Scram Jets

Anyone know the slowest speed at which a scram jet would likely be able to
start?

It seems NASA is using a rocket booster to get to speed, which would make me
think this idea is a bit less than practical for civilian use. Can't see
the Concorde crowd signing up for a rocket powered plane, though I could be
wrong. It would be neat if it worked at a low enough Mach that you could
build a workable SST.

OTOH using one for a cruise missile would be neat. Picture a third world
dictator about to go on live TV. By the time the sycophant finishes the
introduction, the missile will have left CONUS in time to blast the podium
before the "general and president for life" is finished blaming the US for
everything bad in his little banana republic!