Critical Components of the Capsule

Basic as the boosters were for successful manned space flight, they were not the only machines that had to be certified for safety before a man's life could be entrusted to them. The capsule with all its systems and subsystems, designed to operate automatically on unmanned test flights at first, would also have to have reliable provisions for operation with a normal, or even with an incapacitated or unconscious, man aboard. Man-rating the spacecraft, therefore, involved the paradoxical process of dehumanizing it first for rehumanizing later.

When the seven Mercury astronauts first visited the McDonnell Aircraft Corporation laboratories and factory, for three days in May 1959, each was handed an indoctrination manual and given opportunities to inspect the mockup capsule and to review the requests for alterations made by the Mockup Review Board in March. Immediately they expressed some uneasiness about the poor visibility afforded by the two remotely placed portholes and about the difficulty of climbing out the bottleneck top of the capsule.48 So, based on these and numerous other criticisms expressed by the men for whom these machines were being built, redesign studies were begun.

Just as Maxime Faget was the chief NACA-NASA designer of the capsule configuration and mission concept, so John F. Yardley, his closest counterpart in the McDonnell organization, was the chief developer of the Mercury capsule. Neither Faget nor Yardley was the nominal leader of the vast team within which each worked, but both animated the technical talents of their colleagues, from design through the final development stages of the Mercury hardware. John Yardley held a master's degree in applied mechanics, had worked for McDonnell since 1946 as a stress analyst, strength engineer, and project leader, and he was exceptionally talented in his capacity for work and for synthesizing technical knowledge. By telephone, teletype, and face to face, Faget and Yardley consulted each other about the multitude of detailed design and development decisions involved in production throughout 1959. But their bilateral agreements were restricted to details. Larger decisions regarding the development of systems or interaction between subsystems were reserved for the 17 different working groups in STG and the 10 or so at McDonnell. James Chamberlin instigated this capsule coordination system and gradually replaced Faget in relations with Yardley during the next year.49

In 1959 the McDonnell Aircraft Corporation became the 100th-largest industrial company in the United States, employing approximately 24,000 people to produce goods (primarily the F4H-1 Phantom twin-jet fighter for the Navy) and services (mainly computer time, electronic equipment, and systems engineering) [191] valued at $436 million. Within this corporate context, the contract with NASA for about $20 million to manufacture 12 or more spacecraft, requiring only 300 or 400 workers and representing less than five percent of McDonnell's annual sales volume, appeared rather minuscule. The president of the corporation, J. S. McDonnell, in September 1959 wrote for his twentieth annual report to stockholders that "there is no need to stampede away from the aircraft business."50

When the prime contract for Mercury was awarded to McDonnell, the Corporation's vice-president for project management, David S. Lewis, assigned Logan T. MacMillan, a tall, tactful test pilot and mechanical engineer with a winning manner, to be companywide project manager with authority to mobilize the resources of the Corporation for the new venture. MacMillan, of the same age and rank as Faget, soon found it difficult to reconcile McDonnell's development and production phases with NASA's concurrent research and test phases. Time, cost, and quality control were interdependent, and now the astronauts and STG had called for major design changes in the window size and placement, the side entrance-exit hatch, the instrument panel, and switch accessibility. To his top management, MacMillan reported on July 18, 1959:

The Space Task Group is a rather loosely knit organization of former Research Engineers. The Coordination Office is an attempt to channel and control information and requirements against MAC more closely and is a good move. It is clear, however, regardless of whether or not it succeeds, the NASA philosophy of investigation and approval of the smallest technical details will continue, and request for changes will also continue. We will continue to handle this by being responsive to requests for studies and recommendations and to be as flexible as we possibly can to incorporate changes. It is imperative that we continue to improve our capability to make these studies promptly, submit change proposals to cover the increased work as soon as possible, and evaluate the effect of changes on delivery schedules rapidly.51
A month later MacMillan complained by teletype message directly to Paul E. Purser that coordination meetings were being held too frequently for effective action on items from preceding meetings. He suggested that later meetings be scheduled "for one month from time minutes are received at MAC." But the pace did not slow significantly; the finish line simply moved farther away.

