|The Rendezvous That Was Almost Missed:
Lunar Orbit Rendezvous and the Apollo Program
In the opinion of many space historians, NASA Langley's most
important contribution to the Apollo Program was its development of
the lunar-orbit rendezvous (LOR) concept. The brainchild of a few
true believers at Langley, LOR's basic premise was to fire an
assembly of three spacecraft into Earth orbit on top of a single
Pictured is the Apollo lunar module during rendezvous in
lunar orbit with the command module. If rendezvous around the moon
failed, the astronauts would have been too far away to have been
saved. The large dark-colored area in the background is Smith's
Sea. The Earth rises above the lunar horizon.
Astronauts Edwin "Buzz" Aldrin, Neil A.
Armstrong and Michael Collins after their selection to become the
prime crew of the Apollo 11 landing mission.
More than twenty years have passed since July 20, 1969, when the
lunar module "Eagle" with Apollo 11 astronauts Neil Armstrong and
Buzz Aldrin aboard gingerly made its way down to the Sea of
Tranquility, landing men on the moon for the first time.
Thousands of people and organizations in many different places
played key roles in this "giant leap for mankind." As President
Kennedy stated in the May 1961 speech to Congress in which he
announced the nation's commitment to the lunar challenge, "It will
not be one man going to the moon-it will be an entire nation. For
all of us must work to put him there."
One place that was fortunate to participate more than a little
in the achievement of the lunar objective was the NASA Langley
Research Center in Hampton, Va., the nation's oldest civilian
aeronautics laboratory and home of the Space Task Group that
conceived and directed Project Mercury, America's first
NASA Langley helped to establish many of the basic fundamentals
and mission concepts central to the success of the Apollo program.
In the laboratory's unique complex of wind tunnels, researchers
studied the aerodynamic integrity of the Saturn-Apollo launch
configuration and the problem of aerodynamic heating during the
reentry of the Apollo command module into the Earth's atmosphere.
Langley staff members and test facilities also played a major role
in the training programs necessary to prepare NASA's astronauts for
landing on the moon and moving around on its surface.
In the opinion of many space historians, however, Langley's most
important contribution to Apollo was its development of the
lunar-orbit rendezvous concept.
President John F. Kennedy's decision in 1961 to land a man on
the moon "before the decade is out" meant that NASA had to move
quickly to find the best method of accomplishing the journey. NASA
gave serious consideration to three options: Initially, direct
ascent; then, Earth-orbit rendezvous (EOR), and, finally, a
darkhorse candidate, lunar-orbit rendezvous (LOR).
Direct ascent was basically the method that had been pictured in
science fiction novels and Hollywood movies. A massive rocket the
size of a battleship would be fired directly to the moon, land and
then blast off for home directly from the lunar surface. The trip
would be like that of a chartered bus, moving from point A to point
B and back to A again in one brute of a vehicle.
Strong feelings existed within NASA in favor of direct ascent,
largely because it meant the development of a proposed giant
booster named the Nova. After the engineers made their
calculations, however, NASA realized that any single big rocket
that had to carry and lift all the fuel necessary for leaving the
Earth's gravity, braking against the moon's gravity as well as
leaving it, and braking back down into the Earth's gravity again,
was clearly not a realistic option-especially if the mission was to
be accomplished anywhere close to President Kennedy's timetable.
The development of a rocket that mammoth would just take too long,
and the expense would be enormous.
Extensive research into the aerodynamic forces affecting the
Saturn-Apollo launch configuration was performed in Langley wind
tunnel. Here, researchers study the effects of wind on the Saturn I
and escape tower.
The demise of direct ascent led to a scrupulous evaluation of
the second option: Earth-orbit rendezvous. The main idea of EOR was
to launch two pieces into space independently using advanced Saturn
rockets that were then in development; have the two pieces
rendezvous and dock in Earth orbit; assemble, fuel, and detach a
lunar mission vehicle from the modules that had joined up; and then
proceed with that bolstered ship, exactly as in the direct flight
mode, to the moon and back to Earth orbit. The advantage of EOR was
that it required a pair of less powerful rockets that were already
nearing the end of their development.
