Saturn (rocket family)

The Saturn family of American rocket boosters was developed by a team of mostly German rocket scientists led by Wernher von Braun to launch heavy payloads to Earth orbit and beyond. Originally proposed as a military satellite launcher, they were adopted as the launch vehicles for the Apollo moon program. The two most important members of the family were the Saturn IB and the Saturn V.

The predecessor of those two was the Saturn I. President John F. Kennedy identified this booster, and the SA-5 launch in particular, as being the point where US lift capability would surpass the Soviets, after having been behind since Sputnik. This was last mentioned by him in a speech he gave at Brooks AFB in San Antonio on the day before he was assassinated. He never lived to see the capability of any boosters from the Saturn family, started under the Eisenhower administration, realized.

To date, the Saturn V is the only launch vehicle to transport human beings beyond Low Earth Orbit. A total of 24 human beings were flown out to the Moon in the four years spanning December 1968 through December 1972.

History

Early development

In the early 1950s all of the major branches of the US military were actively developing long-range missiles, most with the help of Germans from the V-2 project and based on its technology. These included the US Navy's Viking and US Army's Corporal, Jupiter and Redstone designs. The US Air Force's Atlas and Titan used more technology developed in U.S.

In-fighting between the various branches was constant, with the United States Department of Defense (DoD) often called upon to decide which projects to fund for development. Things were supposed to be settled by the 26 November 1956 "Wilson Memorandum," which stripped the Army of offensive missiles with a range of 200 miles (320 km) or greater,^[1] and forced their Jupiter missiles to be turned over to the Air Force. From that point on the Air Force would be the primary missile developer, especially for dual-use missiles that could also be used for space launchers.

Some time in late 1956 or early 1957 the Department of Defense released a requirement for a heavy-lift vehicle to orbit a new class of communications and "other" satellites (the spy satellite program was top secret). The requirements, drawn up by the then-unofficial Advanced Research Projects Agency (ARPA), called for a vehicle capable of putting 9,000 to 18,000 kilograms into orbit, or accelerating 2,700 to 5,400 kg to escape velocity.^[2]

Since the Wilson Memorandum covered only weapons, not space launchers, the Army Ballistic Missile Agency (ABMA) saw this as a way to continue development of their own large-rocket projects. In April 1957, von Braun directed Heinz-Hermann Koelle, chief of the Future Projects design branch, to study dedicated space launcher designs that could be built as quickly as possible. Koelle evaluated a variety of designs for missile-derived launchers that could place a maximum of about 1,400 kg in orbit, but might be expanded to as much as 4,500 kg with new high-energy upper stages. In any event, these upper stages would not be available until 1961 or 62 at the earliest, and the launchers would still not meet the DoD requirements for heavy loads.^[3]

In order to fill the need for loads of 10,000 kg or greater, the ABMA calculated that a booster (first stage) with a thrust of about 1,500,000 lbf (6,700 kN) thrust would be needed, far greater than any existing or planned missile. For this role they proposed using a number of existing missiles clustered together to produce a single larger booster; using existing designs they looked at concepts named "Super-Atlas", "Super-Titan", and "Super-Jupiter".^[4] Super-Jupiter received the most attention because it used hardware developed by ABMA; the Titan and Atlas were Air Force designs that were suffering from lengthy delays in development.

Two approaches to building the Super-Jupiter were considered; the first used multiple engines to reach the 1,500,000 lbf (6,700 kN) mark, the second used a single much larger engine. Both approaches had their own advantages and disadvantages. Building a smaller engine for clustered use would be a relatively low-risk path from existing systems, but required duplication of systems and made the possibility of one engine failure much higher (paradoxically, adding engines generally reduces reliability). A single larger engine would be more reliable in theory, and would offer higher performance because it eliminated duplication of "dead weight" like fuel plumbing and hydraulics for steering the engines. On the downside, an engine of this size had never been built before and development would be expensive and risky. The Air Force had recently expressed an interest in such an engine, which would develop into the famed F-1, but at the time they were aiming for 1,000,000 lbf (4,400 kN) and the engines would not be ready until the mid-1960s. The engine-cluster appeared to be the only way to meet the requirements on time and budget.^[3]

Super-Jupiter was the first stage booster only; to place payloads in orbit, additional upper stages would be needed. ABMA proposed using either the Titan or Atlas as a second stage, optionally with the new Centaur upper-stage. The Centaur had been proposed by General Dynamics (Astronautics Corp.) as an upper stage for the Atlas (also their design) in order to quickly produce a launcher capable of placing loads up to 8,500 lb (3,900 kg) into low Earth orbit.^[5] The Centaur was based on the same "balloon tank" concept as the Atlas, and built on the same jigs at the same 120-inch (3,000 mm) diameter. As the Titan was deliberately built at the same size as well, this meant the Centaur could be used with either missile. Given that the Atlas was the higher priority of the two ICBM projects and its production was fully accounted for, ABMA focussed on "backup" design, Titan, although they proposed extending it in length in order to carry additional fuel.

