"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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|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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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.
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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"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.
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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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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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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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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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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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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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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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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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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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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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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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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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
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
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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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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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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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.
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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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: