Escape system development trials had come to a halt in August 1963 as the system went through another series of design changes and some of its key parts, particularly pyrotechnics, remained hard to get. Active testing resumed on 22 November, with the first in a projected series of about 30 drops of the ballute, which had been added to the crew parachutes for the sake of high-altitude stability. The first 10 tests, which involved both men and dummies and used a ballute 91 centimeters (36 inches) in diameter attached by a single riser, ended on 9 January 1964. In each case, the subject spun too rapidly on the riser.* This was solved by raising the ballute diameter to 122 centimeters (48 inches) and using two-point suspension.  Fourteen more drops over the next few weeks, the last on 5 February, confirmed the changes, and the ballute was ready for its qualification tests.35
Only two days later, sled-ejection development trials also came to an end. Testing had resumed with the fourth run, on 16 January, and ended with the fifth, on 7 February. Everything worked in both tests. Since simulated off-the-pad and ballute development tests had already been completed, the successful 7 February test brought the development phase of escape-system testing to a close.36 Neither fuel cell nor thruster was so far advanced.
Fuel-cell production had stopped in late November 1963, as a pair of GE task groups sought to resolve the system's stubborn engineering and manufacturing problems. Within six weeks they had finished their work, which furnished the basis for turning the program around. Everyone involved in the fuel-cell program gathered in Houston on 27 January 1964 to review development status and decide what to do about it. All agreed that the system needed redesigning. The current PB2 model was to be discontinued; the units already built were to be used for limited testing and to be carried in Spacecraft 2 to gather data and help qualify the reactant supply system. All future cells were to be the new P3 design, and they were to be installed in every spacecraft beginning with the fifth.37
Major changes in the new model reflected the narrow technical nature of the problems: dams (or baffles) were added to improve hydrogen distribution; the water collection wick was removed from each cell; and the orifice of the hydrogen feed tube of each unit was restricted so that any stoppage caused by water clogging could be cleared. Other changes included adding Teflon to the electrode to cut the loss of active material from the membrane and an anti-oxidant to the membrane to slow the rate of polystyrene breakdown. Tests had also suggested that the crucial problem of short operating life might respond to reduced temperatures. When further tests confirmed this finding, the coolant supplied to fuel cells was adjusted for lower temperatures.38
Although fuel-cell problems were largely technical, GE decided the program could be better managed. It reorganized the Direct Energy Conversion Operation to work solely on the Gemini fuel-cell program. Roy Mushrush, the new manager, had a background as corporate troubleshooter for GE. He arrived on the scene with a blank check on the company's resources for whatever help he needed. Mushrush was seconded by Frank T. O'Brien as Gemini manager. Both men impressed a NASA visitor with their enthusiasm, and morale throughout the plant remained high despite the shakeup.39
The fuel-cell program was still a question mark, and no one could be fully certain that the system would be ready in time for Gemini. But in the early spring of 1964, the program's technical and managerial  problems seemed to have been taken in hand, and prospects were a good deal brighter than they had been. By the end of May, GE had finished switching to the P3 design and had started a broad test program.40
Rocketdyne's thruster development program was also turning a corner. So far, attempts to improve performance had been little more than stopgaps, centered chiefly on cutting the engines' thermal load by dropping the ratio of oxidizer to fuel. But lower working temperatures and longer engine life were being achieved at the expense of combustion efficiency and specific impulse. This was one of three major topics discussed at a review of thruster problems in Houston on 23 December 1963. Rocketdyne was directed to cut the current oxidizer to fuel ratio of 1:1.3 still further, if that could be done without harm to good starting and stable burning.
Study of another expedient was also approved: shifting the sidefiring thrusters to align them more closely with the spacecraft center of gravity and so reduce demands on the smaller attitude thrusters in holding spacecraft attitude during lateral moves. Development of this small engine was the least hopeful aspect of thruster work - no one really understood what its design ought to include, and tests produced large and hard-to-explain variations. No attitude thruster had yet shown itself able to fire through a complete mission duty cycle without failure.
