"More Favored than the Birds":
The Manned Maneuvering
Unit in Space

by Anne Millbrooke

In 1984 a Manned Maneuvering Unit (MMU) enabled a few astronauts to
maneuver in outer space, outside of spacecraft, and free of tether lines.
This manned maneuvering unit and its predecessors are, as the name implies,
maneuvering devices. Flight is the function of the spacecraft. Life support
is the function of the space suit. Maneuvering is an extravehicular activity
independent of the protective and supportive space suit, yet integrated
with the suit and even the spacecraft. The spacecraft and space suit are
prerequisites to extravehicular activity, the craft to transport the astronaut
into outer space, and the suit to protect and support life. The maneuvering
unit is an optional aid. The maneuvering unit, spacecraft, and space suit
are complementary components of the human space flight program. Whereas
all such space flights have involved spacecraft and space suits, only a
few have utilized manned maneuvering units.

Outer space is a micro- or zero-gravity environment that requires special
techniques for moving inside the spacecraft as well as out. Based upon
experience aboard the Space Shuttles Columbia and Discovery, astronaut
Joseph P. Allen described the experience inside a spacecraft:

> During the first few days in space, the act of simply moving
> from here to there looks so easy, yet is so challenging. The veteran of
> zero gravity moves effortlessly and with total control, pushing off from
> one location and arriving at his destination across the flight deck, his
> body in the proper position to insert his feet into Velcro toe loops and
> to grasp simultaneously the convenient handhold, all without missing a
> beat in his tight work schedule. In contrast, the rookies sail across the
> same path, usually too fast, trying to suppress the instinct to glide headfirst
> and with vague swimming motions. They stop by bumping into the far wall
> in precisely the wrong position to reach either the toe loops or the handholds.1

Space writer Harry L. Shipman expressed this more directly: "Velcro
takes the place of gravity" inside the spacecraft.2
Outside the spacecraft, there is no Velcro and no enclosing walls. Civilian
and military engineers thus explored various mechanism to aid astronauts
outside the spacecraft. These aids included foot restraints, hand grips,
tether lines, and self-propelled maneuvering units, yet few space missions
required the technology and capability of manned maneuvering units.

Floating in space was a lesson learned by experience gained gradually
during the Mercury, Gemini, Apollo, Skylab, and Space Shuttle missions.
In fact, the Mercury,



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|Photo of Bruce McCandless in the MMU flying at 45 degrees over the earth.                                                                                                                                                                                                                                                                                                                                                                                     
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Astronaut Bruce McCandless on a spacewalk using the
manned maneuvering unit (MMU) on STS-41B, February 1984. NASA and Martin
Marietta Corporation were awarded the Collier Trophy in 1984 for the development
of the MMU, and for being the NASA teams that rescued three disabled satellites,
with special recognition to astronaut Bruce MeCandless II, NASA's Charles
E. Whitsett, Jr. and Martin Marietta's Walter W Bollendonk. (NASA photo
no. 84-H-71).



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 301

Gemini, and Apollo spacecraft were too small to allow astronauts much
mobility within the craft. Project Gemini included the construction of
two types of maneuvering units and the training of astronauts in their
use. In 1965 Gemini astronaut Edward H. White made the first American spacewalk.
Using a hand-held maneuvering unit, and wearing a space suit for life support,
he spent twenty minutes outside of Gemini 4. He was tethered to
the space capsule for safety. Project Gemini thus provided the first American
experience with extravehicular activity in space; a Soviet cosmonaut had
achieved the first extravehicular activity months before White ventured
out of the Gemini capsule. Later Gemini astronauts also completed extravehicular
activities in the harsh environment of outer space.

Apollo and later Skylab added to NASA's research and development experience
with the concept and technology of maneuvering in space, though not with
the operation of any maneuvering aids in free flight in outer space. Apollo's
objective was the lunar surface, not outer space. The three Skylab missions
in 1973 and 1974 provided astronauts experience with weightless floating
in a relatively large open space within a spacecraft, but not outside.
It was not until the Space Shuttle, a reusable transportation system, that
astronauts acquired operational experience floating both inside and outside
a spacecraft.

The award-winning manned maneuvering unit was designed for a specific
type of mission: satellite rescue missions. All earlier maneuvering units
had been designed for experimental missions, that is to test the technology,
but with the reusable Space Shuttle NASA introduced an operational, mission-oriented
maneuvering unit the award-winning manned maneuvering unit (MMU). This
operational unit was used three times on the tenth, eleventh, and fourteenth
flights of the Space Transportation System, more commonly known as the
Space Shuttle. The year of these flights was 1984. The Collier Trophy for
that year recognizes astronaut Bruce McCandless II, who first used the
unit in space, NASA's Charles E. "Ed" Whitsett, Jr., and Martin Marietta's
Walter W. "Bill" Bollendonk. These three men were instrumental in the development,
and McCandless in the use, of the unit. Behind this award is a story of
technological development involving a variety of institutions within the
national infrastructure of the space program and amid the superpower rivalry
known as the Cold War.

From the preliminary research and development in the 1950s to the achievements
of 1984, civilian and military personnel engineers, technicians, and astronauts
defined and redefined the technology of maneuverability in terms of perceived
needs and capabilities, and within the limitations imposed by budgets and
flight schedules. At each step reviews, tests, and experiments, as well
as political decisions affecting the space program in general, influenced
decisions about whether to continue development, in what direction, and
by which next step. The identification and definition of applications for
maneuvering units actually began in science fiction literature, which included
earthbased as well as outer space missions. Civilian and military agencies
and government contractors, that is industry, participated in the development
of maneuvering units of several types, including finally the award-winning
manned maneuvering unit.

Science Fiction

Before the "science fact" there was science fiction. From novels of
the nineteenth century to moving pictures of this century, humans traveled
in space-sometimes using maneuvering units outside the spaceships and sometimes
not, mostly not. Early literary classics of space travel include Jules
Verne's novel From the Earth to the Moon (1865) and H.G. Wells'
First
Men in the Moon (1901). Both of these books were made into movies of



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the same names, respectively; Verne's in 1958 and Wells' in 1964.3
In both the print and film versions, the space travelers left Earth with
neither space suits nor maneuvering units. In Verne's story the characters
flew in a ballistic projectile, shot from a huge cannon, toward the Moon.
They relied upon the probability that they would be able to survive in
the rarified atmosphere of the Moon.

En route to the Moon in Verne's sequel, Round the Moon (1870),
the French adventurer Michel Ardan asked his traveling companions, "Why
cannot we walk outside like the meteor? Why cannot we launch into space
through the scuttle? What enjoyment it would be to feel oneself thus suspended
in ether, more favored than the birds who must use their wings to keep
themselves up!"4 Practical Impey Barbicane,
president of the Gun Club that had shot their projectile into space, responded
with two reasons. First, there was no air in the ether of outer space.
Second, the density of a man being less than that of the projectile in
which they traveled meant that a man outside the spacecraft would move
at a speed not equal to that of the craft and thus the man would move apart
from the craft.
Later Ardan exclaimed, "Ah! what I regret is not being able to take
a walk outside. What voluptuousness to float amid this radiant ether, to
bathe oneself in it, to wrap oneself in the sun's pure rays. If Barbicane
had only thought of furnishing us with a diving apparatus and an air-pump,
I could have ventured out."5 Again
practical Barbicane countered the proposal: a diving apparatus in space
would burst like a balloon that had risen too high. Barbicane thereupon
prohibited "all sentimental walks beyond the projectile," but his authority
applied only to his fictional companions and not to writers of other science
fiction works.

