Rocket Propulsion: Solid Propellant By: Sashank Gummella COSMOS Summer Program Cluster 3: Introduction to Engineering Mechanics
Dec 28, 2015
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