Some Foreseeable Problems and a Surprise

As Project Gemini moved from design into testing during the spring and summer of 1962, problems multiplied, although not (with one exception) beyond what might be seen as the normal headaches of a large-scale research and development project. Those areas that demanded the longest step beyond current practice were those where trouble threatened. The paraglider program, with its early start, began running into marked delays in planning and design before the rest of Project Gemini. When actual testing began in May 1962, only two contract months remained to settle on the best design for a paraglider landing system.

The first task was qualifying an emergency parachute recovery system for the half-scale vehicle. North American began on 24 May with a successful drop test at the Naval Parachute Facility in El Centro, California, near the Mexican border. Two failures followed before a second success, on 20 June. What should have been the final drop to complete qualification failed on 26 June, when the vehicle's electrical system shortcircuited. North American shuttled the vehicle 260 kilometers back to its plant in Downey for a closer look, which revealed a design flaw. The company reworked the test vehicle and returned it to El Centro for another try, on 10 July, with no better luck. This time the drogue designed to pull out the main parachute failed to do so. After another round trip to Downey for changes, everything worked on 4 September. GPO agreed with North American that the half-scale emergency landing system was now qualified. But two and a half months had been lost.

The full-scale emergency system proved even harder to qualify. First came design problems, then the parachutes were late in arriving. [99] North American could not ship the test capsule to El Centro until 20 July. The Air Force's 6511th Test Group, which ran the El Centro test range, demanded a special test to be certain the vehicle's pyrotechnic devices were safe - that delayed the first qualification flight until 2 August. It was a success, but more delays followed - first bad weather, then the lack of a launch aircraft. The second drop, on 21 August, was marred by one of the three main parachutes breaking loose. Damage was only minor, as it was in the next test, on 7 September, when two parachutes failed. Efforts to correct this problem took over two months. On 15 November, some four months after the full-scale emergency recovery system was supposed to have been qualified, the fourth drop was a disaster. When all three parachutes failed, the test vehicle was destroyed as it hit the ground. Clearly the system could not be relied upon. GPO directed McDonnell to furnish North American with a boilerplate spacecraft for further tests at some later date.13

These problems, however disheartening, should not have cast any shadow on the concept of a paraglider. The emergency parachute systems were intended only to back up testing; they were not part of the Gemini landing system. Yet the pattern of delays, errors, and malfunctions that marked North American's efforts to qualify the emergency system proved to be symptomatic of a lingering malaise. Paraglider advocates knew that the program would be made or broken, so far as Gemini was concerned, by the success or failure of flight testing, and time was limited. North American had been chosen over Ryan and Goodyear because of its first-rate job in testing the design during the summer of 1961.14 But on 28 November, scarcely a week after North American received word to go ahead with paraglider development, NASA notified the company that it had been selected as prime contractor for the Apollo spacecraft. The impact on paraglider was catastrophic. North American froze the number of engineers assigned to paraglider, then allowed even that group to decline. The quality of work suffered as well, becoming, in the opinion of one NASA engineer assigned to the program, "abysmal."15

The pattern of trouble sketched in emergency system testing persisted when North American began testing the paraglider itself by flying half-scale models with wings inflated and deployed before they left the ground. Scheduled to begin in May 1962, these trials got under way in mid-August at Edwards Air Force Base, 100 kilometers north of Downey. North American's first try, on 14 August, got nowhere. Because a plug pulled loose inside the capsule, the wing, which was tied down for takeoff, failed to release after a helicopter had towed it to the proper height. The wing released too soon in the second try, three days later, although the capsule did go brief it into a stable glide. North American also achieved a stable glide in the third flight, on 23 August, but an erroneous radio command caused the vehicle [100] to come down too fast and suffer some damage in landing. The fourth flight was postponed twice, each time because someone forgot to charge the battery. Towed aloft on 17 September, the vehicle failed to release on command, voiding the test. Twice in a row, short circuits forced the contractor to call off the fifth flight test, the second time on 21 September.16

That same day, James Chamberlin, MSC Gemini Project Manager, ordered North American to halt flight tests of the half-scale paraglider. He expressed "growing concern" over "the repeated unsuccessful attempts of S&ID [North American's Space and Information Systems Division] to conduct satisfactory predeployed half-scale paraglider tests." Flights were not to resume until the contractor had reorganized its paraglider project and could spell out just what it intended to do about the test vehicle's electronics and pyrotechnics and the company's own checkout and inspection procedures.17

North American had already made some moves along the lines Chamberlin demanded. The paraglider effort was raised to the status of a major program, and George W. Jeffs was named Paraglider Program Manager on 1 September 1962. Norbert Witte, the former project manager, stayed on as Jeffs' assistant.18 Jeffs was something of a corporate troubleshooter, and he had the respect of the NASA engineers working on paraglider.19 This augured well for the future, but, in the meantime, a fully successful flight test had yet to be performed.