MacMillan and Yardley, together with Edward M. Flesh and William Dubusker, two older, more experienced production engineers, supervised the bulk of the load for McDonnell in tooling up, making jigs and fixtures, and organizing their craftsmen and procedures for production. Kendall Perkins, McDonnell's vice-president for engineering, had deliberately assigned Yardley and Flesh, combining youthful enthusiasm and experienced caution, to start the manufacture - literally the handmaking - of the first spaceframe. The subsequent design and technical development at McDonnell was carried out under their direction.52

By July 1959, Dubusker, the tooling superintendent, had completed McDonnell's first surgically clean "white room" for the later manufacturing phases, had taken on the job of manufacturing manager for Mercury, [193] and had moved some 200 workmen onto the new production lines. Learning to fusion-weld titanium .010-inch thin in an encapsulated argon atmosphere was his first challenge and proudest accomplishment. But before the year was over, Dubusker had to contend with retooling for other unusual materials, with rising requirements for cleanliness, with stricter demands for machined tolerances, and with higher standards for quality control.

Flesh, the engineering manager, and Dubusker drew on all of McDonnell's experience with shingled-skin structures around jet afterburners for heat protection. Their machinists had previously worked with the patented metal, René 41, a nickel-base steel alloy purchasable only from General Electric, but arc-jet tests of the afterbody shingles on the outer shell of the capsule showed a need for some ingenious new fabricating techniques.53

While Yardley and Flesh concentrated on developing the most critical components for the Mercury capsule, two other McDonnell employees began to play significant roles in man-rating this machinery. The company was fortunate to have its own so-called "astronaut" in the person of Gilbert B. North, another test-pilot engineer but one with a unique relationship for the NASA contract. He was always being confused with his identical twin brother, Warren J. North, who served Silverstein and George M. Low in Washington as NASA Headquarters participant and monitor in astronaut training. Gilbert North served McDonnell as chief human guinea pig in the St. Louis ground tests. Warren and "Bert" North actively promoted the incorporation of test-pilot concerns in the Mercury program from two standpoints outside STG.

Most of the astronauts and test pilots, including the North twins, instinctively resented the "interference" of psychologists and psychiatrists in Project Mercury. Willing to wager their careers and perhaps their necks on the automatic systems of the capsule and booster, the pilots preferred to study the reliability of the machines and to assume themselves adaptable and self-reliant in any situation. They were thus unprepared to discover that psychologists would be among their strongest allies in gaining a more active role for man during Mercury missions. Throughout 1959, arguments over the necessity for the three-axis handcontroller, as opposed to the more traditional two-axis stick and one-axis pedal control system, demonstrated these pilots' confidence in themselves. Distrusting what they regarded as tender-minded psychology and psychiatry, the astronauts-in-training studied hard to become more tough-minded electromechanical engineers. And indeed their first complaints regarding spacecraft design resulted in changes adopted formally during September for later models of the capsule.54

John Yardley fortunately was not quite so tough-minded and recognized early an imbalance in detail design considerations. He insisted on having the cross-fertilization of parallel human engineering studies. McDonnell hired in February a "human engineering" expert, Edward R. Jones, to conduct studies of pilot tasks and to analyze the various ways in which the man might fail his machines. Proposing straightaway a thorough training regimen for the astronauts in procedures [194] simulators, Jones went on to program a statistical computation of the human-factors implications of failures in the automatic systems in the Mercury capsule. By November 1959, Yardley and Jones together had convinced a majority of McDonnell engineers that man should more often be in the automatic loop than out of it.55