EOR enjoyed strong support inside of NASA, especially among
those who recognized that selection of EOR as the mode for the
Apollo mission would require the virtual construction of a space
station, a platform in Earth orbit that could have many other uses,
scientific and otherwise, beyond Apollo. For this reason, space
station advocates like Dr. Wernher Von Braun and his associates at
NASA's Marshall Space Flight Center in Huntsville, Alabama, favored
In the end NASA selected neither of the first two options:
instead, it selected the third: lunar-orbit rendezvous.
The brainchild of a few true believers at the Langley Research
Center who had been experimenting with the idea since 1959, the
basic premise of LOR was to fire an assembly of three spacecraft
into Earth orbit on top of a single powerful (three-stage)
Dr. John C. Houbolt explains the lunar orbit rendezvous
concept that, in the opinion of many historians, was chief among
the reasons why the U.S., in less than a decade, managed
humankind's first extraterrestrial excursions.
This assembly included: One, a mother ship, or command module;
two, a service module containing the fuel cells, attitude control
system and main propulsion system; and three, a small lunar lander
or excursion module. Once in Earth orbit, the last stage of the
rocket would fire, boosting the Apollo spacecraft with its crew of
three men in to its flight trajectory to the moon. Reaching lunar
orbit, two of the crew members would don space suits and climb into
the lunar excursion module (LEM), detach it from the mother ship,
and take it down to the lunar surface. The third crew member would
remain in the command module, maintaining a lonely vigil in lunar
orbit. If all went well, the top half of the LEM would rocket back
up, using the ascent engine provided, and re-dock with the command
module. The lander would then be discarded into the vast darkness
of space or crashed onto the moon (as was done in later Apollo
missions for seismic experiments), and the three astronauts in
their command ship would head for home.
President John F. Kennedy's decision in 1961 to land a man on
the moon 'before the decade is out' meant that NASA had to move
quickly to find the best method of accomplishing the journey. NASA
gave serious consideration to three options: initially, direct
ascent; then Earth-orbit rendezvous (EOR); and, finally, a
darkhorse candidate, lunar-orbit rendezvous (LOR).
Although the basics of the LOR concept had been expressed as
early as 1923 by German rocket pioneer Herman Oberth, no one had
recognized the fundamental significance of LOR until two separate
groups of Langley researchers in 1959, not long after Sputnik and
the creation of NASA, quietly began to think about the potential of
LOR for the budding American space program.
One of these groups was the Lunar Mission Steering Group headed
by Clinton E. Brown, head of the Theoretical Mechanics Division.
The other was the Rendezvous Committee headed by Dr. John C.
Houbolt, then the assistant chief of the Dynamics Load Division.
Brainstorming by these two Langley groups, done at first
independently, led to an intensive analysis of what were then
thought to be two distinct subjects: one, the mechanics of a moon
trip; and, two, the role of rendezvous in the operations of an
Earth-orbiting space station. The idea of putting the two analyses
together then led a few creative minds within the Langley study
groups to consider the advantages of LOR for a manned lunar
The basic premise of LOR was to fire an assembly of three
spacecraft into Earth orbit on top of a single powerful rocket (the
Saturn V). With the Apollo spacecraft, the Saturn V stood 363 feet
tall. Pictured is the launch of Apollo 11, the first mission to
land men on the moon, on July 16, 1969.
The first of these studies, a very brief paper by William H.
Michael, Jr., examined the benefits of "parking" the Earth-return
propulsion portion of a spacecraft in orbit around the moon during
a landing mission. The main benefit, according to Michael's
unpublished 1959 paper, was the weight advantage of a small lunar
lander needing less fuel. The chief problems were the
"complications involved in requiring a rendezvous with the
components left in the parking orbit."
