Transiting from Air to Space
The North American X-15


Those concerned with the success of the X-15 had to monitor the development of the proposed XLR99 rocket engine, the auxiliary power plants, an inertial system, a tracking range, a pressure suit, and an ejection seat. They had to make arrangements for support and mother aircraft, for ground equipment, for the selection of pilots, and for the development of simulators for pilot training. It was necessary to secure time on centrifuges, in wind tunnels and on sled tracks. The NACA ”Q-ball” nose had to be developed, studies made of the compatibility of the X-15 and the mother aircraft, other studies on the possibility of extending the X-15 program beyond the goals originally contemplated and on the potential of the X-15 as a trainer in other space programs. In addition to such tasks, funds to cover ever increasing costs had to be secured if the project were to have any chance of ultimate success, and at certain stages, the effects of possibly harmful publicity had to be considered. With such multiplicity of tasks, it could be expected that difficulties would be encountered and several serious problems did arise. Probably the most serious difficulties, and certainly those which gave rise to the greatest concern, arose during the development of the XLR99 engine.

A suitable engine for the X-15 had been somewhat of a problem from the earliest stages of the project, when the WADC Power Plant Laboratory had pointed out that the lack of an acceptable rocket engine was the major shortcoming of the NACA's original proposal. While the Power Plant Laboratory felt that the Hermes A-1 engine selected by the NACA planners was not capable of being developed into a safe engine for a manned vehicle, no very practical alternative was immediately available. The laboratory did suggest several engines ”more suitable” for manned aircraft, but essentially WADC urged further study before the final selection of a specific engine. In October 1954, the representatives of the Air Force, Navy, and NACA, who were planning the X-15 competition, selected four engines as possible X-15 power plants. They did not forbid proposals to use engines other than those named, but a bidder who desired to utilize another engine was faced with the additional complication of joining with the manufacturer of the proposed engine to produce a justification for the selection of a non-listed item. The justification was to be presented to the Weapon System Project Office and that office could approve or disapprove the use of the engine. 1

The first really concrete descriptions of the proposed X-15 engines appeared in correspondence of 15 November 1954. Mr. T. J. Keating, chief of the Non-Rotating Engine Branch, Power Plant Laboratory, wrote Mr. J. B. Trenholm, of the systems directorate, as a result of a conference of 22 October 1954. The conference, held at the Directorate of Laboratories and attended by representatives of the Navy, Air Force, and the NACA, had been for the purpose of planning the procurement procedures to be followed in selecting a contractor for the X-15. Those attending the conference evidently felt that they did not have adequate information on rocket engines; Mr. Keating's note constituted a summary of the status of rocket engines under development at that time, particularly those that seemingly could, with further development, be made into suitable power plants for the X-15.

The Power Plant Laboratory did not believe that any available engine was entirely suitable for the X-15 and held that no matter what engine was accepted, a considerable amount of development work could be anticipated. Most of the possible engines were either too small or would need too long a development period. In spite of these reservations, the laboratory listed a number of engines worth considering and drew up a statement of the requirements for an engine that would be suitable for the proposed X-15 design. The laboratory also made clear its stand that the government should ”… accept responsibility for development of the selected engine and … provide this engine to the airplane contractor as Government Furnished Equipment.” 2

The primary requirement for .an X-15 engine, as outlined by the Power Plant Laboratory in 1954, was that it be capable of operating safely under all conditions. Service life would not have to be as long as for a production engine, but engineers hoped that the selected engine would not depart too far from production standards. The same attitude was taken toward reliability, that is, the engine need not be as reliable as a production article, but it should approach such reliability as nearly as possible. There could be no altitude limitations for starting or operating the engine, and the power plant would have to be entirely safe during start, operation or shutdown, no matter what the altitude. The engine was also to be capable of safe operation under the highest ”g” conditions to be encountered during the operation of the X-15.

The Power Plant Laboratory did not try to define the exact thrust values to be attained by the selected engine, holding that such a determination would have to await a more complete definition of the aircraft itself. However, the laboratory did make it quite clear that a variable thrust engine capable of repeated restarts was essential. Again, laboratory specialists did not try to set the range of variability or the number of restarts, preferring to wait until more was known about the X-15 design itself.

