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Overview

Main article: Rocket propellant

The propellant used in a rocket engine plays an important role in both engine design and in design of the launch vehicle and related ground equipment to service the vehicle. Weight, energy density, cost, toxicity, risk of explosions, and other problems make it important for engineers to design rockets with appropriate propellants. The major classes of rocket fuels are:

A common fuel in small maneuvering thrusters is hydrazine. It is liquid at room temperature and, having a positive enthalpy of formation, can be used as a monopropellant to greatly simplify system design. But it is also extremely toxic and has a relatively high freezing point of +1C. It is also unstable, an inherent property of any substance with a positive enthalpy of formation.

Nitrous oxide can be used as an oxidizer with various fuels; it is popular mainly in hybrid rockets. It is far less toxic than hydrazine and has a much lower boiling point, though it can be liquified at room temperature under pressure. Like hydrazine it has a positive enthalpy of formation that makes it both potentially unstable and a viable monopropellant. It can be decomposed with a catalyst to produce a hot mixture of nitrogen and oxygen.¹ When mixed with a fuel and stored before use, it becomes a mixed monopropellant.

History

German rocket scientists were experimenting with nitrous oxide fuel blends as early as 1937. Nitrous oxide fuel blends testing continued throughout World War II. The promise of high performance, greater range and lighter feed systems drove experimentation with blends of nitrous oxide and ammonia, which resulted in numerous explosions and demolished motors.² The complexities involved in building propulsion systems that can safely handle nitrous oxide fuel blend monopropellants have been a deterrent to serious development.

Subsequent development of nitrous oxide fuel blends picked up again in the 2000s, and in 2011 an in-space flight test mission was planned. In the event, the flight test was cancelled. Innovative Space Propulsion Systems had announced plans to test the NOFBX mono-propellant on the NASA portion of the International Space Station (ISS), with an initial tentative flight date no earlier than 2012.³ NASA formally approved the mission to the ISS on a 2013 launch slot in May 2012.⁴ The mission had been slated to travel to the ISS in the unpressurized cargo compartment of a SpaceX Dragon spacecraft during one of the contracted NASA cargo re-supply missions in mid-2013. The "ISPS NOFBX Green Propellant Demonstration" will utilize a deep-throttling 100 pounds-force (440 N)-thrust-class engine burning NOFBX rocket engine that will be mounted to the outside the European Columbus module on the ISS, and had been expected to remain on-orbit for approximately one year while undergoing a "series of in-space performance tests."⁵

NOFBX was a trademarked name for a proprietary nitrous oxide/fuel/emulsifier blended mono-propellant developed by Firestar Technologies.⁶ The NOFBX patent claimed a mixture of nitrous oxide as the oxidizer with ethane, ethene or acetylene as the fuel.[8] NOFBX has a higher specific impulse (Isp) and is less toxic than other monopropellants currently used in space applications, such as hydrazine. Flight testing of NOFBX engines had been planned on the International Space Station,⁷ but, in the event, did not go forward.

NOFBX had previously been used to fuel a reciprocating engine to power high-altitude, long-endurance drone aircraft under a DARPA contract.⁸ NOFBX was promoted by the company at the time as a "game changing" technology⁹ with the several characteristics that underline why safer monopropellants were of interest in the industry:

• constituents are widely available from chemical suppliers, inexpensive and safe to handle¹⁰
• can be transported and handled without undue precautions or hazards¹¹
• its end products (N2, CO, H2O, H2 and CO2)¹² are all substantially less toxic than traditional long-duration storable monopropellants and produce no accumulated deposits or contamination;¹³ whereas hydrazine emits ammonia¹⁴
• hydrazine has an Isp of about 230 s; NOFBX was reported to have an Isp of 300 s¹⁵
• has better energy density, more than three times greater than hydrazine¹⁶
• is tolerant to a wide thermal range; storable at room temperature on the ground as well as in temperatures found in outer space¹⁷
• was projected to lower cost compared to existing propulsion systems of comparable performance¹⁸
• is a monopropellant, which significantly reduces the need for auxiliary hardware, saving cost, volume, and mass for launch systems
• utilizes thrusters that run cooler, reducing thermal design challenges¹⁹

Safety concerns

A 2008 AIAA paper on the decomposition of nitrous oxide has raised concerns about the safety risks of mixing hydrocarbons with nitrous oxide. By adding hydrocarbons, the energy barrier to an explosive decomposition event is lowered significantly.²⁰

See also

• Nitrous oxide

• Sutton, George P.; Biblarz, Oscar (2001). Rocket Propulsion Elements (7th ed.). John Wiley & Sons. p. 6. ISBN 0-471-32642-9.

Further reading

• Doug Mohney (May 17, 2012). Brooke Neuman (ed.). "Green Propulsion Demo Passes Space Station Safety Review". Satellite News. (talks about the (then upcoming) NASA safety review)
• Schmidt, Eckart W. (2023). "Nitrous Oxide Monopropellants". Encyclopedia of Monopropellants. De Gruyter. pp. 1215–1436. doi:10.1515/9783110751390-009. ISBN 978-3-11-075139-0.

