1. Propellants
Dr. Andrew Ketsdever

2. Propellants
Several Factors Must Be Addressed When Deciding on a Propellant
Performance
Chemical energy content, Achievable Isp
Economics
Availability, logistics of production and supply
Physical Hazards
Stability, corrosiveness, carcinogens

3. Liquid Propellants Desirable Properties Low Freezing Point
High Specific Gravity
Good Stability
High Specific Heat
Low Vapor Pressure (better pumping)
Easy Ignition (hypergolic?)

4. Liquid Propellants Highest Potential Specific Impulse
Fluorine Oxidizer
Hydrogen Fuel with suspended Beryllium
Isp=480 sec at Po = 1000 psia (sea level)
Oxidizer highly corrosive (not storable)
Beryllium suspension can not be maintained uniformly

5. Liquid Propellants Oxidizers Liquid Oxygen Boils at 90K
Heat of Vaporization 213 kJ/kg
High attainable performance
Does not burn spontaneously with hydrocarbons at ambient pressures and temperatures
Noncorrosive and nontoxic
Cryogenic temperature poses handling issues

6. Liquid Propellants Liquid Fluorine Boils at 53.7K
Highest values of performance (typically)
High specific gravity
Extremely toxic and corrosive
Poisonous exhaust gases
Low commercial consumption
Expensive

7. Liquid Propellants Hydrogen Peroxide (H2O2) Nitric Acid (HNO3)
Requires high concentration (70-99%)
Storage concerns
Decomposition with certain metal catalysts
Nitric Acid (HNO3)
Highly corrosive
Certain stainless steels and gold containers required
Skin burns

8. Liquid Propellants Nitrogen Tetroxide (N2O4)
Most common storable oxidizer used in the US
High density
Relatively high freezing point
Mildly corrosive
Hypergolic with many fuels
High vapor pressure
Used with hydrazine (UDMH, MMH) propellants

9. Liquid Propellants Fuels Hydrocarbon Fuels RP-1 (Kerosene-like)
Easy to handle
Cost effective
Methane (CH4)
Cryogenic (denser than liquid hydrogen)

10. Liquid Propellants Liquid Hydrogen Boils at 20K Specific Gravity 0.07
Bulky fuel tanks, large volumes
Increased drag
Feed system must be cryogenic compatable
Increased insulation
Nontoxic products (typically)

11. Liquid Propellants Hydrazine Monomehtylhydrazine (MMH)
Unsymmetrical dimethylhydrazine (UDMH)
Toxic
High freezing point 274.3K (MMH) / 216K (UDMH)
Hypergolic with some oxidizers
Spontaneous ignition with air can occur
Positive heat of formation (good)
Good monopropellants with the right catalyst
Reasonable stability

12. Solid Propellants Classes
Double Base Propellant: forms a homogeneous propellant grain of a nitrocellulose and a solid ingredient dissolved in nitroglycerin plus minor additives
Composite Propellant: form a heterogeneous propellant grain with the oxidizer crystals and a powdered fuel held together in a matrix of synthetic rubber binders.
Less hazardous than double base

13. Solid Propellants Oxidizers Ammonium Perchlorate (NH4ClO4)
Most widely used crystalline oxidizer
Good performance
Good availability
Potassium Perchlorate (KClO4)
Medium performance
Higher density than AP
Low burning rate

14. Solid Propellants Fuels Powdered Aluminum Other metallic fuels
5-60 micron diameter
14-18% of propellant by weight (typical)
Small particles can burn spontaneously in air
Oxide particles can agglomerate and form larger particles (two phase issues)
Other metallic fuels
Boron, Beryllium

15. Solid Propellants Binders Other Additives can be included
Hydroxy Terminated Polybutadiene (HTPB)
Binder provides the structure or matrix in which solid ingredients are held together (composite propellant)
Polymer, synthetic rubber
Primary effect on motor reliability, storability and cost
Other Additives can be included
Improve burn rate, storability, curing

16. Hybrid Propellants
Fuel and Oxidizer mixtures of liquid oxidizer and solid propellants (typically)
Combinations of propellants already discussed
Fuel: HTPB, PMMA, HS
Oxidizer: LOx, H2O2, N2O

17. Nuclear Propellants Fuels Low molecular weights
Hydrogen, Water, Methane
No chemical reactions necessary