Part of the problem faced by Jones, Yardley, and the astronauts in regard to human factors and the "inhuman" automatic control systems was the initial position taken by seven members of a study group at the Minneapolis-Honeywell Regulator Company in March 1959. Assigned to recommend approaches to mission analysis and cockpit layout, this group, led by John W. Senders, James Bailey, and Leif Arneson, had reported to McDonnell that since "this vehicle does not behave like an airplane . . . . There is no apparent need for a complex, highly integrated display configuration at a sacrifice of reliability."56 Jones studied the Minneapolis-Honeywell reports carefully and said they expressed a "wooden man" approach. Assuming pilot safety would be provided for, Jones believed more provisions should be made for the pilot to assure mission success. In August, Jones and a colleague, David T. Grober, wrote for Yardley a description of the quantifiable differences between flying this spacecraft and flying aircraft. They admitted: "Primary control is automatic. For vehicle operation, man has been added to the system as a redundant component who can assume a number of functions at his discretion dependent upon his diagnosis of the state of the system. Thus, manual control is secondary."57 But Jones and Grober pointed to at least eight ways in which automation for reliability could interact with the autonomy of the astronaut to vary the chances both for pilot safety and for mission success. They warned McDonnell's reliability engineers against assuming, as they had in their latest formal reliability program given STG, that the reliability of the astronaut is unity:

It has been assumed naively by those who are not familiar with the capsule that the operation of the systems will not be difficult because of the automatic programming of the normal mission and because of an assumed simplicity of the systems. However, preliminary analysis indicates that the operation of the capsule, considering the stringent mission requirements and the physiological environment, will be as difficult or probably more difficult than high performance aircraft. A vast number of different potential malfunctions may occur in the capsule's systems, and the isolation of these malfunctions can be extremely difficult. Mission reliability determinations assume the astronaut can detect and operate these systems without error.
Only three months later Jones read a paper before the American Rocket Society that, while not a reversal of primary and secondary control modes for the manned satellite, marked a symbolic shift from automation to monitored automatic flight. Man's function in space flight, argued Jones, should now be recognized as something more than secondary, if still less than primary:
[195] Serious discussions have advocated that man should be anesthetized or tranquillized or rendered passive in some other manner in order that he would not interfere with the operation of the vehicle . . . . As equipment becomes available, a more realistic approach evolves. It is now apparent with the Mercury capsule that man, beyond his scientific role, is an essential component who can add considerably to systems effectiveness when he is given adequate instruments, controls, and is trained. Thus an evolution has occurred . . . with increased emphasis now on the positive contribution the astronaut can make.58
Jones spoke, presumably, of the general attitudes prevailing around McDonnell. His fellow psychologist in STG, Robert B. Voas, supported his evaluation.

Nevertheless, until some Mercury missions were flown automatically to qualify the integration of all systems, man would not be allowed to fly one. Of all the critical systems in Mercury, therefore, the automatic controls, a part of which was the "autopilot," were most crucial for man-rating the capsule.

Guidance and control engineers in Project Mercury were often plagued by semantic confusions between the different electromechanical systems they designed and developed to stabilize, guide, control, or adjust relative motion. Their nomenclature helped confound confusion by the similarity of initials in official use to denote their orientation systems: ACS, ASCS, RCS, and RSCS all looked similar to men with other concerns, but some evolutionary reasons help explain the technical differences behind the initials. ACS, for Attitude Control System, applied specifically only to the Big Joe capsule, becoming a generic term in Mercury nomenclature after that launch in September 1959. In its place the redundant designation ASCS, for Attitude (or Automatic) Stabilization and Control System, grew up as a name for the autopilot, an airborne electronic computer that compared inputs of electronic sensory information with any deviation from preset reference points on gyroscopes or with the horizon. Outputs from the autopilot could then command small jets called thrusters to spew out small quantities of hot gas in order to maintain balance in space. These hydrogen peroxide jets, their fuel tanks, plumbing, and valves were called simply the RCS, or Reaction Control System.59 The last of this quartet of initials, RSCS, requires a more thorough explanation.

In August and September 1959, the stabilization controls and drag-braking drogue chute were proving troublesome, and everyone in STG knew this. Provisions for the astronaut, or "human black box," in the control loop complicated every facet of the system, and yet the pilot had little choice over its operation. Robert G. Chilton, Thomas V. Chambers, and other STG controls engineers reconsidered the several different ways in which the Mercury capsule was being designed to act by chemical reflexes with complete self-control.