External links

• NOFBX patent application
• USPAT 20090133788 Nitrous oxide fuel blend monopropellants

References

1. Joiner, Stephen (May 1, 2011). "The Mojave Launch Lab". Air & Space Smithsonian. Retrieved March 18, 2011. (online publication date precedes print edition) http://www.airspacemag.com/space-exploration/The-Mojave-Launch-Lab.html ↩

2. Clark, John D. (1972). Ignition!: An Informal History of Liquid Rocket Propellants. Rutgers University Press. ISBN 978-0-8135-0725-5.[page needed] 978-0-8135-0725-5 ↩

3. Messier, Doug (August 9, 2011). "A Non-Toxic Fuel From the Mojave Desert". Parabolic Arc. Archived from the original on October 7, 2011. Retrieved August 9, 2011. http://www.parabolicarc.com/2011/08/09/a-non-toxic-fuel-from-the-mojave-desert/ ↩

4. Morring, Frank Jr. (May 21, 2012). "SpaceX To Deliver Green-Propulsion Testbed To ISS". Aviation Week and Space Technology. Retrieved May 24, 2012. http://www.aviationweek.com/Article.aspx?id=/article-xml/AW_05_21_2012_p24-458579.xml ↩

5. "ISS-bound Propellant Demo Passes NASA Safety Review". Space News. May 29, 2012. p. 9. Retrieved June 26, 2012. http://www.spacenews.com/article/iss-bound-propellant-demo-passes-nasa-safety-review ↩

6. "Firestar Technologies • Advanced Chemical Propulsion and Power Systems". Firestar-engineering.com. Retrieved December 30, 2013. http://www.firestar-engineering.com/NOFBX-MP.html ↩

7. "NOFBX Monopropulsion Overview" (PDF). Firestar Technologies. February 9, 2011. Archived from the original (PDF) on July 24, 2011. https://web.archive.org/web/20110724232730/http://www.aiaa.org/pdf/industry/presentations/Greg_Mungas.pdf ↩

8. Joiner, Stephen (May 1, 2011). "The Mojave Launch Lab". Air & Space Smithsonian. Retrieved March 18, 2011. (online publication date precedes print edition) http://www.airspacemag.com/space-exploration/The-Mojave-Launch-Lab.html ↩

9. Messier, Doug (August 9, 2011). "A Non-Toxic Fuel From the Mojave Desert". Parabolic Arc. Archived from the original on October 7, 2011. Retrieved August 9, 2011. http://www.parabolicarc.com/2011/08/09/a-non-toxic-fuel-from-the-mojave-desert/ ↩

10. Messier, Doug (August 9, 2011). "A Non-Toxic Fuel From the Mojave Desert". Parabolic Arc. Archived from the original on October 7, 2011. Retrieved August 9, 2011. http://www.parabolicarc.com/2011/08/09/a-non-toxic-fuel-from-the-mojave-desert/ ↩

11. Messier, Doug (August 9, 2011). "A Non-Toxic Fuel From the Mojave Desert". Parabolic Arc. Archived from the original on October 7, 2011. Retrieved August 9, 2011. http://www.parabolicarc.com/2011/08/09/a-non-toxic-fuel-from-the-mojave-desert/ ↩

12. "NITROUS OXIDE FUEL BLEND MONOPROPELLANTS - Patent application". Faqs.org. Patent Docs. Retrieved December 30, 2013. http://www.faqs.org/patents/app/20090133788 ↩

13. Messier, Doug (August 9, 2011). "A Non-Toxic Fuel From the Mojave Desert". Parabolic Arc. Archived from the original on October 7, 2011. Retrieved August 9, 2011. http://www.parabolicarc.com/2011/08/09/a-non-toxic-fuel-from-the-mojave-desert/ ↩

14. "NITROUS OXIDE FUEL BLEND MONOPROPELLANTS - Patent application". Faqs.org. Patent Docs. Retrieved December 30, 2013. http://www.faqs.org/patents/app/20090133788 ↩

15. "NITROUS OXIDE FUEL BLEND MONOPROPELLANTS - Patent application". Faqs.org. Patent Docs. Retrieved December 30, 2013. http://www.faqs.org/patents/app/20090133788 ↩

16. "NITROUS OXIDE FUEL BLEND MONOPROPELLANTS - Patent application". Faqs.org. Patent Docs. Retrieved December 30, 2013. http://www.faqs.org/patents/app/20090133788 ↩

17. "NOFBX Monopropulsion Overview" (PDF). Firestar Technologies. February 9, 2011. Archived from the original (PDF) on July 24, 2011. https://web.archive.org/web/20110724232730/http://www.aiaa.org/pdf/industry/presentations/Greg_Mungas.pdf ↩

18. Messier, Doug (August 9, 2011). "A Non-Toxic Fuel From the Mojave Desert". Parabolic Arc. Archived from the original on October 7, 2011. Retrieved August 9, 2011. http://www.parabolicarc.com/2011/08/09/a-non-toxic-fuel-from-the-mojave-desert/ ↩

19. "NOFBX Monopropulsion Overview" (PDF). Firestar Technologies. February 9, 2011. Archived from the original (PDF) on July 24, 2011. https://web.archive.org/web/20110724232730/http://www.aiaa.org/pdf/industry/presentations/Greg_Mungas.pdf ↩

20. Karabeyoglu, A. (2008). "Modeling of N2O Decomposition Events". American Institute of Aeronautics and Astronautics. 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit. Hartford, CT: Aerospace Research Central. doi:10.2514/6.2008-4933. /wiki/Doi_(identifier) ↩