NASA
Solid rocket booster
Enormous thrust from a tube of rubbery fuel that cannot be throttled or shut off.
A solid motor is a casing packed with propellant that burns from a shaped channel down the middle; the shape of that channel is the entire thrust profile, decided at the factory. They are simple, storable for years and extremely powerful for their size, which is why they are strapped to the sides of vehicles that need help off the pad. The catch is absolute: once lit, a solid burns until it is done. It cannot be throttled, restarted or stopped, and the Challenger investigation turned on exactly that. Segmented casings — stacking factory-cast sections at the pad rather than casting one enormous tube — are what make the largest ones transportable, and the joints between those segments are where the risk lives, because a solid at full burn is a pressure vessel at around 6 MPa with flame on the inside of every seal.
Where it has come up lately
Related terms
Delta-v
The currency of spaceflight: how much you can change your velocity, in metres per second.
NET (no earlier than)
A launch date that is a lower bound, not a promise.
Max-Q
The moment of peak aerodynamic pressure on an ascending rocket.
Staging
Throwing away the empty part of the rocket so you stop accelerating it.
Questions
What is Solid rocket booster?
Enormous thrust from a tube of rubbery fuel that cannot be throttled or shut off.
Why does it matter?
It cannot be throttled, restarted or stopped, and the Challenger investigation turned on exactly that. Segmented casings — stacking factory-cast sections at the pad rather than casting one enormous tube — are what make the largest ones transportable, and the joints between those segments are where the risk lives, because a solid at full burn is a pressure vessel at around 6 MPa with flame on the inside of every seal.