In November 1971 Shuttle Phase B Double Prime studies were initiated. In yet another iteration of shuttle design studies, $ 2.8 million contracts were given to Grumman/Boeing, Lockheed, McDonnell-Douglas/Martin Marrietta, and North American Rockewell. The development costs for the Phase B Prime contracts had still been over the Nixon administration's budget cap, and still further ways to reduce development cost had to be found. The studies were to run through 15 March 1972 and study lower cost booster concepts, one of which was a fully recoverable stage but with a new pressure-fed engine
The new-design pressure fed liquid propellant booster would be parachute-recovered and reused. Using liquid oxygen/kerosene propellants, each booster would be 9.93 m in diameter, 48.5 m long, and be equipped with two 612,000 kgf engines. Three boosters would be assembled in parallel, with the external tank for the shuttle orbiter atop the core booster. This design would have a gross lift-off mass of 2,626,000 kg. Another design used 4 x 475,000 kgf engines in each stage, resulting in a 2,394,000 kg vehicle. It was estimated the LRB's would cost $4.2 billion to develop, plus $ 8.9 billion to operate, making shuttle cost $275/kg to orbit. The study assumed a series burn, with the shuttle orbiter igniting at altitude.
Status: Study 1972.
Gross mass: 2,626,000 kg (5,789,000 lb).
Thrust: 36,010.00 kN (8,095,370 lbf).