What Ardan missed both in print and on film, Buck Rogers and Flash Gordon
achieved. These twentieth-century fictional heros provided inspiration
and humor to the astronauts and engineers involved with maneuverability
in space. Mission specialists Bruce McCandless and Robert Stewart even
called each other Buck and Flash in the cabin of the Space Shuttle on that
historic mission when the award-winning manned maneuvering unit was first
used.6 Originally the star of a comic
strip, Flash Gordon entertained movie audiences via three serials: Flash
Gordon (1936), Flash Gordon's Trip to Mars (1938), and Flash
Gordon Conquers the Universe (1940). Created by Alex Raymond and played
by Buster Crabbe, Flash Gordon fought the evil forces of Ming the Merciless.
He traveled in Dr. Zarkov's rocketship and other spacecraft. The technology
of life support and maneuverability did not clutter his adventures.

Buck Rogers similarly appeared in print and on film. Under the name
Anthony Rogers, he made his debut on the pages of a pulp magazine in 1928.
Using the name Buck, he moved into a comic strip the following year. A
decade later he appeared on film in twelve episodes of Buck Rogers(1939);
like Flash Gordon, he was played by Buster Crabbe. In the original story,
written by Philip Francis Nowlan, Rogers awoke from suspended animation
in a future time year 2419 when Americans wore "inertron" belts, both
'Jumpers" and



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 303

"floaters" that increased their mobility.7
A jumper made the wearer weigh "in effect" as little as desired and therefore
able to jump considerable distances. Floaters were advanced jumpers equipped
with rocket motors that enabled the wearers to float in air similar to
a diver floating in water; directional control came through the wearer
twisting his body and moving his arms and legs. These rocket-powered mobility
units inspired science fiction writers and the recent Walt Disney-Silver
Screen movie The Rocketeer (1991), which like the original Nowlan
story involved maneuverability on Earth, not in outer space.

Generally, spaceships and space suits received more attention in science
fiction stories than did technology for maneuvering. Robert A. Heinlein
is an example. His Rocket Ship Galileo (1947) is about three boys,
recent high school graduates, who accompany an atomic scientist to the
Moon and while there defeat Nazis. The heroes wore pressurized stratosphere
suits that look like diving suits. The helmets were bowl-shaped plexiglass,
and the soles and seats of the suits were insulated with asbestos. The
characters in print had no maneuvering devices. Heinlein's thin book became
the loose basis of Destination Moon (1950), a good Cold War movie
about combined American industry racing to get to the Moon before the Russians.
In both book and movie the space vehicle is an atomic-powered rocketship;
and Woody Woodpecker gives a delightful explanation of rocketry in the
movie.

Traveling to the Moon was a race, not simply a space race, but also
a military arms race. In Destination Moon the fictional General
Thayer announced, "there is absolutely no way to stop an attack from outer
space" and thus "the first country that can use the Moon for the launching
of missiles will control the Earth."8
In the movie private industry supported the lunar mission because government
was unable to mobilize the necessary resources during peacetime; the movie
script thus failed to anticipate federal appropriations in time of a Cold
War. The film travelers performed extravehicular activities in space. Wearing
space suits and tethered to the spacecraft, they unstuck an antenna. One
man released hold of his safety line and drifted away from the ship. He
was rescued by another man who carried a large oxygen bottle, released
gas for propulsion, and steered by manually facing the nozzle away from
the desired direction of travel.

Science Fact

Michel Ardan's wish for "a diving apparatus and an air-pump" was not
far afield from the early development of special suits for high-altitude
flight, the predecessors of early space suits. In the 1930s aviator Wiley
Post attempted and achieved stratospheric flight. As he said, "The main
objective of high-altitude flight is to increase the speed of



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304 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

travel." 9 He foresaw transcontinental
and transoceanic flights for the transportation of passengers and freight.
But to fly in the thin air of high altitudes, he needed both oxygen and
sufficient pressure to protect the cells of the body. He recognized that
the aircraft's cabin could be sealed and filled with air under pressure,
but at the addition of "prohibitive weight." More specifically, it would
be impossible to pressurize the plywood shell of his Winnie Mae,
a Lockheed Vega that he had flown twice around the world and that he used
in his high flying. He therefore approached the B.F. Goodyear Company with
the idea of "a suit, something like a diver's outfit, which the pilot can
wear, and which can be blown up with air or oxygen to the required pressure
." 10

In response to Post's request, Goodyear built him three pressurized
suits. The first cost less than $75 (equivalent to about $800 in 1994 dollars).
It ruptured during an unmanned test, before flight testing. Post got stuck
in the second suit, which literally had to be cut off him, again before
any flight test. The third suit not only passed tests in the Army's low-pressure
chamber at Wright Field, but also met requirements during the 25 hours
that Post logged in the suit. That suit proved compatible with his airplane
and allowed sufficient mobility for him to operate the plane's controls;
though when inflated, the suit allowed only very limited mobility. In a
series of flights in 1934 and 1935 Post successfully demonstrated the utility
of the pressure suit. To continue his experiments in high altitude flight,
he acquired another airplane. He and the humorist Will Rogers died in a
crash of that experimental plane, a crash from very low altitude.11

Post's successful pressure suit, however, influenced research programs
of the Army and Navy, which contracted with manufacturers Goodrich, Bell
Aircraft, U.S. Rubber, National Carbon, and later others for pressure
suits, initially for experimental designs, later for production suits.
Military contracts, that is military money and military specifications,
defined technical progress in the development of pressure suits. One goal
was to increase the mobility of the person inside the suit, to allow the
pilot more range of movement. Although progress was slow, two key developments
were achieved in the 1950s. One was the linknet restraint. This linknet-nylon
restraining layer prevented a suit from ballooning under pressure. Introduced
in 1956 by the David Clark Company and the Air Force, this feature helped
make the A/P22S-2 pressure suit standard Air Force equipment. Test pilots
flying the X-15 experimental plane wore this pressure suit in supersonic
flight. In 1957 B.F. Goodrich and the Navy built swivel joints with airtight
rotating bearings, and also fluted joints (semirigid accordion pleats),
into the Mark II suit, made of a rubberized fabric. Improved versions appeared
in 1958-Mark III-and 1959-Mark IV.

