Rocket Propulsion:

Solid Propellant

By: Sashank GummellaCOSMOS Summer ProgramCluster 3: Introduction to Engineering Mechanics

Background

Solid propellants ‐ investigated briefly by Robert H. Goddard (father of the liquid‐fueled rocket) during the 1920s

Looked into for missile propulsion during WWII

John Whiteside Parsons of Caltech ‐ combining asphalt with potassium perchlorate would make for the first castable composite solid propellant 

Background Why asphalt?

It’s a binder and source of fuel. It would be combined with potassium perchlorate (KClO4), an oxidizer, to form a solid propellant for rocket propulsion 

Years later, Charles Bartley improved Parson’s design by replacing asphalt with a polysulfide polymer (LP‐2). Became world’s first elastomeric solid propellant (better)

New design led to Polaris and Minuteman missiles

Background

Keith Rumbel and Charles Henderson (Atlantic Research Corporation) – adding aluminum increases specific impulse (force with respect to the amount of propellant used per unit  time) of composite propellant, thus increasing thrust

All this research and modifications led from the Polaris and Minutemen missiles to the Titan rockets to the solid rocket boosters on NASA’s Space Shuttles

Missiles with Solid Propellant

Polaris Missile

Minuteman ICBM

Rockets with Solid Propellant

Titan 3E Rocket

Titan 4 Rocket

Space Shuttles with Solid Propellant (in SRBs)

Space Shuttle Discovery

Solid Rocket Boosters containing solid propellant inside

Solid Composite Propellant Components

16% Atomized aluminum powder (fuel)

69.8% Ammonium perchlorate (oxidizer)

0.2% Iron oxide powder (catalyst)

12% Polybutadiene acrylic acid acrylonitrile (binder)

2% Epoxy curing agents

How It Works Rocket propulsion relies on burning of the solid fuel with an

oxidizer:

1. Oxidizer (grain) is ignited. Propellant becomes oxidized.

2. Combustion produces gases through deflagration (subsonic combustion)

3. High-temp pressurized gases spread adiabatically (no heat transfer within system)

4. Reaction takes place in a high-pressure combustion chamber.

How It Works5. Resultant high-energy exhaust is then channeled into converging section of nozzle (subsonic flow), through the throat, and then out the diverging section (supersonic flow) to give the rocket the boost to push against Earth’s gravitational force and into the outer atmosphere.

****Perfect representation of Newton’s Third Law of Motion because the system is producing a reaction force and goes upwards.****

Rocket Nozzle

Types of PropellantsBlack Powder Propellants – sulfur, charcoal, potassium nitrate

Zinc-Sulfur Propellants – sulfur and zinc metal

“Candy” Propellants – potassium nitrate and sugar fuel (dextrose, sucrose, etc.)

Double-Base Propellants – nitroglycerin dissolved in nitrocellulose gel and solidified with additives

Types of PropellantsComposite Propellants (most commonly used because of high performance, moderate ease of manufacturing, and moderate cost) - Heterogeneous and oxidizer is mineral salt

High-Energy Composite Propellants

Composite Modified Double-Base Propellants

Minimum-signature Propellants (smokeless) – non pollutant, CL 20 used

Composite PropellantsConsists of a fuel, oxidizer, catalyst, binder, and curing agent

Fuel – mainly fine aluminum powder (high specific impulse)

Oxidizer – Ammonium perchlorate – salt, grain material (NH4ClO4)

Catalyst – Iron oxide powder

Binder – Polybutadiene acrylic acid acrylonitrile (binds fuel, oxidizer, catalyst, and curing agent together into compact rubber form)

Curing agent – Epoxy curing agent (hardens polymer material so it stays together)

Solid Propellant FactsSolid Propellants are mixed and casted into segments prior to being assembled in Solid Rocket Boosters

Cured solid propellant looks and feels like a hard rubber eraser. (Synthetic rubber)

Flexibility of the propellant controlled by ratio of binder to curing agent and solid ingredients (oxidizer and aluminum mainly)

Once propellant becomes oxidized, there is no possible way to reverse or stop the process. The fuel and oxidizer will combust and high energy exhaust will be expelled

Must burn propellant from outside and inside to keep the sum of the surfaces of burning constant.

Solid Propellant FactsVe = √(2CpTc)

Exit velocity of gases based on combustion and

temperature

Solid Propellant FactsSolid combustion produces thermal energy -> changes to kinetic energy when exiting nozzle

r = c(Pcn)

mg = (r)(Ab)(ρp)

n

Velocity (speed) of mass burning

Mass flow rate of gases produced by combustion

of solid propellant“n” is a number (exponent) that

determines whether or not a rocket is in stable or unstable

equilibrium based on its numerical value

Solid Rocket Motor Equilibrium

dPc/dt = APcn - BPc

Must lose temperature gained and stabilize rocket

or it will explode

Stabilize energy (temperature) and mass

in rocket for stability

Solid Rocket Motor Equilibrium

mg that goes through nozzle: BPc

mg that is produced by combustion: APcn

**** BPc = APcn ****

The equation above MUST hold true for STABLE equilibrium

Amount of gas that goes through nozzle

Amount of gas combusted

Solid Rocket Motor Equilibrium

mg = Pcn

If n > 1, then rocket is in unstable equilibrium (NOT GOOD!). If amount of gas combusted is too much or gas is not released, rocket will EXPLODE! Too much accumulation of mass and retention of it is not good.

