the first of only two booster systems designed specifically and solely for manned capsule qualifications, little joe was also one of the pioneer operational launch vehicles using the rocket cluster principle. since the four modified sergeants (called either castor or pollux rockets, depending upon modification) and four supplemental recruit rockets were arranged to fire in various sequences, the takeoff thrust varied greatly, but maximum design thrust was almost 230,000 pounds (1,020 kilonewtons). theoretically enough to lift a spacecraft of about 4,000 pounds (1,800 kg) on a ballistic path over 100 miles (160 km) high, the push of these clustered main engines should simulate the takeoff profile in the environment that the manned atlas would experience. furthermore, the additional powerful explosive pull of the tractor-rocket escape system could be demonstrated under the most severe takeoff conditions imaginable. the engineers who mothered little joe to maturity knew it was not much to look at, but they hoped that their ungainly rocket would prove the legitimacy of most of the ballistic capsule design concepts, thereby earning its own honor. a successor, little joe ii, would later be used for flight testing of the apollo crew escape system.