The laboratory also warned that none of the engines tentatively selected was entirely satisfactory for the proposed program; the list was composed of engines with the best possibilities for development into a suitable power plant for the X-15. To assist in evaluation, the Power Plant Laboratory prepared a summary of the current status of each engine, and forwarded an estimate of necessary changes to development objectives and development schedules in order to produce an adequate engine within the time limit imposed by the X-15 program.

The engine ultimately selected was not one of the four originally presented as possibilities by the Power Plant Laboratory. The original list included the Bell XLR81, the Aerojet General XLR73, North American's NA-5400 and Reaction Motors' XLR10. The ultimate selection was foreshadowed, however, in discussions of Reaction Motors' XLR10, during which attention was drawn to what was termed ”… a larger version of Viking engine (XLR30).” 3 In the light of subsequent events, it was interesting to note that the laboratory thought the XLR30 could be developed into a suitable X-15 engine for ”less than $5,000,000” and with ”approximately two years' work.” 4 a

(The AMC letter of 30 December 1954, which invited selected members of the aircraft industry to participate in the development of a new research aircraft, incorporated the Power Plant Laboratory's recommendations of November, in their entirety.) 5

During the month of January, additional interest was shown in the XLR30 engine as a possible X-15 power plant; on 25 January 1955, AMC asked Reaction Motors for additional details on that company's engines. 6Reaction Motors replied on 3 February 1955 by elaborating on the details of both the XLR10 and the XLR30. The firm recommended four possible combinations as being suitable for the X-15 program: an XLR30 using liquid oxygen and anhydrous ammonia, an XLR30 using liquid oxygen and a hydrocarbon fuel, an XLR10 using liquid oxygen and ethanol, and an engine to be composed of two XLR10 chambers fed by a single XLR30 turbopump. All four versions utilized hydrogen peroxide for turbopump drive. Evidently Reaction Motors already had an idea of what the airframe contractors were planning, for the company frankly stated doubt that one XLR10 was ”… adequate to perform the objectives of this type of aircraft.” Reaction Motors also recommended against an attempt to make the XLR30 operable with hydrocarbon fuel, largely because the company felt this version of the engine would require a longer development period than would the version utilizing anhydrous ammonia. Again, Reaction Motors preferred the XLR30 over the proposed combination of XLR10 thrust chambers with an XLR30 turbopump. This last choice was made because, at relatively the same cost, the single chamber XLR30 would result in a simpler and more reliable engine. Reaction Motors also pointed out that the volatility of anhydrous ammonia would make for safer restarts, that the XLR30 would need fewer parts, it would be simpler to install than the configuration utilizing two XLR10 chambers.

In summing up arguments for the XLR30 utilizing ammonia as a fuel, Reaction Motors stated that the cost of such an engine would be as low as any of the configurations, that it would be simpler and more reliable, and that its weight would be only 420 pounds compared to 815 pounds for the double-chambered engine. The company also estimated that the XLR30 could be throttled to 30 percent of full thrust, permitting a variation between 17,000 and 57,000 pounds of thrust at 40,000 feet. A specific impulse of 278 seconds seemed possible at full rated thrust. The compact size of the XLR30 (installation space was to be 30 inches in diameter and only 70 inches in length) was given as an additional reason for preferring that engine over the larger XLR10-XLR30 combination. 7

While Reaction Motors was clearly interested in promoting the anhydrous ammonia version of the XLR30, the Air Force still favored the XLR10. On 4 February 1955, AMC asked Reaction Motors for still more detailed information on the XLR10. 8 On the same date a conference between Reaction Motors and the Air Force decided that all data submitted for the proposed X-15 engine would be for the XLR30 rather than for the XLR10. The Reaction Motors' representatives indicated that the XLR10 would need considerable development if it was to be made into a safe engine at all flight attitudes. They contended that since both engines required further development, the XLR30 was the better choice because it would ultimately be a superior engine. Reaction Motors' opinion prevailed, and on 24 February, the company was advised that it ”… should make all further estimates on the basis of the XLR30's development.” 9

The engine information submitted by Bell, Aerojet, and Reaction Motors was forwarded to the prospective airframe bidders on 18 March 1955. 10

On 22 March the project office forwarded its comments on the data furnished three days earlier. Among the comments was the statement that the Bell and Aerojet engines would probably have to be used in multiples if the thrust requirements of the X-15 were to be met. Prospective contractors were also advised that the engine that was eventually to be furnished would be capable of safe operation, whether or not fuel and oxidizer exhaustion was signaled to the pilot. The fact that the developed engine was not being considered as a production item was made clear, and the airframe manufacturers were told that the operating time of the engine should only be limited by the amount of the propellants available. The prospective contractors were optimistically told they could expect the selected engine to be ready for flight test use within 30 months after the airframe contract was signed, but they were also warned that there probably would be some change in weights as a result of the development effort. 11

