Chamberlin later justified this approach in an enlightening lecture on the design philosophy of the Gemini spacecraft (which Mercury Mark II was to become).60 The main trouble with the Mercury capsule was that
most system components were in the pilot's cabin; and often, to pack them in this very confined space, they had to be stacked like a layer cake and components of one system had to be scattered about the craft to use all available space. This arrangement generated a maze of interconnecting wires, tubing, and mechanical linkages. To replace one malfunctioning system, other systems had to be disturbed; and then, after the trouble had been corrected, the systems that had been disturbed as well as the malfunctioning system had to be checked out again.61Mercury designers had been preoccupied with solving such basic problems of manned space flight as reentry heating and human tolerance of both high acceleration and zero gravity, for "the sole purpose of placing a man in orbit in a minimum time." Thus they paid no great attention to making a convenient, serviceable spacecraft. That, however, was precisely what the new design offered. In it,
systems are modularized and all pieces of each system are in compact packages. The packages are so arranged that any system can be  removed without tampering with any other system, and most of the packages ride on the outside walls of the pressurized cabin for easy access. This arrangement allows many technicians to work on different systems simultaneously.62The Mercury capsule, in contrast, could only be worked on from the inside, which meant, as a rule, only one person working at a time.
The new design attacked a number of other Mercury trouble spots. Perhaps the most troublesome was the sequencing system. Chamberlin argued that one of his chief motives for keeping systems in the new design separated was to avoid the endless complications Mercury experienced because so many sequentially controlled operations were built into it. Most of Mercury's flight operations could be controlled by the pilot, but safety demanded that they also be automatic, each complex series of events triggered by an appropriate signal and ordered through a predetermined sequence by a tangle of electrical circuitry.63 So complex was Mercury sequencing that Chamberlin recalled it as "the root of all evil and anybody that really worked on Mercury - that's all they talked about."64 The new design relied on pilot control, instead of merely allowing it and backing it up with automatic sequencing. The result was a much simpler machine; the 220 relays in Mercury, for example, were reduced to 60 in Mark II.65
What may have been the most complex sequencing of all was demanded by the automatic abort modes in Mercury, which depended on a rocket-propelled escape tower to pull the capsule away from the booster in an emergency during or just after liftoff.66 In Chamberlin's mind, "the sequencing of the escape system was one of the major problem areas in Mercury in all its aspects - its mechanical aspects in the first part of the program, and the electronic aspects later."67 What made this peculiarly frustrating was that the escape tower added hundreds of kilograms to the capsule's weight, even though it was essentially irrelevant to the function of the capsule itself; in a successful flight it was jettisoned shortly after launch. Yet its many relays and complex wiring, besides making it inherently untrustworthy, were major factors in prolonging checkout time. To make matters worse, the Mercury abort modes - NASA shorthand for the methods that allowed the pilot to escape when a booster malfunction threatened his life - were automatic. Some circumstances not actually calling for an aborted mission - including a malfunction of the abort system itself - could trigger one, as happened more than once in the Mercury development program.68
Artist's sketch of ejection seats propelling the astronauts to escape distance from a launch failure. They would be used in emergencies before launch (pad-abort) and in flight to about 18,000 meters altitude.
A Drawing of the Titan II, built by the Martin-Marietta Corporation, as proposed to be adapted for manned space flight.
To Chamberlin, however, Titan II looked very good for the improved Mercury. Weight was the most serious constraint in spacecraft design. An improved Mercury meant a heavier Mercury, since the price for packaged components was extra kilograms. This, in turn, meant that the new design called for a launcher more powerful than Atlas. Titan II had power to spare, its total thrust being almost two and a half times that of Atlas. Not only could it easily lift the heavier spacecraft, but it could also carry the redundant systems that would make it a safer booster for manned space flight. This, in a way, merely augmented what may have been Titan II's outstanding features - simplicity and reliability.72
Titan II ran on storable hypergolic propellants: a blend of hydrazine and unsymmetrical dimethyl hydrazine (UDMH) as fuel with nitrogen tetroxide as oxidizer. Because this combination is hypergolic - fuel and oxidizer burn spontaneously on contact - Titan II needed no ignition system. Since both fuel and oxidizer can be stored and used at normal temperatures - instead of the supercold required by the liquid oxygen of Atlas or Titan I - Titan II required no cold storage and handling facilities. The design and the lessons learned from Titan I combined to reduce the 172 relays, umbilicals, valves, and regulators in the first version of the missile to 27 in Titan II.73 This simplification struck a responsive chord in Chamberlin, who saw in it something to match what he had been trying to achieve in redesigning the Mercury capsule. Booster and spacecraft seemed almost to have been made for each other.74
Titan II's self-igniting propellants had still another advantage.  They reacted much less violently with each other than did the cryogenic propellants of Atlas or Titan I. In June 1961, there was still some question about whether a Titan II explosion would be sufficiently less violent, compared to Atlas, to permit the use of an ejection seat. Chamberlin was not yet ready to spell out his plans for using Titan II, but that was the way he was thinking. And his active distaste for escape towers made him eager to include ejection seats in his design.
