Saturn the Giant by Wernher
Note: The following article
by Dr. Wernher von Braun, who directed the Marshall Space Flight
Center from 1960 until 1970, is extracted from Apollo Expeditions
to the Moon, edited for NASA by Edgar M. Cortright. The essay
is one of a series in the book by leading participants in the
Saturn/Apollo program. The book was published by NASA's Scientific
and Technical Information Office in 1975 and is NASA SP-350.)
With the beep-beep-beep of Sputnik on October 4, 1957, the Soviet
Union had inaugurated the Space Age. It had also presented American
planners with the painful realization that there was no launch
vehicle in the U.S. stable capable of orbiting anything approaching
Responding to a proposal submitted by the Army Ballistic Missile
Agency, the Department of Defense was in just the right mood to
authorize ABMA to develop a 1,500,000-pound-thrust booster. That
unprecedented thrust was to be generated by clustering eight S-3D
Rocketdyne engines used in the Jupiter and Thor missiles. The
tankage for the kerosene and liquid oxygen was also to be clustered
to make best use of tools and fixtures available from the Redstone
and Jupiter programs. The program was named "Saturn"
simply because Saturn was the next outer planet after Jupiter
in the solar system.
Gen. John B. Medaris, commander of ABMA and my boss, felt that
for a good design job on the booster it was necessary for us also
to study suitable upper stages for the Saturn. On November l8,
1959, Saturn was transferred to the new National Aeronautics and
Space Administration. NASA promptly appointed a committee to settle
the upper-stage selection for Saturn. It was chaired by Dr. Abe
Silverstein who, as associate director of NASA's Lewis Center
in Cleveland, had spent years exploring liquid hydrogen as a rocket
fuel. As a result of this work the Air Force had let a contract
with Pratt & Whitney for the development of a small 15,000-pound-thrust
liquid hydrogen/liquid oxygen engine, two of which were to power
a new "Centaur" top stage for the Air Force's Atlas.
Abe was on solid ground when he succeeded in persuading his committee
to swallow its scruples about the risks of the new fuel and go
to high-power liquid hydrogen for the upper stage of Saturn.
In the wake of Gagarin's first orbital flight on April 12, 1961,
Saturn gained increased importance. Nevertheless, when the first
static test of the booster with all eight engines was about to
begin, at least one skeptical witness predicted a tragic ending
of "Cluster's last stand." Doubts about the feasibility
of clustering eight highly complex engines had indeed motivated
funding for two new engine developments. One was in essence an
uprating and simplification effort on the S-3D, and it led to
the 188,000-pound-thrust H-1 engine. The other aimed at a very
powerful new engine called F-1, which was to produce a full 1.5-million-pound
thrust in a single barrel. Both contracts went to Rocketdyne.
Following up on the recommendation of the Silverstein committee,
NASA awarded a contract to the Douglas Aircraft Company for the
development of a second stage for Saturn that became known as
S-IV. It was to be powered by six Centaur engines. On September
8, 1960, President Eisenhower came to Huntsville to dedicate the
new Center, named after Gen. George C. Marshall. It was to become
the focal point for NASA's new large launch vehicles, and I was
appointed as its first director.
DETERMINING SATURN'S CONFIGURATION
The first launch of the Saturn booster was still five months
away when, on May 25, 1961, President John F. Kennedy proposed
that the United States commit itself to land a man on the Moon
"in this decade." For this ambitious task a launch vehicle
far more powerful than our eight-engine Saturn would be needed.
To determine its exact power requirements, a selection had to
be made from among three operational concepts for a manned voyage
to the Moon: direct ascent, Earth orbit rendezvous (EOR), and
lunar orbit rendezvous ( LOR ) .
With direct ascent, the entire spacecraft would soft-land on
the Moon carrying enough propellants to fly back to Earth. Weight
and performance studies showed that this would require a launch
vehicle of a lift-off thrust of 12 million pounds, furnished by
eight F-1 engines. We called this hypothetical launch vehicle
Nova. The EOR mode envisioned two somewhat smaller rockets that
were to rendezvous in Earth orbit where their payloads would be
combined. In the LOR mode a single rocket would launch a payload
consisting of a separable spacecraft toward the Moon, where an
onboard propulsion unit would ease it into orbit. A two-stage
lunar module (LM) would then detach itself from the orbiting section
and descend to the lunar surface. Its upper stage would return
to the circumlunar orbit for rendezvous with the orbiting section.
In a second burst of power, the propulsion unit would finally
drive the reentry element with its crew out of lunar orbit and
back to Earth.