When the United States began its man-in-space program, high-altitude
pressure suits were adapted into space suits. As stated in a Smithsonian
publication, Goodyear engineer "Russell Colley is considered the father
of the American space suit for constructing the first successfully pressurized
flying suit for Wiley Post."12 Project
Mercury provided the spacecraft in which astronauts first used space suits
and proved the technological basis of human space flight. The Mercury space
suits were adapted from the Goodyear-Navy Mark IV suit. The space suit
was a protective system made of aluminized nylon, Neoprene-coated nylon,
and vulcanized nylon. It would pressurize only in the event of an emergency.
In that sense,



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 305

equipping the suit for pressurization was a precaution against the possibility
that the spacecraft might decompress, a redundancy built into the Mercury
program for the protection of the astronaut. Still the suit was specially
adapted for ventilation of the astronaut, for waste removal, and for safety
and comfort. Changes were made as experience warranted.

One astronaut at a time, and safely confined in the spacecraft, Mercury
astronauts orbited the earth. No Mercury astronaut ventured outside the
spacecraft into outer space. The importance of integration of all aspects
of the space program became apparent during Project Mercury. As one historian
concluded, "The greatest lesson learned from the Mercury flights was probably
the unique importance of people to machines. The Mercury program began
with a machine that had a man in it. And by the end of the program, it
truly became a manned spacecraft."13
Spacecraft, crew, space suit, and other mission equipment needed to be
integrated. This lesson applied to maneuvering units then and later under
development.

Although maneuvering units were not specifically a part of Project Mercury,
the possibilities of maneuvering in space were explored concurrent with
the Mercury flights. The Air Force, for example, began testing space propulsion
units, hand-held, pistol-like, compressed-air devices, at its Aerospace
Medical Laboratory in 1958. That work was done at the laboratory at Wright-Patterson
Air Force Base, Ohio, with some testing also conducted at NASA's Air Beating
Facility in Houston. The main problem of a hand-held unit was "the difficulty
of aligning the thrust vector with the center of mass of the man, causing
rotation with translation resulting in unworkable flight paths";14 
in other words, the astronaut could not maintain control. The Air Force's
Aerospace Medical Division issued a report on "Self-Maneuvering for the
Orbital Worker" in 1960. That year the Rocket Propulsion Laboratory at
Edwards Air Force Base, California, provided assistance in designing the
propulsion system for an experimental maneuvering unit, a research device
designed for testing under weightless conditions, but not for use in the
environment of outer space.

This early work of the Air Force led to maneuvering units for Project
Gemini, during which astronauts wore space suits and remained tethered
to the spacecraft during extravehicular activity. Only briefly using maneuvering
units, astronauts began maneuvering in space, outside the spacecraft, during
Project Gemini.

Maneuvering in Space

Project Gemini provided NASA experience with extravehicular activity
in space and with two maneuvering devices. One device was the Hand-Held
Maneuvering Unit (HHMU) that White used in 1965, also known as the self
maneuvering unit, pressure gun, or simply gun. The second device was a
backpack called variously an Astronaut Maneuvering Unit (AMU), the Modular
Maneuvering Unit (MMU), Modular Astronaut Maneuvering Unit (MAMU), and
Department of Defense experiment D-12. Gemini crews accomplished extravehicular
activities, six hours of tethered time and six hours of standing up in
the open hatch of the spacecraft. The five crews who accumulated the tethered
time were aboard Gemini 4, 9A, 10, 11, and 12. Both the hand-held
and backpack maneuvering



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306 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

devices were scheduled for testing during tethered activity on these
flights, but only the handheld unit was ever used in space and only on
Gemini
4 and 10. Both maneuvering units, however, provided experience
and established precedents that contributed to the Collier-winning manned
maneuvering unit of 1984. From the 1960s to 1984, however, the developers
of maneuvering units explored several directions.

Civilian and military branches of the Federal government and contractors
and subcontractors in industry participated in the design and development
of maneuvering units for the Gemini program and thereby established the
pattern of collaboration that continued thereafter in the development of
maneuvering units. NASA was the lead agency. Project Gemini was phase two
of NASA's manned space flight program; Project Mercury had been phase one,
and Project Apollo would be phase three. NASA's Manned Spacecraft Center
in Houston managed the agency's manned space flight program. The prime
contractor for Project Gemini was McDonnell Aircraft Corporation, headquartered
in St. Louis. Other contractors designed, developed, built, or delivered
a variety of products incorporated in the Gemini missions, including space
suits, life support systems, and maneuvering units.

The Manned Spacecraft Center managed the development of the hand-held
maneuvering unit. Per policy, this NASA center participated in research,
design, and testing, but contracted out construction. In developing the
Gemini hand-held unit, NASA balanced the advantages of tractor or tow thrusters
and the pusher mode. It developed a proportional thrust system, allowing
the astronaut more control than an on-off system. The unit accommodated
the limited dexterity of the gloved hands of an astronaut. The initial
unit used on Gemini 4 had two one-pound tractor jets and one two-pound
pusher jet. The gas was oxygen, deemed safe to store in the cabin of the
spacecraft. This was a self-contained system. A later model, intended for
use on Gemini 8, received its propellant, Freon 14 gas, from a tank
packed on the astronaut's back. In a still later model used on Gemini
10, a hose bundled in the astronaut's umbilical cord transported nitrogen
gas from the spacecraft to the hand-held unit. Refinements in the handle
of the unit were also made as the Gemini program progressed. Equipment
to train astronauts to use the hand-held units included air-bearing simulators
in the Air Bearing Facility.15

The Air Force managed what it called the "modular maneuvering unit"
(MMU) program, initiated in 1963, and the Air Force's Space Systems Division
became the lead division for developing this maneuvering backpack unit.
Why was the Air Force participating in the civil space program? First,
NASA requested the Air Force's assistance because the Air Force had launch
vehicles (like the Titan II rocket modified for use as the Gemini launch
vehicle) and other resources.16 Also,
the Air Force had effectively supported NASA's Mercury program. The Air
Force, in fact, had pursued its own human space flight program, Dyna-Soar,
from 1957 into 1963. Canceled three years before the scheduled first flight,
the Dyna-Soar program provided important technical information about hypersonic
flight, reentry flight control, and heating problems. Secondly, the Air
Force, and Department of Defense in general, approached space in terms
of national security and military strategy. Dyna-Soar, for example, grew
out of military interest in a piloted boost-glide bomber-missile (called
Bomi), a reconnaissance system (called Brass Bell), and a hypersonic weapon
and research and development system (HYWARDS). The three programs were
consolidated into Dyna-Soar in response to the Soviet's successful orbiting
of Sputnik in



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 307

October 1957. Even after the cancellation of Dyna-Soar, the Air Force
retained military objectives for a space program. 17

In the United States, civilian and military objectives became interwoven
in national policy. Congress responded to Sputnik by establishing three
space organizations in 1958: the civilian National Aeronautics and Space
Administration (NASA), the military Advanced Research Projects Agency (ARPA),
and the executive National Aeronautics and Space Council (an advisory panel
reporting to the President). At that time the country publicly entered
a technological and scientific, as well as political, space race. Of the
early years of that space race, NASA historian Roger D. Launius concluded,
"First, NASA's projects were clearly cold war propaganda weapons that national
leaders wanted to use to sway world opinion about the relative merits of
democracy versus the communism of the Soviet Union.... Second, NASA's civilian
effort served as an excellent smoke-screen for the DOD's [Department of
Defense] military space efforts."18

From the military perspective, General Bernard A. Schriever explained
the nature of civil-military cooperation:

> NASA programs by themselves will not build a military capability.
> That is not their purpose, nor should it be their purpose. A military capability
> can be created only by a military organization which possesses a combination
> of technical knowledge and operational experience with suitable military
> equipment. Both NASA and the Department of Defense have valid and distinctive
> roles in the national space program. Their efforts are complementary, not
> competitive; their programs are cooperative, not conflicting.19

The Air Force had particular interest in launch vehicles, operation
of spacecraft, communications systems, and in General Schriever's words
"techniques needed to transport and support man in space and to permit
him to function effectively there." To function effectively in space implied
maneuverability, and thus the Air Force's research and development of maneuvering
units, including experiment D-12 in the Gemini flight program.

