Solid Rocket Propulsion

How Solid Rocket Motors Work

Photo Solid Rocket Motor Conceptually, solid rocket motors (or SRMs) are simple devices with very few moving parts. An electrical signal is sent to the igniter which creates hot gases which ignite the main propellant grain (see image below). The propellant contains both fuel and oxidizer; therefore these devices can operate in the vaccuum of space. Thrust is developed as the high thermal energy of the combustion gases is converted to kinetic energy in the exhaust. The simplicity of SRMs make them an attractive choice for many rocket propulsion applications. Because there are few structural components, the SRM is efficient in that the vast majority of its weight is actually usable propellant. SRMs can be ignited in a moments notice and don't require tanking of liquids prior to operation. On the downside, their efficiency (specific impulse) is generally lower than liquid systems, and they cannot be readily throttled. Once ignited, the motor will burn to extinction unless special provisions are included to terminate thrust during the middle of a firing.

Details of Various Solid Rocket Motors

Comparison Tables of Various Engines

Strap-on Boosters
Make Model Thrust Weight Propellant Total Impulse Burn time Applications
Thiokol SRSM 3,300,000 lb 1,300,000 lb ammonium perchlorate/aluminum Information not available 75 s Shuttle SRB
Castor IVA Information not available Information not available Information not available Information not available Information not available Delta I, Atlas strap-on
Alliant GEM 112,241 lb 28,592 lb 88% HTPB 7,090,000 lb-s 55 s Delta II strap-on


Stand-alone solid rocket boosters
Make Model Thrust Weight Propellant Total impulse Burn time Application
Thiokol Castor 120 435,000 lb 116,275 lb HTPB 29,900,000 lb-s 81 s Athena I, II first stage, Athena II second stage
Alliant Orion 50S AL 130,500 lb 29,581 lb HTPB 7,893,000 lb-s 72.4 s Pegasus air-launch space booster


Upper stage engines
Make Model Thrust Weight Propellant total impulse Burn time Applications
Thiokol STAR 48A 17,300 lb 5674 lb Ap / Al 1,528,409 lb-s 88 s STS Payload Assist Module
Pratt Orbus 6 23,800 lb 6515 lb Information not available 1,738,000 lb-s 101 s STS Inertial Upper Stage
Orbus 21S 59,460 lb 22,703 lb Information not available 6,190,000 lb-s 138 s INTELSAT-VI perigee kick


Tactical missile engines
Make Model Weight Propellant Operating temps
Alliant Sidewinder 99 lb RS HTPB -65F to 160F
AMRAAM Information not available 156 lb -65F to 145F


Model rocket engines
Make Model Propellant Thrust Impulse Weight Propellant Weight Burn time
Aerotech F50-4T disposable Blue Thunder composite 50 N 80 N-s 83 g 38.3 g 1.6 s
H180W reloadable White Lightning composite 180 N 230 N-s 263.6 g 123 g 1.27 s
Estes 1/2A6-2 Black powder 6 N 1.25 N-s Information not available 2.6 g .21 s
D12-7 12 N 17 N-s Information not available 10.8 g 1.42 s

Arrow pointing left picture Information Page : Liquids Engines arrow pointing right picture