1

MAE 4262: ROCKETS AND MISSION ANALYSIS

Overview of Solid Propellant Rockets

Mechanical and Aerospace Engineering DepartmentFlorida Institute of Technology

D. R. Kirk

2

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

3

OVERVIEW: SOLID ROCKET COMPONENTS

4

SPACE SHUTTLE SOLID ROCKET BOOSTERS• SRBs are largest solid propellant motors ever

flown and first designed for reuse– Diameter = 12.17 ft– Length = 149.16 ft

• Sea Level Thrust: 3,300,000 lb• Weight

– With propellant: 1,300,000 lb– Inert: 192,000 lb

• Provide ~ 71% of thrust at lift-off and ascent• Propellant mixture by weight

– Ammonium perchlorate: 69.6%– Aluminum: 16%– Iron oxide (catalyst): 0.4%– Polymer binder: 12.04%– Epoxy curing agent: 1.96%

• Propellant is 11 point star shape in forward motor segments and double truncated cone in aft segments

5

ADDITIONAL EXAMPLES

6

MINUTEMAN SOLID ROCKETMinuteman first stage motor

Minuteman missile systems, operated by Air Force Combat Command are long-range,solid-fuel, three-stage intercontinental ballistic missiles capable of carrying singleor multiple nuclear warheads. The program began in 1958 and is one of Boeing'slongest military contracts.

7

PEGASUS SOLID ROCKET

8

GRAIN DESIGNS

9

GRAIN CROSS-SECTIONAL GEOMETRIES

10

SOLID PROPELLANT ROCKETS

11

DIMENSIONS SUMMARY OF CURRENT SRBs

12

MASS SUMMARY OF CURRENT SRBs

13

PERFORMANCE SUMMARY FOR CURRENT SRBs

14

SOLID ROCKET FUEL DATA

15

SOLID ROCKETS AND NOZZLE FLOW• Special issue with solid propellants that use powdered metals as a fuel additive

• Adding aluminum to formation of solid propellant increases gas temperature, but incurs performance penalties related to solid particles that are generated– Aluminum burns with oxygen to form Al2O3 particles

• Particles are initially liquid and solidify during expansion process• Also tend to agglomerate to become large particles• Large particles do not accelerate as quickly as the gas surrounding them• These particles may constitute as much as 10-25% of total mass• Need to consider this in nozzle design, which must account for two-phase flow

• Simplified models exist for analysis of performance:– Results indicate that large particle sizes are a detriment– However, for small particles, there is an optimum amount of Al to add

16

ROCKET FUEL SELECTION GUIDE• Desirable Physical Properties

– Low freezing point– High specific gravity (dense propellant)– Stability (with time)– Heat transfer properties– Pumping properties (low vapor pressure, low viscosity)– Small variation in physical characteristics with temperature– Ignition, combustion, and flame properties

• Performance of Propellants• Economic Factors• Physical Hazards (Explosion, Fire, Spills)• Health Hazzards• Corrosion

17

HYBRID ROCKETSSolid Fuel, Liquid Oxidizer Example