On 26 April 1955, WADC received approval from Headquarters ARDC for a plan to require detail configurations of the engines involved in the X-15 program. Command headquarters requested that "the engine program be subjected to a final critical review apart from, but concurrent with the evaluation of the airframe proposals." WADC was advised to get a firm commitment from each of the engine contractors and to include the results of the engine evaluations in support of the recommendations on the X-15 itself. 12

On 20 June 1955, the Directorate of Weapon Systems Operations asked the Power Plant Laboratory for an evaluation of the proposed engines for the X-15. The laboratory was advised that the evaluation was to be conducted in cooperation with the Navy and NACA, and that the results were needed by 12 July. 13 Results of the requested evaluation were forwarded to the project office in mid-July. Evaluations were based in part on briefings presented by the contractors on 14 June and on the outcome of evaluation meetings held on 15–16 June and 6–7 July .

The evaluation group reported that none of the proposed power plants had sufficient superiority over the others to justify changing the engine selected by the contractor with the best X-15 design. As none of the X-15 proposals included the Aerojet engine as a first choice, that company's XLR73 was eliminated from final consideration. b The evaluators felt that the Bell engine was more likely to be developed within the time limits of the project but that its superiority in this respect was so small as not to dictate its choice over the engine proposed by Reaction Motors. At the time of the evaluation, the cost of the Bell engine was estimated at $3,614,088 while a figure of $2,699,803 was given for the engine proposed by Reaction Motors.

In comparing the relative merits of the Bell and Reaction Motors' proposals, the Power Plant Laboratory pointed out that the internal fuel and gas generator systems of the Bell design each utilized two fuels interchangeably and that this feature made for complicated valving and fuel flow systems. It seemed probable that the separate starting system for meeting the repeated start requirements of the X-15 engine would create some problems of safety and reliability. The Reaction Motors' engine, while more orthodox than the Bell, had been little tested. The laboratory correctly predicted that difficulties would be encountered in attempting to achieve an acceptable service life and the required degree of reliability. In considering the safety of the two designs, the laboratory reported that Bell had more experience than had Reaction Motors, but that both designs would need additional development before either could be considered a safe engine for a manned aircraft. The laboratory was also correct in predicting that the thrust chamber cooling of the Reaction Motors' design might present some difficulty.

The Power Plant Laboratory judged the designs on the basis of their feasibility, safety, reliability, performance characteristics, weight, installation requirements, the magnitude of development problems, the capability of the contractor, and the applicability of the engine for the proposed missions of the X-15. The laboratory's report pointed out that the airframe designers would undoubtedly take other factors into account, factors such as the nature of the propellants and their weight, the number of controls required, and the merits of multiple versus single engine installations.

An additional factor which, in the view of the Power Plant Laboratory, had not been given adequate consideration by the airframe contractors or by the evaluation rules, was that of minimum thrust. The laboratory stated that if a requirement existed for operation of the engine at less than 50 percent of the rated thrust, such a requirement would have an important bearing on engine selection. It was intimated that the laboratory's evaluation would have been different if one of the design objectives had specified an engine capable of operating at half or less than half of the rated thrust.

The Power Plant Laboratory's evaluation, while making no major distinction between Reaction Motors' proposals and those of Bell, left the definite impression that the Bell design was favored. Nowhere was this more clearly apparent than in the laboratory's statements that the ”… Bell engine would have potential tactical application for piloted aircraft use whereas no applications of the RMI engine are foreseen,” and ”in the event that the XLR73 development does not meet its objectives, the Bell engine would serve as a 'backup' in the Air Force inventory.”

Looking forward to the actual selection of one of the two proposals under consideration, the laboratory made recommendations on the course of development that should be followed. In the case of the Bell engine, evaluators suggested that hydrogen peroxide be considered for the turbine drive, and that an effort be made to simplify starting and to reduce the development effort by substituting unsymmetrical dimethyl hydrazine for JP-X. If the Reaction Motors' design emerged as the final selection, it would meet laboratory recommendations that the throttling range be restricted in order to reduce the development effort, that consideration be given to converting the engine from ammonia to JP-4 to reduce corrosion and handling problems, and finally, that an NACA suggestion to use an interim ”off-the-shelf” engine for initial flight testing be adopted. 14

Apparently little attention was paid to these recommendations as the throttling range was not reduced, ammonia was retained as a fuel, and no consideration was given to the use of an interim engine until development difficulties compelled the selection of such an engine in early 1958.

