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.
The key to high-energy stages was to use liquid hydrogen as the fuel. Liquid hydrogen fuel appealed to rocket designers because of its high specific impulse, which is a basic measure of rocket performance. Specific Impulse is the impulse delivered per unit of propellant consumed. You might think of it as the efficiency of the rocket. Compared to an RP-1 (kerosene) fueled engine of similar size, liquid hydrogen fuel could increase the specific impulse or efficiency of an engine by 40 percent. The combination of hydrogen and oxygen for propellants made the moon shot feasible.
Saturn 1, SA-6 was the first orbital launch of an Apollo Spacecraft by a Saturn Launch Vehicle and also the first flight utilizing an active ST-124 Stabilized Platform.