North American reworked the half-scale vehicle in its plant, then shipped it back to Edwards Air Force Base on 15 October for another try. A bad ground transmitter stalled matters for a while but, on 23 October, the fifth test flight was a complete success.20 Even with all its problems, the series of tests had met its main goal, showing that the paraglider was stable in free flight.21 But predeployed flight testing ended more than two months late, and the crucial deployment flight tests - spreading the paraglider wing in flight - had not even begun.

In the meantime, other problems were beginning to compete for the attention of the overworked project office. Like the paraglider, ejection seats had been a controversial innovation in manned spacecraft, and their development problems also gave critics an early opening. The reasons were much the same. Both systems were a long step beyond current practice, both presented test problems not clearly related to their final roles, and both were subject to changing requirements that imposed makeshift adjustments, further complicating matters.

Although ejection seats were widely used in military aircraft, they were designed to give pilots a chance to survive, not to guarantee that survival. Manned spacecraft levied more stringent demands. Most critical was the "off-the-pad abort mode." Before liftoff, the spacecraft perched some 45 meters from the ground atop a shell filled with potentially explosive chemicals, the Titan launch vehicle. [101] However rigorous the precautions, there was always the danger of some mischance setting it off. For a length of time that might stretch into hours before they were airborne, the crew would be aboard with no recourse, should that mishap occur, save their ejection seats. The Gemini seat had to be able to propel itself from a starting point 45 meters in the air in a trajectory stable enough to get clear of an exploding booster and high enough to allow parachutes to open. No existing seat could do that, and developing one that could was the crux of the Gemini effort.22

McDonnell chose Rocket Power, Inc., of Mesa, Arizona, to supply the rocket catapult (or rocat) for the Gemini escape system.23 For the seat itself, McDonnell turned to Weber Aircraft, of Burbank, California.24 As luck would have it, the Naval Ordnance Test Station at China Lake in the middle of California's Mojave Desert had earlier constructed a 45-meter tower for Sidewinder missile tests. This tower was admirably suited for simulated off-the-pad ejection (or, acronymically, Sope) tests.25 Kenneth F. Hecht, who left the ordnance test station in January 1962 to take charge of Gemini escape and recovery systems, set up a special working group to oversee seat development and qualification.* He was convinced, and in this he was seconded by those who knew most about ejection seats, that the key problem was finding ways to control the relationship between the rocat's line of thrust and the shifting center of gravity of the seat-man combination while the rocket was burning. Without this control, a trajectory of the proper height and stability could not be achieved. This was one of the reasons why Hecht insisted the tests be conducted with a dummy in the seat, rather than with a solid mass. He also knew that haste was vital, since the seat design could not be settled until the answers were in.26

The first Sope test came off on schedule 2 July 1962, followed by four more over the next month. All produced their share of problems and mechanical failures, each dealt with as quickly as possible to get on with the next test. None of these mechanical problems much bothered Hecht and his colleagues, because they had their eyes on the dynamic problem of rocket thrust and center of gravity. They were concerned with ejection at this point, not the complete escape sequence through recovery, and thought they were close to solving that key problem.27 From this viewpoint, the first five tests were a success. But if the goal were seen as a complete system with all parts working as they should in the final version, the tests left much to be desired. The seat seemed to be turning into a maze of makeshift fixes, and the personnel recovery parachute system (the crewman's landing device) had failed twice.

[103] At an extended meeting in Houston on 6 and 7 August, the total system viewpoint prevailed. Sope testing was halted until a complete design of the whole system was ready and the personnel parachute had been fully tested.28

A month elapsed before McDonnell was able to report on 6 September that seat design and testing were complete, clearing the way for a new round of Sope trials. Tests on 12 and 26 September went well but highlighted a set of problems with the rocket motor. Some were functional and some structural, but all affected, however slightly, the direction of thrust and so made accurate control impossible. Testing stopped again, pending the availability of the rocat in its final form.29 This delay was much prolonged, lasting well into 1963.

