Nitrous oxide fuel blend

Nitrous Oxide Fuel Blend propellants are a class of liquid rocket propellants intended to replace hydrazine as the standard rocket fuel. The fuel and oxidizer are blended and stored; this is sometimes referred to as a mixed monopropellant. Upon use, the propellant is heated or passed over a catalyst bed and the nitrous oxide decomposes into oxygen-rich gasses. Combustion then ensues. Special care is needed in the chemical formulation and engine design to prevent detonating the stored fuel.

NOFBX is a recent example, developed by Firestar Technologies.^[1]

Overview

The agent used for rocket fuel in a shuttle is paramount; weight, thrust, cost, toxicity, risk of explosions and other problems make it important for scientists 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.^[2] 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.^[3] Until recently (ca. 2003), the complexities involved in building propulsion systems that can safely handle nitrous oxide fuel blend monopropellants have been a deterrent to serious development since the end of WWII.

Innovative Space Propulsion Systems

A NOFBX flight test mission has been planned since 2011. Innovative Space Propulsion Systems announced plans to test the NOFBX mono-propellant on the NASA portion of the International Space Station (ISS), with an initial tentative flight date of late 2012.^[1] NASA formally approved the mission to the ISS on a 2013 launch slot in May 2012.^[4] This mission has since been removed from the launch manifest and has not yet been rescheduled.

The mission had been scheduled 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 is expected to remain on-orbit for approximately one year as it undergoes a "series of in-space performance tests."^[5]

NOFBX

NOFBX is the trademarked name for a proprietary nitrous oxide/fuel/emulsifier blended mono-propellant developed by Firestar Technologies.^[6] The NOFBX patent claims a mixture of nitrous oxide as the oxidizer with ethane, ethene or acetylene as the fuel.^[8] NOFBX has a higher specific impulse (I_sp) and is less toxic than other monopropellants currently used in space applications, such as hydrazine. Flight testing of NOFBX engines is planned on the International Space Station in 2012.^[7]

NOFBX has been used to fuel a reciprocating engine to power high-altitude, long-endurance drone aircraft under a DARPA contract.^[2]

NOFBX is being promoted as a "game changing" technology^[1] with the following characteristics:

• constituents are widely available from chemical suppliers, inexpensive and safe to handle^[1]
• can be transported and handled without undue precautions or hazards^[1]
• its end products (N
  2, CO, H
  2O, H
  2 and CO
  2)^[8] are all nontoxic (except carbon monoxide; carbon dioxide is toxic above ~8%) and produce no accumulated deposits or contamination;^[1] whereas hydrazine emits ammonia^[8]
• hydrazine has an I_sp of about 230 s; NOFBX has an I_sp of 300 s^[8]
• has far better lift capability (energy density 3.5 to 3.9 times greater) than hydrazine^[8]
• is tolerant to a wide thermal range; storable at room temperature on the ground as well as in temperatures found in outer space^[7]
• (is projected to) lower cost compared to existing propulsion systems of comparable performance^[1]
• is a monopropellant, which significantly reduces the need for auxiliary hardware, saving cost, volume, and mass for launch systems
• utilizes cool running thrusters that dramatically reduce thermal design challenges
• burns in liquid, gas, and two-phase flow^[7]
• does not have the materials compatibility constraints of traditional hypergolic systems (a system in which the fuel ignites upon contact with the oxidizer)^[1]

Safety Concerns

Recent work on the decomposition of nitrous oxide has raised concerns about the safety risks of mixing hydrocarbons with nitrous oxide. By adding hydrocarbons, the barrier to an explosive decomposition event is lowered significantly.^[9]

See also

• Nitrous oxide

References

• 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)

External links

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

Spacecraft propulsion
Chemical rockets	State Liquid-fuel rocket Solid-fuel rocket Hybrid rocket Propellants Liquid propellants Cryogenic Hypergolic Monopropellant Bipropellant Staged combustion cycle Expander cycle Gas-generator cycle Tap-off cycle Pressure-fed engine Pump-fed engine Electric pump-fed engine Tripropellant
Electrical thrusters	Electrostatic Colloid thruster Ion thruster Gridded Hall effect thruster Field-emission electric propulsion Ionocraft Electromagnetic Pulsed inductive thruster Magnetoplasmadynamic thruster Electrodeless plasma thruster VASIMR Electrothermal Pulsed plasma thruster Helicon Double Layer Thruster Arcjet rocket Resistojet rocket Other MagBeam High Power Electric Propulsion Mass driver Resonant cavity thruster
Nuclear propulsion	Closed system Nuclear electric rocket Nuclear thermal rocket Radioisotope Salt-water Gas core "Lightbulb" Open system Nuclear pulse propulsion Antimatter-catalyzed Pulsed nuclear thermal rocket‎ Fusion rocket Bussard ramjet Fission-fragment rocket Fission sail Nuclear photonic rocket
Other	Cold gas thruster Solar sail Electric sail Magnetic sail Beam-powered propulsion Solar thermal rocket Tethers Gravity assist Anti-gravity
Spaceflight portal