The Gemini fuel cell that supplied electrical power to the spacecraft consisted of three stacks connected to form a battery section. Each stack was made up of 32 cells between the end plates. This is a sketch of a fuel cell stack and its location in the spacecraft adapter section.
A schematic of the principle of its operation.
The test failures, design changes, and revised production techniques combined to delay the fuel-cell program. GPO began looking for ways to increase the rate of fuel-cell production and to install fuel cells at a later point in spacecraft assembly. A visit to GE in May 1963 convinced both GPO and McDonnell that the current program was unrealistic; schedules allowed too little time for testing and failed to provide for contingencies or troubleshooting.35 Throughout the spring and summer of 1963, McDonnell and GE kept juggling test and production units, trying to meet ever less tenable schedules, as slippage in the fuel-cell program mounted.36 These efforts were complicated by further development problems.
The project office was far from certain that fuel cells would be ready on schedule, even when GE began shifting its main effort from engineering and development to making fuel-cell stacks on the production line.37 On 27 August 1963, GPO asked McDonnell for an engineering evaluation of batteries for electrical power in Spacecraft 3, the first man-carrying ship, scheduled for October 1964; the fuel cells were to remain aboard to be used only on a test load for purposes of flight qualification. When and if proper operation was confirmed, they might then be hooked into the spacecraft main electrical system. McDonnell had a plan for dual installation of batteries and fuel cells ready within a month.38 Mathews then requested a design study of substituting batteries for fuel cells in all seven spacecraft planned for two-day rendezvous missions.39
NASA Headquarters also took action.  George E. Mueller, NASA's new Deputy Associate Administrator for Manned Space Flight, arranged for three senior engineers from Bell Telephone Laboratories* to visit the GE plant to assess the status of the fuel-cell program.40 Rumors were already circulating that fuel-cell problems might force NASA to limit all Gemini missions to two days.41 GE experiments had shown that Gemini fuel cells had an operating life of 600 hours in theory, but a number of factors, among them the high operating temperatures imposed by a newly redesigned cooling system, had reduced that figure to less than 200 hours in practice.42 Fuel-cell problems were never conceptual. As a source of electrical power for long-term orbital missions, no one doubted that cells had a solid edge over batteries. The rub came in trying to convert that concept into hardware to meet Gemini specifications - essentially a matter of nuts and bolts, compounded to some extent by managerial shortcomings. This was clearly pointed up in the findings of the Bell experts, who toured the GE plant on 29-30 October 1963.
Their key tasks were to spot the development problems that remained and to answer two questions: Could GE solve these problems? What were the contractor's prospects of meeting Gemini production schedules? The team pinpointed technical matters of fuel-cell structures, materials, and the like, as exemplified by uneven current distribution because of poor contact between membrane and catalyst or catalyst and rib. The Bell engineers thought that GE could solve these problems, given enough time. Whether there was time, however, was something else; the team suggested that NASA might want to think about a backup program. GE was already six months late. Despite its stated intent to make up the lost time, GE would be doing well to maintain the current schedule. The Bell recommendations, like those put forward a little later by McDonnell in a survey of possible fuel-cell changes to meet Gemini operational needs, were restricted to narrow technical considerations.43
Fuel-cell production came to a halt on 26 November, as two GE task groups tried to resolve persistent engineering and manufacturing problems. Testing of the stacks on hand continued, but GE could build no new ones until a thorough study had revealed the causes of poor fuel-cell performance.44
Still fearing that fuel cells might not be ready for Spacecraft 3, Mathews instructed Walter Burke to alter the spacecraft's electrical system to accept either batteries or fuel cells as power sources when the spacecraft reached Cape Canaveral. By mid-December, convinced that the fuel-cell system could not be qualified in time, GPO opted to fly  the first manned mission with batteries. But Spacecraft 2 would be fitted with both systems, chiefly to afford a chance to qualify the fuel-cell reactant system. The reactant supply system was a distinct development. The system, subcontracted to AiResearch, stored and fed to the cells the hydrogen and oxygen they ran on.45
There was still little reason to believe that fuel-cell problems could be resolved even for later Gemini flights. On 20 January 1964, Mathews asked Burke to begin work on a battery-operated system for Spacecraft 4. Switching from fuel-cell to battery power for these two spacecraft cost Project Gemini almost $600,000.46 The GE task groups having completed their intensive six-week search for the causes of the problems, a meeting was scheduled in Houston on 27 January 1964, between NASA and its contractors to review fuel-cell status and to decide what to do about it.47
