A grain is the shaped block of solid propellant housed inside a rocket motor casing. It contains both fuel and oxidizer mixed together and cast into a specific geometry, such as a star or cylinder with a hollow core. The cross-sectional shape of the grain dictates the surface area exposed to combustion, which precisely controls the thrust profile as the rocket burns.
Heard on the job
The star-shaped grain gives us high initial thrust right off the pad before tapering down during max Q.
Insider tip
Cracks in a solid rocket grain are catastrophic. A crack increases the burning surface area, causing a massive pressure spike that usually destroys the motor.
Also heard as
- propellant grain