From the very beginning of controls design for a manned ballistic satellite, Honeywell had suggested using the same digital electronic system, for simplicity's sake, to control all Mercury flights. But this "simple" equipment was unnecessarily [196] complicated for the first flight tests and could cause some unnecessary problems. Also, a direct mechanical linkage to a completely independent, completely redundant reaction control system had been provided to ensure that the pilot could adjust manually and proportionally his capsule's attitude in orbit. But this overweight and oversize manual redundancy, fundamental to the Mercury objective of testing man's capability as a pilot in space, was an exceedingly uneconomical part of the original design.

McDonnell and Honeywell controls engineers moved ahead with their development of the digital system while Chilton wrestled with the problem of raising the efficiency of the thirsty manual proportional thrusters. A wired jumper from the handcontroller to the jets for the ASCS should enable the astronaut to tilt or rotate his craft in its trajectory by electrically switching on and off the tiny solenoid valves that supplied hydrogen peroxide gas to the automatic thruster combustion chambers. Because this "fly-by-wire" system completely circumvented the autopilot, inserting the astronaut's senses and brain in its stead, it was not automatic. Rather, it operated semi-automatically; it would allow the pilot to aid or interfere with the automatic adjustment of rotation around his pitch, roll, and yaw axes. Thus in the autumn of 1959 the automatic attitude control system was already compromised by the addition of the semi-automatic fly-by-wire feature.

But this redundancy still seemed inadequate for mission success. Both McDonnell and STG controls engineers proposed various approaches to other attitude control systems for the Mercury capsule in the spring and summer, but Logan MacMillan resisted all such suggestions, awaiting NASA's formulation of a definite policy for judging the urgency of contract change proposals. Every change would invite inevitable delays, and the long lead time for a new alternate control system (an AASCS!) made MacMillan, Yardley, and Flesh very skeptical of that approach.60

The fresh insight of one of the Canadians in STG's flight controls section, Richard R. Carley, helped Chilton to see the need for a second completely independent rate-command orientation system. Together they wrote a compromise proposal early in July that served as the midwife for a "rate damping" system for stabilization control:

There is a natural reluctance to relinquish the mechanical linkage to the solenoid valves but the redundant fly-by-wire systems offer mechanical simplification with regard to plumbing and valving hydrogen peroxide so the overall reliability may not change appreciably. In fact, considering the controlability of the capsule as a factor in mission reliability, a net gain should result. Simulation tests indicate that manual control of the capsule attitude during retrograde firing will be a difficult task requiring much practice on the part of the pilot. By changing the command function from acceleration to rate, the task complexity will be greatly reduced and the developmental effort on display and controller characteristics can be reduced accordingly.61
[197] Out of interminable meetings and proliferating technical committees, a compromise did finally emerge. Chilton's group, together with J. W. Twombly of McDonnell, worked out the design for a semi-automatic rate augmentation system. By connecting three more wires from the handcontroller to the three pairs of solenoid valves guarding the fuel flow to the manual reaction jets, the designers built a bench version of a rate-command control system that utilized the small rate gyros formerly supplying the references only for cockpit instruments. For the production model, rate command fuel would be taken only from the manual supply tank. By the end of October, Chilton's group and Minneapolis-Honeywell had completed preliminary designs of this rate orientation system, now officially sanctioned as contract change No. 61 and called the "RSCS." But the difficult electrical circuit for its independent rate logic system was only in the breadboard stage: wires had been stretched over the two-dimensional drawings as a preliminary test of the circuit designs.

The manual proportional method of slewing the capsule around required an extravagant use of fuel, but the rate mode relegated the manual to a last-ditch method of attitude control. Now with "rate command," essentially another fly-by-wire system superimposed on the manual reaction controls, the astronaut might control precisely his movements in pitch, yaw, and roll by small spurts of gas that would tip him up or down, right or left, and over on one side or the other. The exact attitude of the capsule at the critical time of retrograde firing could be held by this method, and the slow-roll stabilization of the capsule during reentry also could be accomplished by this system. Thus the quest for reliability led to four different methods of orienting the capsule by the end of 1959. Making both the automatic mode (through fly-by-wire provisions) and the manual mode (through the rate command, or RSCS) redundantly operable gave the astronaut three out of four options.

