Hydyne is a mixture of 60% unsymmetrical dimethylhydrazine (UDMH) and 40% diethylenetriamine (DETA), developed in 1957 at Rocketdyne for use in liquid-fuel rockets. Hydyne was used as the fuel for the first stage of the Juno I rocket that launched Explorer 1, the first successful satellite launch conducted by the United States.
In 1955 Wernher von Braun, employed by the U.S. Army, calculated his Redstone rocket could launch a satellite into orbit if its performance could be improved. A contract to develop a more powerful propellant was awarded to the Redstone's main stage builder, Rocketdyne. The contract required the replacement of the PGM-11 Redstone fuel (including 25% water and 75% ethyl alcohol) with a compound that would boost the rocket's performance by at least 8%. Mary Sherman Morgan was assigned to head up a small team of engineers to find a solution. 
The Jupiter-C and Juno I rockets used the same first-stage engines as the missile, but needed more thrust due to the increased size of the payload/warhead. With the use of the newly developed Hydyne, composed of a blend of 60% unsymmetrical dimethylhydrazine (UDMH) and 40% diethylenetriamine (DETA), the Jupiter-C and Juno I engines gained a 12% increase in thrust and higher specific impulse. The resulting fuel was more powerful than alcohol, but also more toxic. The first Hydyne-powered Redstone R&D flight took place on November 29, 1956. After three Jupiter C and six Juno I launches including the launch of America's first satellite, Explorer I), Hydyne was discontinued in favor of higher performing fuels.
'Bagel' was the whimsical name suggested by Morgan, who engineered the Hydyne-LOX (Liquid OXygen) propellant combination used by North American Aviation in their early U.S. rocket designs of the incipient space race. Morgan was considered a rocketry pioneer as she was the only female technical analyst employed by NAA in Downey, California. Morgan suggested calling her new fuel invention 'Bagel', allowing the Redstone propellant combination to be then called 'Bagel and LOX' (a tongue in cheek reference to the brined salmon, Lox, which is served with bagels and cream cheese). Her suggested name for the new fuel was not accepted, and 'Hydyne' was chosen instead by the U.S. Army.
The creation of Hydyne was dramatized in a stage play entitled Rocket Girl which tells a historical fictionalization of Mary Sherman Morgan, Hydyne's inventor. The play was written by Morgan's son, George D. Morgan and ran at the California Institute of Technology in November, 2008, .
- Morgan, George. It was created by Mary Sherman Morgan. America's First Lady of Rocketry, Caltech News, California Institute of Technology, Vol.42, No.1.
- Lerner, Preston, "Soundings: She Put The High In Hydyne". Air & Space Smithsonian Magazine, March 2009, Vol.23, No.6, pp.10, ISSN 0886-2257.
- NASA. The Mercury-Redstone Project, p. 2-2.
- Rocket Girl. Prometheus Books. July 2013. https://books.google.com/books?isbn=1616147407. Retrieved 5 January 2019.
- Missiles and Rockets. American Aviation Publications. January 1958. https://books.google.com/books?id=Ct8iAQAAMAAJ. Retrieved 7 June 2013. ""Nicknamed Hydyne""
- George Paul Sutton (2005). History of liquid propellant rocket engines. American Institute of Aeronautics and Astronautics. pp. 413. ISBN 1-56347-649-5.
- NASA. The Mercury-Redstone Project, p. 3-2, 4-42.
- History of the Redstone Missile System, p. 60
- History of the Redstone Missile System, p. 166
- "America's First Lady of Rocketry" (PDF). California Institute of Technology. 2008. http://calteches.library.caltech.edu/711/2/Random.pdf. Retrieved 2013-06-05.
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