As all the world knows, the LOR mode was ultimately selected.
But even after its adoption, the number of F-1 engines to be used
in the first stage of the Moon rocket remained unresolved for
quite a while. H. H. Koelle, who ran our Project Planning Group
at Marshall, had worked out detailed studies of a configuration
called Saturn 1V with four F-1's, and another called Saturn V
with five F-1's in its first stage. Uncertainty about LM weight
and about propulsion performance of the still untested F-1 and
upper-stage engines, combined with a desire to leave a margin
for growth, finally led us to the choice of the Saturn V configuration.
Despite the higher power offered by liquid hydrogen, Koelle's
studies indicated that little would be gained by using it in the
first stage also, where it would have needed disproportionately
large tanks. (Liquid hydrogen is only one twelfth as dense as
kerosene, so a much larger tank volume would have been required.)
In all multistage rockets the upper stages are lighter than the
lower ones. Thus heavier but less energetic kerosene in the first
stage, in combination with lighter but more powerful hydrogen
in the upper stages, made possible a better launch-vehicle configuration.
Saturn V, as it emerged from the studies, would consist of three
stages—all brand new. The first one, burning kerosene and
oxygen, would be powered by five F-1 engines. We called it S-IC.
The second stage, S-II, would need about a million pounds of thrust
and, if also powered by five engines, would call for the development
of new 200,000-pound hydrogen-oxygen engines. A single engine
of this thrust would just be right to power the third stage. The
Saturn I's S-IV second stage was clearly not powerful enough to
serve as the Saturn's third one. A much larger tankage and at
least thirteen of Pratt & Whitney's little LR-10 engines would
be required; this did not appear very attractive.
When bids for the new J-2 engine were solicited, Pratt &
Whitney with its ample liquid-hydrogen experience was a strong
contender. But when all the points in the sternly controlled bidding
procedure were counted, North American's Rocketdyne Division won
North American had been involved in the development of liquid
fuel rocket engines since the immediate postwar years and the
Navajo long range ramjet program. The engines it developed for
the Navajo booster and their offspring later found their way into
the Atlas, Redstone, Thor, and Jupiter programs. For the testing
of these engines NAA's Rocketdyne Division had acquired a boulder-strewn
area high in the Santa Susana mountains, north of Los Angeles,
that had previously served as rugged background for many a Western
movie. The Santa Susana facility would henceforth serve not only
for the development of the new J-2 engine, but also for short
duration "battleship" testing of the five-engine cluster
of these engines powering the S-II stage. (Safety and noise considerations
ruled out the use of Santa Susana for the 1.5-million-pound-thrust
F-1 engine. Test stands for its development were therefore set
up in the Mojave desert, adjacent to Edwards Air Force Base.)
CHOOSING THE BUILDERS
How many prime contractors, we wondered, should NASA bring in
for the development of the Saturn V? Just one, or one per stage?
How about the Instrument Unit that was to house the rocket's inertial-guidance
system, its digital computer, and an assortment of radio command
and telemetry functions? Who would do the overall systems engineering
and monitor the intricate interface between the huge rocket and
the complex propellant-loading and launching facilities at Cape
Canaveral? Where would the various stages be static-tested?
Understandably, the entire aerospace industry was attracted by
both the financial value and the technological challenge of Saturn
V. To give the entire plum to a single contractor would have left
all others unhappy. More important, Saturn V needed the very best
engineering and management talent the industry could muster. By
breaking up the parcel into several pieces, more top people could
be brought to bear on the program.
The Boeing Company was the successful bidder on the first stage
(S-IC); North American Aviation won the second stage (S-II); and
Douglas Aircraft fell heir to the Saturn V's third stage (S-IVB).
Systems engineering, and overall responsibility for the Saturn
V development was assigned to the Marshall Space Flight Center.
The inertial-guidance system had emerged from a Marshall in-house
development, and as it had to be located close to other elements
of the big rocket's central nervous system, it was only logical
to develop the Instrument Unit (IU) to house this electronic gear
as a Marshall in-house project. IU flight units were subsequently
produced by IBM, which had developed the launch-vehicle computer.
Uniquely tight procurement procedures introduced by NASA Administrator
Jim Webb made it possible to acquire billions of dollars' worth
of exotic hardware and facilities without overrunning initial
cost estimates and without the slightest hint of procurement irregularity.
Before it could issue a request for bids, the contracting NASA
Center had to prepare a detailed procurement plan that required
the Administrator's personal approval, and that could not be changed
thereafter. It had to include a point-scoring system in which
evaluation criteria—technical merits, cost, skill availability,
prior experience, etc.—were given specific weighting factors.
