The Origins of Liquid-Fueled Rockets

It wasn’t much to look at, and it only lasted three seconds, but nonetheless, the flight of Robert H. Goddard’s first liquid-fueled rocket on a relative’s farm near Auburn, Massachusetts, was the “Kitty Hawk” event of space exploration. This pioneering work in liquid-fuel rocketry became the cornerstone of Goddard’s legacy, but equally important for spaceflight was his research ruling out other proposed methods of reaching orbit.

While perhaps underwhelming by today’s standards, that first launch was the culmination of years of research into efficient space travel — work that Goddard was conducting at a time when few others around the world recognized its potential.

Like many in the aerospace profession, science fiction was the root of Goddard’s motivation and excitement about the possibility of exploring space. After reading these stories in his childhood, at 19 he wrote his 1901 short paper, “The Navigation of Space,” arguing that one could reach orbit by firing several cannons “arranged like a ‘nest’ of beakers.” While not fully developed, this idea eventually led him to propose multistage rockets for reaching space.

When Goddard began seriously working on spaceflight as an undergraduate physics major in the latter half of the 1900s, several methods of reaching space had been proposed by various theorists and writers. While some of these had a degree of practicality, many more would still be considered unfeasible.

Consider, for example, shooting people into orbit with two oppositely polarized magnets, one of which would carry a spacecraft. Jules Verne famously shot a spacecraft to the moon in his 1865 novel, “De la Terre à la Lune” (“From the Earth to the Moon”), from a giant cannon. Another method, championed by novelist Edward Everett Hale in his 1869 The Atlantic Monthly story, involved two spinning flywheels hurling a space station into orbit: “It was not to be by any of your sudden explosions. It was to be done as all great things are done — by the gradual and silent accumulation of power. You all know that a flywheel — heavy, very heavy on the circumference, light, very light within it — was made to save up power, from the time when it was produced to the time when it was wanted.”

What separated Goddard from other spaceflight enthusiasts and their theoretical imaginings was his emphasis on systematic experimentation. Early on, he calculated the energy released with solid-fuel rockets and found it insufficient to escape the Earth’s gravity. He also calculated the energy required to be expended by a cannon to reach Earth orbit and concluded that the high G-forces required would smash a human passenger into mush. By 1908, Goddard had determined that magnetic, atomic, cannon, flywheel and solid fuels were, based on the state of technology, impractical if not fantastic ways to launch payloads. Consequently, only liquid fuels — and then only the less efficient but easier to handle options — provided a feasible path to orbit.

That brought him to the next question: Many believed rockets held the most promise, but what kind of rocket? While gunpowder rockets had existed for almost 1,000 years, Goddard determined that these did not generate enough thrust to reach space. Indeed, it was not until the 1960s that solid-fuel rockets reached that capability with the Minuteman ICBM. Goddard captured his uniquely systematic approach to these and other experiments in his famous “Green Notebook.” In one entry, written in July 1907 while he was an undergraduate at Worcester Polytechnic Institute, he posed three related research questions:

Problem 1: Find minimum of energy required to leave the planet, in a swarm [a concept eventually called staging].

Problem 2: Find mass to be ejected, and velocity of ejection, allowance for changing total mass.

Problem 3: Find velocity of explosion, molecules or group — on what does the temperature depend — slow burning = same temp, is instantaneous burning? What influence has suddenness intend. Know V: consider mass, em [ejected] as potential.

Solving those problems proved a challenge. By the end of 1908, he had learned through considerations of theory and copious laboratory experimentation that none of the options in vogue at the time produced the necessary energy to achieve space access. Now pursuing graduate studies at Clark College (later University) in Worcester, Massachusetts — where he later became a professor of physics — Goddard turned to the possibility of propelling a spacecraft using atomic energy, which he explored in his essay “On the Possibility of Navigating Interplanetary Space.” Several publishers rejected the article, even though the editor at Scientific American called it “most ingenious” and rejected it only because of length. The essay was published later in Goddard’s 1960 collected papers.

After a stint with the military in World War I, where he worked on solid rocket technology for use in combat, Goddard turned his full attention to liquid rocket propulsion. He theorized that liquid oxygen and liquid hydrogen were the best fuels in terms of specific impulse, or ISP — the measure of the number of seconds it takes a rocket engine to produce a pound of thrust from a pound of propellant — but that a combination of liquid oxygen and gasoline was less volatile and therefore more practical. To support his investigations, Goddard applied to the Smithsonian Institution in 1916 and received a $5,000 grant from its Hodgkins Fund. By providing the funding necessary to move from theoretical predictions to laboratory experimentation, this grant proved a critical milestone in rocket development.

His research was ultimately published by the Smithsonian in 1919 as the classic study “A Method of Reaching Extreme Altitudes.” In it, Goddard argued from a firm theoretical base that only liquid-fueled rockets could reach the upper atmosphere and Earth orbit. More ambitiously, he calculated that with a velocity of 6.95 miles/second, without air resistance, an object could escape Earth’s gravity and head into infinity or to other celestial bodies — what soon became known as the Earth’s “escape velocity.” The study also became the great joke for those who believed spaceflight either impossible or impractical. Some ridiculed his ideas in the popular press, much to the consternation of the already reserved Goddard. Soon after the appearance of his publication, he commented that he had been “interviewed a number of times, and on each occasion have been as uncommunicative as possible.” The New York Times was especially harsh in its criticisms, referring to him as an impractical academic dreamer whose ideas had no scientific validity. The editorial also compared his theories to those advanced by the novelist Verne, indicating that such musing is “pardonable enough in [Verne] as a romancer, but it is not so easily explained when made by a savant who isn’t writing a novel of adventure.” The Times questioned both Goddard’s credentials as a scientist and the Smithsonian’s rationale for funding his research and publishing his results.

The negative press prompted Goddard to be even more secretive and reclusive. It did not, however, stop his work, which eventually led him to that Auburn farm for that fateful flight on March 16, 1926. This early liquid oxygen-gasoline rocket was oddly shaped, sporting a thrust chamber and nozzle at the top of a structure that looked more like an erector set contraption than anything resembling the rockets routinely flown today. That more common configuration we have come to associate with launchers would come just a few years later.

The flight itself must have appeared rather uneventful. The rocket flew for only 2.5 seconds, climbed 41 feet and landed 184 feet away in a cabbage patch. Regardless, it demonstrated that this was the core technology needed to reach space. Like the Wright brothers at Kitty Hawk in 1903, Goddard’s 1926 flight proved an inauspicious beginning to a spectacular future. And to its credit, the Times admitted it was wrong about his ideas — on July 17, 1969.