Other major Gemini systems seemed less troublesome. Through the summer and early fall of 1962, such problems as appeared could be, and were, regarded as nothing more than the routine hurdles in a large program. One possible exception was the fuel cell, which, like paraglider and ejection seats, was new to manned spacecraft and had aroused some debate, at least in its General Electric version.

The basic source of electrical power in the spacecraft was to be batteries. The weight of ordinary batteries, however, became prohibitive as missions increased in length. Something more was needed, and the choice was fuel cells. That choice was resolved in January 1962. After analyzing the merits and defects of competing approaches, Robert Cohen of MSC strongly recommended the General Electric fuel cell as lighter, simpler, and more generally suited to Gemini needs than other designs he had investigated.30

In a fuel cell, hydrogen and oxygen react to produce water and heat. The unique feature of the General Electric design was its use of a solid ion-exchanging membrane in which electrolyte and water were chemically bound; most other cells diffused gases into a liquid electrolyte. A separate stream of coolant condensed the water produced at the cell, then removed it through a series of wicks to keep the reaction going at a constant rate. This used little of the cell's own power, in contrast to the gas-diffusion cells that required a complex self-powered process of flushing with hydrogen, condensation, and centrifuging to remove the water produced. General Electric had devoted intense research to the design since 1959 and had already set up a fuel-cell facility, the Direct Energy Conversion Operation in West Lynn, Massachusetts.31 McDonnell shared Cohen's view and formally recommended General Electric for a subcontract, to which NASA agreed.32

Nonetheless, in early 1962 the General Electric fuel cell was still no more than a laboratory device, however promising.33 NASA Headquarters was looking into fuel cells for Apollo, which raised some questions about Gemini's choice of General Electric. The Office of Manned Space Flight's survey of General Electric alleged that the company was [104] understaffed, slow in getting started, and unlikely to meet Gemini schedules - all this in addition to what seemed to be an untested and questionable design concept.34 Cohen responded to these charges for GPO. He saw no reason to doubt that General Electric would meet its commitments: the company was adding to its staff and improving its effort, which had only begun with an order from McDonnell two and a half weeks earlier. More important, the much tested General Electric design was at least as far along as any other and was inherently simpler to boot.35 That settled the issue.

As development got under way, General Electric began to run into problems that seemed to suggest that theory had outpaced practice. The most serious in mid-1962 was how to achieve a satisfactory bond between cell membrane and frame. Solving these problems appeared more likely to tighten the schedules than to threaten the program as a whole. In any case, the worst appeared to be over by the end of August.36

During the last half of 1962, the paraglider's troubles probably posed the greatest threat to an approved Gemini objective, that of land landing, although ejection seats and, to a lesser extent, fuel cells were also worrisome. The paraglider was a major new system that demanded a large-scale effort. Ejection seats and fuel cells, though not so novel, were still major innovations in manned space flight. In all three cases, the novelty of the application and the advance beyond current practice imposed a greater development effort than required for other Gemini systems. Given that fact, the problems should have come as no surprise. A quite unexpected source of trouble loomed in another quarter. The suitability of Titan II as a launch vehicle for manned space flight came into question.

Responsibility for developing the Titan II missile belonged to the Ballistic Systems Division (BSD), like SSD a part of Air Force Systems Command. Titan II research and development test flights began on 16 March 1962, with a launch from the Atlantic Missile Range in Florida. In its first flight, Titan II displayed a disquieting characteristic. A minute and a half after it lifted off, while the first-stage engine was still firing, the missile began to vibrate lengthwise like an accordion about 11 times a second for roughly 30 seconds. This was not likely to bother a missile too much, but it implied real trouble for a launch vehicle with a manned payload. The steady acceleration of a booster like Titan II pressed a crewman to his couch with about two and a half times the force of gravity at that point in a normal flight. Bouncing at an extra two and a half gravities (+ 2.5g) could badly hamper a pilot's efforts to respond to an emergency, a matter of special concern in Gemini since the crew played so large a role in flying the spacecraft.37

