Solid-fuel rocket

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The Space Shuttle was launched with the help of two solid-fuel boosters known as SRBs

A solid-fuel rocket or solid rocket is a rocket with a rocket engine that uses solid propellants (fuel/oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Chinese, Indians, Mongols and Arabs, as early as the 13th century.[1]



Basic concepts[edit]

Solid Rocket Motor.


The grain behaves like a solid mass, burning in a predictable fashion and producing exhaust gases. The nozzle dimensions are calculated to maintain a design chamber pressure, while producing thrust from the exhaust gases.






  • Allowable chamber pressure is a function of casing design.


Common modes of failure in solid rocket motors include fracture of the grain, failure of case bonding, and air pockets in the grain. All of these produce an instantaneous increase in burn surface area and a corresponding increase in exhaust gas[clarification needed] and pressure, which may rupture the casing.


Grain geometry[edit]

Solid rocket fuel deflagrates from the surface of exposed propellant in the combustion chamber. In this fashion, the geometry of the propellant inside the rocket motor plays an important role in the overall motor performance. As the surface of the propellant burns, the shape evolves (a subject of study in internal ballistics), most often changing the propellant surface area exposed to the combustion gases. The mass flow rate (kg/s) [and, therefore, pressure] of combustion gases generated is a function of the instantaneous surface area A_s, (m2), and linear burn rate b_r (m/s):

\dot{m} = \rho \cdot A_s \cdot b_r




The casing may be constructed from a range of materials. Cardboard is used for small black powder model motors, whereas aluminum is used for larger composite-fuel hobby motors. Steel is used for the space shuttle boosters. Filament wound graphite epoxy casings are used for high-performance motors.




Main article: Rocket engine nozzle


Some designs include directional control of the exhaust. This can be accomplished by gimballing the nozzle, as in the Space Shuttle SRBs, by the use of jet vanes in the exhaust similar to those used in the V-2 rocket, or by liquid injection thrust vectoring (LITV).




An exhaust cloud engulfs Launch Pad 39A at NASA's Kennedy Space Centre in Florida as space shuttle Endeavour lifts off into the night sky.

A typical, well-designed ammonium perchlorate composite propellant (APCP) first-stage motor may have a vacuum specific impulse (Isp) as high as 285.6 seconds (Titan IVB SRMU).[5] This compares to 339.3 s for kerosene/liquid oxygen (RD-180)[6] and 452.3 s for hydrogen/oxygen (Block II SSME)[7] bipropellant engines. Upper stage specific impulses are somewhat greater: as much as 303.8 s for APCP (Orbus 6E),[8] 359 s for kerosene/oxygen (RD-0124)[9] and 465.5 s for hydrogen/oxygen (RL10B-2).[10] Propellant fractions are usually somewhat higher for (non-segmented) solid propellant first stages than for upper stages. The 53,000-kilogram (117,000 lb) Castor 120 first stage has a propellant mass fraction of 92.23% while the 14,000-kilogram (31,000 lb) Castor 30 upper stage recently developed for Orbital Science's Taurus II COTS (International Space Station resupply) launch vehicle has a 91.3% propellant fraction with 2.9% graphite epoxy motor casing, 2.4% nozzle, igniter and thrust vector actuator, and 3.4% non-motor hardware including such things as payload mount, interstage adapter, cable raceway, instrumentation, etc. Castor 120 and Castor 30 are 2.36 and 2.34 metres (93 and 92 in) in diameter, respectively, and serve as stages on the Athena IC and IIC commercial launch vehicles. A four-stage Athena II using Castor 120s as both first and second stages became the first commercially developed launch vehicle to launch a lunar probe (Lunar Prospector) in 1998.

Solid rockets can provide high thrust for relatively low cost. For this reason, solids have been used as initial stages in rockets (the classic example being the Space Shuttle), while reserving high specific impulse engines, especially less massive hydrogen-fueled engines for higher stages. In addition, solid rockets have a long history as the final boost stage for satellites due to their simplicity, reliability, compactness and reasonably high mass fraction.[11] A spin-stabilized solid rocket motor is sometimes added when extra velocity is required, such as for a mission to a comet or the outer solar system, because a spinner does not require a guidance system (on the newly added stage). Thiokol's extensive family of mostly titanium-cased Star space motors has been widely used, especially on Delta launch vehicles and as spin-stabilized upper stages to launch satellites from the cargo bay of the Space Shuttle. Star motors have propellant fractions as high as 94.6% but add-on structures and equipment reduce the operating mass fraction by 2% or more.


An attractive attribute for military use is the ability for solid rocket propellant to remain loaded in the rocket for long durations and then reliably launched at a moment's notice.

Propellant families[edit]

Black powder (gunpowder) propellants[edit]


Zinc–sulfur (ZS) propellants[edit]


"Candy" propellants[edit]


Double-base (DB) propellants[edit]


Composite propellants[edit]


Polyurethane-bound aluminum-APCP solid fuel was used in the submarine launched Polaris missiles.[16] APCP used in the space shuttle Solid Rocket Boosters consisted of ammonium perchlorate (oxidizer, 69.6% by weight), aluminium (fuel, 16%), iron oxide (a catalyst, 0.4%), polybutadiene acrylonitrile(PBAN) polymer (a non-urethane rubber binder that held the mixture together and acted as secondary fuel, 12.04%), and an epoxy curing agent (1.96%).[17][18] It developed a specific impulse of 242 seconds (2.37 km/s) at sea level or 268 seconds (2.63 km/s) in a vacuum. The 2005-2009 Constellation Program was to use a similar PBAN-bound APCP.[19]

In 2009, a group succeeded in creating a propellant of water and nanoaluminum (ALICE).