After North American had been selected as the winner of the X-15 competition, plans were instituted to procure the modified XLR30 engine that had been incorporated in the winning design. Late in October, Reaction Motors was notified that North American had won the X-15 competition and that the winner had based his proposals upon the XLR30 engine. 15

On 1 December 1955, the New Developments Office of Fighter Aircraft Division, Directorate of Systems Management, asked the Power Plant Laboratory to initiate a purchase request that would provide $1,000,000 for a proposed letter contract with Reaction Motors. 16 On 8 December the Air Materiel Command asked Reaction Motors to submit a proposal that would permit the Air Force to prepare a contract covering the development of an engine for the X-15. AMC suggested that the proposal contain visual presentations of a proposed development program, a chart of important milestones, and various cost estimates. The materiel organization also asked Reaction Motors to provide information on the amount of testing anticipated and contractor capabilities for conducting the required tests. 17 The letter requesting a proposal from Reaction Motors included a preliminary informal work statement and list of the minimum requirements for the modified XLR30 engine. The content of the attachments differed only slightly from the requirements eventually incorporated in the formal contract. 18

While preliminary steps were being taken to procure the required engine, the Power Plant Laboratory raised a further question as to the desirability of the engine selected. The NACA had, as a result of preliminary discussions with Reaction Motors, expressed concern that the ammonia fuel might have an adverse effect on planned instrumentation and had asked that the possibility of converting to another fuel be given further study. The Power Plant Laboratory, already convinced that the contractor's estimate of a two-year development period was much too optimistic, viewed any change with disfavor. The laboratory had been reluctant to accept a two-and-one-half year estimate during the original evaluation of the proposed X-15 engines, holding that a three year period was probably more realistic. Propulsion engineers estimated that a change in fuels would extend the development period to four years, and the laboratory held that such an extension would make the original evaluation invalid. If a four-year development period was to become acceptable, the laboratory recommended a reevaluation that would permit reconsideration of engines that had considerable potential but which had been eliminated from the original evaluation because their development period had been estimated at more than two and one-half years. 19

In late December, the Power Plant Laboratory advised the project office that whatever procurement procedure was followed in securing an engine for the X-15, certain features should be insisted upon. Among the features that the laboratory felt to be important were the retention of Reaction Motors as the engine contractor, a requirement that North American could not change the engine selection without prior approval of the project office and the Power Plant Laboratory, and a provision for close coordination and direct contact between the laboratory and Reaction Motors, no matter what contractual procedure was utilized. 20

The end of 1955 was also marked by a skirmish over the assignment of cognizance for the development of the engine. The skirmish began with a letter to Air Force headquarters for Rear Admiral W. A. Schoech, assistant chief for research and development in the Bureau of Aeronautics. Admiral Schoech contended that since the XLR30-RM-2 rocket engine was the basis for the X-15 power plant, and the Bureau of Aeronautics had already devoted about three years to the development of that engine, it would be logical to assign the responsibility for further development to the Navy. The admiral felt that retention of the program by the bureau would expedite development, especially as the Navy could direct the development toward an X-15 engine by making specification changes rather than by negotiating a new contract. Other arguments advanced for bureau retention of the project included the close and satisfactory working relationships between the bureau and Reaction Motors and the ability of the Navy to make the facilities at Lake Denmark available for the program. The Navy's extensive experience with hydrogen peroxide was also put forth as a justification for continuing the program under the Bureau of Aeronautics. 21

Air Force headquarters sent the admiral's letter to the commander of the Air Research and Development Command on 9 December asking for resolution and comment by 3 January. 22 On 29 December a teletype conference was held between ARDC headquarters and personnel from ARDC Detachment One at Wright Field. The Navy's bid for responsibility for the development of the engine had apparently been forwarded to Detachment One and the Power Plant Laboratory for comment, as the conference was devoted to refutation of the arguments advanced by the Bureau of Aeronautics for retention of the engine program. 23

ARDC headquarters summarized the arguments of Detachment One and the Power Plant Laboratory and forwarded the summary to Air Force headquarters on 3 January 1956. The Navy's bid for control of the engine development was rejected on the grounds that the management responsibility should be vested in a single agency, that conflict of interest might generate delay, and that the Bureau of Aeronautics was underestimating the time and effort that would be needed to make the XLR30 a satisfactory engine for manned flight.