Ejection seats not only promised to relieve a major source of trouble by getting rid of the escape tower, but they also furthered the concept of modularization, keeping each spacecraft system, so far as possible, independent. "The paramount objective in the program," according to Chamberlin, "was to dissociate systems." Ejection seats, in what he called "very happy coincidence that was fully realized at the time," also fitted in nicely with another design change, substituting paraglider for parachute recovery.75
STG had not displayed much active interest in Francis Rogallo's flexible wing concept after the initial flurry in early 1959.76 Rogallo and his co-workers at Langley had pushed ahead with their studies in the meantime. By mid-1960, they had convinced themselves that a controllable, flexible wing could carry a returning spacecraft safely to land, thus providing "a lightweight controllable paraglider for manned space vehicles."77 STG rediscovered the paraglider at the start of 1961 as a by-product of work on Apollo. A technical liaison group on Apollo configuration and aerodynamics met at Langley on 12 January.** In the course of describing his center's work for Apollo, the Langley representative mentioned the paraglider landing system: "The feeling at Langley is that if the paraglider shows the same type of reliability in large-scale tests . . . that it has achieved in small-scale tests, the potential advantages of this system outweigh other systems." Engineering design of large paragliders appeared to be no problem and would be demonstrated in manned and unmanned drop tests.78
Space Task Group engineers met informally with Rogallo and his colleagues in February, March, and April to explore the use of a paraglider in the Apollo program.*** The STG team was less than enthusiastic. They believed much work was yet to be done before the device  could be seriously considered as a landing system for Apollo. The biggest unknown was the deployment characteristics of an inflatable wing; no inflatable structure had ever been successfully deployed in flight. Other questions - how the paraglider was to be packaged, whether the pilot's view from the capsule would be good enough for flying and landing with it - were nearly as important and also largely unanswered. The STG team advised gathering at least six months of data before awarding any paraglider development contract.79 At the same time, however, McDonnell engineers were looking at a paraglider for the modified Mercury, and Marshall Space Flight Center had already let two contracts to study paraglider as a booster recovery system. The idea clearly had promise, and in May 1961 Gilruth decided to contract for further study.
Three contractors each got $100,000 for two and a half months to design a paraglider landing system and define potential problem areas.**** The best design was expected later to become the basis for a development contract to "provide the modified [Mercury] spacecraft with the capability of achieving a controlled energy landing through the use of aerodynamic lift."80 In fact, the design studies soon received a new name - Phase I of the Paraglider Development Program.81 Observed by a small technical monitoring group from STG, the paraglider design studies were under way before May ended.# 82 McDonnell engineers also maintained close liaison with paraglider work, independent though it was of the Mercury Mark II study contract.83 The redesigned Mercury, as presented by Chamberlin and Blatz to the Capsule Review Board in June, could he adapted to a paraglider landing system, once it was developed.84
One other significant innovation marked the new design, an enlarged overhead mechanical hatch, which would allow the pilots to get in the spacecraft more easily and to get out more quickly in an emergency. It was another way of making the new spacecraft a truly operational machine, one that could be entered and left like an airplane. Such a hatch was also needed if ejection seats were to be used. But it also had a special virtue that its designers were well aware of, though they did not talk about it. A large mechanical hatch would enable the pilot to leave and return to the spacecraft while it was in orbit and  thus permit what later became known as extravehicular activity, or EVA.85
The many changes proposed by Chamberlin and Blatz did not make the redesigned spacecraft a totally new machine. Though somewhat enlarged, it retained the fully tested and proved shape and heat protection of the Mercury capsule. It was still to be a one-man craft, and its designers expected to use mostly Mercury parts, packaged and rearranged but not otherwise substantially altered. The new design would not be much longer- lived in orbit than Mercury, 18 orbits (or one day) being the most the designers were aiming at.86 Nevertheless, members of the Capsule Review Board seemed staggered by the scope of the changes presented to them. They refused to accept the complete Chamberlin-Blatz package but agreed to reconvene after the weekend to decide if any of the new features might be worth pursuing.87
Chamberlin came back again Monday morning, since he was a regular member of the board, but Blatz had returned to St. Louis.## The board talked over the design of the ejection seat and hatch, simpler sequencing, better accessibility, and an 18-orbit capability. Each of these ideas had its own appeal, but most of them carried a price tag far too high to fit within the scope of the follow-on Mercury program STG was then thinking about, a program budgeted for less than $10 million in the coming fiscal year.88
Although reaching no clear-cut decision, the board still hesitated to endorse Chamberlin's plans in full. Instead, he was allowed to continue working on alternative approaches to an improved Mercury, while McDonnell studied "the minimum modifications that could be made to the present capsule to provide 18-orbit capability" and looked into "a larger retro and posigrade pack."89 This amounted to little more than reviving an early Mercury objective, once the ultimate goal of the program. Growing capsule weight and power requirements, as well as the limitations of the manned space flight tracking network, had forced STG to scrap the 18-orbit mission by October 1959.90 The idea lived on, however, in the form of a proposal to fit the capsule with its own rocket motors to provide the final increment of velocity needed to attain an orbit high enough to resist Earth's gravity for 18 revolutions.91 This was the idea the Capsule Review Board again endorsed at its meeting on 12 June.