Among the companies involved in the early maneuvering work was Aero-Jet
General, which prepared an influential report entitled "A Rocket System
for Limited Manned Flight" (1959) and proposed an "AeroPak Flight Vehicle."
As early as 1953, Wendell F. Moore of Bell Aerosystems had begun designing
a rocket belt. He continued his effort, and in 1960 Bell obtained an Army
contract to produce the Army's A-1 prototype rocket belt. In 1962 President
John F. Kennedy viewed a Bell rocket belt in flight demonstration at Fort
Bragg, North Carolina.20  The
next year Ling-Temco-Vought (LTV) prepared for the Department of Defense
preliminary designs of a Remote Maneuvering Unit (RMU) to be ejected from
the spacecraft and then remotely moved, by an astronaut inside the spacecraft,
toward a target that had also been ejected. The unit was to be man-rated
so that



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308 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

manual operation would also be possible. Bota Reaction Motors also did
relevant small rocket work under government contract.

In November 1963 the Air Force's Aero Propulsion Laboratory proposed
to develop "an individual back-pack experiment which would permit the astronaut
to maneuver independently around the Gemini vehicle."21
This was the beginning of the Gemini astronaut or modular maneuvering unit.
The Air Force's proposed extravehicular experiments for Gemini had priority
".05A, equivalent to that of the Ballistic Missile Program," and thus required
White House approval.22 The Rocket
Propulsion Laboratory in California accepted technical responsibility for
the rocket propulsion system, which used hydrogen peroxide as the monopropellant.
For design and fabrication, the Air Force initially planned to grant a
sole-source contract to Ling-Temco-Vought, but soon issued a request for
technical proposals. LTV and Bell responded.

The Air Force evaluated these technical proposals on nine points: propulsion,
environmental control system, electronics, flight controller, power, aerospace
ground equipment, overall system, reliability and quality control, and
program plan. Bell was "very strong" in propulsion and scored a ninety
percent overall for its proposal, and LTV scored only sixty percent, but
"both were considered acceptable."23
LTV then thoroughly amended its technical proposal into something "greatly
improved" though still a bit weaker than the Bell proposal, but LTV's cost
proposal was $750,000 less than Bell's. The Air Force negotiated a cost-plus-incentive-fee
contract with LTV for the construction and delivery of three backpack maneuvering
units.

As the prime Gemini contractor, McDonnell Aircraft Corporation integrated
the maneuvering units and related experiments into the Gemini spacecraft.
Although B.F. Goodrich had received the first contract to design Gemini
space suits, even delivered two prototypes, the David Clark Company won
the contract to produce the Gemini space suits.24
Clark thus participated in integrating the space suits with both the spacecraft
and the maneuvering units and maneuvering experiments.

Clark produced three models of space suits actually worn on Gemini flights
and continually modified the models in response to the astronauts' comments.
Like their Air Force predecessor (the A/P22S-2 pressure suit), these space
suits had linknet Dacron woven throughout one layer of the suit. The linknet
held the pressurized containment layer to the contours of the body and
thereby aided mobility. The basic extravehicular model G4C weighed thirty-five
pounds, ten pounds more than model G3C worn only inside the spacecraft
and only on Gemini 3. G4C weighed more mostly because of additional
outer layers of nylon, aluminized Mylar, unwoven Dacron insulation, and
Nomex heat-resistent material that formed a protective hazardous-environment
shield. The G4C helmet similarly had additional protective layers: visual,
thermal, and impact shields. Like the rest of the suit, the helmet was
continually modified. The lightest Gemini suit, just sixteen pounds, was
the G5C, worn inside the spacecraft on only the Gemini 7 mission.
Variants of G4C were worn by both members of crews of Gemini 4, 5, 6A,
8, 9A, 10, 11, and 12, whether or not extravehicular activities
were planned, as any opening of the spacecraft's hatch exposed the crew
to the space environment.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 309

Integration of the backpack maneuvering unit and the space suit posed
a particular challenge to Gemini engineers within government and industry.
In 1964, for example, LTV uncovered a problem while testing the modular
maneuvering unit. The company's exhaust plume analyses revealed that rocket
exhaust plumes impinged on the space suit. The exhaust heated the suit,
particularly the helmet and the legs. NASA opposed adding insulation patches
to the space suit as a solution, so LTV proposed other solutions that involved
modifying either the maneuvering unit or the space suit or both. One way
to avoid overheating the suit was to extend all thruster nozzles far enough
to avoid impingement. A second method was to extend the upper forward nozzles
beyond the helmet impingement and to add a leg restraint device to prevent
the astronaut's leg from moving into a lower plume. Third, UV proposed
modifying the space suit, extending the upper forward nozzles beyond the
helmet, and rebuilding the lower suit of materials to withstand higher
temperatures. A thermal skirt, a fourth idea, was proposed to cover the
astronaut's legs. All the proposals posed their own problem "delays of
varying length to the MMU delivery schedule."25

The decision was to extend two forward nozzles on the maneuvering unit
and to rebuild the lower section of the space suit, but without altering
the delivery schedule, something "not possible if we are to meet NASA flight
dates," according to the director of the Air Force Aero Propulsion Laboratory.26
This colonel explained, "The only other alternative is termination of the
program." He urged close monitoring of contractors and subcontractors,
also simultaneous qualification testing, reliability testing, and hardware
fabrication, yet "there must be no compromise with the astronaut's safety
during space flight." This approach worked. It meant, however, additional
weight to the special suit the astronauts wore outside the spacecraft,
doubling the weight of the fabric in the legs over that of other G4C suits.
As modified for the first in-space test of the backpack maneuvering unit,
the suit's legs included neoprene-coated nylon, uncoated nylon, fiberglass
cloth, aluminized hightemperature film, and Chromel-R cloth (stainless
steel).27

As the modular maneuvering units neared completion in February 1966,
an accident occurred. There was an explosion during a reliability test
of one unit-at hour 96 of the planned 100-hour operating time. A quick
investigation revealed the problem to be in LTV's now damaged test equipment,
in the company's Space Environment Simulator (also known as the SES). There
was no problem with the maneuvering unit. With the design and development
phases complete, and the final verification tests in progress or on schedule,
the explosion merely delayed tests conducted in that one facility.