In December 1957, ABMA delivered Proposal: A National Integrated Missile and Space Vehicle Development Program to the DoD, detailing their clustered approach.^[6] They proposed a booster consisting of a Jupiter missile airframe surrounded by eight Redstones acting as tankage, a thrust plate at the bottom, and four Rocketdyne E-1 engines of 360 to 380,000 lbf (1,700 kN). The ABMA team also left the design open to future expansion with a single 1,500,000 lbf (6,700 kN) engine, which would require relatively minor changes to the design. The upper stage was the lengthened Titan, with the Centaur on top. The result was a very tall and skinny rocket, quite different from the Saturn that eventually emerged.

Specific uses were forecast for each of the military services, including navigation satellites for the Navy; reconnaissance, communications, and meteorological satellites for the Army and Air Force; support for Air Force manned missions; and surface-to-surface logistics supply for the Army at distances up to 6400 km. Development and testing of the lower stage stack was projected to be completed by 1963, about the same time that the Centaur should become available for testing in combination. The total development cost of $850 million during the years 1958-1963 covered 30 research and development flights, some carrying manned and unmanned space payloads.^[7]

Sputnik stuns the world

While the Super-Juno program was being drawn up, preparations were underway for the first satellite launch as the US contribution to the International Geophysical Year in 1957. For complex political reasons, the program had been given to the US Navy under Project Vanguard. The Vanguard launcher consisted of a Viking lower stage combined with new uppers adapted from sounding rockets. ABMA provided valuable support on Viking and Vanguard, both with their first-hand knowledge of the V-2, as well as developing its guidance system. The first three Vanguard suborbital test flights had gone off without a hitch, starting in December 1956, and a launch was planned for late 1957.

On 4 October 1957, the Soviet Union unexpectedly launched Sputnik I. Although there had been some idea that the Soviets were working towards this goal, even in public, no one considered it to be very serious. When asked about the possibility in a November 1954 press conference, Defense Secretary Wilson replied "I wouldn't care if they did."^[8] The public did not see it the same way, however, and the event was a major public relations disaster. Vanguard was planned to launch shortly after Sputnik, but a series of delays pushed this into December, when the rocket exploded in spectacular fashion. The press was harsh, referring to the project as "Kaputnik"^[9] or "Project Rearguard".^[8] As Time Magazine noted at the time:

But in the midst of the cold war, Vanguard's cool scientific goal proved to be disastrously modest: the Russians got there first. The post-Sputnik White House explanation that the U.S. was not in a satellite "race" with Russia was not just an after-the-fact alibi. Said Dr. Hagen ten months ago: "We are not attempting in any way to race with the Russians." But in the eyes of the world, the U.S. was in a satellite race whether it wanted to be or not, and because of the Administration's costly failure of imagination, Project Vanguard shuffled along when it should have been running. It was still shuffling when Sputnik's beeps told the world that Russia's satellite program, not the U.S.'s, was the vanguard.^[8]

von Braun responded to Sputnik I's launch by claiming he could have a satellite in orbit within 90 days of being given a go-ahead. His plan was to combine the existing Jupiter C rocket with the solid-fuel engines from the Vanguard, producing the Juno I. There was no immediate response while everyone waited for Vanguard to launch, but the continued delays in Vanguard and the November launch of Sputnik II resulted in the go-ahead being given that month. von Braun kept his promise with the successful launch of Explorer I on February 1, 1958. Vanguard was finally successful on March 17, 1958.