* Those who attended the Capsule Review Board meetings of 9 and 12 June were Gilruth, Walter Williams, Paul Purser, Max Faget. Charles Mathews, Robert Piland, Wesley L. Hjornevik, George Low, and John Disher.
** The group comprised Alan Kehlet as chairman, and William W. Petynia as secretary (both of STG), Hubert Drake (Flight Research Center), Edward L. Linsley (Marshall), Eugene S. Love (Langley), Edwin Pounder (JPL), and Clarence A. Syvertson (Ames). During January and April meetings of the group, visitors were John Disher (Headquarters), Alvin Seiff (Ames), and John B. Lee and Bruce G. Jackson (STG). The large-scale program got under way in April, using a fully deployed 19-foot paraglider. Tests with partially deployed and packaged paragliders were to follow.
*** The STG engineers were John W. Kiker, Richard C. Kennedy, Fred J. Pearce, Jr., and Gerard J. Pesman. Rogallo's team consisted of Delwin R. Croom, Robert T. Taylor, Donald E. Hewes, Lloyd J. Fisher, Jr., and Lou S. Young.
**** They were Goodyear Aircraft Corporation, Akron, Ohio; Ryan Aeronautical Company, San Diego, California; and North American Aviation Space & Information Systems Division, Downey, California. Goodyear was an experienced builder of inflatable aerial devices, and Ryan and North American were already working on the Marshall contracts.
# The technical monitors were Rodney G. Rose, Harry C. Shoaf, Kenneth W. Christopher, and Lester A. Stewart; in mid-June, they visited each of the contractors' plants to review progress on the study. The group continued to meet with the contractors at regular intervals until the studies were completed.
## Hjornevik, Low, and Disher, all of NASA Headquarters, had also gone home.
58 Memo, Low to Dir., Space Flight Programs, "Report of Meeting with Space Task Group on June 2, 1961," 6 June 1961.
59 Purser, "Notes on Capsule Review Board Meeting, June 9 and June 12, 1961"; Chamberlin comments, 26 March 1974.
60 James A. Chamberlin, "Project Gemini Design Integration," Lecture 36 in a series on engineering design and operation of manned spacecraft presented during the summer of 1963 at the Manned Spacecraft Center and to graduate classes at Louisiana State University, the University of Houston, and Rice University. The series was later edited and published; Chamberlin's lecture became Chapter 35 in Paul E. Purser, Maxime A. Faget, and Norman F. Smith, eds., Manned Spacecraft: Engineering Design and Operations (New York, 1964), pp. 365-74.
61 Ibid., p. 365.
63 Donald G. Wiseman, "Principles of Power Distribution and Sequencing," in Purser, Faget, and Smith, eds., Manned Spacecraft, pp. 195-96; William H. Allen, ed., Dictionary of Technical Terms for Aerospace Use, first edition, NASA SP-7 (Washington, 1965), p. 249.
64 Chamberlin interview.
65 Purser, "Notes on CRB, June 9 and 12, 1961"; Chamberlin, "Project Gemini Design Integration," p. 372.
66 Philip M. Deans, "Launch-Escape Systems," in Purser, Faget, and Smith, eds., Manned Spacecraft, pp. 322-24.
67 Chamberlin interview.
68 Ibid.; Blatz interview; Chamberlin, "Project Gemini Design Integration," p. 372.
69 Purser, "Notes on CRB, June 9 and 12, 1961."
70 James L. Decker, "A Program Plan for a Titan Boosted Mercury Vehicle," Vol. I, July 1961.
71 Seamans, interview, Washington, 26 May 1966.
72 Decker, "A Program Plan."
73 Gemini-Titan II Air Force Launch Vehicle Press Handbook, published by Martin-Baltimore for issuance to news media ca. December 1964, p. II-2. This press handbook was later issued in a second edition, on manned flight, and thereafter was updated for each Gemini flight, beginning with Gemini 3.