Titan II's longitudinal oscillations quickly acquired the nickname "pogo stick," soon simply Pogo. Its cause remained unclear, how to get [105] rid of it a matter of guesswork. By July, Pogo was becoming a regular topic at MSC's weekly senior staff meetings, and BSD had formed a special Committee for Investigation of Missile Oscillations.** 38 The problem turned out to be surprisingly easy to solve for the missile: higher pressure in the first-stage fuel tank cut Pogo in half during the fourth test flight, on 25 July, although nobody was quite sure why.39

There were some ideas, however. Martin engineers thought the culprit might be oscillating pressure in propellant feedlines, analogous to the chugging of water in pipes, or "water hammer." This suggested the use of something like the surge tanks familiar as devices to stabilize pressure in the flow lines of hydroelectric plants and pumping stations. Martin proposed to install a surge-suppression standpipe in the oxidizer line of a later Titan II. MSC endorsed the plan, and BSD agreed. By the end of August, GPO was cautiously optimistic. The lowered Pogo level of plus or minus 1.25g achieved in the fourth Titan II test flight was still too high for manned space flight, but the water hammer analogy at least suggested an answer.40

GPO was also watching another problem. In two of its first four test flights, Titan II's second-stage engine failed to reach full thrust. The causes appeared to be different in each case and unrelated to one another. Just how serious this might be could not be foreseen. Much depended upon whether or not it recurred, and GPO adopted a wait-and-see stance.41

Project Gemini's technical problems in the summer and fall of 1962 might have aroused more concern if a far more serious threat had not intruded. The financial structure of the program began to totter. Two circumstances combined to produce a major crisis. On one hand, Gemini contractors were spending money at a much faster rate than the project office had expected. On the other, Congress was slow to approve NASA's appropriation for fiscal year 1963, which restricted the funds available to Gemini. However serious development problems might be, or become, they could always be resolved if there were enough money. But now the question was how to spread limited funds over an ever more costly program.

* Hecht's group included Edward A. Armstrong, Louis A Bernardi, Frederick T. Burns, Paul R. Penrod, Hilary A. Ray, and Stanley White.

** Chairman of the special committee was Abner Rasumoff of Space Technology Laboratories.

13 Letter, R. L. Thomas to MSC, Attn: Ronald C. Bake, 62MA-7227, 5 July 1962, with enclosure, "Monthly Progress Letter No. 7, Paraglider Development Program, Phase IIA, 20 May 1962 to 20 June 1962"; letter, Thomas to MSC, Attn: Bake, 62MA-7728, 1 Aug. 1962, with enclosure, "Monthly Progress Letter No. 8, Paraglider Development Program, Phase IIA, 20 June 1962 to 20 July 1962"; letter, Norbert F. Witte to MSC, Attn: Bake, "Contract NAS 9-167, Paraglider Development Program, Phase II, Part A, Monthly Progress Letter No. 9," 62MA10200, 1 Sept. 1962; letter, George W. Jeffs to MSC, Attn: Bake, "Contract NAS9-167, Paraglider Development Program, Phase II, Part A, Monthly Progress Letter No. 10 (21 August-21 September 1962)," 62MA13775, 26 Nov. 1962; letter, H. C. Godman to NASA Office of Manned Space Flight (OMSF), "C-130 Support of NASA Gemini Program (Paraglider Development)," 18 Sept. 1962; TWX, A. A. Tischler to MSC, Attn: Bake, "Preliminary Test Evaluation Review - Full Scale Dummy Drop No. 2," MA21334, 28 Aug. 1962; Quarterly Status Report No. 2, for period ending 31 Aug. 1962, p. 13; Quarterly Status Report No. 3, for period ending 30 Nov. 1962, p. 13; letter, Jeffs to MSC, Attn: Bake, "Contract NAS 9-167, Paraglider Development Program, Phase II, Part A, Monthly Progress Letter No.12 (21 October-20 November 1962)," 62MA15807, 31 Dec. 1962, p. 6 (with annotation, probably by Bake); memo, Lester A. Stewart to Joe W. Dodson, "Performance by Northrop Ventura in Developing Parachute Systems for Use in Project Gemini," GPO-00493, 13 Dec. 1962.

14 Letter, Paul F. Bikle to STG, Attn: Rodney G. Rose, "Synopsis of Flight Test Portion of Paraglider Development Study - Phase I," 12 Sept. 1961; memo, Stewart et al. to Dir., STG, "Paraglider Development Program; Evaluation of Design Studies; Contract NAS 9-135, Ryan Aeronautical Company; Contract NAS 9-136, North American Aviation, Inc.; Contract NAS 9-137, Goodyear Aircraft Corporation," 22 Sept. 1961.