McDonnell and STG already were working with nine major subcontractors and 667 third-tier vendors, and the effort to man-rate all their products and all these subsystems - indeed each part from tiny diodes to the pressure vessel - required thawing out and refreezing the specification control drawings several times. When at the beginning of October NASA approved the funds for installation of an explosive side-egress hatch, a trapezoidal observation window, and another stabilization and control system, McDonnell engineers had already undertaken these and consequent redesign requirements. This independent advance action was evidence of a more advanced approach to the need for concurrent development and production.62

To save weight without sacrificing reliability, the electronic specialists - like all other Mercury design engineers - looked for microminiaturized, solid-state components. But they found less than they hoped. Miniature parts were evolving rapidly into microminiaturized parts, but the latter did not have good reliability records yet. Collins Radio Company, for example, holding the subcontract for [198] capsule communications equipment,emphasized the conservative use of miniaturized but not superminiaturized components to achieve greater reliability.63 Since the beginning of the development program the target of an effective capsule launch weight of 2,700 pounds had been overshot continuously, primarily because of slight but cumulative increments in electrical circuitry weights. Vendors consistently seemed to underestimate the weights of the parts they supplied. At the beginning of October the effective capsule weight was estimated at 2859 pounds. This seemed likely to grow to 3,000 pounds unless firm action was taken. A special coordination meeting in St. Louis at the beginning of October established a weight-reduction diet for the capsule development program and admonished NASA "all along the line to decide how much weight reduction should be sought and what items of capsule equipment should be sacrificed in order to achieve the desired reduction."64

At the time STG was considering the RSCS, it was also thinking of eliminating the 17.5-pound drogue parachute in the interest of weightsaving. The "fist-ribbon" drogue stabilizer, six feet in diameter and composed of concentric and radial strips of nylon, was being tested at Edwards Air Force Base and at the El Centro Naval Parachute Test Facility, at subsonic and transonic speeds and at altitudes down from 70,000 feet over the Salton Sea. One of the first canopies, released at a speed of mach 1.08 from an F-104 jet fighter at an altitude above 10 miles, plummeted into denser air whipping, fluttering, and spinning so badly that it disintegrated after a minute of this punishment. This test had put a special premium on development of the rate stabilization control system.

The recent decision to substitute a ring-sail for the extended-skirt main landing parachute made Gilruth fear that there might not be enough experience with big parachutes to determine whether they had similar bad characteristics. Gilruth and Donlan were so unsettled by the chute tests in general that they appealed to Washington for an expansion of applied research programs aimed at the development of more reliable parachute systems:

It is apparent that the large load cargo type of parachute is far from as reliable as the personnel parachute that most people are familiar with. Part of this lack of reliability is due to unknown scale effects, perhaps. However, it is known that a great deal of this loss of reliability is due to the various fixes that are employed on large parachutes to attenuate the opening shock. Such fixes as extended skirts, slots, reefing, and other devices are designed to cause a parachute to open more slowly. Therefore, it is not surprising that this tendency to open slower is also accompanied by a tendency not to open at all.65
Continued tests of the main parachute revealed few additional problems, but the drogue chute tests were getting worse. By the end of September the problem of drogue behavior at relatively high altitudes and barely supersonic speeds was so critical that the director of Langley thought it might be "easier to avoid than to solve."66 All sorts of alternatives, including a flexible inflatable-wing glider proposed by Francis M. Rogallo of Langley,a string of discs trailing like a Chinese [199] kite, and simple spherical balloons, were proposed as possible means of avoiding the instability of porous parachute canopies at high altitudes, where the air to inflate them is so rare.

