An orbital rocket does not fly straight up: soon after liftoff it tips into a gravity turn, because what it really needs is horizontal speed, not altitude. The harder it burns, the sooner perigee and apogee separate into a definite orbit. An early cutoff leaves perigee below the ground, so the vehicle falls back on a suborbital arc; about 7.9 km/s closes a low orbit; 11.2 km/s leaves Earth for good.
An orbital rocket does not fly straight up: soon after liftoff it tips into a gravity turn, because what it really needs is horizontal speed, not altitude. The harder it burns, the sooner perigee and apogee separate into a definite orbit. An early cutoff leaves perigee below the ground, so the vehicle falls back on a suborbital arc; about 7.9 km/s closes a low orbit; 11.2 km/s leaves Earth for good.
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