A third decision, of greatest impact on grew out of the 23 December review. André Meyer, chief of GPO administration, had been urging a change in the design of the ablation material lining the thrust chamber. A newly developed parallel-laminate material showed promise as an answer to thruster-life problems. Meyer wanted the laminates oriented nearly parallel to the motor housing, instead of perpendicular as before. His efforts to convince both McDonnell and Rocketdyne to make this change had been resisted because of its expense, but now, strongly backed by MSC Director Robert Gilruth, the idea was accepted and an engine to test the concept was ordered built.41
The thruster picture brightened perceptibly over the next month. Further tests confirmed that reduced oxidizer-to-fuel ratios prolonged engine life, bringing the maneuvering thrusters within sight of their required mission duty cycles. The performance of the smaller attitude thrusters also improved, though not as much. By mid-January 1964, NASA Headquarters felt sanguine about the prospects for Gemini's big thrusters but saw little hope for so happy an outcome to the development of the smaller thrusters. There was strong support for a study of a radiation cooled engine as a backup.42
Meanwhile, Rocketdyne's efforts during the last two months of 1963 to work out the basic problems of small ablative engines had also borne fruit. A search through the files uncovered a research report on  the problem of heat flux in small engines and an answer in the technique of "boundary-layer cooling." The injector of a maneuvering thruster was modified to spray about a quarter of its fuel down the walls of the thrust chamber before firing. On 25 January 1964, Rocketdyne tested the engine through its full mission duty cycle without failure, its liner charring only to a depth of little more than a centimeter (one-half inch). A second thruster produced the same results. Since the lining of the flight weight engine was twice that thick, the margin seemed ample. Buoyed by these results, GPO, after a meeting at the McDonnell plant in St. Louis on 13-14 February, ordered McDonnell to have boundary-layer cooling designed into the larger thrusters in time for Spacecraft 5.43
The smaller attitude thrusters did not respond as well to boundary-layer cooling, although it helped. A modified injector, combined with an oxidizer-to-fuel ratio of 0.7:1, allowed one small engine to survive a 570-second firing on 15 February with some of its liner intact; in earlier tests with the same ratio but without the injector, the liner had not lasted beyond 380 seconds. Two flight-weight engines with the new injector and lower ratio lasted for 435 and 543 seconds. Another change made these results look even better. Canting the lateral engines to direct the thrust vector closer to spacecraft center of gravity (as suggested at the 23 December meeting) was shown to reduce the thruster life needed to less than 400 seconds.44
By mid-March 1964, thruster development and qualification appeared likely to be completed in time, though without much leeway to handle any new problems and with performance that was still marginal. In April, that status was transformed. Thrust chambers lined with laminated ablative material oriented almost parallel (at an angle of only 6 degrees) to the motor housing achieved dramatically better performance. The first modified attitude thruster endured 2,100 seconds of burning without failure on 14 April, a fourfold increase over the best prior test. And the next day, a maneuver thruster with boundary-layer cooling and the 6-degree wrap fired for 1,960 seconds, the test ending only when fuel was exhausted. Just as striking was the first test of a lateral thruster with the new wrap: 3,049 seconds of firing time without failure. George F. MacDougall, Jr., Deputy Manager of Program Control in GPO, reported the results to the MSC senior staff as "a major breakthrough."45
Convinced that the answer had been found, GPO lost no time. Within two days after the first tests of the small and large thrusters, McDonnell and Rocketdyne had orders to replace 90-degree with 6-degree wraps in all thrusters and to see that the new thrusters were' installed in the orbital attitude and maneuvering systems of all spacecraft beginning with the fifth and in the reentry control systems of all spacecraft as soon as possible. By 1 May, however, Spacecraft 5 looked  too early for a complete set of new engines. Instead, all its attitude thrusters would have the modified injector and 6-degree wrap, but only the aft-firing maneuvering engines would feature the new design. The less critical lateral- and radial-firing engines would be the old model. All thruster designs were now frozen, with further testing limited strictly to qualification.46
Rocketdyne was by no means home free, but the worst of the spacecraft propulsion systems' technical problems did appear to be over by the spring of 1964. The fuel cell also seemed to be in good shape. Gemini's escape system, already through its development test program, may have looked best of all. As later events were to show, the promise was not quite that easy to fulfill. But none of these three most stubborn systems was slated for the first Gemini spacecraft which McDonnell had been building in its St. Louis plant.
* The Air Force furnished the human subjects for these tests - Colonel Clyde S. Cherry, Chief Warrant Officer Charles O. Laine (who made the first jump), and Chief Warrant Officer Mitchell B. Kanowski.