15 NASA News Release 61-263, "Apollo Contractor Selected," 28 Nov.1961; Rose, telephone interview, 13 June 1969. A widely known and influential RAND study first published in 1960 had pointed out the dangers of limiting competition between prospective contractors to the design phase instead of continuing it through early development; Charles J. Hitch and Roland N. McKean, The Economics of Defense in the Nuclear Age (New York, 1965), p. 251.

16 Witte letter, 62MA10200, 1 Sept. 1962; Jeffs letter, 62MA13775, 26 Nov. 1962, pp. l-3; letter, Jeffs to MSC. Attn: Bake, "Contract NAS9-167, Paraglider Development Program, Phase II, Part A, Monthly Progress Letter No. 11, 20 September - 20 October 1962," 62 MA 13843, 26 Nov. 1962, p. 1.

17 TWX, Chamberlin to North American, Attn: Harrison A. Storms, Jr., "One-Half Scale Paraglider Program," GPO-50222, 21 Sept. 1962.

18 Witte letter, 62MA 10200, 1 Sept. 1962.

19 Rose interview.

20 Jeffs letters, 62MA13843, 26 Nov. 1962, pp. 1-2, and 62MA15807, 31 Dec. 1962. n. 2.

21 "Final Report of Paraglider Research and Development Program, Contract NAS 9-1484," North American, SID65-196, 19 Feb. 1965, p. 188.

22 Quarterly Status Report No. 1, pp. 20-21; Gordon P. Cress, interview, Burbank, Calif., 5 July 1966.

23 Memo, Chamberlin to Gemini Procurement Office, Attn: James I. Brownlee, "Contract NAS 9-170, Ejection Seat Rocket Catapult - Recommendation for Authorization for Procurement," GPO-00024, 28 March 1962; Arthur H. Atkinson, "Gemini - Major Subcontracts, McDonnell Aircraft Corporation," 3 July 1962.

24 Atkinson, "Gemini Major Subcontracts"; memo, Chamberlin to Gemini Procurement Office, Attn: Berg, "Project Gemini Ejection Seat Development Test Program," GPO-00097, 21 May 1962.

25 Chamberlin, activity report, 28 May 1962, p. 1; Chamberlin memo,, GPO-00097, 21 May 1962; Cress interview.

26 [Kenneth F. Hecht], "Comments on Chapter 5, Expansion and Crisis," [10 Feb. 1970], p. 1; memo, Hecht to Historical Office, "Comments on Chapter 6: The Nadir," 22 Sept. 1970; Hecht, telephone interview, 14 Nov. 1972; memo, Hecht to Mgr., GPO, "Gemini Escape System Management," 26 March 1962; "Abstract of Meeting on Ejection Seats, March 29, 1962," 3 April 1962.

27 "Abstract of Meeting on Ejection Seat Developmental Test Program, May 29, 1962," 4 June 1962; memo, Chamberlin to Dir., "Gemini Weekly Status Report (June 18, 1962)," GPO-00145, 18 June 1962; Quarterly Status Report No. 2, p. 17; Richard S. Johnston, "Life Systems Division Weekly Activities Report, 7/16/62 - 7/20/62," p. 3; Raymond L. Zavasky, recorder, "Minutes of Senior Staff Meeting, July 27, 1962," p. 4; memo, Richard P. Parten to Chief, Flight Operations Div., "Project Gemini Coordination Meeting on Mechanical Systems," 30 July 1962; memo, Chamberlin to Dir., "Gemini Weekly Status Report (August 6, 1962)," GPO-00257, 6 Aug. 1962; "Abstract of Meeting on Mechanical Systems, August 1-2, 1962," 7 Aug. 1962; Hecht, "Comments on Chapter 5," p. 1.

28 "Abstract of Meeting on Ejection Seats, August 3, 1962," 17 Aug. 1962; TWX, R. W. Miller to MSC, Attn: Chamberlin, "Gemini Ejection Seat Tests," 306-450-23281, 10 Aug. 1962; "Abstract of Meeting on Ejection Seats, August 6-7, 1962," 9 Aug. 1962; Weekly Activity Report for Office of the Director, Manned Space Flight, 5-11 Aug. 1962, MSC, p. 2; memo, Chamberlin to Dir., "Gemini Weekly Status Report (August 13, 1962)," GPO-00263, 13 Aug. 1962; Chamberlin, activity report, 27 Aug. 1962, p. 1.