ARPA selects Juno

Concerned that the Soviets continued to surprise the U.S. with technologies that seemed beyond their capabilities, the DoD studied the problem and concluded that it was primarily bureaucratic. As all of the branches of the military had their own research and development programs, there was considerable duplication and inter-service fighting for resources. Making matters worse, the DoD imposed its own Byzantine procurement and contracting rules, adding considerable overhead. To address these concerns, the DoD initiated the formation of a new research and development group focused on space launchers and given wide discretionary powers that cut across traditional Army/Navy/Air Force lines. The group was given the job of catching up to the Soviets in space technology as quickly as possible, using whatever technology it could, regardless of the origin. Formalized as Advanced Research Projects Agency (ARPA) on 7 February 1958, the group examined the DoD launcher requirements and compared the various approaches that were currently available.

At the same time that ABMA was drawing up the Super-Juno proposal, the Air Force was in the midst of working on their Titan C concept. The Air Force had gained valuable experience working with liquid hydrogen on the Lockheed CL-400 Suntan spy plane project and felt confidant in their ability to use this volatile fuel for rockets. They had already accepted Krafft Ehricke's arguments that hydrogen was the only practical fuel for upper stages, and started the Centaur project based on the strength of these arguments. Titan C was a hydrogen-burning intermediate stage that would normally sit between the Titan lower and Centaur upper, or could be used without the Centaur for low-Earth orbit missiles like Dyna-Soar. However, as hydrogen is much less dense than "traditional" fuels then in use, essentially kerosene, the upper stage would have to be fairly large in order to hold enough fuel. As the Atlas and Titan were both built at 120" diameters it would make sense to build Titan C at this diameter as well, but this would result in an unwieldy tall and skinny rocket with dubious strength and stability. Instead, Titan C proposed building the new stage at a larger 160" diameter, meaning it would be an entirely new rocket.

In comparison, the Super-Juno design was based on off-the-shelf components, with the exception of the E-1 engines. Although it too relied on the Centaur for high-altitude missions, the rocket was usable for low-Earth orbit without Centaur, which offered some flexibility in case Centaur ran into problems. ARPA agreed that the Juno proposal was more likely to meet the timeframes required, although they felt that there was no strong reason to use the E-1, and recommended a lower-risk approach here as well. ABMA responded with a new design, the Juno V (as a continuation of the Juno I and Juno II series of rockets, while Juno III and IV were unbuilt Atlas- and Titan-derived concepts), which replaced the four E-1 engines with eight H-1s, a much more modest upgrade of the existing S-3D already used on the Thor and Jupiter missiles, raising thrust from 150,000 to 188,000 lbf (670 to 840 kN). It was estimated that this approach would save as much as $60 million in development and cut as much as two years of R&D time.^[2]

Happy with the results of the redesign, on 15 August 1958 ARPA issued Order Number 14-59 that called on ABMA to:

Initiate a development program to provide a large space vehicle booster of approximately 1 500 000-lb. thrust based on a cluster of available rocket engines. The immediate goal of this program is to demonstrate a full-scale captive dynamic firing by the end of CY 1959.

This was followed on 11 September 1958 with another contract with Rocketdyne to start work on the H-1. On 23 September 1958, ARPA and the Army Ordnance Missile Command (AOMC) drew up an additional agreement enlarging the scope of the program, stating "In addition to the captive dynamic firing..., it is hereby agreed that this program should now be extended to provide for a propulsion flight test of this booster by approximately September 1960." Further, they wanted ABMA to produce three additional boosters, the last two of which would be "capable of placing limited payloads in orbit."

By this point many in the ABMA group were already referring to the design as Saturn, a reference to "the planet after Jupiter".^[10] The name change became official in February 1959.

NASA involvement

In addition to ARPA, various groups within the US government had been considering the formation of a civilian agency to handle space exploration. After the Sputnik launch, these efforts gained urgency and were quickly moved forward. NASA was formed on 29 July 1958, and immediately set about studying the problem of manned space flight, and the launchers needed to work in this field. One goal, even in this early stage, was a manned lunar mission. At the time, the NASA panels felt that the direct ascent mission profile was the best approach; this placed a single very large spacecraft in orbit, which was capable of flying to the Moon, landing and returning to Earth. To launch such a large spacecraft, a new booster with much greater power would be needed; even the Saturn was not nearly large enough. NASA started examining a number of potential rocket designs under their Nova program.

NASA was not alone in studying manned lunar missions. von Braun had always expressed an interest in this goal, and had been studying what would be required for a lunar mission for some time. ABMA's Project Horizon proposed using fifteen Saturn launches to carry up spacecraft components and fuel that would be assembled in orbit to build a single very large lunar craft. This Earth orbit rendezvous mission profile required the least amount of booster capacity per launch, and was thus able to be carried out using the existing rocket design. This would be the first step towards a small manned base on the moon, which would require several additional Saturn launches every month to supply it.