The arguments for Air Force retention of control were based on the fact that the Power Plant Laboratory was acquainted with the status of Reaction Motors' developments, that it had experience with several similar projects for the development of rocket engines for manned aircraft, and that experienced personnel were available to monitor the program. The ARDC letter also pointed out that past experience had shown that more problems could be expected in the assembly of components into an operating engine and adaptation of the engine to the airframe than in the development of components-and the Navy's experience with the XLR30 had been largely with component development. As the original Bureau of Aeronautics letter had raised the problem of the availability of test facilities, ARDC noted that the Air Force was already using Reaction Motors' facilities and could expect that those facilities would be made available for the XLR30 program. Admiral Schoech's letter had also stated that plans called for the use of an XLR8-RM-8 as an interim engine and that the Bureau of Aeronautics' knowledge of this engine was an additional reason for assigning engine development to the Navy. This last contention was denied with the flat statement that there were no plans for the use of an interim engine. 24 c

Apparently the Bureau of Aeronautics accepted the Air Force's decision that engine development was to remain an Air Force responsibility for there was no evidence of additional correspondence on the subject.

The Navy's bid for cognizance over engine development may have served to hasten the procurement procedures; Reaction Motors was furnished with a final work statement and the performance requirements for the engine on 4 January 1956, the day after ARDC's comments on the Bureau of Aeronautics' letter went forward to Air Force headquarters. 25 The Power Plant Laboratory received Reaction Motors' technical proposal on 24 January and the company's cost proposals on 8 February. 26

The cover letter which accompanied the various reports and cost breakdowns from Reaction Motors promised delivery of the first complete system ”… within thirty (30) months after we are authorized to proceed.” 27 The same letter marked the abandonment of the XLR30 designation that had been used for convenience in previous discussions of the proposed X-15 engine. Reaction Motors, recognizing that the developed engine was going to have numerous differences from the XLR30, gave the new design a ”company designation,” TR-139. (On 21 February the Power Plant Laboratory formally requested assignment of an XLR99-RM-1 designation.) d Reaction Motors also estimated that the entire cost of the program would total $10,480,718, stated that the company would prefer that the fee be determined by later negotiation, and noted that preliminary design and liaison work had begun on 1 January in anticipation of a contract award. 28

Evidently the rate at which the procurement negotiations were proceeding was unsatisfactory to the NACA, for on February 15 Brigadier General V. R. Haugen, then the WADC deputy commander for development, felt it necessary to reassure the NACA that he had investigated the apparent delay in awarding the engine contract and had determined that the procurement procedures were moving at an acceptable pace.

General Haugen pointed out that nearly one month of the time that had elapsed since procurement was authorized on 27 October 1955 had been consumed by a study of the NACA suggestion for changing from ammonia to another fuel. The general estimated that a letter contract would be issued no later than 1 March. 29 (As a matter of fact, his letter was dated one day after the date of the letter contract.) 30

While the procurement difficulties were relatively minor, and in retrospect seemed to have consumed a relatively small portion of the time eventually devoted to the new engine, it was not long before other and serious questions were being posed.

Less than two months after General Haugen's letter to the NACA, that organization was criticizing Reaction Motors' conduct of the program. Mr. John L. Sloop, of the NACA's Lewis Laboratory, visited the company's facilities on 11 April 1956, and his report of the visit contained a list of the anticipated development problems. The problems included the provision of an adequate ignition system for the ammonia fuel, achievement of safety under all conditions, assurance that the design would be capable of meeting the severe environmental temperatures to be encountered, attainment of the performance requirements, and the development of a throttling system that would give combustion and cooling stability throughout the throttled range.

