[Boundless]

>> ... solids can't be throttled or shut down

> Actually it's done all the time. They blow a hole
> in the end opposite the nozzle.

But not while the solid is still attached to a stack,
manned or otherwise.

As I look at the proposed Crew Vehicle, I'm seriously
wondering under just what scenarios, and during which
windows the use of the escape rocket is a survivable event.

[null and void]

El Gato also suggested having an adjustable nozzle to control the thrust.

Rutan used a solid fuel, liquid oxidizer system.

NASA experimented with similar systems for restartable engines, it didn't work as residual vaporized propellant tended to explode on restart. This is a non-issue if you don't restart...