Solid propulsion

Solid propellant rockets are found in several space and military applications.

They are used as strap-on boosters (as in Ariane V or the former Shuttle)
They can be launcher stages (as in Vega, see the picture on the right)
Embarked missiles are propelled with this technology (e.g. sidewinder)

Solid propulsion grants high thrust in a compact volume, readiness, and simplicity of the propulsion system architecture. As opposite, they feature low specific impulse performance and lack of flexibility because the motor thrust cannot be regulated on real time nor it can be switched on and off.

The solid propellant is the core of this propulsion technology. Most of civil applications work with so called “heterogeneous” propellants (a.k.a. composite solid propellants).
This common category of energetic material is a mixture of solid oxidizer powders, metal (if present), and additives, kept together by a polymeric matrix, which grants consistency and mechanical stability to the ensemble. This material contains all the ingredients to self-sustain the combustion in solid form, grainting high energy density.

The combustion of solid propellants involves complex phenomena and is strongly dependent on the ingredients and their interactions.