Toward the end of 1959 still another lesson learned from studies of the aerodynamic stability of the capsule in the rarefied upper atmosphere added a slight refinement to the Mercury configuration. To break a possible "freeze" if the stable capsule should reenter the atmosphere small end forward, a spring-loaded destabilizing flap was installed under the escape pylon. Donlan and Purser asked George Low to explain around Washington why this "mousetrap" destabilizing flap was added to the antenna canister and why this innovation would require further wind tunnel tests:

The Mercury exit configuration ( antenna canister forward without escape tower) has been shown to be statically stable at mach numbers greater than four. This stability is undesirable because of the possibility of the capsule reentering the atmosphere antenna canister forward. Tunnel tests at a mach number of six have indicated that a destabilizing flap prevents this undesirable stability region. It is therefore necessary to know the effect of this destabilizing flap at subsonic and supersonic speeds.67

Continued poor performance of the fist-ribbon drogue convinced Faget, Chamberlin, and Yardley by the end of 1959 that the drogue chute should be eliminated altogether, but Gilruth and Purser, among others, saw as yet no cheaper insurance and no more workable alternative.68 The mousetrap destabilization flap and the rate stabilization system would help to fill only the mid-portion of the gap in the reentry flight profile. It was still a long way down from 100,000 to 10,000 feet above sea level - roughly 17 miles as a rock might drop. But by this time, the big questions concerning the first part of the reentry profile had been answered by the Big Joe flight.

48 Minutes, "Mock-Up Review," 12 through 14 May, 1959, with enclosure addressed to C. H. Zimmerman and Low, June 23, 1959.

49 Faget interviews; John F. Yardley, interview, St. Louis, Aug. 31, 1964; and MAC "Biographical Information" on Yardley, June 10, 1964. Until the redesignation of STG as MSC on Nov. 1, 1961, and the reorganization of MSC into the Mercury, Gemini, and Apollo Project Offices on Jan. 15, 1962, systems engineering in STG was shared by the Flight Systems Division and the Engineering Division under Faget and James A. Chamberlin, respectively. See Grimwood, Mercury Chronology, 219-220.

50 McDonnell Aircraft Corporation, "Twentieth Annual Report," June 30, 1959, foreword. Cf. "McDonnell Aircraft Corporation, Nineteenth Annual Report, 1958." "Achievements, 1939-1956," "Orientation Manual, 1960-61," 7, and "McDonnell: The First Twenty-Five Years, 1939-1964," 18-28, brochures, McDonnell Aircraft Corp.

51 Memo, Logan T. MacMillan to D. S. Lewis, "Project Mercury Daily Report, 18 July 1959 - Coordination Committee Results," McDonnell Aircraft Corp. inter-office memo No. 344; memo, E. M. Flesh to E. Akeroyd, "Capsule Coordination Committee," McDonnell Aircraft Corp. inter-office memo No. 3606, July 2, 1959. See also message, MacMillan to STG, Sept. 16, 1959. Cf. MacMillan, interview, St. Louis, Aug. 31, 1964.

52 Kendall Perkins, interview, St. Louis, Aug. 31, 1964.

53 William Dubusker, interview, St. Louis, Sept. 1, 1964; Flesh, interview, St. Louis, Sept. 2, 1964. For a more detailed description of fabricating technique and fusion welding, see David S. Anderton, "How Mercury Capsule Design Evolved," Aviation Week, LXXIV (May 22, 1961).

54 Regarding the Slayton-Carpenter dispute over the best kind of pilot control system, see John Dille, ed., We Seven, by the Astronauts Themselves (New York, 1962), 15. Memo, D. P. Murray, MAC Manager of Contracts, to Project Mercury, Engineering and Contract Administration Division, "Mercury Capsule Contract NAS5-59, Contract Change Proposals Nos. 58-1, 61-2, 73 and 76," Sept. 23, 1959.

55 Edward R. Jones, interview, St. Louis, Sept. 2, 1964. Jones had earned his doctorate in experimental psychology from Washington University in St. Louis, in 1954, and since the first of the decade he had worked in flight safety research.