Although some missions might have to be curtailed, the Gemini spacecraft could carry men aloft without fuel cells by using conventional batteries. No such easy answer existed for the escape system. Any effort to replace it with something else would not only be difficult but far more costly. In the spring of 1963, some thought the change would be worth whatever it cost. MSC's Flight Operations Division revived a proposal to replace ejection seats with an escape tower, the system used in Project Mercury. Doubtful that the seat could be qualified in time and skeptical of its value as an escape device in any case, chief of Flight Operations Christopher Kraft urged Gilruth to start a backup program to see, at least, if an escape tower could be used for Gemini.48
Gemini Project Office, seconded by the astronauts and Flight Crew Operations, still believed that Gemini ejection seats could be made to work. Hard-to-solve problems were only to be expected in the development of so advanced a system.49 Things were, in fact, starting to look up. Simulated off-the-pad ejection (Sope) tests had been suspended in the fall of 1962 until all system components were ready and the complete escape sequence, including recovery of dummy astronauts, could be demonstrated. The system had also grown more complex; it now included a device - a hybrid of BALLoon and parachUTE called a ballute - to prevent an astronaut from spinning during free fall if he had to eject from an altitude much higher than the 2,000 meters at which his personal parachute was set to deploy.50
When Sope testing resumed on 7 February 1963, the results were disappointing from the standpoint of proving the complete escape sequence - the ballutes failed to inflate and release and the personal parachute did not deploy properly. But, in the view of Kenneth Hecht and his colleagues in GPO who were in charge of escape-system development, the test marked a real breakthrough. They had been convinced that the key problem was dynamic, the relationship between rocket-motor thrust vector and the shifting center of gravity of the seat-man combination.  Analysis of the data from the test revealed that they had been overlooking a significant factor in their calculations - the tendency of the ejecting mass to tip as a result of its inertia when it left the end of the guide rails. With that factor accounted for, the key problem was solved. "The remaining technical problems," Hecht later recalled, "were in debugging the details of a very complex design."51
That, however, was no small order. Measures were taken to ensure that the personal parachute would deploy at the low dynamic pressure associated with off-the-pad aborts. McDonnell and Weber engineers also cleaned up the makeshift additions to seat design that had piled up in the course of development. But the complete escape sequence still had to be proved. All that took time. The new package was given its final checkout on 22 April 1963.52 Three weeks later, on 15 May, Sope testing was under way again, with heartening results.  The last four tests in the series of 12, which had begun in July 1962, were almost flawless, only an insignificant failure of part of the test gear marring the final test, on 16 July. The development phase of pad ejection testing was now complete.53
Still unfinished, however - indeed, scarcely begun - was a second series of development tests, sled-ejection tests. These were not so novel as the Sope tests, being in common use for all ejection-seat development. They simulated ejection at high dynamic pressures - as might be met in an escape during first-stage booster firing. In the Gemini tests, conducted at the Naval Ordnance Test Station in California, two ejection seats were mounted side by side in a boilerplate spacecraft carried on a rocket-propelled sled running on tracks. Known as the Supersonic Naval Ordnance Research Track, it was, obviously, called "Snort." But the delays met in Sope tests, compounded by the reprogramming of late 1962, slowed the sled program.54
This may have been just as well, because the test vehicle was badly damaged in its first run, on 9 November 1962. This was not an ejection-seat test. The test station needed a trial run to confirm its data on sled performance and structural soundness. It got what it wanted, but a rocket motor broke loose and smashed into the boilerplate, starting a fire. Although both boilerplate and sled needed a lot of work, GPO foresaw no delay in the sled-test program itself, since other factors had already required it to be rescheduled, leaving ample time for repairs.55
Flawless Sope tests on 15 and 25 May 1963 showed that the new seat design was working and sled tests could begin. A dynamic dual ejection on 20 June was a success, followed by a second good run on 9 August. That turned out to be the last test in 1963. The seat system went through still another redesign, this time to provide for the automatic jettison of backboard and egress kits.56 A more serious problem, and one that persisted, had little to do with the system itself. Testing was continuously hampered by shortages and slow delivery of parts, particularly the pyrotechnic devices that were crucial to so many of the system's functions.** 57
Although fuel-cell and escape systems had begun to look troublesome in 1962, the thrusters on which the Gemini spacecraft relied for attitude control and maneuvering in orbit and for control during reentry seemed at first to present no special problems.  The subcontractor for both these systems, Rocketdyne Division of North American, focused its research effort on developing an engine of 111 newtons (25 pounds of thrust) able to perform within specification for five minutes of constant burning. McDonnell and Rocketdyne engineers assumed that a thruster design able to meet that standard could also sustain the pulsed, or cyclic, firing that would be called for in practice. They also thought that a working, 111-newton-thruster design need only be scaled up to meet the performance demanded of the 445-newton (100 pound-thrust) maneuvering thrusters. They were wrong on both counts.58
The schematic shows the arrangement of the thrusters on the Gemini spacecraft; the inset shows a cutaway of a thruster.