By mid-April 1966 all the testing had been completed, and the three
experimental modular maneuvering units had been delivered to the Air Force.
Gemini astronauts were in final training for using the units. Wearing training
packs, they experienced brief periods of zero gravity aboard a KC-135 aircraft.28
To obtain zero gravity in flight, the pilot pushed the jet airplane into
a dive, pulled the nose up, and flew over a parabolic arc; the weightless
condition occurred going "over the hump."



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310 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

Gemini flights had already begun. In fact, Ed White had accomplished
the first extravehicular activity on June 3, 1965, as part of Gemini
4.29 He used the Hand-Held Maneuvering
Unit, the pressure gun. In case of emergency, that is in case White dropped
the gun, it too was tethered. Command pilot James A. McDivitt kept the
spacecraft in a stable attitude while White maneuvered outside the vehicle,
and McDivitt took pictures of White's space walk. After White used all
the gas in the hand-held maneuvering unit, he could still maneuver with
the aid of the tether line, but that gave McDivitt problems controlling
the spacecraft. White confirmed the earlier Soviet finding: Man can maneuver
in space.

For extravehicular activity, the astronauts wore the Clark G4C suit
and a life-support chest pack, either a Ventilation Control Module (Gemini
4) or an Extravehicular Life Support System (ELSS, Gemini 9A, 10,
11, and 12). In the spacecraft, astronauts connected their suits
to the craft's life support system. Outside the craft an oxygen hose, electrical
and communication wires, and a safety tether connected the astronaut to
the spacecraft. These were bundled in the umbilical cord between the chest
pack, astronaut, and spacecraft. Outside the spacecraft, according to plans
for six Gemini flights, the astronauts would carry either the hand-held
maneuvering device or wear the LTVmade astronaut maneuvering unit, the
backpack.

Gemini 4, 8, 10, and 11 included among their missions
experimenting with the Hand-Held Maneuvering Unit. White walked in space
during Gemini 4. For reasons unrelated to the maneuvering unit,
the Gemini 8 extravehicular activity was canceled. Gemini 10
and 11 carried an improved maneuvering unit, one supplied nitrogen
through a hose within the umbilical cord. The hose connected the gun to
two tanks aboard the spacecraft. During a Gemini 10 docking exercise,
Michael Collins successfully recovered a package from a target vehicle.
In the process he lost hold of and drifted away from the target vehicle.
He used the hand-held unit to maneuver back to place. This was an unscheduled
use of the device; the scheduled use was canceled. Before using the maneuvering
aid outside Gemini 11, Richard F. Gordon managed to tether the spacecraft
and target vehicle together. Due to exhaustion from the physical effort
involved in such early extravehicular activities, the crew halted the extravehicular
experiment before using the Hand Held Maneuvering Unit. Evaluation of the
mission focused on the workload and body restraints rather than the maneuvering
unit.30

Gemini 9A provided the first opportunity to test the modular
or astronaut maneuvering unit. That was June 1966. Astronaut Eugene A.
Cernan experienced difficulty donning the maneuvering unit due to the problem
of maintaining body position in zero gravity and the necessity of holding
on to hand and foot bars. Outside the craft, he discovered that extravehicular
tasks required both more time and more effort than ground simulations.
Also, his visor fogged, reducing visibility the result of his exceeding
the design limits of the Extravehicular Life-Support System, the chest
pack. Due to these problems, particularly the reduced vision, the extravehicular
activity ended before any operational evaluation of the maneuvering unit.
As a result of Gemini 9A, NASA changed the foot restraints on future
Gemini craft, added underwater simulation of the weightless environment
(this proved more effective than the brief periods of zero-gravity training
aboard the KC-135 aircraft), and supplied astronauts an anti-fog solution
to be applied to their visors before extravehicular activity. Such changes
in equipment and technique were made after each mission.31
The unused maneuvering unit required no modification.



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 311

Gemini 12 again featured the backpack modular maneuvering unit
in a plan that changed before flight. The unit was not even carried aboard
the spacecraft. Both astronauts, James A. Lovell and Edwin E. Aldrin, completed
extravehicular activities, aided by body restraints like waist tethers,
foot restraints, and portable handholds that had been added to this mission
based on previously identified need. These spacecraft-based aids to extravehicular
activity had taken precedence over the rocket-powered units-foreshadowing
the fate of the award-winning MMU.

The development, delivery, and integration of flight-ready maneuvering
units, not the operation of the units in space, proved to be main accomplishments
of the Gemini maneuvering programs.32
The hand-held unit was tested in space twice, briefly during Gemini
4 and 10. Problems with the spacecraft or the environmental
control systems occurred before the unit could be evaluated on other Gemini
flights. Similarly, an environmental control problem caused the cancellation
of the backpack experiment planned for Gemini 9A, and plans to test
it on the Gemini 12 mission were dropped before launch. No operational
test of the backpack unit was achieved during Project Gemini.

Before Project Gemini drew to a close in 1966, the Manned Spacecraft
Center awarded Rocket Research Corporation a contract to improve the Gemini
hand-held maneuvering unit; improvements included using hydrazine as the
propellant.33 Under Air Force contracts,
both LTV and Bell Aerosystems designed maneuvering units that could be
operated remotely or controlled by an astronaut wearing the unit.34
LTV's Remote Maneuvering Unit (RMU) could be worn on the back, whereas
Bell's Dual-Purpose Maneuvering Unit (DMU) was to be mounted in front of
the astronaut. Both units incorporated television cameras, stabilization
and control systems, electronic sensors, and communications equipment.
As unmanned units, they were intended for work too hazardous for a man,
such as inspecting an enemy satellite, as well as for rescue, repair, and
transfer operations. As manned units, they could be used during any extravehicular
activity.

NASA explored these and other maneuvering technologies. Some units were
considered for later Gemini missions, for the Apollo Applications Program
(AAP), for even Project Apollo, and for Skylab. Project Apollo accumulated
a total of 170 hours of extravehicular activity, mostly lunar surface time-walking
on the Moon or riding the lunar rover. None of the Apollo extravehicular
time involved the use of a maneuvering unit in free or tethered flight;
none was needed to fulfill Apollo's lunar missions. Yet Apollo and the
other early space programs provided opportunity not only to experiment
with maneuvering units, but also for many companies and individuals to
acquire space contracts and experience. Ed Whitsett, then with the Air
Force, for example, worked on several extravehicular activity support devices
for Apollo, including a hand-held, self-propulsion gun used in the low-gravity
environment of the Moon's surface. One group of space scientists had recommended
a "Lunar Flying Unit (LFU)" to increase lunar surface mobility and thereby
to increase the scientific return from lunar missions;35
the lunar rover, a wheeled vehicle, provided the increased surface mobility
on the Moon. Whitsett also worked on the AAP that became Skylab.

