McDonnell Douglas series-burn booster for Shuttle

An early 1971 design from McDonnell Douglas for the Space Shuttle Phase B extension program. As an alternative to solid rocket boosters, this concept used a single liquid rocket booster underneath the external tank. Several concepts were studied, including pressure fed systems. This particular design used four F-1 rocket engines from the Saturn V, in an entirely new booster. The booster would be recovered at sea, splashing down nose first; large flaps would stabilize it nose-down during descent, and solid rocket motors would provide terminal deceleration.