Business and technical criteria were evaluated by separate teams
not permitted to know the other's rankings. The total matrix was
then assembled by a Source Evaluation Board that gave a complete
presentation of all bids and their scoring results to the three
top men in the agency, who themselves chose the winner. There
was simply no room for arbitrariness or irregularity in such a
The tremendous increase in contracts needed for the Saturn V
program required a reorganization of the Marshall Space Flight
Center. Most of our resources had been spent in-house, and our
contracts had either been let to support contractors or to producers
of our developed products. Now 90 percent of our budget was spent
in industry, much of it on complicated assignments which included
design, manufacture, and testing. So on September 1, 1963, I announced
that Marshall would henceforth consist of two major elements,
one to be called Research and Development Operations, the other
Industrial Operations. Most of my old R&D associates then
became a sort of architect's staff keeping an eye on the integrity
of the structure called Saturn V, and the other group funded and
supervised the industrial contractors.
That same year Dr. George Mueller had taken over as NASA's Associate
Administrator for Manned Space Flight. He brought with him Air
Force Maj. Gen. Samuel Phillips, who had served as program manager
for Minuteman, and now became Apollo Program Director at NASA
Headquarters. Both men successfully shaped the three NASA Centers
involved in the lunar-landing program into a team. I was particularly
fortunate in that Sam Phillips persuaded his old friend and associate
Col. (later Maj. Gen.) Edwin O'Connor to assume the directorship
of Marshall's Industrial Operations.
On September 7, 1961, NASA had taken over the Michoud Ordnance
plant at New Orleans. The cavernous plant—46 acres under
one roof—was assigned to Chrysler and Boeing to set up production
for the first stages of Saturn I and Saturn V. In October 1961,
an area of 13,350 acres in Hancock County, Miss., was acquired.
Huge test stands were erected there for the static testing of
Saturn V's first and second stages.
Shipment of the oversize stages between Huntsville, Michoud,
the Mississippi Test Facility, the two California contractors,
and the Kennedy Space Center in Florida required barges and seagoing
ships. Soon Marshall found itself running a small fleet that included
the barges Palaemon, Orion, and Promise. For shipments through
the Panama Canal we used the USNS Point Barrow and the SS Steel
Executive. For rapid transport we had two converted Stratocruisers
at our disposal with the descriptive names "Pregnant Guppy"
and "Super Guppy." Their bulbous bodies could accommodate
cargo up to the size of an S-IVB stage.
AN ALL-UP TEST FOR THE FIRST FLIGHT
In 1964 George Mueller visited Marshall and casually introduced
us to his philosophy of "all-up" testing. To the conservative
breed of old rocketeers who had learned the hard way that it never
seemed to pay to introduce more than one major change between
flight tests, George's ideas had an unrealistic ring. Instead
of beginning with a ballasted first-stage flight as in the Saturn
I program, adding a live second stage only after the first stage
had proven its flight worthiness, his "all-up" concept
was startling. It meant nothing less than that the very first
flight would be conducted with all three live stages of the giant
Saturn V. Moreover, in order to maximize the payoff of that first
flight, George said it should carry a live Apollo command and
service module as payload. The entire flight should be carried
through a sophisticated trajectory that would permit the command
module to reenter the atmosphere under conditions simulating a
return from the Moon.
It sounded reckless, but George Mueller's reasoning was impeccable.
Water ballast in lieu of a second and third stage would required
much less thank volume than liquid-hydrogen-fueled stages, so
that a rocket tested with only a live first stage would be much
shorter than the final configuration. Its aerodynamic shape and
its body dynamics would thus not be representative. Filling the
ballast tanks with liquid hydrogen? Fine, but then why not burn
it as a bonus experiment? And so the arguments went on until George
in the end prevailed.
In retrospect it is clear that without all-up testing the first
manned lunar landing could not have taken place as early as 1969.
Before Mueller joined the program, it had been decided that a
total of about 20 sets of Apollo spacecraft and Saturn V rockets
would be needed. Clearly, at least ten unmanned flights with the
huge new rocket would be required before anyone would muster the
courage to launch a crew with it. (Even ten would be a far smaller
number than the unmanned launches of Redstones, Atlases, and Titans
that had preceded the first manned Mercury and Gemini flights.)
The first manned Apollo flights would be limited to low Earth
orbits. Gradually we would inch our way closer to the Moon, and
flight no. 17, perhaps, would bring the first lunar landing. That
would give us a reserve of three flights, just in case things
did not work as planned.
