It seems a physical piston is involved, then airborne missile is deflected in the correct direction, and the main motor fires.
A good description on wiki -
“...both use a “soft vertical launch” system, whereby the missile is ejected from a tube by a piston. A short booster uses squib thrusters to point the missile at the target before the main motor fires. The lack of toxic fumes on launch makes launches safer for users, avoids corrosion of the launch platform and the lack of exhaust vents allows the launch cells to be much more compact....”
True, as much as 1/3 the volume of conventional boost-launch VLS is to intercept, direct and re-direct the exhaust gasses back vertically. So, a soft-boost is more efficient use of space.
Now, about the number of reloads carried..... Where are the ammo ships, and what is protecting them?
Interesting. Thanks!