Mr. Sloop reported that Reaction Motors had assigned about a dozen engineers to the project and that they were receiving support from some 28 other staff members. He also included a summary of the company's development schedule which showed integration of a complete engine was to start in May 1957. Neither of these items drew approval from the NACA spokesman, who thought Reaction Motors' effort inadequate. Mr. Sloop also questioned the validity of the company's estimate that essential test stands would be ready in late 1956; NACA felt this date to be optimistic by a year. Sloop also suggested that Reaction Motors place considerably more effort on the development of the engine, that the company was pursuing too many different goals without adequate basic information, and that a company proposal to study ”spaghetti tube” bundle fabrication e had small potential value in view of the fact that they had already been studying the problem for about five years. 31

The first indication of Air Force concern with Reaction Motors' progress appeared in a letter from Mr. H. P. Barfield, assistant chief of the Non-Rotating Engine Branch of the Power Plant Laboratory on 1 August 1956. Barfield inquired as to why the tests of the thrust chamber, programmed for April in Reaction Motors' original proposals, had not yet taken place. 32

Reaction Motors explained that the delay was the result of using the company's facilities for work on other Air Force projects, such use extending beyond the period originally contemplated. The company also admitted having subordinated the preparation of hardware to a program of engine design studies. It was the company's opinion that the preliminary design studies were of more importance in the maintenance of the schedule than were the thrust chamber tests. The delay in testing was also attributed to the modification of the two available test chambers, modifications intended to extend the chambers' utility for test purposes. Pump failures that had required three teardowns were also offered as justification for the company's failure to meet its planned development schedule. 33

By 1 February 1957, North American was also becoming perturbed at the lack of progress in engine development. R. H. Rice, vice president and general manager of North American, estimated that the engine was already four months behind schedule. He also held that the engine's weight was growing while its specific impulse was deteriorating. North American, in an attempt to accelerate the development of the engine, asked Major General H. M. Estes Jr., ARDC's assistant deputy commander for weapon systems, to cooperate in securing ”… additional effort on the part of Reaction Motors, Inc.” 34

North American's request for cooperation initiated a flurry of activity that included meetings between Air Force and Reaction Motors on 12 and 18 February and a meeting of personnel from those organizations with representatives of North American and the NACA on 19 February. The meeting confirmed North American's fears that the engine program was four months behind schedule and that engine weight was increasing. The deterioration of performance appeared to be less serious than North American had anticipated. General~Estes, in his reply to Mr. Rice's letter of 1 February , advised that ”… every effort will be expended to prevent further engine schedule slippages.” 35

Although General Estes' letter appeared to be reassuring, the NACA report of the February meetings was not optimistic. Hartley A. Soule , NACA's research airplane projects leader, reported that the meeting of 19 February had resulted in a decision to accept the four months' delay in delivery, but that Reaction Motors had agreed to deliver two operable engines instead of one by 1 September 1958. The decrease in specific impulse (from 241 to 236 seconds) was also accepted. The weight had increased from 588 to 618 pounds. Mr. Soule pointed out that no thrust chamber runs had been made and expressed doubt that the new schedule could be achieved. It was his opinion that the Power Plant Laboratory might be forced to accept delivery of a lower performance ”first phase” engine if the proposed flight schedule for the X-15 were to be maintained. He also noted that additional engine progress meetings were to be held in June and September, and that the NACA had promised Reaction Motors its assistance in a program to increase performance by redesigning the exhaust nozzle for higher altitudes. 36

Additional assistance was to be provided by WADC's Power Plant Laboratory. Reaction Motors had been concentrating on a ”spaghetti” type fuel injector which consisted of bundled metal tubing. Captain K. E. Weiss, the Power Plant Laboratory's XLR99 project engineer, designed a number of ”spud” injectors that utilized small perforated disks. Several of Captain Weiss' designs were built in Wright Field machine shops and run through firing tests during the first part of 1958. By March, one of the designs had proved so promising that Reaction Motors considered adapting it to the XLR99 engine. The company, however, had had some success with its own ”spud” designs, and eventually it utilized its own design in.preference to the laboratory-developed injector. 37

(On 29 March 1957, Captain Weiss – then a lieutenant – had submitted a management report that indicated an increase in engine costs to a new total of $14,000,000 – plus fee!) 38

Unfortunately, Mr. Soule's premonition that the revised schedule and performance specifications established in February were unrealistic proved entirely correct. On 10 July 1957, Reaction Motors advised Wright Air Development Center that an engine satisfying the February specifications could not be developed unless the government agreed to a nine-month schedule extension and an increase in cost from $15,000,000 to $21,800,000. At the same time, Reaction Motors offered to provide an engine of the specified performance within the established time limits if permitted to increase the weight from 618 pounds to 836 pounds. The company estimated that this overweight engine could be provided for $17,100,000. Representatives of North American, Reaction Motors, and of all the government agencies involved in the X-15 program met at WADC on 29 July to consider the effects of an overweight engine on the performance of the X-15. The deterioration of performance was generally considered to be a lesser evil than the increased cost and additional delay that would be incurred by insistence upon a ”specification” engine.