Mueller changed all this, and his bold telescoping of the overall
plan bore magnificent fruit: With the third Saturn V ever to be
launched, Frank Borman's Apollo 8 crew orbited the Moon on Christmas
1968, and the sixth Saturn V carried Neil Armstrong's Apollo 11
to the first lunar landing. Even though production was whittled
back to fifteen units, Saturn V's launched a total of two unmanned
and ten manned Apollo missions, plus one Skylab space station.
Two uncommitted rockets went into mothballs.
But let us go back to 1962. To develop and manufacture the large
S-II and S-IVB stages, two West Coast contractors required special
facilities. A new Government plant was built at Seal Beach where
North American was to build the S-ll. S-IVB development and manufacture
was moved into a new Douglas center at Huntington Beach, while
static testing went to Sacramento. The Marshall Center in Huntsville
was also substantially enlarged. A huge new shop building was
erected for assembly of the first three S-IC stages. A large stand
was built to static-test the huge stage under the full 7,500,000-pound-thrust
of its five F-1 engines. These engines generated no less than
180 million horsepower. As about I percent of that energy was
converted into noise, neighborhood windows could be expected to
break and plaster rain from ceilings if the wind was blowing from
the wrong direction or the clouds were hanging low. A careful
meteorological monitoring program had to be instituted to permit
test runs only under favorable weather conditions.
Although the most visible and audible signs of Marshall's involvement
in Saturn V development were the monstrous and noisy S-1C engines,
equally important work was done in its Astrionics Laboratory.
The Saturn V's airbearing-supported inertial guidance platform
was born there, along with a host of other highly sophisticated
electronic devices. In the Astrionics Simulator Facility, guidance
and control aspects of a complete three-stage flight of the great
rocket could be electronically simulated under all sorts of operating
conditions. The supersonic passage of the rocket through a high-altitude
jet stream could be duplicated, for instance, or the sudden failure
of one of the S-II stage's five engines. The simulator would faithfully
display the excursions of the swivel-mounted rocket engines in
response to external wind forces or unsymmetrical loss of thrust,
establishing the dynamic response of the entire rocket and the
resulting structural loads.
The Saturn V's own guidance system would guide the Apollo flights
not only to an interim parking orbit but all the way to translunar
injection. It fed position data to the onboard digital computer,
which in turn prepared and sent control signals to the hydraulic
actuators that swiveled the big engines for flight-path control.
As propellant consumption lightened the rocket, and as it traversed
the atmosphere at subsonic and supersonic speeds, the gain settings
of these control signals had to vary continuously, for proper
control damping. Serving as the core of the Saturn V's central
nervous system, the computer did many other things too. It served
in the computerized prelaunch 4 checkout procedure of the great
rocket, helped calibrate the telemetry transmissions, activated
staging procedures, turned equipment on and off as the flight
proceeded through various speed regimes, and even watched over
the cooling system that stabilized the temperatures of the array
of sensitive blackboxes within the IU. So although the working
flight lifetime of the Saturn computer was measured in minutes,
it performed many exacting duties during its short and busy life.
In planning the lunar mission, why did we plan to stop over in
a parking orbit? The reason was twofold: For one, in case of a
malfunction it is much easier and safer for astronauts to return
from Earth orbit than from a high-speed trajectory carrying them
toward the Moon. A parking orbit offers both crew and ground controllers
an opportunity to give the vehicle a thorough once-over before
committing it to the long voyage. Second, there is the consideration
of operational flexibility. If the launch came off at precisely
the right instant, only one trajectory from the launch pad to
the Moon had to be considered. But as there was always the possibility
of a last-minute delay it appeared highly desirable to provide
a launch window of reasonable duration. This meant not only that
the launch azimuth had to be changed, but due to Earth rotation
and to orbital motion the Moon would move to a different position
in the sky. A parking orbit permitted an ideal way to take up
the slack: the longer a launch delay, the shorter the stay in
the parking orbit. Restart of the third stage in parking orbit
for translunar injection would take place at almost the same time
of day regardless of launch delays. (As it happened, all but two
of the manned Apollo-Saturns lifted off within tiny fractions
of a second of being, precisely on time. One was held for weather
and the other was held because of a faulty diode in the ground-support
Why was the big rocket so reliable? Saturn V was not overdesigned
in the sense that everything was made needlessly strong and heavy.