The maneuvers possible with various thruster combinations.
To make matters worse, new tests revealed that the larger maneuvering thrusters could not be simply enlarged versions of the attitude engines. Rocketdyne had, so far, done very little work on the maneuver thrusters, partly because of its focus on the smaller model and partly because it had been slow to provide test hardware and facilities. During April 1963, testing of the larger OAMS thrusters had ceased altogether. The new findings now compelled the company to reactivate that test program at once.60
Rocketdyne made one design change after another in an effort to put together a thruster that worked, with no striking success. By July 1963, McDonnell was willing to accept a version of the attitude thruster that could not be ready until Spacecraft 5.  Relaxed test requirements and less stringent performance standards - lower oxidizer to fuel ratios, shorter firing times, and reduced thrust ratings and specific impulse for all engines - helped a little, but grounds for real optimism were slight.61 As the summer of 1963 drew to a close, no small OAMS thruster had achieved a full mission duty cycle. A few larger OAMS thrusters had, but too few to be sure and with too small a margin of life beyond the duty cycle. The reentry control thrusters looked a little better, largely because of the lesser demands placed on them. They had to function only for a relatively brief time during reentry and could be expected to run dry before burning through.62
Even the reentry thrusters, however, hardly inspired confidence. Stabilizing the spacecraft at subsonic speeds during the last phase of reentry, from roughly 15,000 to 3,000 meters, had been intended as one function of these motors. (The other, and more important, was to hold the spacecraft in the correct attitude for retrofire to control the angle of reentry and thus to prevent either too steep or too shallow a flight back into Earth's atmosphere.) But, in September 1963, GPO decided that the thruster problems were severe enough to warrant seeking another way to steady the spacecraft. Since the first six Gemini spacecraft were then slated for parachute recovery, GPO decided to add a drogue parachute to the system for this purpose. Development testing of the parachute recovery system had finished in February, and qualification testing was well advanced. Mathews ordered a halt to these tests on 3 September and directed McDonnell to add the drogue.  The first hope, that the new system could be ready for Spacecraft 2, did not survive a close look at the effort required. It was slated instead for Spacecraft 3, the first manned spacecraft; Spacecraft 2 would fly with the non-drogue version.63
Rocketdyne, still struggling to meet the 232.5 seconds of pulse operation required of the small attitude thrusters and the 288.5 seconds demanded on the larger maneuvering thrusters, received a jolt in October 1963 from a McDonnell warning that thruster life would have to be doubled or tripled. Astronauts flying simulated missions used the thrusters even more strenuously than they were designed for, and there seemed to be no choice but to widen the margin of performance. Several months elapsed before the new demands were settled at 557 seconds of pulse operation for the small thrusters and 757 seconds for the larger ones. In the meantime, however, thruster testing at Rocketdyne ground to a halt, and the program threatened to founder. No end to development testing was yet in sight, and the start of qualification testing was a long way off. During November and December, Rocketdyne undertook an intense study of the basic features of small ablative rocket engines; McDonnell began work on an alternative design, cooled by radiation rather than ablation; and GPO was thinking seriously about the drastic step of starting qualification tests before development tests were completed.64
* N. Bruce Hannay, Frank J. Biondi, and Upton B. Thomas.