56 Minutes, "MAC Project Mercury - Human Factors; Phase A2, Mission Analysis and Preliminary Cockpit Layout," manuscript minutes of oral report by Minneapolis-Honeywell human factors group to McDonnell, March 2, 1959, 3.

57 Memo, Jones to Yardley, "Failure Analysis," with enclosure, David T. Grober and Jones, "Human Engineering Implications of Failures in the Mercury Capsule," Aug. 10, 1959. These two quotations are from pp. 2, 4, and 5.

58 Jones, "Man's Integration into the Mercury Capsule," paper, 14th annual meeting, American Rocket Soc., Washington, Nov. 16-19, 1959, 1, 2.

59 The input of sense data into the ASCS and its output of nervous commands suggests the classic cybernetic approach to understanding the Mercury attitude control system. Consider the machine as if it were an organism in which sensors (like small rate gyros, larger position gyros, and infrared sensitive horizon scanners) provide the brain (ASCS) with the data it needs to compute through its amplifier-calibrators and logic boards the actions required by the muscles (RCS motors) in order to maintain a certain position. Sense organs, a brain, and muscles are necessary black boxes to the performance of any self-regulating system, but Mercury design engineers seldom bothered at first to produce "glass boxes" for operating engineers to determine how to build, work, and improve them. For a helpful introduction to the intricacies of modern gyroscopes, accelerometers, and inertial guidance systems, see "Inertial Guidance Primer," pamphlet, Minneapolis-Honeywell Regulator Company, 1963.

60 Robert Chilton, interview, Houston, June 2, 1964; Paul F. Horsman, interview, Houston, Feb. 12, 1964; Thomas V. Chambers and Richard R. Carley, comments, Sept. 25, 1965. See also Horsman drafts., "Manned Spacecraft Stabilization and Control System," for Mercury Technical History, June 19, 1963.

61 Memo for files, Chilton, "Alternate Attitude Control System for the Mercury Capsule," July 8, 1959, 3. Cf. memo, Chilton to Project Dir., "Alternate Attitude Control System for the Mercury Capsule," July 1, 1959. See also Chilton, "Attitude Control Systems," progress report, Oct. 21, 1959.

62 Kurt P. Wagenknecht, McDonnell Aircraft Corp. procurement officer, interview, St. Louis, Sept. 2, 1964.

63 Roger J. Pierce, "Mercury Capsule Communications," Astronautics, IV (Dec. 1959), 24-27, 86-88. Another constant problem was the discovery of toxic byproducts from electrical insulation, which required much equipment redesign.

64 Minutes, "Special Coordination Meeting at McDonnell," Norman F. Smith, secretary, Oct. 1 and 2, 1959, sec. 2a.0.1, 5.

65 Letter, Gilruth to Ira H. Abbott, "Required Basic Research on Parachute to Support Manned Space Flight," July 6, 1959, 2. See also memos, G. A. White, J. B. Lee, and Alan B. Kehlet to Chief, Flight Systems Div., "Drogue parachute," Oct. 15, 1959.

66 Letter, Henry J. E. Reid to NASA, "Required Basic Research on Parachute to Support Manned Space Flight," Sept. 22, 1959; cf. Joe W. Dodson, transcript of taped discussion, "Mercury Parachute History," Sept. 1962, and Russell E. Clickner, comments, Nov. 5, 1965.

67 Letter, Charles J. Donlan to Low, "Langley Support for Project Mercury," Dec. 9, 1959. The addition of the better "mousetrap" is best described in Aleck C. Bond and Kehlet, "Review, Scope, and Recent Results of Project Mercury Research and Development Program," paper, 28 annual meeting, Inst. of Aeronautical Sciences, New York City, Jan. 25, 1960.

68 Purser, log for Gilruth, Dec. 21, 1959. Parachute systems and technology are well described in Ms., Bond and Faget, "Technologies of Manned Space Systems," Chap. 14, "The Role of Ground Testing in Manned Spacecraft Programs," 166-177.

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