In December 1960, after different LOR mission concepts had been
formulated, several Langley researchers, including Ralph W. Stone,
Clinton E. Brown, John D. Bird, Max C. Kurbjun and Houbolt, made
formal presentations on their concepts to the incoming associate
administrator of NASA, Dr. Robert C. Seamans. Although Seamans
seemed sufficiently impressed, the LOR concept was to remain
something of an orphan within the NASA family at every place except
Langley for some time to come.
A stage-by-stage lunar mission profile.
Twenty months later, on July 11, 1962, after much technical
debate and in-fighting, Seamans and NASA Administrator James E.
Webb announced during a press conference at NASA Headquarters in
Washington, D.C., that lunar-orbit rendezvous had been selected as
the primary mission mode for the initial manned moon landing.
Considering the strong opposition to LOR during NASA's intensive
evaluation of possible mission modes for Apollo, the choice seemed
Once in Earth orbit, the last stage of the Saturn rocket
fires, boosting the Apollo spacecraft and its three-man crew into
its flight trajectory to the moon.
Once in lunar orbit, two of the crew members donned
spacesuits and climbed into the lunar excursion module, detached it
from the mother ship and "flew" it down to the lunar
When Langley engineers first suggested the concept of
lunar-orbit rendezvous, NASA had rejected it out of hand for being
too complicated and risky. If rendezvous had to be part of Project
Apollo, critics of LOR felt that it should be done only in Earth
orbit. if that rendezvous failed, the threatened astronauts could
be brought back home simply by allowing the orbit of their
spacecraft to deteriorate. But, if a rendezvous around the moon
failed, the astronauts would be too far away to be saved. Nothing
could be done.
In retrospect, we know that LOR enjoyed several advantages over
the other two options. It required less fuel, only half the
payload, and less brand new technology than the other methods; it
did not require the monstrous Nova rocket; and it called for only
one launch from Earth whereas EOR required two. Only the small,
lightweight lunar module, not the entire spacecraft, would have to
land on the moon. This was perhaps LOR's major advantage. Because
the lander was to be discarded after use and would not need return
to Earth, NASA could tailor the design of the LEM for maneuvering
flight in the lunar environment and for a soft lunar landing. In
fact, the beauty of LOR was that it meant that NASA could tailor
all of the modules of the Apollo spacecraft independently.
The second man on the moon, Buzz Aldrin, descends from the
lunar module on July 20, 1969. He and astronaut Neil Armstrong
spent two hours and 20 minutes walking on the moon. The small,
lightweight Lunar Module was a major advantage of the LOR concept
because it did not need to be returned to Earth.
But in 1962 all these advantages were theoretical. On the other
hand, the fear that American astronauts might be left in an
orbiting coffin was quite real. It was a specter that haunted the
dreams of those responsible for the Apollo program and one that
made objective evaluation of the lunar-orbit rendezvous concept by
NASA unusually difficult.
The lunar module ascent stage (upper portion) is shown using
its ascent engine to rocket back into lunar orbit and rendezvous
with the Command Module (still orbiting the moon). Success depended
on Langley's ability to train the astronauts to master the
techniques of landing the lunar module on the lunar surface and
returning the ascent stage to orbit to dock with the mother
In late 1961 and early 1962 NASA convened a number of internal
task forces to help in the selection of the mission mode for
Apollo. One of these committees (the Lundin Committee) evaluated
the option of direct ascent and another (the Heaton Committee)
investigated the feasibility of Earth-orbit rendezvous. But there
was no committee to look into LOR. Only one of these study groups
(the Lundin Committee) wanted to hear anything about lunar-orbit
rendezvous, and in its final report LOR finished a distant third
behind EOR and direct ascent.
But at least one tenacious Langley engineer, Dr. John Houbolt,
would not let the advantages of LOR be ignored. As a member of of
Lunar Mission Steering Group, Houbolt had been studying various
technical aspects of space rendezvous since 1959 and was convinced,
like several others at Langley, that LOR was not only the most
feasible way to make it to the moon before the decade was out, it
was the only way. He had reported his findings to NASA on various
occasions but felt strongly that the internal task forces (to which
he made presentations) were following arbitrarily established
"ground rules." According to Houbolt, these ground rules were
constraining NASA's thinking about the lunar mission -- and causing
LOR to be ruled out before it was fairly considered.