** The ejection seat was not the only system in Gemini having troubles with pyrotechnics. They seemed to be causing problems throughout the program, so much so that, in August 1963, Charles Mathews established an ad hoc committee to review the Gemini pyrotechnics systems - design, qualification, and functions. Headed by Russell E. Clickner (Mercury), the committee consisted of Joe W. Dodson (Mercury), Roger N. Messier (Technical Services), Chester Vaughan (Systems Evaluation and Development), and Robert Cohen and Percy Miglicco (Gemini). The work of the committee had a widespread influence on Gemini pyrotechnics and associated systems - circuitry, redundancy, system design, logic, and qualification testing.
32 Quarterly Status Report No.4, for period ending 28 Feb. 1963, p. 1.
33 Zavasky, "Minutes of Senior Staff Meeting, November 16, 1962," p. 4; Quarterly Status Report No. 3, for period ending 30 Nov 1962, p. 26, Zavasky, "Minutes of Senior Staff Meeting, December 6, 1962," p. 5; "Gemini Spacecraft Status, December 13, 1962," prepared for Gilruth's presentation at the 13th Management Council Meeting, 18 Dec. 1962, pp. 1-2.
34 Quarterly Status Report No. 4, p. 26; Consolidated Monthly Activity Report, 24 Feb. - 23 March 1963, p. 56; Meyer notes, 9 May 1963; Quarterly Status Report No. 5, pp. 35-36.
35 Quarterly Status Report No. 5, p. 36; letter, William Parker to James E. Webb, 14 July 1966, with enclosure, "United States General Accounting Office Report to the Congress of the United States: Review of the Gemini Spacecraft Fuel Cell Electrical Power Supply Systems, by the Comptroller General of the United States," draft, [July 1966], pp. 22-23.
36 "Abstract[s] of Meeting[s] on Electrical Systems, April 30, 1963," 8 May 1963; "May 14, 1963," 21 May 1963; "May 28, 1963," 29 May 1963; "June 11, 1963," 14 June 1963; Mathews, activity report, 5-11 May 1963, p. 2; Consolidated Activity Report, 28 April - 18 May 1963, p. 69; Weekly Activity Report, 1622 June 1963, p. 2; Consolidated Activity Report, 16 June - 20 July, 1963, p. 87; Weekly Activity Report, 4-10 Aug. 1963, p. 1.
37 Quarterly Status Report No. 6, pp. 1, 63-64.
38 TWX, Mathews to Burke, "Contract NAS 9-170 Use of Batteries on Spacecraft 3," [26 Aug. 1963]; TWX, Brown to MSC, Attn: Mathews, "Use of Batteries for Electrical Power in Spacecraft Nbr. 3," 18 Sept. 1963; G[eorge] J. Weber, "Dual Fuel Cell/Silver Zinc Battery Installation for 7 Orbit, S/C 3 Gemini Mission," McDonnell Electrical Design Note 24, 25 Sept.1963; TWX, Mathews to Burke, GPO- 54285-A, 16 Oct. 1963.
39 TWX, Mathews to Burke, "Contract NAS 9-170, Power System Design Study," GPO-54230-A, 1 Oct. 1963.
40 TWX, Low to MSC, Attn: Elms, "Apollo and Gemini Fuel Cells," M-C S 1000.578, 7 Oct. 1963.
41 John W. Finney, "Power-System Snags May Cut First Gemini Flights to 2 Days," The New York Times, 30 Oct. 1963.
42 Mathews, activity report, 29 Sept. - 5 Oct. 1963, p. 2; Consolidated Activity Report, 22 Sept. - 19 Oct. 1963, p. 95.
43 TWX, Mathews to Burke, "Contract NAS 9-170 Visit to GE by Bell Labs Committee," GPO-54277-A, 14 Oct.1963; N. B. Hannay, F. J. Biondi, and U. P. Thomas, "Report on Fuel-Cell Work at General Electric and Pratt & Whitney," Bell Telephone Laboratories, Inc., n.d., pp. 6-9; letter, Schneider to Burke, 8 Jan. 1964, with enclosure; G. J. Weber, J. C. Waldner, and K. A. Rogers, "Fuel Cell Interface Review," McDonnell Electrical Design Note 33, 16 Dec. 1963.
