Thomas Mueller is an American rocket engineer and engine designer, best known as a founding employee of SpaceX and for his pioneering work on the TR-106 and key SpaceX rocket engines.
Tom Mueller was born in October 1963 in St. Maries, Idaho, a small logging town with a population of about 2,500. His father worked as a logger. While many of his peers spent their free time outdoors, Mueller developed a deep fascination with technology and space from a young age. He frequently visited the local library and was an avid viewer of the TV series Star Trek. By the age of 10, he had taught himself to repair clocks, lawnmowers, and other mechanical devices.
Mueller's passion for space exploration extended to building model rockets, beginning with Estes kits. At 12, he constructed a model of the Space Shuttle with working boosters that could land safely. Encouraged by his success, he progressed to experimenting with functional rocket engines, using his father's oxy-acetylene welder. Drawing upon books and hands-on research, he began testing engine performance. His efforts were recognized in school science fairs, where he won multiple competitions.
Coming from a lower-middle-class family, financial limitations made attending prestigious universities unfeasible. Mueller’s father had hoped he would pursue logging for a steady income. However, Mueller remained focused on his academic goals and enrolled at the University of Idaho—the only in-state university offering affordable tuition. To fund his studies, he worked summers as a logger, operating heavy machinery.
After graduating, Mueller relocated to California to pursue opportunities in aerospace—a field more aligned with his interests. Despite receiving job offers in Idaho and Oregon, he accepted a position at Hughes Aircraft, a satellite manufacturer. Although the role did not directly involve rocketry, Mueller appreciated its connection to the space industry.
Mueller eventually joined TRW Inc., where he worked on liquid-fueled rocket engines. One of his major projects was the TR-106, a low-cost, high-thrust engine using liquid hydrogen and oxygen, producing approximately 2,900 kN of thrust—making it one of the most powerful engines of its time. While working at TRW, Mueller also earned a Master’s degree in Mechanical Engineering from Loyola Marymount University.
Feeling constrained within TRW's large corporate structure, Mueller began pursuing his passion independently. As a hobby, he built rocket engines and became involved with the Reaction Research Society, an amateur experimental rocketry group. He quickly became a key member, regularly testing sizable, functional engines at the RRS site in California's Mojave Desert.
In late 2001, Mueller started constructing a new liquid-propelled engine at home and in a friend's warehouse. By 2002, he had successfully tested a 36 kg engine producing 58 kN of thrust. His innovative work earned him recognition among rocket enthusiasts, eventually catching the attention of Elon Musk. Impressed by Mueller’s hands-on expertise, Musk visited the group and quickly realized Mueller possessed the specialized knowledge essential to SpaceX’s vision.
Mueller became one of the founding members of SpaceX in 2002, joining Elon Musk and a small initial team. At the time, many companies had sought to recruit Mueller, but he was drawn to Musk's long-term goals and passion for space exploration. Reflecting on the transition, Mueller once said, “TRW is a huge company with a tiny propulsion department, whereas here at SpaceX I’m kind of a king.”
At SpaceX, Mueller led the propulsion engineering team, fulfilling a lifelong dream. He served as Vice President of Propulsion Engineering for over a decade before becoming Chief Technology Officer (CTO) of Propulsion in 2014. In this role, he oversaw the design and development of critical engines including the Kestrel for Falcon 1 and the Merlin for Falcon 9 and Falcon Heavy. He was also involved in the development of other spacecraft engines within SpaceX’s growing portfolio.
Mueller's contributions were central to the success of the Falcon 9 launch system. As of his retirement, SpaceX had launched over 100 Falcon 9 rockets, with more than 65 landings and 45 successful reuses—an achievement that marked a new chapter in the commercial spaceflight era. Notably, Falcon 9 enabled the return of U.S. astronauts to space under NASA’s Commercial Crew Program, flying the Crew Dragon spacecraft to the International Space Station for the first time since the retirement of the Space Shuttle in 2011.
After nearly two decades with SpaceX, Tom Mueller announced his retirement on November 30. He shared the news on Twitter, writing, "I retired from SpaceX today! Thank you, Elon Musk, it was quite a ride!" To which Musk responded, "Thanks for everything you did to help build SpaceX! Some of the best memories ever."