29 "Abstract of Meeting on Ejection Seats, September 6, 1962," 11 Sept. 1962; TWXs, Miller to MSC, Attn: Chamberlin, "Gemini Ejection Seat Tests," 306-450-23965, 13 Sept. 1962, and 306-450- 24240, 28 Sept. 1962; "Abstract of Meeting on Ejection Seats, September 26, 1962," 3 Oct.1962; Quarterly Status Report No. 3, p. 18.

30 Robert Cohen, "Summary of analysis for selecting the power source for the Gemini Project," Gemini Project Note of January 23, 1962, 27 Jan. 1962.

31 Ibid., pp. 3-4; letter, Walter F. Burke to Wilbur H. Gray, "Selection of Equipment, Contract NAS 9-170, Fuel Cell System," 306101-142, 23 Feb. 1962, with enclosures, "Chosen System Advantages, General Electric Fuel Cells" and "Substantiation of Selected Vendor Capability"; R. H. Blackmer and G. A. Phillips, "Ion-Exchange Membrane Fuel Cell for Space Vehicle Electric Power," presented at the Society of Automotive Engineers National Aerospace Engineering and Manufacturing Meeting, Los Angeles, 9-13 Oct. 1961; J. L. Schanz and E. K. Bullock, "Gemini Fuel Cell Power Source - First Spacecraft Application," ARS Paper No. 2561-62, presented at the American Rocket Society Space Power Systems Conference, Santa Monica, Calif., 25-28 Sept. 1962; "Fuel Cells for Spacecraft, Including Determination of Fuel Battery Size for Specific Application," brochure by Direct Energy Conversion Operation, General Electric, January 1964, pp. 3-4.

32 Burke letter, 306-101-142; letter, Gray to Burke, "Selection of Equipment, Contract NAS 9- 170, Fuel Cell System," NAS/170-265, 21 Feb. 1962.

33 John H. Russell, interview, West Lynn, Mass., 24 April 1968.

34 Memo, George F. Esenwein to George M. Low, "Informal Visit to General Electric Direct Energy Conversion Operation on March 26, 1962 to discuss possible Apollo Fuel Cell Backup and Polymer A Status," 2 April 1962; James F. Saunders, Jr., telephone interview, 14 Nov. 1972.

35 Letter, Chamberlin to NASA Hq., Attn: Low, "Fuel Cell for Gemini," GPO-00026, 5 April 1962, with enclosures, memo, Cohen to Mgr., Project Gemini, "Status of General Electric Co. Fuel Cell Development for Gemini," 5 April 1962, and Cohen, "Summary of Analysis."

36 Memo, Gray to Chamberlin, "Visit to Direct Energy Conversion Operation, General Electric Go., West Lynn, Mass.," NAS/170-706, 5 Sept. 1962; Quarterly Status Report No. 2, pp. 21-22.

37 R. H. Prause and R. L. Goldman, "Longitudinal Oscillation Instability Study: POGO," Martin ER-13374, December 1964, pp. 1-3; Quarterly Status Report No.6, for period ending 31 Aug. 1963, fig. 4; Jerome B. Hammack, interview, Houston, 19 Aug. 1966.

38 Zavasky, "Minutes of Senior Staff Meeting[s], July 13, 1962," pp. 1, 3, "July 20, 1962,"p. 3, and "July 27, 1962," pp. 1, 3; Prause and Goldman, "POGO Study," p. 3.

39 Zavasky, "Minutes of Senior Staff Meeting[s], July 27, 1962,"p. 3, and "August 3, 1962," p. 2; Quarterly Status Report No. 6, fig. 4.

40 Quarterly Status Report No. 2, pp. 24-25; Prause and Goldman, "POGO Study," pp. 3, 20; Zavasky, "Minutes of Senior Staff Meeting, August 10, 1962," p. 4; "Joint Titan II/Gemini Development Plan on Missile Oscillation Reduction and Engine Reliability and Improvement," [Air Force Systems Command], 5 April 1963 (revised 7 May 1963), enclosure 3, "Missile Configuration/Oscillation Summary."

41 Quarterly Status Report No. 2, p. 25.

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