Those who hoped that the over-all performance of the X-15 could be maintained were somewhat encouraged by Reaction Motors' report that the turbopump was more efficient than anticipated and that this would allow a reduction of 197 pounds in the weight of the hydrogen peroxide necessary to its operation. The decrease in the amount of required hydrogen peroxide, the possibility that North American might remain under specified airframe weight and reduce ballast requirements, together with the increase in launch speeds and altitudes provided by the substitution of a B-52 for the B-36 carrier, offered some hope that the original goals might still be achieved. At the time of the July meeting, Reaction Motors was still experiencing difficulties with the thrust chamber and the injector assemblies. The chief problem was the burnout of the oxidizer tubes of the ”spaghetti” type injector at low thrust levels. NACA and the Air Force advised the company to continue the development of the injectors and agreed to consider relaxing the minimum thrust requirements if the difficulties continued. The possibility of switching to a spud injector was also discussed, but a final decision on such a change was deferred. 39

Despite the relaxation of the weight requirements, the engine program failed to proceed at a satisfactory pace. On 11 December, during a meeting at the propulsion Laboratory, f Reaction Motors reported a new six-month slippage in the schedule. At that point, the company attributed its continued difficulties to a malfunction which destroyed the first development engine, to a series of pump failures, and to inability to produce an injector that would meet both performance and durability requirements. The failures were compounded because pump shortages had delayed the injector tests.

The threat to the entire X-15 program posed by these new delays was a matter of serious concern. Major General S. T. Wray, Wright Air Development Center's commander, working with General Haugen, then ARDC's director of systems management, decided to have the Directorate of Laboratories explore the technical and managerial problems involved. As a result, on 7 January 1958, Reaction Motors was asked to furnish a detailed schedule and to propose means for solving the difficulties. The new schedule, which reached WADC in mid-January, indicated that the program would be delayed another five and one-half months and that costs would rise to $34,400,000 – almost double the cost estimate of the previous July. 40

On 28 January 1958, General Haugen and General Wray, accompanied by Propulsion Laboratory and X-15 project office personnel, visited Reaction Motors to discuss the lack of progress on the XLR99 and to determine what steps the company was taking to improve its performance. General Haugen emphasized the importance of the X-15 project and commented upon Reaction Motors' record up to that time. Evidently the comments were rather forceful, as a company spokesman felt compelled to admit to ”past deficiencies.” Nevertheless, Reaction Motors asserted that its latest proposals were firm and expressed complete confidence in the company's ability to meet the revised schedules. 41

The Propulsion Laboratory and the project office, after evaluating Reaction Motors' program, reported their recommendations to General Haugen on 17 February, and to Lieutenant General S. E. Anderson, ARDC commander, Major General R. P. Swofford Jr., director of.research and development in Air Force headquarters, and General Wray on 21 February. The recommendations included the continuation of Reaction Motors' program, the use of an XLR11 rocket engine for initial X-15 flights, the approval of overtime, the assignment of a top Defense Department priority (DX rating) to the project, increased effort by Reaction Motors, the establishment of a technical advisory group, and the start of a backup engine development program. The use of the XLR11 engine and an increase in effort by Reaction Motors were approved. Additional funds to cover the increased effort were also approved, as was the establishment of an advisory group. The top priority was denied (although the request eventually led to an improved priority) 42 and it was decided to postpone a decision on the possibility of using an alternate engine. g

The most immediate result of the recommendations was the establishment of the technical advisory group which first met at Reaction Motors' plant on 24 February 1958. The group consisted of representatives from the NACA, the Bureau of Aeronautics, ARDC's weapon system group, and WADC. It was immediately apparent that the injectors and the thrust chamber presented the greatest development difficulties and that these were the areas in which the advisory group could render the greatest assistance to Reaction Motors. 43