The Air Force had also started their Lunex Project in 1958, also with a goal of building a manned lunar outpost. Like NASA, Lunex favored the direct ascent mode, and therefore required much larger boosters. As part of the project, they designed an entirely new rocket series known as the Space Launch System (SLS), which combined a number of solid-fuel boosters with either the Titan missile or a new custom booster stage to address a wide variety of launch weights. The smallest SLS vehicle consisted of a Titan and two strap-on solids, giving it performance similar to Titan C, allowing it to act as a launcher for Dyna-Soar. The largest used much larger solid-rockets and a much enlarged booster for their direct ascent mission. Combinations in-between these extremes would be used for other satellite launching duties.

Silverstein Committee

A government commission, the "Saturn Vehicle Evaluation Committee" (better known as the Silverstein Committee), was assembled to recommend specific directions that NASA could take with the existing Army program. The committee recommended the development of new, hydrogen-burning upper stages for the Saturn, and outlined eight different configurations for heavy-lift boosters ranging from very low-risk solutions making heavy use of existing technology, to designs that relied on hardware that had not been developed yet, including the proposed new upper stage. The configurations were:

• Saturn A
  • A-1 - Saturn lower stage, Titan second stage, and Centaur third stage (von Braun's original concept)
  • A-2 - Saturn lower stage, proposed clustered Jupiter second stage, and Centaur third stage

• Saturn B
  • B-1 - Saturn lower stage, proposed clustered Titan second stage, proposed S-IV third stage and Centaur fourth stage

• Saturn C
  • C-1 - Saturn lower stage, proposed S-IV second stage
  • C-2 - Saturn lower stage, proposed S-II second stage, proposed S-IV third stage
  • C-3, C-4, and C-5 - all based on different variations of a new lower stage using F-1 engines, variations of proposed S-II second stages, and proposed S-IV third stages.

Contracts for the development of a new hydrogen-burning engine were given to Rocketdyne in 1960 and for the development of the Saturn IV stage to Douglas the same year.

Launch history

Project Apollo

The challenge that President John F. Kennedy put to NASA in May 1961 to put an astronaut on the Moon by the end of the decade put a sudden new urgency on the Saturn program. That year saw a flurry of activity as different means of reaching the Moon were evaluated.

Both the Nova and Saturn rockets were evaluated for the mission, which shared a similar design and could share some parts. However, it was judged that the Saturn would be easier to get into production, since many of the components were designed to be air-transportable. Nova would require new factories for all the major stages, and there were serious concerns that they could not be completed in time. Saturn required only one new factory, for the largest of the proposed lower stages, and was selected primarily for that reason.

The Saturn C-5, (later given the name Saturn V), the most powerful of the Silverstein Committee's configurations, was selected as the most suitable design. At the time the mission mode had not been selected, so they chose the most powerful booster design in order to ensure that there would be ample power. This proved to be a wise decision; although the Lunar orbit rendezvous was eventually selected and reduced the launch weight requirements, as the weight of the spacecraft crept upwards the extra launch capability of the C-5 proved very useful.

At this point, however, all three stages existed only on paper, and it was realized that it was very likely that the actual lunar spacecraft would be developed and ready for testing long before the booster. NASA therefore decided to also continue development of the C-1 (later Saturn I) as a test vehicle, since its lower stage was based on existing technology (Redstone and Jupiter tankage) and its upper stage was already in development. This would provide valuable testing for the S-IV as well as a launch platform for capsules and other components in low earth orbit.

Ultimately, the members of the Saturn family that made it to the launch pad were:

• Saturn I - ten rockets flown to evaluate the S-I and, in later flights, the S-IV stages.
• Saturn IB - nine launches, a refined version of the Saturn I with a more powerful first stage (designated the S-IB) and using the Saturn V's S-IVB as a second stage. These carried the first crewed Apollo flight into orbit, and later provided the boosters for the Skylab and Apollo-Soyuz flights.
• Saturn V - 12 launches, the Moon rocket that carried Apollo astronauts to the Moon.
• Saturn INT-21 - one launch, used to place the Skylab space station in orbit.

References

External links

• NASA History Series Publications (many of which are on-line)