[Pontiac]

The lower, or first stage, of the Ares I will be a juiced-up version of the reusable solid-fuel rocket boosters made by ATK Thiokol for space shuttle launches.

I never have liked solid-fueled rocket boosters for manned space flight.

Even if they were 100% reliable once they are lit you can’t shut them down.

If something totally unrelated to the booster themselves goes wrong you have to wait till they have completed their burn to jettison the booster.

[Erasmus]

If something totally unrelated to the booster themselves goes wrong you have to wait till they have completed their burn to jettison the booster.

With the solid boosters currently on the Shuttle, they still have a little fuel left over at the end of their burn phase.

I think the main reason for this is that they want to make sure that thrust from both boosters ends within a small fraction of a second; otherwise, the induced yaw would destroy the vehicle.

But they can't make a solid booster burn so precisely that it exhausts its fuel within a small fraction of a second of a nominal period. So, they equip the booster with a pyrotechnically-actived vent at the top.

When the solid boost phase is complete, they blow the vents on the boosters simultaneously, and this cuts off thrust immediately even though there's a small bit fuel remaining (varying slightly among the boosters).

Maybe solid boosters can be designed to be capablie of this early in the burn, for emergency aborts.

Restarts are not feasible in any solid booster design I know of, but present-day designers don't see this as a problem, so long as they add a liquid-fuel booster which gives a part of the total thrust, and which burns beyond the duration of the solid boosters.

[Moonman62]

But if the crew capsule can separate or eject that should solve that problem.

[RightWhale]

Blow the forward port. Thrust falls to zero quickly.

[r9etb]

If something totally unrelated to the booster themselves goes wrong you have to wait till they have completed their burn to jettison the booster.

Not true. You just have to size the escape rockets to outrun the booster.

[Rockingham]

You are correct. The same criticism was made about the Shuttle design by the old German engineers who had made the Moon program work so well. Von Braun is said to have been moved to tears when asked about the Shuttle and to have warned that it would kill people. We shall see if the new design has some way to jettison the solid booster if it starts going wrong.