Lunar-orbit rendezvous required docking the lunar module with
the command module in lunar orbit. Astronauts practiced the complex
task of separating and uniting spacecraft to master docking
techniques with Langley's Rendezvous and Docking Simulator, today a
National Historic Landmark, pictured.
In November 1961, Houbolt took the bold step of skipping proper
channels and writing a private letter, nine pages long, directly to
Seamans, the associate administrator. "Somewhat as a voice in the
wilderness," Houbolt protested LOR's exclusion. "Do we want to go
to the moon or not?" the Langley engineer asked. "Why is Nova, with
its ponderous size simply just accepted, and why is a much less
grandiose scheme involving rendezvous ostracized or put on the
defensive? I fully realize that contacting you in this manner is
somewhat unorthodox," Houbolt admitted, "but the issues at stake
are crucial enough to us all that an unusual course is
It took two weeks for Seamans to reply to Houbolt's
extraordinary letter. The associate administrator agreed that "it
would be extremely harmful to our organization and to the country
if our qualified staff were unduly limited by restrictive
guidelines." He assured Houbolt that NASA would in the future be
paying more attention to LOR than it had up to this time.
Upon return to Earth, the command and service modules
separate, leaving the command module to plunge into the Earth's
atmosphere at a velocity of 25,000 mph.
In the following months, NASA did just that, and to the surprise
of many both inside and outside the agency, the darkhorse
candidate, LOR, quickly became the front runner. Several factors
decided the issue in its favor. First, there was growing
disenchantment with the idea of direct ascent due to the time and
money it was going to take to develop the huge Nova rocket. Second,
there was increasing technical apprehension over how the relatively
large spacecraft demanded even by Earth-orbit rendezvous would be
able to maneuver to a soft landing on the moon. As one NASA
engineer who changed his mind explained: "The business of
eyeballing that thing down to the moon really didn't have a
satisfactory answer. The best thing about LOR was that it allowed
us to build a separate vehicle for landing."
The first major group to break camp in favor of LOR was Robert
Gilruth's Space Task Group, which was still located at Langley but
was soon to move to Houston. The second to come over was the Von
Braun team in Huntsville. Then these two powerful groups of
converts, along with the original true believers at Langley,
persuaded key officials at NASA Headquarters, notably Administrator
James Webb, who had been holding out for direct ascent, that LOR
was the only way to land on the moon by 1969. With the key players
inside NASA lined up behind the concept, Webb approved LOR in July
1962. He did it even though President Kennedy's science advisor,
Jerome Wiesner, remained firmly opposed to LOR.
Sequences of lunar de-orbit to Earth, which Michael Collins
called the "get us out of here, we don't want to be a permanent
moon satellite" maneuver.
Whether NASA's choice of LOR would have been made in the summer
of 1962 or at any later time without the research information, the
commitment, and the crusading zeal of Houbolt and his associates at
NASA Langley is a matter for historical conjecture. However, the
basic contribution made by the Langley researchers is beyond
debate. They were the first in NASA to recognize the fundamental
advantages of the LOR concept, and for a critical period of time in
the early 1960s they were also the only ones inside of the agency
to foster it and fight for it.
Thousands of factors contributed to the ultimate success of
Apollo, but no single factor was more essential than the concept of
lunar-orbit rendezvous. Without NASA's adoption of this
stubbornly-held minority opinion, we may still have gotten to the
moon, but almost certainly it would not have been accomplised by
the end of the decade, as President Kennedy had wanted.
This NASA Facts was prepared by the NASA Langley
Research Center Office of Public Affairs, with the assistance of
Dr. James R. Hansen, author of Engineer in Charge: A History
of the Langley Aeronautical Laboratory, 1917 - 1958