Initially part of the AAP, Skylab experiment T020 consisted of a foot-controlled
maneuvering unit (FCMU). Donald E. Hewes of NASA's Langley Research Center
was the principal investigator; he built on the earlier work of John D.
Bird, also of Langley. Some engineers at



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312 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

the Manned Spacecraft Center opposed the Langley foot-control experiment
and expressed "skepticism about the worth of the experiment's objective
and concern over the monetary and manpower expenditures connected with
its implementation."36 The program
continued. The main purpose of foot control was to free the astronaut's
hands. The experimental unit used a cold gas, high-pressure nitrogen, supplied
from a tank mount on the astronaut's back. Called "Jet shoes" because the
thrusters were mounted under the astronaut's feet, four thrusters per foot,
the maneuvering unit was pedal operated. Astronauts tested the jet shoes
inside Skylab's Orbital Workshop, a "shirt-sleeve" environment as astronauts
no longer needed to wear space suits inside the protective environment
of the spacecraft. They also conducted a space suit test of the maneuvering
unit since the ultimate goal was a unit to be used outside of a spacecraft
and thus by a suited astronaut.

Building upon the Gemini example and experience, Skylab's experiment
M509 included both a backpack maneuvering unit called the Automatically
Stabilized Maneuvering Unit (ASMU) and an improved hand-held maneuvering
unit. Both units were propelled by high-pressure nitrogen drawn from a
tank on the astronaut's back. In fact, both units could be used at the
same time. These units were tested inside Skylab, which contained almost
12,000 cubic feet of living space. Skylab allowed the comparative testing
of the jet shoes, the improved hand-held unit, and the backpack. On the
three Skylab missions five astronauts flew the M509 experimental units
on eleven sorties that totaled fourteen hours of orbital flight testing
all inside Skylab, some in shirt sleeves and some in space suits. The
backpack proved superior in flight qualifies and precision control. As
an experimental unit designed for testing inside Skylab, the backpack lacked
the system redundancy deemed necessary for safety outside a spacecraft,
and it required a second person to assist the astronaut into the unit.
Under NASA contract, the Martin Marietta company built and supported the
M509 backpack maneuvering unit; North American Rockwell had also been a
contender for the contract.

On assignments to the Manned Spacecraft Center and the Air Force Space
and Missile Systems Organization (SAMSO), Major Whitsett headed the M509
experimental program. NASA admired his ability to balance experiment objectives,
hardware development cost, and schedule constraints, and his efforts toward
consolidating Air Force and NASA research into a single national program,
important during that period of limited funding for space programs. Captain
Bruce McCandless of the Navy and David C. Schultz of the Manned Spacecraft
Center (renamed the Johnson Space Center in 1973) were co-investigators
for the M509 experiment, generically labeled "astronaut maneuvering equipment."
Whitsett later summarized the backpack program: "An experimental MMU tested
onboard the NASA Skylab Program orbital workshop established key piloting
characteristics and capability base for future MMU systems" and contributed
to the "operational MMU" used on



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 313

the Space Shuttle.37 Only ten years
after Skylab, NASA called the Skylab backpack unit the "ancestor" of the
Space Shuttle MMU.38 In turn, Gemini's
modular maneuvering unit was the "ancestor" of Skylab's automatically stabilized
maneuvering unit.

Manned Maneuvering Unit

Engineer and historian Walter G. Vincenti wrote in What Engineers
Know and How They Know It, "Engineering knowledge reflects the fact
that design does not take place for its own sake and in isolation. Artifactual
design is a social activity directed at a practical set of goals intended
to serve human beings in some direct way. As such, it is intimately bound
up with economic, military, social, personal, and environmental needs and
constraints."39 That is true not only
of the experimental MMUmodular maneuvering unit of Project Gemini, but
also of the operational MMUmanned maneuvering unit of the Space Shuttle
program. Spacecraft, like maneuvering technology, made the transition from
experimental (Gemini and Skylab) or exploratory (Apollo) to operational
(Space Shuttle). The reusable and operational nature of the Space Shuttle
influenced the design and fabrication of the Shuttle's MMU, as did the
experimental experience with earlier maneuvering technology. In the post-Apollo
environment of reduced NASA budgets, both the Space Shuttle, like a commercial
truck, and the MMU, like a worker's tool, were expected to pay for themselves.40 
Neither would.

NASA, Rockwell International, Martin Marietta, Thiokol, "and the entire
government/industrial team that improved the concept of manned reusable
spacecraft" won the Collier Trophy for 1981. 41
That was the year that the Space Shuttle made its maiden flight (in April)
and made the first flight of a reused spacecraft (in November)both in
the orbiter vehicle named Columbia and designated OV-102. Then officially
called the Space Transportation System (STS), the Space Shuttle program
was in fact a small fleet of orbiter vehicles. Other space shuttles built
by the end of 1984 were Challenger (OV-099), Enterprise (OV-101),
and Discovery (OV-103); Atlantis (OV-104) was under construction.42
MMUs were used on two flights of Challenger and one of Discovery,
all three flights in 1984.



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314 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

With the Space Shuttle, NASA introduced a new type of spacecraft, but
the shuttle's MMU represented an evolutionary development of maneuvering
technology, based heavily upon the M509 backpack tested on Skylab and the
earlier Gemini backpack. What was the award-winning manned maneuvering
unit? Whitsett defined it as "a self-contained propulsive backpack" and
"a miniature spacecraft which an astronaut straps on for space walking."43
Shuttle astronaut Joseph P. Allen called it "this spaceship's special dinghy,"
which "resembles a backpack with armrests, or some kind of overstuffed
rocket chair. "44 In a brochure for
the "payload community," NASA advertised the MMU: "Since the Manned Maneuvering
Unit has a six-degree-of-freedom control authority, an automatic attitude-hold
capability and electrical outlets for such ancillary equipment as power
tools, a portable light, cameras and instrument monitoring devices, the
unit is quite versatile and adaptable to many payload task requirements.
"45

Although approved for development in 1975, the shuttle maneuvering unit
remained in the design definition stage until funding became available
in 1979. Under preliminary design contract NAS9-14593, Martin Marietta
established the operational MMU design definition and developed subsystems
hardware.46 During that period Martin
Marietta also worked with Rockwell International on the MMU/shuttle interface
and with NASA on the MMU's interface with the astronaut's space suit and
life support system. Finally in 1979, NASA let the MMU fabrication contract,
number NAS9-17018, to Martin Marietta. Preliminary designs and specifications
were updated, technical changes were adopted, parts were procured, verification
requirements were defined, components and then the MMUs were assembled,
the units were qualified, mission profiles were drawn, training requirements
were defined, and finally flight hardware was delivered. The astronaut
representative for the MMU was Bruce McCandless, who as a member of the
astronauts corps had served a CapCom or capsule communicator transmitting
voice messages to Apollo spacecraft 10, 11, and 14, and who
had participated in Skylab Experiment M509. Whitsett, who had moved from
the Air Force to NASA, also brought experience with Apollo and Skylab.
He worked in the Crew Systems Division of the Johnson Space Center. Walter
W. Bollendonk managed the Martin Marietta program that built the manned
maneuvering units. Martin Marietta delivered the two operational units
to the Johnson Space Center in September 1983. Each MMU was valued at $10
million.47

New features of the shuttle maneuvering units included fingertip control
(rather than the tiring hand-grip control of the Skylab unit), and storage
in the cargo bay. Once in the MMU, an astronaut controlled position (forward/backward,
left/right, up/down) with the left hand and rotation with the right hand.
Tolerance of extreme temperatures was achieved in part by painting the
MMU white to keep the temperature below 150° Fahrenheit and by using
electrical heaters to keep components above their minimum temperature limits.
An astronaut could recharge the propulsion system at the shuttle's cargo
bay from airborne support equipment called the flight support station;
this support station also provided storage of the MMU when not in use.

