The original impetus for Saturn envisioned a brawny booster to launch Department of Defense payloads. The von Braun team at the Army Ballistic Missile Agency (ABMA) received money from the Department of Defense's Advanced Research Projects Agency to demonstrate the concept. Furthermore, von Braun's group eventually became the nucleus of NASA's Marshall Space Flight Center (MSFC). Like most major development projects, the evolution of the Saturn I changed between conception and execution, although the configuration that emerged in 1958 was subjected to remarkably few major design variations before its first launch in 1961.
In April 1957, ABMA began design studies on an advanced booster concept. With a total thrust of approximately 6 800 000 newtons (1.5 million pounds) in the first stage alone, the proposed vehicle was referred to as the Super-Jupiter. The impetus for the development of a Super-Jupiter class apparently evolved from Department of Defense plans for "certain advanced missions using space devices in communication," as well as space probes and weather satellites. However, such payloads, especially satellite programs, required a booster much larger than existing launch vehicles. The Department of Defense guidelines called for a launch vehicle capable of putting 9000 to 18 000 kilograms into Earth orbit or accelerating space probes of 2700 to 5400 kilograms to escape velocity.
ARPA issued more specific instructions to ABMA, granting authority and authorizing funds for the Juno V on 15 August 1958. The booster that began to take shape on the Redstone Arsenal drawing boards and in the shops was definitely a bargain-basement and patchwork affair. The volume of the tankage posed a special problem. The fabrication and welding of a single 6-meter-diameter tank, with separate compartments for fuel and oxidizer, meant new techniques and working jigs. Consumption of time and money threatened to become exorbitant. A different approach to the problem evolved, and existing tanks were used instead. From its own earlier production runs, ABMA located partial rejects and incomplete 1.78-meter tanks from the Redstone and 2.67-meter tanks from the Jupiter missiles. Since the engines were going to be clustered, why not the tanks? The tank arrangement settled on by MSFC gave an alternate pattern of the four fuel and four oxidizer tanks, clustered around the 267-centimeter center oxidizer tank. The oxidizer tanks carried the load from the upper stages of the Saturn, the fuel tanks only contributing to the lateral stiffness of the cluster.
Design drawings of Saturn B and Saturn C studies during the first few months of 1959 showed clustered tank-and-engine first stages of 6.5 meters diameter and various combinations of upper stages of 6.5-meter and 3-meter diameters towering as high as 76 meters. The use of new hardware was apparently not contemplated; given ARPA's guidelines for economy in the program, a more realistic possibility was to add upper stages that used Titan or Atlas ICBM vehicles fitted directly to the clustered tankage and engines. <>By 1960 plans focused on a three-stage Saturn C-1 that used Centaur engines in the LH2 upper stages. The second stage had four uprated Centaur engines, designated the S-IV stage, and the S-V top stage was the Centaur itself, with two engines. The hop-scotch numbering occurred because of the "building block" concept, in which hardware was used as available, the concept, was tested, and then newer and advanced stages were incorporated in the next major configuration. During C-1 development and flight, for example, a new S-III stage for Saturn C-2 would be prepared with the use of a newer, more powerful generation of LH2 engines. As the development and flight test of Saturn C-2 proceeded, the S-II stage would be worked up with four of the newer LH2 engines. In January 1961 the C-1 vehicle changed from a three-stage to a two-stage booster, eliminating the S-V upper stage to leave only S-I and S-IV stages, the later now with six RL-10 Centaur engines. The size of the original S-IV was significant but largely overshadowed in light of subsequent evolution of the Saturn V stages, the S-IC and the S-II.
More than any of the Saturn vehicles, the Saturn I S-I stage configuration evolved during flight tests. NASA developed the Saturn I as first-generation and second-generation rockets, designated Block I and Block II. The first four launches used the Block I vehicle, with inert upper stages and no fins on the first stage, the S-I. Block II versions carried a live second stage, the S-IV, sported a corona of aerodynamic fins at the base, and used uprated H-I engines.
The Pegasus satellite was named for the winged horse of Greek mythology and was lofted into space by a Marshall-built Saturn I rocket on Feb.16, 1965. Like its namesake, the Pegasus I satellite was notable for its wings; however, the 96-foot-long, 14-foot-wide wings were not for flying. They carried 208 panels to report punctures by potentially hazardous micrometeoroids at high altitudes where the manned Apollo missions would orbit. Spacecraft designers were keenly interested in the information because the Apollo spacecraft and crew were in jeopardy if tiny particles could puncture a spacecraft skin.
Micrometeoroid detectors and sample protective shields were mounted on the satellite's wing-like solar cell arrays. The sensors successfully measured the frequency, size, direction and penetration of scores of micrometeoroid impacts. The Marshall Center was responsible for the design, production and operation of Pegasus I and two additional Pegasus satellites which were also launched by Saturn I rockets in 1965. At launch, an Apollo command and service module boilerplate and launch escape system tower were atop the Saturn 1, with Pegasus I folded inside the service module.
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