year before accepting a research fellowship at Princeton University’s Palmer Physical Laboratory in 1912. During his spare time at Princeton, Goddard had worked out the equations needed to predict the performance of rockets so that he could calculate the position and velocity of a rocket as a function of time using basic information about the rocket’s mass, propellant load and the engine’s exhaust velocity.

In early 1913, however, Goddard became seriously ill with tuberculosis which was more commonly known at that time as consumption because of the effects of this chronic infection. While today this disease can usually be successfully treated with antibiotics, a century ago there was no ready cure for tuberculosis aside from rest and hoping that the patient’s own immune system would be able to successfully fight off the infection. Because of his illness, Goddard left Princeton and returned to Worcester to recover. It was while he was recuperating that Goddard began to review his notes on rocketry that he had made while at Princeton and began to produce some of his most important work.

During Goddard’s time in Worcester, it was impressed on him about the importance of protecting his intellectual property so that he would not be forced to pay royalties to someone else in order to continue his work in rocketry. With the help of his father and the Worcester law firm of Southgate & Southgate, on October 1, 1913 Goddard filed for a patent for the multistage rocket – another key innovation that makes spaceflight possible today. On May 15, 1914, Dr. Goddard filed his next patent application for a high altitude rocket which included the concept of a liquid propellant rocket engine that employed gasoline and liquid nitrous oxide. On July 7, 1914 he was granted US Patent Number 1,102,653 for his invention of the multistage rocket and just one week later he was granted US Patent Number 1,103,503 for the liquid propellant rocket engine. These would be the first of his eventual 214 patents.

While he was granted the patent for the liquid propellant rocket, there was still much research and development effort needed to turn his idea into working hardware and it would be over a decade before the first flight test would be made. After recovering his health, Dr. Goddard took up a post as a part time instructor at Clark University in the fall of 1914 and began his experiments with rocket propulsion. Since liquid hydrogen and liquid oxygen were so difficult to procure at this time, he started to refine the design of his rocket engines and especially the nozzles in a series of experiments using gunpowder. He was eventually able to boost the efficiency of these solid propellant engines from 2% typical for fireworks to 63% with exhaust velocities in excess of 2100 m/s. Based on the success of this early work, in January 1917 Dr. Goddard received an initial grant of $5000 over a total five years from the Smithsonian Institution to fund his research – the first of many more grants to come.

In September 1921, Goddard finally began experimenting with liquid propellants and in November 1923 he successfully static tested his first liquid propellant rocket engine employing gasoline and liquid oxygen. Over the next two years he continued to refine his design and developed a simple pressure-fed propellant system of the sort still in use today. On December 6, 1925 he successfully static tested his new pressure-fed liquid propellant rocket engine. Goddard conducted an additional test later in the month and another two static tests in January 1926. With a working engine of sufficient power now available, Dr. Goddard built a rocket incorporating his new power plant and on March 16, 1926 successfully flew the world’s first liquid propellant rocket in Auburn, Massachusetts. And the rest, as they say, is history.

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General References

David Baker, The Rocket: The History and Development of Rocket & Missile Technology, Crown, 1978

Werhner von Braun and Frederick I. Ordway III, History of Rocketry and Space Travel, Thomas Y. Cromwell Co., 1966

Robert H. Goddard, Rocket Apparatus, US Patent No. 1,102,653, Issued July 7, 1914 [Patent]

Robert H. Goddard, Rocket Apparatus, US Patent No. 1,103,503, Issued July 14, 1914 [Patent]