74 Chamberlin interview.
76 See pp. 18-19.
77 Francis M. Rogallo et al., Preliminary Investigation of a Paraglider, NASA Technical Note (TN) D-443, August 1960; Rogallo and John G. Lowry, "Flexible Reentry Gliders," presented at the Society of Automotive Engineers National Aeronautics Meeting, New York, 4-8 April 1960.
78 William W. Petynia, secretary, "Minutes of Meeting on [sic] Apollo Technical Liaison Group - Configurations and Aerodynamics, January 12, 1961," 17 Jan. 1961, pp. 12, 14; Petynia, "Minutes of Meeting of Apollo Technical Liaison Group - Configurations and Aerodynamics, April 10-12, 1961," 18 April 1961,
79 Memo, John W. Kiker et al. to Dir., "Interim report on paraglider - Apollo application investigation," 4 April 1961.
80 Memo, Gilruth to Procurement Officer, "Design Study of a Paraglide Landing System for a Manned Spacecraft," 17 May 1961, with enclosure, "Statement of Work for a Design Study of a Manned Spacecraft Paraglide Landing System," 17 May 1961.
81 See, for example, Glenn F. Bailey to North American Aviation, Inc., "Contract for Design Study of Paraglide Landing System for Manned Spacecraft," NAS 9-136, 27 May 1961; "Paraglider Development Program, Phase I - Design Study: Test Programs," STG, 30 June 1961.
82 Letter, Bailey to North American, Attn: H. H. Cutler, "Contract NAS 9-136, Paraglide Landing System Design Study Technical Direction," PASO-B-2426, 16 June 1961; letter, Bailey to Goodyear Aircraft Corp., Attn: R. T. Madden, "Contract NAS 9-137, Paraglide Landing System Design Study Technical Direction," PASO-B-2427, 16 June 1961; letter, Bailey to The Ryan Aeronautical Go., Attn: T. Echols, "Contract NAS 9-135, Paraglide Landing System Design Study Technical Direction," PASO-B-2428, 16 June 1961; Lester A. Stewart, "Minutes of Meeting of Goodyear Aircraft Corporation (Contract NAS 9-137), Study Review Meeting, June 13, 1961," 21 June 1961; Stewart, "Minutes of Meeting of North American Aviation, Inc. (Contract NAS 9-136), Study Review Meeting, June 14, 1961," 21 June 1961; Stewart, "Minutes of Meeting of Ryan Aeronautical Company (Contract NAS 9-135), Study Review Meeting, June 15, 1961," 21 June 1961.
83 Memo, Gilruth for Procurement Officer, "Design Study of a Paraglide Landing System for a Manned Spacecraft," 22 May 1961; letter, Brown to Bailey, "Contract NAS 9-119, MK-11 Mercury Study Contract, Information Concerning," 832-16-12, 18 Aug. 1961, enclosure 1," NAS 9-119, MAC Job 832, Estimated Engineering Manhour Expenditures by Element," No. C-58496, ca. 6 Aug. 1961.
84 Purser, "Notes on CRB, June 9 and 12, 1961."
85 Ibid.; Chamberlin interview.
86 Purser, "Notes on CRB, June 9 and 12, 1961."
87 Ibid.; memo, Purser to Gilruth, "Log for week of June 5, 1961," 13 June 1961.
88 Purser, "Notes on CRB, June 9 and 12, 1961"; "NASA Manned Space Flight, Space Task Group Financial Plan FY 62, Follow-On Mercury, June 14, 1961," pp. F-1 through F-4.
89 Memo, Purser to Gilruth, "Log for week of June 12, 1961," 20 June 1961.
90 Loyd S. Swenson, Jr., James M. Grimwood, and Charles C. Alexander, This New Ocean: A History of Project Mercury, NASA SP-4201 (Washington, 1966), p. 487.
91 "Follow-On Experiments, Project Mercury Capsules," McDonnell Engineering Rept. 6919, 1 Sept. 1959 (rev. 5 Oct. 1959), p. 4.1-1; memo, Warren J. North to Dir., "Advanced Technology Follow-On Tests for the Mercury Capsule," 6 July 1960; memo, David L. Winterhalter to Caldwell C. Johnson, "High Performance Retrograde Rockets," 26 Jan. 1961; memo, Winterhalter to Johnson, "Higher Performance Posigrade-Retrograde Package for Mercury Follow-on Missions," 15 April 1961; memo, Winterhalter to Assoc. Dir., "Higher Performance Mercury Posigrade-Retrograde Package," 26 May 1961.