But great care was devoted to identifying the real environment
in which each part was to work—and "environment"
included accelerations, vibrations, stresses, fatigue loads, pressures,
temperatures, humidity, corrosion, and test cycles prior to launch.
Test programs were then conducted against somewhat more severe
conditions than were expected. A methodology was created to assess
each part with a demonstrated reliability figure, such as 0.9999998.
Total rocket reliability would then be the product of all these
parts reliabilities, and had to remain above the figure of 0.990,
or 99 percent. Redundant parts were used whenever necessary to
attain this reliability goal.
Marshall built an overall systems simulator on which all major
subsystems of the three-stage rocket could be exercised together.
This facility featured replicas of propellant tanks that could
be loaded or unloaded, pressurized or vented, and that duplicated
the pneumatic and hydraulic dynamics involved. Electrically, it
simulated the complete network of the launch vehicle and its interfacing
ground support equipment.
THE PERILS OF POGO
An important Marshall facility was the Dynamic Test Tower, the
only place outside the Cape where the entire Saturn V vehicle
could be assembled. Electrically powered shakers induced various
vibrational modes in the vehicle, so that its elastic deformations
and structural damping characteristics could be determined. The
Dynamic Test Tower played a vital role in the speedy remedy of
a problem that unexpectedly struck in the second flight of a Saturn
V. Telemetry indicated that during the powered phases of all three
stages a longitudinal vibration occurred, under which the rocket
alternately contracted and expanded like a concertina. This "pogo"
oscillation (the name derived from the child's toy) would be felt
particularly strongly in the command module.
Analysis, supported by data collected in engine tests, confirmed
that the oscillation was caused by resonance coupling between
the springlike elastic structure of the tankage, and the rocket
engines' propellant-feed systems. Susceptibility to pogo (a phenomenon
not unknown to missile designers) had been thoroughly investigated
by the Saturn stage contractors, who had certified that their
respective designs would be pogo-free. It turned out that these
mathematical analyses had been conducted on an inadequate data
Once the problem was understood, a fix was quickly found. "In
sync" with the pogo oscillations, pressures in the fuel and
oxidizer feed lines fluctuated wildly. If these fluctuations could
be damped by gas-filled cavities attached to the propellant lines,
which would act as shock absorbers, the unacceptable oscillation
excursions should be drastically reduced. Such cavities were readily
available in the liquid-oxygen prevalves, whose back sides were
now filled with pressurized helium gas tapped off the high pressure
control system. After a few weeks of hectic activity, a pogo-free
Saturn flight no. 3 successfully boosted the Apollo 8 crew to
their Christmas flight in lunar orbit.
ARTIFICIAL STORMS AT THE ARM FARM
The connections between the ground and the towering space vehicle
posed a tricky problem. An umbilical tower, even higher than the
vehicle itself, was required to support an array of swingarms
that at various levels would carry the cables and the pneumatic,
fueling, and venting lines to the rocket stages and to the spacecraft.
The swingarms had to be in place during final countdown, but in
the last moments they had to be turned out of the way to permit
the rocket to rise. There was always the possibility, however,
of some trouble after the swingarms had been disconnected. For
instance, the hold down mechanism would release the rocket only
after all five engines of the first stage produced full power.
If this condition was not attained within a few seconds, all engines
would shut down. In such a situation, unless special provisions
were made for reattachment of some swingarms, Launch Control would
be unable to "safe" the vehicle and remove the flight
crew from its precarious perch atop a potential bomb.
These considerations led to the establishment, at Marshall, of
a special Swingarm Test Facility, where detachment and reconnection
of various arms was tested under brutally realistic conditions.
On the "Arm Farm" extreme conditions (such as a launch
scrub during an approaching Florida thunderstorm) could be simulated.
Artificial rain was blown by aircraft propellers against the swingarms
and their interconnect plugs, while the vehicle portion was moved
back and forth, left and right, simulating, the swaying motions
that the towering rocket would display during a storm.
Throughout Saturn V's operational life, its developers felt a
relentless pressure to increase its payload capability. At first,
the continually growing weight of the LM (resulting mainly from
additional operational features and redundancy) was the prime
reason. Later, after the first successful lunar landing, the appetite
for longer lunar stay times grew. Scientists wanted landing sites
at higher lunar latitudes, and astronauts like tourists everywhere
wanted a rental car at their destination. How well this growth
demand was met is shown by a pair of numbers: The Saturn V that
carried Apollo 8 to the Moon had a total payload above the IU
of less than 80,000 pounds; in comparison, the Saturn that launched
the last lunar mission, Apollo 17, had a payload of 116,000 pounds.
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