44 Quarterly Status Report No. 7, p. 61; memo, Mathews and Wesley L. Hjornevik, "United States General Accounting Office draft report to Congress regarding fuel cells," GP-62337, 11 Aug. 1966, with enclosure, "Detailed Comments on GAO Draft Report," p. 1.
45 TWX, Mathews to Burke, "Contract NAS 9-170, Procurement of Batteries for Spacecraft 3," GPO-54229-A, 30 Sept. 1963; TWX, Mathews to Burke, GPO-53110-S, 12 Nov. 1963; Weekly Activity Report, 17-23 Nov. 1963, p. 1; Kline to McDonnell, "Change Notice No. 16," 20 Jan. 1964; Consolidated Activity Report, 17 Nov. - 21 Dec. 1963, p. 18; memo, Mathews to Chief, Gemini Spacecraft Procurement, "Contract NAS 9-170, CCP No. 16, Battery Module for Spacecraft No. 3," GPO-03307-A, 4 Dec. 1962 [sic].
46 Consolidated Activity Report, 22 Dec. 1963-18 Jan 1964, p. 9; TWX, Mathews to Burke, GS-53158, 20 Jan. 1964; Consolidated Activity Report, 19 Jan. - 15 Feb. 1964, p. 17; memo, Edward E. Winchester to Donald D. Blume, "GAO Review of the Gemini Fuel Cell Power Supply System," 15 Nov. 1965; memo, Mathews to GAO Liaison Representative, "General Accounting Office inquiry regarding fuel cell power," GS-64098, 10 Jan. 1966, with enclosure.
47 Quarterly Status Report No. 8, p. 48; Weekly Activity Report, 19-25 Jan. 1964, p. 10; TWX, Mathews to Burke, "Contract NAS 9-170: Fuel Cell Program," GP-54541, 10 Feb. 1964; TWX, Mathews to McDonnell, Attn: Burke, GS-53211, 18 March 1964.
48 Memo, Marlowe D. Cassetti and Richard E. Charters to Chief, FOD, "Analysis of the Effect of Adding an Escape Tower to Gemini S/C on GLV Performance," 27 March 1963; memo, Kraft to Dir., "Gemini Escape System," 10 April 1963.
49 B. Porter Brown, "Minutes of Meeting of Gemini Egress Group of the Master Egress Committee, April 17, 1963," 17 April 1963, enclosure 1, "Gemini Ejection Seat Review Presented to Gemini Egress Group, April 17, 1963, Cape Canaveral, Florida," n.d.
50 "Abstract of Meeting on Ejection Seats, September 26, 1962," 3 Oct. 1962; letter, Floyd L. Thompson to MSC, Attn: GPO, "Request for support of Project Gemini," 5 Dec. 1962, with enclosure, memo, Jerry L. Lowery to Assoc. Dir., Langley, "Visit of Goodyear Aircraft Corporation representatives to discuss proposed wind tunnel tests of an inflatable decelerator attached to an astronaut," 20 Nov. 1962; C. E. Heimstadt and Gordon P. Cress, interviews, Burbank, Calif., 5 July 1966; letter, Cress and Heimstadt to MSC Historical Office, 12 May 1967; letter, Cress to MSC Historical Office, "Comment Draft on Chapters 7 & 8 of Gemini Narrative History," 511/GPC/2120, 1 Dec. 1971; Hecht memo, 22 Sept. 1970.
51 Gregory, "Minutes of Senior Staff Meeting, February 8, 1963," p. 3; Quarterly Status Report No. 4, pp. 18-19; Quarterly Status Report No. 5, p. 26; Cress interview; Cress and Heimstadt letter, 12 May 1967; Hecht memo, 22 Sept. 1970.
52 Consolidated Monthly Activity Report, 24 Feb. - 23 March 1963, p. 3; Cress interview; Quarterly Status Report No. 5, pp. 6, 26; Hecht memo, 22 Sept. 1970.
53 Mathews, activity report, 24 April - 19 May 1963, p. 1; Quarterly Status Report No. 5, p. 6; Quarterly Status Report No. 6, p. 41.
54 [Kenneth F. Hecht], "Comments on Chapter 5, Expansion and Crisis, " [10 Feb. 1970], pp. 1-2; "Abstract of Meeting on Ejection Seat Developmental Test Program, May 29, 1962," 4 June 1962; Weekly Activity Report, 27 May - 2 June 1962, p. 7; Cress interview; Quarterly Status Report No. 1, for period ending 31 May 1962, pp. 2-22.
