“The S-II stage was a nightmare the minute it was conceived, and it only got worse from there. During the course of its creation, it would grind up people and careers the way the transcontinental railway devoured laborers. Though the methods and materials used to build the S-II were reasonably well known, nobody had ever tried to apply them on such a titanic scale. Originally, it was to be somewhere around 8 stores tall with a diameter of 22 feet, but the width ballooned from there to 27 feet before the contract was even signed, then to 30, and finally to 33 feet. And all the while as the size of thing increased, NASA was trimming the allowable weight.” Harrison Storms of NAA.
The structural efficiency of the S-II stage, in terms of the weight and pressures taken by its extra-thin walls, was comparable only to the capacity of one of nature’s most refined examples of structural efficiency, the egg.
Apollo Saturn 201 employed the Saturn IB launch vehicle, which was the up-rated version of the Saturn I rocket flown in ten earlier Saturn-Apollo missions. It featured an upgrade of the first stage engines to increase thrust from 1,500,000 lb-ft of thrust to 1,600,000 lb-ft. The second stage was the S-IVB. This stage used a new liquid hydrogen-burning J-2 engine which would also be used on the S-II second stage of the Saturn V lunar launch vehicle…
The Pegasus satellite was named for the winged horse of Greek mythology. Like its namesake, the Pegasus was notable for its “wings”, a pair of 29 meter long, 4.3 meter wide arrays of 104 panels fitted with sensors to detect punctures by micrometeoroids at high altitudes. In its stored position with panels folded inside the Apollo service module, the Pegasus was 5.3-meters high, 2.1 meters wide, and 28-cm deep.