Solid Rocket Motor Equilibrium

If n < 1, then rocket is in stable equilibrium (GOOD!). Rocket can stabilize itself if perturbed.

*** “n” must be less than 1 at ALL times ***

this will ensure stability of combustion process. If “n” is not less than 1, then reject nozzle design.

Solid Rocket Motor Equilibrium

If energy produced by combustion is greater than the energy lost due to cooling, the rocket will explode because it is in UNSTABLE EQUILIBRIUM.

If energy produced by combustion is less than the energy lost due to cooling, the rocket will be fine since it is in STABLE EQUILIBRIUM.

Solid Rocket Motor Equilibrium

e(-Ea)/(RT) = h(T∞ - T)

Energy generated because of

combustion

Energy lost due to cooling

Arrhenius

Newton’s Cooling Law

Solid Propellant FactsAdvantages: low cost, easy to store because it is premade into compact rubber form, good thrust

Disadvantages: low specific impulse (efficiency) compared to liquid/hybrid propellants, volatile burn rate, all fuel is burned (no way of stopping/reversing combustion)

Exploded View of Solid Rocket Booster

Stored solid propellant

Solid Rocket BoosterHere is an example of a solid rocket booster being tested:

Company’s name is Alliant Techsystems (ATK)

Testing the DM-3 5 Segment Solid Rocket Booster

It is stationary because they are just doing a motor test.

SRB operates for approx. 2 minutes.

Propellant ignites and starts to combust instantly because of the very reactive and strong oxidizer: Ammonium perchlorate

SCIENTISTS!Hermann von Helmholtz

Hermann Glauert

Hermann von HelmholtzAugust 31, 1821 – September 8, 1894

Born in Potsdam, Kingdom of Prussia

Not financially stable

Father encouraged to study medical field but Helmholtz’s work influenced by and attributed to philosophy of Fichte and Kant

BackgroundGerman physicist and physician

Interested in natural sciences as young man

Law of Conservation of Total Energy

Mechanical foundation of Thermodynamics

Fluid dynamics – theorems for vortex dynamics in inviscid fluids

Background1849: Associate Professor of physiology at Prussian University of Königsberg

1855: Professor of anatomy and physiology at University of Bonn

1871: Professor of physics at University of Berlin

Research and Contributions

Law of Conservation of Energy – physics

Studied physiology of senses and optics:

Stressed importance of materialism, unity of mind and body

Invented ophthalmoscope – examine inside of human eye

On the Conservation of Force: conservation of energy (1847)

Research and Contributions

Studied:

Mechanics

Physiology (nerve and sensory)

Optics

Acoustics and aesthetics

Electromagnetism

Mechanics, heat, light, electricity, and magnetism are all manifestations of a single force (energy)

Hermann GlauertOctober 4, 1892 – August 6, 1934

Born in Sheffield, Yorkshire

Wrote a plethora of reports and notes/records about aerofoil and propeller theory

BackgroundBritish aerodynamicist and Principal Scientific Officer of Royal Aircraft Est., Farnborough (Head of Aerodynamics Dept.)

Extensive work with airplane performance – stabilityand control, propellers, aerodynamics, autogyros and helicopters

Royal Aeronautical Society

Research and Contributions

The Elements of Aerofoil and Airscrew Theory

Spread Prandtl’s airfoil and wing theory

Independently developed Prandtl-Glauert method from the aerodynamic theory of his time

Research and Contributions

Ludwig Prandtl

Research and Contributions

Prandtl-Glauert Method:

Published in The Proceedings of the Royal Society in 1928

Mathematical technique to solve compressible flow problems with incompressible flow calculation methods

Can only use when Mach number is greater than

0.7

Research and Contributions

Plot of the subsonic and supersonic Prandtl—Glauert transformations as

a function of the Mach Number

Works Citedhttp://www.nasa.gov/centers/dryden/pdf/88635main_H-2330.pdf

http://inventors.about.com/od/rstartinventions/a/SolidPropellant.htm

http://www.nasa.gov/returntoflight/system/system_SRB.html

http://en.wikipedia.org/wiki/Solid-fuel_rocket

http://www.astronautix.com/articles/comlants.htm

http://en.wikipedia.org/wiki/Hermann_von_Helmholtz#Research

http://en.wikipedia.org/wiki/Hermann_Glauert

http://aerosociety.com/Assets/Docs/Publications/The%20Journal%20of%20Aeronautical%20History/2011-02HermannGlauert_AckroydandRiley.pdf

Fundamentals of Solid-Propellant Combustion edited by Kenneth K. Kuo and Martin Summerfield