35 Weekly Activity Report, 17-23 Nov. 1963, p. 1; Gemini Press Reference Book (McDonnell, St. Louis, Mo., ca. March 1965), pp. 57-58; 1st Lt. Dennis R. Mans and A1C John R. Younger, "History of the 6511th Test Group (Parachute), 1 January-30 June 1964," AFSC Historical Publications Series 64-1 10-V, n.d., p. 26; Kenneth F. Hecht, telephone interview, 22 July 1971; Weekly Activity Report, 1-7 Dec. 1963, p. 1; Consolidated Activity Report, 22 Dec. 1963 - 18 Jan. 1964, p. 18; Weekly Activity Report, 2- 8 Feb. 1964, p. 12; Consolidated Activity Report, 19 Jan. - 15 Feb. 1964, p. 19; TWX, Mathews to Walter F. Burke, GP-54571, 14 Feb. 1964; Col. Clyde S. Cherry, interview, Edwards AFB, 20 April 1966; "Just in Case of Trouble," in Goodyear Aerospace Profile, Vol. II, No. 2 (Ohio, 2nd Quarter 1964), pp. 10-11.
36 Quarterly Status Report No. 8, for period ending 29 Feb. 1964, pp. 29-30; Gordon P. Cress and C. E. Heimstadt, interviews, Burbank, Calif., 5 July 1966.
37 Quarterly Status Report No. 8, pp. 48-49; TWX, Mathews to Burke, Attn: George J. Weber, "Contract NAS 9-170: Fuel Cell Program," GP-54541, 10 Feb.1964; TWX, Mathews to McDonnell, Attn: Burke, GS-53211, 18 March 1964.
38 Quarterly Status Report No. 7, for period ending 30 Nov. 1963, pp. 61-62; Weekly Activity Report, 2-8 Feb. 1964, p. 11; Quarterly Status Reports No. 8, pp. 48-49, and No. 11, pp. 15-16; "Fuel Cell Development" in "Gemini Administrators Review, 1964."
39 Memo, Wilbur H. Gray to Mathews, "Visit to General Electric Company, DECO, West Lynn, Mass.," GM-4224, 31 March 1964.
40 Quarterly Status Report No. 9, p. 31.
41 Consolidated Activity Report, 22 Dec. 1963 - 18 Jan. 1964, pp. 15-16; Ron Helsel, interview, Canoga Park, Calif., 16 May 1967; Schneider interview; memo, Meyer to MSC Historical Office, "Comments on Draft Chapters 7 and 8 of Gemini Narrative History," 6 Jan. 1972.
42 Meyer, notes on GPO Staff meeting, 8 Jan. 1964; memo, James R. Flanagan to Mueller, "Gemini OAMS Engines," 16 Jan. 1964; Larry E Stewart, interview, Canoga Park, Calif., 16 May 1967.
43 Quarterly Status Report No. 8, pp. 19-20; Consolidated Activity Report, 19 Jan-15 Feb. 1964, p. 16; Meyer, telephone interview, 25 Jan.1973; Meyer, notes on GPO staff meeting, 30 Jan. 1964, p. 1; TWX, Mathews to McDonnell, Attn: Burke, GS-53192, 25 Feb. 1964; Stephen J. Domokos, interview, Canoga Park, Calif., 16 May 1967.
44 TWX, Mathews to McDonnell, Attn: Burke, GP-54605, 6 March 1964; memo, Flanagan to Mueller, "Gemini OAMS Engines," 20 March 1964.
45 TWXs John Brown to MSC, Attn: Mathews, "Gemini Bidaily System Status Report[s] No. 51, RCS and OAMS," 306-16-5792, 15 April, "No. 52," 306-16-5800, 17 April, and "No. 62," 306-16-6272, 22 May 1964; Raymond L. Zavasky, recorder, "Minutes of Senior Staff Meeting, April 17, 1964," p. 4.
46 TWX, Mathews to McDonnell, Attn: Burke, GS-53233, 16 April 1964; letter, John Brown to MSC, Attn: Mathews, "Minutes of NASA/MAC Management Meeting of 17 April 1964," 306-16-6187, 22 April 1964, with enclosure, minutes, p. 4; TWX, Brown to MSC, Attn: Mathews, "Contract NAS 9-170, Project Gemini - Incorporation of 6 Degree Ablative Material in Gemini Thrust Chamber Assemblies," 306-16-6189, 29 April 1964; TWX, Brown to MSC, Attn: Mathews, "TCA Configurations for Spacecraft 5 and Subsequent," 306-16-6195, 7 May 1964; TWX, Mathews to McDonnell, Attn: Burke, GS-53253, 2 June 1964.