Yvonne Brill was a pioneering rocket scientist, who, after an eight-year break to raise a family, went on to develop a propulsion system to help keep satellites from slipping out of their orbits. The system, invented in the early 1970s, remains the industry standard for unmanned spacecraft and earned her recognition in 2011 when she received the National Medal of Technology and Innovation from President Obama, who cited the US Patent and Trademark Office: "Satellites using her invention form the backbone of the worldwide communication network."
She was described by the American Institute of Aeronautics and Astronautics as "a trailblazer at a time when women were not encouraged to enter the science and technology fields". Her remarkable success was achieved with no official engineering degree and in the face of much male prejudice, particularly remarkable given that she is believed to have been the only woman in the United States working in rocket science in the mid-1940s. She said, "You just have to be cheerful about it and not get upset when you get insulted." She was still encouraging women to become engineers and scientists well into her 80s.
Brill, an expert in the chemistry of space propulsion, developed the hydrazine resistojet, a more efficient rocket thruster to keep orbiting satellites in place; it also allowed satellites to carry less fuel and more scientific equipment and to stay in space longer. The thrusters have the delicate task of manoeuvring a weightless satellite that can weigh more than 2.5 tons on Earth.
A determined woman, Brill was not afraid of risking her job to further ideas that, she said, "I thought should be adopted, that were good technical ideas, that maybe somebody considered were a little bit far out... I just kept pushing. I didn't care whose shins I kicked... And the ideas got adopted."
Brill was subsequently associated with numerous notable projects. She contributed to the propulsion systems of Tiros, the first weather satellites; Nova, a series of rocket designs used in Apollo lunar missions; the Atmosphere Explorer, the first upper-atmosphere satellite; and the Mars Observer, launched in 1992 and which in 1993 almost entered orbit round Mars before it lost contact with Earth.
Born in a suburb of Winnipeg, in the state of Manitoba, central Canada, in 1924, Yvonne Madelaine Claeys was the youngest of three daughters born to Belgian immigrants; both parents had left Flanders separately. Her father had a carpentry business while her mother raised the family.
Showing an early flair for science, Brill applied to study engineering at the University of Manitoba. However, she was turned down on the basis that there was no accommodation for women at a special summer outdoor engineering camp, which students were required to attend. Undeterred, she read mathematics and chemistry, graduating at the top of her class in 1945.
Upon graduation, although without a relevant degree, Brill went to work for the Douglas Aircraft Co in Santa Monica, California and gravitated to the chemistry of propellants. "I didn't have engineering but the engineers didn't have the chemistry and math," she later said. She subsequently earned a master's degree in chemistry from the University of Southern California. While at a chemistry lecture given by the Nobel prize-winner Linus Pauling, she met her future husband, Bill Brill, who held a PhD in chemistry. They began dating and married in 1951.
For many years they faced a challenge: his job opportunities lay in the east, hers in the west. Her decision was to follow his career. She recalled that it was based on her belief that "good jobs are easier to find than good husbands". In spite of the move, the post-war rush into rocket technology and her expertise meant that she was rarely out of work. She was employed at the Rand Corporation, a Douglas spin-off, and then Wright Aeronautical in New Jersey until she left full-time work, feeling "very put upon" to raise her family.
Brill did some consultancy work, and in 1966 returned full-time to RCA's rocket subsidiary, Astro Electronics, where she developed her satellite propulsion system, also known as the electro-thermal hydrazine thruster, which allowed engineers to more efficiently alter and monitor the position of satellites in a geosynchronous orbit around Earth. She patented her system in 1972, and the first communications satellite using it was launched in 1983.
From 1981 to 1983 she worked at Nasa headquarters in Washington as the director of the space shuttle's solid rocket motor programme. She worked in London for the International Maritime Satellite Organisation (from 1986-91) until her retirement.
Brill received many national and international honours including, the Nasa Distinguished Public Service Medal (2001), and was elected to the US National Academy of Engineering and inducted into the National Inventors Hall of Fame in 2010, along with the creators of Post-it notes; this prompted comments that it took two men to come up with adhesive stationery but one woman to discover how to keep satellites aloft and in place. Her personal and professional balancing act also gained recognition in 1980, when Harper's Bazaar magazine and the DeBeers Corporation gave her their Diamond Superwoman Award for returning to a successful career after starting a family.
In retirement, Brill travelled all over the US urging young women to follow her example by studying maths and science, and helped foster the careers of women in technical fields. The former president of the Society of Women Engineers, Jill Tietjen, said, "She was a mentor, a champion and a role model for so many of us. She was determined, absolutely determined to help young engineers and scientists get to the next step and get the awards and recognition they deserved."
Brill is survived by her children. Her husband died in 2010.
Yvonne Madelaine Claeys, scientist: born St Vital, Winnipeg, Canada 30 December 1924; married 1951 William Brill (died 2010; two sons, one daughter); died Princeton, New Jersey 27 March 2013.