The shuttle MMU system had redundancy. Two silver-zinc batteries provided
electricity. The propellant was gaseous nitrogen, GN2, stored in two tanks.
The propulsion systems



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 315

were arranged in two parallel sets, each set operating twelve thrusters;
usually both sets twenty-four thrusters were operational at once, but
the MMU was capable of full operations on only one set. Furthermore, the
Space Shuttle normally carried two MMUs, the second in case of emergency,
and the shuttle could be maneuvered into position to rescue an astronaut
should an MMU fail. In conjunction with the propulsion system, three gyros
one each for the yaw, pitch, and roll axes provided an attitude hold
capability. Constructed mostly of aluminum, an MMU weighed 340 poundsmassive,
though weightless in space. The operating time was six hours, and the operating
range, 450 feet from the Space Shuttle.

Martin Marietta trained astronauts to fly the MMU at its Space Operations
Simulator in Denver. A magazine editor who flew the MMU in that simulator
reported, "The minimal training and precision flying features were demonstrated
by my ability, with only a few minutes practice, to maneuver the unit safely
in close proximity to fixed objects."48
Astronauts received eighteen hours, not a few minutes, of training in the
simulator. The two main features in the simulator were a six-degree-of-freedom
moving-base carriage and a large-screen television display. NASA of course
provided the standard astronaut and extravehicular-activity training.

NASA carried two MMUs (serial numbers 002 and 003) aboard three Space
Shuttle flights in 1984: 41-B in February, 41-C in April, and 51-A in November.
Six astronauts Bruce McCandless II, Robert L. Stewart, George D. Nelson,
James D. van Hoften, Joseph P. Allen, and Dale A. Gardner flew the MMU.
These mission specialists flew the MMU on a total of nine sorties for a
total of ten hours and 22 minutes. Each astronaut donned and doffed the
maneuvering unit in the open cargo bay.

Before exiting the pressurized spacecraft, the astronaut donned an extravehicular
mobility unit (EMU) that consisted of the spacesuit and a portable life
support system. A NASA brochure explained, "The Extravehicular Mobility
Unit consists of a self-contained (no umbilicals) life support system and
an anthropomorphic pressure garment with thermal and micrometeoroid protection."49
The Hamilton Standard division of United Technologies Corporation, aided
by subcontractor ILC (formerly International Latex Corporation), produced
the
space suit. The suit consisted of modular parts; the torso, for example,
available in five sizes. Gloves were still custom-made for a particular
astronaut. The life support system, also supplied by Hamilton Standard,
was in a backpack that could attach to the MMU, which became in effect
an outer backpack. The EMU was essential to extravehicular activity, but
the MMU was one of several extravehicular aids available for a mission;
the remote manipulator system, tools, tethers and other restraints, and
portable workstations were the other aids. The astronaut and the extravehicular
mobility unit, and any tools needed for an assignment, comprised the MMU's
payload.
The shuttle manned maneuvering unit was a tool with a specific mission.
That mission was the recovery of satellites. The astronaut using the manned
maneuvering unit was a "serviceman" who serviced satellites. NASA offered
this recovery service to civilian agencies, the military services, and
commercial customers, all of which had satellites in orbit. To retrieve
a satellite meant reaching the satellite, grabbing it, stopping its rotation,
and moving it into the Space Shuttle's cargo bay. Although weightless in
space, the satellite still had inertia, against which the maneuvering unit
needed power to stop the rotation. Retrieving the Solar Maximum (Solar
Max)satellite was to be the first operational assignment of the MMU.



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316 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

Launched in 1980, the Solar Max solar observatory had experienced
electrical failures within six months, and NASA planned to repair the satellite
in the cargo bay of a Space Shuttle.

Other missions were considered for the MMU, including inspection and
repair of thermal tiles on shuttle orbiters, handling and transferring
payload, construction of space structures (like a Space Station), and rescuing
loose material or personnel floating in space. Martin Marietta promoted
the MMU as support of shuttle extravehicular activities like inspection
of the shuttle orbiter and like deploying, retrieving, and servicing payloads.
But satellite retrieval was the primary mission in plans and in practice.50

The first use of the MMU occurred on the tenth flight of a Space Shuttle,
mission 41-B, during which the MMU was flown on demonstration flights.
These MMU flights demonstrated capabilities deemed appropriate for use
in the planned retrieval of the Solar Max satellite on a later shuttle
mission. Courtesy of the manned maneuvering unit, McCandless, then a Navy
captain, became the first person to fly free, untethered in space; the
date was February 7, 1984. While orbiting around the Earth at a speed of
17,500 miles per hour, McCandless floated from the cargo bay into outer
space, 150 nautical miles above Earth, an experience he described as "a
heck of a big leap."51 Mission specialist
Robert L. Stewart, an Army lieutenant colonel, also flew the MMU on shuttle
mission 41-B. While flying the MMU, these men were in a journalistic phrase
of the time "human satellites."52
They checked out the equipment, maneuvered within the cargo bay, flew away
from and back to the orbiter, performed docking exercises, recharged the
MMU nitrogen tanks, and collected engineering data. The MMU, according
to Martin Marietta's post mission report, "performed as expected and no
anomalies were reported."53

The main purpose of flight 41-B, the fourth using the orbiter Challenger,
was the deployment of two commercial communication satellites, Western
Union's Westar VI and the Indonesian Palapa-B2. These satellites
were released, but failed to reach geostationary orbit due to problems
with the commercial upper-stage technology designed to lift the satellites
from the low orbit of the Space Shuttle to the higher geosynchronous orbit
justifying a later rescue mission using MMUs. Also, in scheduled extravehicular
activity during flight 41-B, astronauts demonstrated the shuttle orbiter's
manipulator arm. One man at a time rode on the manipulator foot restraint
work platform (a Grumman product) attached to the remote manipulator arm
(a Spar Aerospace product), while mission specialist Ronald E. McNair inside
the spacecraft controlled the movement of the arm. On this mission the
arm developed a little problem with its wrist joint yaw motion capability,
but on a later mission the manipulator arm would achieve a satellite rescue
after MMU-retrieval attempts failed.

In April NASA launched the eleventh Space Shuttle mission, 41-C, which
again used the orbiter Challenger. In response to the previous mission,
Martin Marietta had made only two minor changes to the MMU hardware: new,
adjustable lap belts installed on the MMU itself and a modification of
the flight support station in the cargo bay. The main purpose of the 41-C
mission was repairing Solar Max, and the main purpose of the MMU
on the mission was retrieving the satellite. If successful, NASA predicted,
this "Shuttle mission could launch an era of satellites with replaceable
parts," satellites repairable in space.54



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 317

Again in the post-mission report, Martin Marietta concluded that its
"hardware performed as expected with no anomalies" for both mission specialists,
George Nelson and James D. van Hoften.55
But the astronauts using the MMU failed to retrieve the satellite.

