Solid Propellant Isp Credit - Aerojet

Solid propellants have the fuel and oxidiser embedded in a rubbery matrix. They were developed to a high degree of perfection in the United States in the 1950's and 1960's. In Russia, development was slower, due to a lack of technical leadership in the area and rail handling problems. The disadvantages of solid propellants include:

• Slightly higher empty mass for the rocket stage

• Slightly lower performance than storable liquid propellants

• Transportability issues: Solid propellants are cast into the motor in the factory, unlike liquid fuel rockets which can be fueled at the launch pad. This means they have to either be: 1) limited in size to be transportable (as for the Delta and Ariane strap-on motors); 2) cast in segments, with the segments assembled at the launch base (as for Titan and the Space Shuttle); or 3) cast in a factory at the launch site (actually done for large test motors intended for Saturn V upgrades).

• Once ignited, they cannot be easily shut down or throttled. Thereafter they have to be pre-cast or milled out for a specific mission.

• Nearly always catastrophic results in the event of a failure

Advantages of solid rocket motors, many of which make them ideal for military applications:

• High density and low volume

• Nearly indefinite storage life

• Instant ignition without fuelling operations

• High reliability