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MAE 4262: ROCKETS AND MISSION ANALYSISOverview of Solid Propellant

Rockets

Mechanical and Aerospace Engineering Department

Florida Institute of Technology

D. R. Kirk

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SOLID PROPELLANT ROCKETS

• Solid fuel rockets rely on controlled explosion of a mixture of substances

• Nearly a homogeneous material that is burned

• Similar to gunpowder ~ (75% potassium nitrate, 10% carbon, and 15% sulfur)

• Example: STS Solid Rocket Boosters:

– Contain ammonium perchlorate as an oxidizer and aluminum as a fuel

– Rest of mixture devoted to bonding two reactants

– Once a solid rocket is ignited, can not be turned off

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GRAIN DESIGNS

Solid & hybrid propellant rockets

Solid propellant rocket motors (SRM) are the first type of the rocket motors in history. Initially they were a barrels (made from paper or, later, steel) with gunpowder. Nowadays SRMs have evolved into quite sophisticated and effective rocket engines. That happened thanks to enormous progress in chemistry and physics of combustion, to development of new effective solid propellants and to technological advances.

The main advantages of SRM:• high thrust;• high reliability and low cost;• simple to change thrust profile;• simple to handle and to hold;• simple to develop and to scale.However, they also have certain disadvantages:• relatively low specific impulse (compared to liquid propellants);• relatively short working time;• relatively low thrust-to-weight ratio;• difficult to control inflight;• need advanced technology to produce effective engines.

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HYBRID ROCKETSSolid Fuel, Liquid Oxidizer Example

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Part 1

LIQUID ROCKET ENGINES

LIQUID ROCKET ENGINE TYPES

NUCLEAR THERMAL FUELNUCLEARREACTOR

SOLID

GRAIN

LIQUID PROPELLANTS

MONOPROPELLANTS :

BIPROPELLANTS :

Hydrazine,

Hydrogen peroxyde

FUELS : OXIDIZERS :

Kerosine, ethanol

Liquid hydrogen,

UDMH, MMH, Hydrazine

Liquid oxygen,

N2O4,

Hydrogen peroxyde

HYBRID PROPELLANTS

liquid propellant : oxidizer - solid propellant : fuel

(solid oxidizers are problematic and lower performing than liquid oxidizers)

oxidizers :

gaseous or liquid oxygen

nitrous oxide.

fuels :

polymers (e.g.polyethylene),

cross-linked rubber (e.g.HTPB),

liquefying fuels (e.g. paraffin).

Solid fuels (HTPB or paraffin) allow for the incorporation of high-energy fuel additives (e.g.aluminium).

Dimethylhydrazine (UDMH) :H2N – N (CH3)2 (l)+ 2 N2O4 (l)  - > 3 N2 (g) + 4 H2O (g) + 2 CO2 (g)  Hydrazine hydrate (N2H4,H2O) :2 (N2H4,H2O) (l) + N2O4 (l)  - > 3 N2 (g) + 6 H2O (g)  Monomethylhydrazine (MMH) : 4 H2N – NHCH3 (l) + 5 N2O4 (l)  - > 9 N2 (g) + 12 H2O (g) + 4 CO2 (g)  Kerosene (CH2 is the approximate formula ) with hydrogen peroxide :CH2 + 3H2O2 → CO2 + 4H2OKerosene and liquid oxygen (LOX)CH2 + 1.5O2 → CO2 + H2O Hydrogen and oxygen (liquids) :2 H2 (g)+ O2 (g)   - > 2 H2O (g)

MONOPROPELLANTSHydrogen peroxyde (H2O2) H2O2 (l) - > H2O (l) + 1/2 O2 (g)Hydrazine (N2H4) N2H4 (l) - >  N2 (g) + 2 H2 (g)

CHEMICAL REACTIONSBIPROPELLANTS

Hybrid rocket

• A hybrid rocket is a rocket with a rocket motor which uses propellants in two different states of matter - one solid and the other either gas or liquid

Common oxidizers include gaseous or liquid oxygen or nitrous oxide.

Common fuels include polymers such as polyethylene, cross-linked rubber such as HTPB or liquefying fuels such as paraffin wax.

•Less explosion hazard - Propellant grain more tolerant of

processing errors such as cracks.

•More controllable - Start/stop/restart and throttling are all • achievable with appropriate oxidize

control•Safe and non-toxic oxidizers such as liquid oxygen and

nitrous oxide can be used•Can be transported to site in a benign form and loaded with

oxidizer remotely immediately before launch, improving safety.

Advantages compared with solid rockets

Advantages compared with bipropellant liquid rockets

• Mechanically simpler - requires only a single liquid propellant resulting in less plumbing, fewer valves, and simpler operations.

• Denser fuels - fuels in the solid phase generally have higher density than those in the liquid phase, reducing overall system volume.

• Metal additives - reactive metals such as aluminum, magnesium, lithium or beryllium can be easily included in the fuel grain increasing specific impulse, density specific impulse, or both.

Disadvantages of hybrid rockets • Oxidizer-to-fuel ratio shift ("O/F shift") - with a constant oxidizer flow-

rate, the ratio of fuel production rate to oxidizer flow rate will change as a grain regresses. This leads to off-peak operation from a chemical performance point of view.

• Low regression-rate (rate at which the solid phase recedes) fuels often drive multi-port fuel grains. Multi-port fuel grains have poor volumetric efficiency and, often, structural deficiencies. High regression-rate liquefying fuels developed in the late 1990s offer a potential solution to this problem.[4]

• Compared with Liquid based propulsion, re-fuelling a partially or totally depleted hybrid rocket would present significant challenges, as the solid propellant cannot simply be pumped into a fuel tank. This may or may not be an issue, depending upon how the rocket is planned to be used.

Hybrid rocket cycle

Pros :

- Higher performance than solids

- Lower complexity than liquids

Cons :

- Lower performance than liquids

- Higher complexity than solids

Solar-heated steam rocket