Wearing the MMU, Nelson performed the equipment checkout flight, moved
150 feet to Solar Max, matched rates with the satellite, and attempted
to dock three times. He was unable to stabilize the satellite, to stop
its spinning. The failure was later attributed not to the MMU but to the
trunnion pin attachment device mounted on the arms of Nelson's MMU, in
front of him; this device was supposed to lock onto a trunnion on the satellite.
Once Nelson had docked, he was to use the MMU thrusters to halt the satellite's
rotation. With the satellite stabilized, the manipulator arm would grasp
the satellite and move it into the cargo bay for repair. The MMU rather
than the manipulator arm was to capture Solar Max in order to avoid
the possibility of the rotating satellite snapping the manipulator arm.
But Nelson in the MMU failed to stabilize the satellite, so NASA personnel
in space and on Earth improvised.

Engineers at NASA's Goddard Space Flight Center in Maryland managed
through radio commands to exert some control over the spinning satellite
and by reprogramming the satellite's computer to slow the spin. Shuttle
commander Robert L. Crippen flew the orbiter for a precision rendezvous
with the satellite. Then astronaut Terry J. Hart operated the manipulator
arm to capture the slowly rotating satellite. As an extravehicular activity
in the open cargo bay, Nelson and van Hoften repaired Solar Max,
and the Challenger crew released the repaired satellite back into
orbit. The mission, though not the MMU's role in it, was a success. "Hart's
small grab," not Nelson's free flight, quickly became the symbol of the
utility of human space flight.56

Despite the docking problem experienced during mission 41-C and the
use of the manipulator arm to achieve capture, NASA personnel still believed
that the MMU could "provide an extra measure of control in the retrieval
process" of future satellite recovery operations.57
NASA scheduled the MMU for its next recovery mission for November. Mission
51-A, using the orbiter Discovery, was to rescue the Westar
and Palapa satellites that mission 41-B had deployed in February.
This time mission specialist Joseph Allen in MMU serial number three captured
the Palopa satellite, and Dale A. Gardner in MMU serial number two
recovered the Westar satellite. They used a new, improved capture
device, a stinger, in the successful recoveries. The capture mechanism
worked, and the MMU's automatic attitude hold function stopped the satellite
rotation. Again, the MMUs "performed as expected with no anomalies."58
And again, the recovery operations did not proceed as planned; the retrieval
equipment did not fit one of the satellites, and the men had to hold the
satellites and manually move them into the payload instead of using the
manipulator arm. Despite the problems, Allen concluded, "the capture had
been far easier than rodeo calf-roping."59
Both satellites were secured aboard the Discovery and returned to
earth for refurbishment and resale by insurance companies that had acquired
the salvage rights.60



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318 "MORE FAVORED THAN THE BIRDS:" THE MANNED MANEUVERING UNIT IN SPACE

On three missions in 1984, the Manned Maneuvering Unit performed as
expected and with precision and versatility. Humans could safely maneuver
in outer space free of both spacecraft and tether. In recognition of the
development of the MMU and the NASA-industry satellite rescue team, the
National Aeronautic Association awarded the Robert J. Collier Trophy for
1984 to NASA and Martin Marietta, with special recognition of astronaut
Bruce McCandless II, NASA's Charles E. Whitsett, Jr., and Martin Marietta's
Walter W. Bollendonk.

Conclusion

The MMU was only one piece of space news in 1984. President Ronald Reagan
had opened the year with a State of the Union address reminiscent in part
of John F. Kennedy's 1961 "goal, before this decade is out, of landing
a man on the moon."61 Reagan directed
"NASA to develop a permanently manned Space Station-and to do it within
a decade."62 The Air Force and Navy
claimed no military requirement for a Space Station, which was seen as
competition for funds the Department of Defense sought for military space
operations. The Defense Advanced Research Projects Agency, for example,
was studying a manned space cruiser, a light spacecraft in contrast to
the heavy-cargo Space Shuttle. General James V Hartinger, Commander of
the Air Force Space Command, claimed the Soviets had "the world's only
space weapon," an orbital anti-satellite system that threatened the low
orbiting satellites of the United States.63
This country needed, according to Hartinger, "to protect our assets in
space." Regarding the arms race in space, a defense contractor declared
that "the Soviets have taken the high ground on the technology, and we're
left with the high ground on the debate."64
Reagan's Strategic Defense Initiative, including controversial laser systems,
addressed these military concerns.

In 1984 Congress appropriated funds for both the Strategic Defense Initiative
and the Space Station, and the government's civilian and military agencies
continued their routine cooperation in space matters. The Air Force, for
example, had provided contingency support for Space Shuttle flights since
the beginning, and it increased that contingency support in 1984. Furthermore,
in August, the United States adopted a new National Space Strategy that
delineated roles for NASA and the Department of Defense.65
The civil-military-commercial infrastructure adapted to the changing space
environment, which remained in part a political environment shaped by the
international competition known as the Cold War. The Strategic Arms Limitation
Talks (SALT) and Strategic Arms Reduction Talks (START), for example, had
increased the importance of reconnaissance satellites, which were increasingly
needed for verifying compliance with disarmament agreements. NASA and its
hundreds of contractors began development of the civilian Space Station.
In this context Whitsett forecasted ample roles for the manned maneuvering
unit in the Space Station program: assembly, transportation, inspection,
contingency, and rescue.66



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FROM ENGINEERING SCIENCE TO BIG SCIENCE 319

Yet the MMU has not been used since 1984. There are several reasons
for this. First, most extravehicular activities were effective without
use of the MMU. Tethers, safety grips, hand bars, and other restraints
allowed astronauts to work in the open cargo bay. Furthermore, the maneuverability
of the Space Shuttle itself and the utility of the shuttle's robotic manipulator
arm had proved capable of rescuing satellites-the primary function for
which the MMU had been designed. The orbiter could be piloted with such
accuracy that on mission 41-B, for example, commander Vance D. Brand piloted
the Challenger into position so that McCandless on the manipulator
arm could grab a foot restraint that had broken loose and floated away
from the orbiter. On flight 41-C, the MMU failed to achieve mechanical
mating to the Solar Max satellite, but the orbiter and manipulator
arm recovered the satellite. On the Discovery mission, 51-A, commander
Henry W. Hartsfield operated the remote manipulator arm to knock ice off
a waste-water port, the ice being a reentry hazard. This sort of contingency
was a potential MMU activity, but the manipulator arm solved the problem.

Another reason for lack of use of the MMU was the Challenger
accident. In January 1986 the Challenger exploded 73 seconds after
launch. The crew of seven, the spacecraft, and the payload were lost. That
accident initially prompted a suspension of space flights that lasted into
September 1988. The accident and resulting investigations also prompted
new safety rules that would require expensive changes to the existing MMU,
changes pending both a customer and a mission for the MMU. Still another
reason for not using the MMU has been the lack of a new user with adequate
funding and appropriate mission. Finally, since the Space Station is still
under discussion, the Space Shuttle remains the main space human flight
program of the United States. The MMU is not necessary to its operations.

> Thus today, as Robert Frost observed in 1959:





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