55 Quarterly Status Report No. 3, p. 18; Zavasky, "Senior Staff Meeting, November 16, 1962," p. 3; Cress and Heimstadt letter, 12 May 1967; [Hecht], "Comments on Chapter 5," p. 2; Hecht memo, 22 Sept. 1970.
56 Quarterly Status Report No. 5, p. 26; Weekly Activity Report, 16-22 June 1963, p. 3; Mathews, activity report, 4-10 Aug. 1963, p. 2; Quarterly Status Report No. 7, p. 42, 44; "Abstract of Meeting on Ejection Seat System, October 30, 1963," 5 Nov. 1963; W. M. Weeks, "Aerodynamic Characteristics of the Gemini Ejection Seat-Man Configuration," McDonnell Aerodynamic Information Note No. 50, 28 Oct. 1963, p. 4.
57 Weekly Activity Report, 16-22 June 1963, pp. 2-3; memo, Jack A. Kinzler to MSC Public Affairs Officer, "Comment Draft of Project Gemini Technology and Operations: A Chronology, " 31 May 1967, with enclosure; Heimstadt interview; Robert Provart and John Swanson, interviews, Newbury Park, Calif., 7 July 1966.
58 Zavasky, "Minutes of Senior Staff Meeting, March 8, 1963," p. 4; William J. Blatz, interview, St. Louis, 14 April 1966; Larry E. Stewart, interview, Canoga Park, Calif., 16 May 1967.
59 "MSC Status Report," prepared for Gilruth's presentation at the 14th Management Council Meeting, 29 Jan. 1963, pp. 34-35; Quarterly Status Report No. 4, pp. 16-17; Zavasky, "Senior Staff Meeting, March 8, 1963," p. 4; memo, Meyer to MSC Historical Office, "Comments on Chapter 6 of Gemini Narrative History," 16 Nov. 1970.
60 Quarterly Status Report No. 5, pp. 23-26; Mathews, activity report 24 April - 19 May 1963, p. 3; Quarterly Status Report No. 6, p. 28; Steven J. Domokos, interview, Canoga Park, Calif., 16 May 1967.
61 Quarterly Status Report No. 6, p. 29; Zavasky, "Senior Staff Meeting, July 12, 1963," p. 6; Meyer, interview, Houston, 9 Jan. 1967; Meyer memo, 16 Nov. 1970.
62 Zavasky, "Senior Staff Meeting, September 13, 1963," pp. 5-6; "Gemini Report for Management Council Meeting," prepared for meeting of 24 Sept. 1963, p. 2; Consolidated Activity Report, 22 Sept. - 19 Oct 1963, p. 93.
63 "Gemini Report for Management Council Meeting," p. 2; Quarterly Status Report No. 4, pp. 11-12; Quarterly Status Report No. 5, p. 17; Zavasky, "Senior Staff Meeting, September 13, 1963," pp. 4-5; Quarterly Status Report No. 7, pp. 31-32; Bailey to McDonnell, "Change Notice No.10," 6 Nov. 1963; Swanson interview; TWXs, Mathews to Burke, GPO-52058-LV, 9 Sept., GPO-54240-A, 7 Oct., and GPO-54437-A, 12 Dec. 1963.
64 Weekly Activity Report, 20-26 Oct. 1963, p. 2; Quarterly Status Report No. 7, pp. 17, 27-28; TWX, James R. Flanagan to McDonnell, Attn: Burke, M-C L 4000.532, 13 Nov. 1963; Ron Helsel, interview, Canoga Park, Calif., 16 May 1967; "Gemini Propulsion by Rocketdyne - A Chronology," 15 May 1967, p. 6; Stewart interview; memo, Robert H. Voigt to dist., "Report on Review of Business Management Activities at Rocketdyne, A Division of North American Aviation, Inc. (Report No. WR 65-12), MSC 32-0-65G," 5 May 1965, with enclosure, Raymond Einhorn, "Review of Business Management Activities at Rocketdyne . . . ," Western Region Audit Office Report WR 65-12, April 1965, p. 67; TWX, John Brown to Armstrong, "Contract NAS 9-170, Gemini, Radiation Cooled Thrust Chamber," 306-16-6817, 13 July 1964.