High-energy composite (HEC) propellants[edit]


Composite modified double base propellants[edit]

Composite modified double base propellants start with a nitrocellulose/nitroglycerin double base propellant as a binder and add solids (typically ammonium perchlorate and powdered aluminum) normally used in composite propellants. The ammonium perchlorate makes up the oxygen deficit introduced by using nitrocellulose, improving the overall specific impulse. The aluminum also improves specific impulse as well as combustion stability. High performing propellants such as NEPE-75 used in Trident II D-5, replace most of the AP with HMX, further increasing specific impulse. The mixing of composite and double base propellant ingredients has become so common as to blur the functional definition of double base propellants.

Minimum-signature (smokeless) propellants[edit]


Electric Solid Propellants[edit]

Electric Solid Propellants (ESPs) are a family of high performance plastisol solid propellants that have the unique property of being ignited and throttled by the application of electric current. Unlike conventional rocket motor propellants that are difficult to control and extinguish, ESPs can be ignited reliably at precise intervals and durations. Moreover, the technology is attractive because it requires no moving parts and the propellant is insensitive to flames or electrical sparks.[20]

Hobby and amateur rocketry[edit]



Designing solid rocket motors is particularly interesting to amateur rocketry enthusiasts. The design of a successful solid-fuel motor requires application of continuum mechanics, combustion chemistry, materials science, fluid dynamics (including compressible flow), heat transfer, geometry (particle spectrum packing), and machining. The vast majority of amateur-built rocket motors utilize a composite propellant, most commonly APCP and candy rocket propellant.[citation needed]


Solid rockets were invented by the Chinese, the earliest versions were recorded in the 13th century. Hyder Ali, king of Mysore, developed war rockets with an important change: the use of metal cylinders to contain the combustion powder.

Castable composite solid rocket motors were invented by John Whiteside "Jack" Parsons at Caltech in 1942 when he replaced double base propellant with roofing asphalt and potassium perchlorate. This made possible slow-burning rocket motors of adequate size and with sufficient shelf-life for jet-assisted take off applications. Charles Bartley, employed at JPL (Caltech), substituted curable synthetic rubber for the gooey asphalt, creating a flexible but geometrically stable load-bearing propellant grain that bonded securely to the motor casing. This made possible much larger solid rocket motors. Atlantic Research Corporation significantly boosted composite propellant Isp in 1954 by increasing the amount of powdered aluminum in the propellant to as much as 20%.[21][dead link]

The largest solid rocket motors ever built were Aerojet's three 6.60-metre (260 in) monolithic solid motors cast in Florida.[22] Motors 260 SL-1 and SL-2 were 6.63 metres (261 in) in diameter, 24.59 metres (80 ft 8 in) long, weighed 842,900 kilograms (1,858,300 lb) and had a maximum thrust of 16 MN (3.5×10^6 lbf). Burn duration was two minutes. The nozzle throat was large enough to walk through standing up. The motor was capable of serving as a 1-to-1 replacement for the 8-engine Saturn I liquid-propellant first stage but was never used as such. Motor 260 SL-3 was of similar length and weight but had a maximum thrust of 24 MN (5.4×10^6 lbf) thrust and a shorter duration.


Sounding rockets[edit]

Almost all sounding rockets use solid motors.


Due to reliability, ease of storage and handling, solid rockets are used on a number of missiles and ICBMs.

Orbital rockets[edit]



Main article: Solid rocket booster


Some rockets, like the Antares (manufactured by Orbital ATK), have mandatory solid-fuel upper stages. The Antares rocket uses the Aerojet Rocketdyne-manufactured Castor 30 as an upper stage.

Advanced research[edit]

  • Environmentally sensitive fuel formulations such as ALICE propellant
  • Ramjets with solid fuel
  • Variable thrust designs based on variable nozzle geometry

See also[edit]


  2. ^
  3. ^
  5. ^ ATK Space Propulsion Products Catalog, May 2008, p. 30
  6. ^
  7. ^
  8. ^ a b
  9. ^
  10. ^
  11. ^ Solid
  12. ^
  13. ^ Minotaur IV User's Guide, Release 1.0, Orbital Sciences Corp., January 2005,p. 4
  14. ^ a b
  16. ^
  17. ^ "Shuttle Solid Rocket Boosters". NASA. 
  18. ^ "Solid Rocket Boosters". NASA. 
  20. ^
  21. ^ M. D. Black (2012). The Evolution of Rocket Technology. Native Planter, SLC. p. 39. under ebook/History[dead link]
  22. ^ "The 260 - The Largest Solid Rocket Motor Ever Tested" (PDF). June 1999. Retrieved July 2014. 

External links[edit]