That measures taken as a result of the February meetings were not completely satisfactory to all of the parties concerned was quite evident. A summary of the NASA-ARDC position dated 20 February 1958 and retained in the files of the X-15 project office stated that there was ”… only a remote possibility of getting any engine for the 1960 flight period.” The same document contained an estimate that the value of the X-15 equipped with the XLR11 engines would ”… diminish to almost zero by start of 1960 flight period.” The frustration produced by the engine situation at that time was evidenced by another statement – that even at this late date North American and Aerojet were better prospects to complete satisfactory engine developments before Reaction Motors, but not before the 1961 flight period. 44

Despite severe criticism of the contractor, continued development of Reaction Motors' engine offered the only practical source, so project monitors decided that the contract should be continued. 45

Of the three types of assistance offered to Reaction Motors (a government technical supervisory group, a government advisory group, and participation by other rocket engine contractors), the multi-contractor effort appeared to promise the greatest success. A government supervisory group was ruled out because of a lack of manpower. An advisory group was thought desirable for purposes of keeping Reaction Motors' progress under close surveillance, but fear was expressed that such a group would not be capable of providing the desired improvement in the company's efforts. The assistance of other engine contractors seemed to promise the greatest benefits, so the February conferees recommended that the possibility of obtaining such assistance be explored. 46

During March, the Air Force opened negotiations with the Rocketdyne Division of North American Aviation in an effort to secure alternate injectors and an alternate thrust chamber. 47 North American was reluctant to undertake the development and it was not until General Wray and General Haugen arranged a personal conference wit.h North American's vice president, Mr. Lee Atwood, that Rocketdyne agreed to render general assistance to Reaction Motors and to undertake the development of injectors and a thrust chamber that could serve as alternates for the items that were giving Reaction Motors so much difficulty. 48

Once North American's reluctance had been overcome, Rocketdyne immediately began tests of an S-4 injector and chamber from an XLR105-NA-1 (Atlas sustainer) engine, in an effort to adapt them to the Reaction Motors' design. 49

In addition to the numerous meetings held in February and March, and the important decisions emanating from them, an additional factor of some importance influenced the development of the XLR99, and while this factor apparently did not materially alter the course of events, it could not help but add to the confusion that already existed. The additional factor was the absorption of Reaction motors by the Thiokol Chemical Corporation. Negotiations for the proposed combination were conducted throughout the early part of 1958. The anticipated reorganization and pruning undoubtedly created a state of mind that was not conducive to the best efforts of Reaction Motors' management. 50

The absorption of Reaction Motors by Thiokol was not completed until 17 April 1958, when stockholders of Reaction Motors approved the merger. Reaction Motors was subsequently renamed and became the Reaction Motors Division of the Thiokol Chemical Corporation. 51

The decision to turn to Rocketdyne for assistance apparently spurred Reaction motors' efforts toward the development of a ”backup” design, for by the end of April, the Air Force felt it necessary to point out that the funds available were not sufficient to permit the development of both a Rocketdyne and a Reaction Motor design. Reaction motors was urged to subcontract with Rocketdyne for further developments of the XLR105 chamber. The president of Reaction Motors agreed to a study to determine whether his own company's approach or Rocketdyne's offered the most promise. The results of the study were presented at a meeting held on 27 May at WADC. Reaction Motors, Rocketdyne, and NASA representatives, as well as Air Force personnel, attended the meeting and reviewed the alternate proposals. It appeared that Reaction Motors' alternate design (a concentric shell thrust chamber) would not solve the problem of chamber burnout, and that the design could not be translated into hardware in time to meet the schedules for the X-15 engine. As Reaction Motors' proposals were considered unsuitable, it was decided that the company should not pursue the concentric shell chamber further. On the other hand, Rocketdyne's proposals seemed to offer some hope of success, so the conferees agreed to continue the development of that firm's design. 52

The decisions reached at the 27 May 1958 meeting were officially transmitted to Reaction Motors two days later. The letter specifically instructed Reaction Motors to subcontract for the development of the Rocketdyne designs. The same letter warned Reaction Motors that a ”… demonstration of thrust chamber performance and satisfactory progress in all other areas must be apparent by mid-July.” 53

Complying with instructions, Reaction Motors provided $500,000 to fund Rocketdyne's program from 28 May until mid-July; the firm also made arrangements for continued development after that date. Rocketdyne's chamber development cost estimate was $1,746,756, with an additional $811,244 for the delivery of 14 research and development chambers and a further $657,300 for 14 flight chambers. 54

While the increased efforts by Reaction Motors appeared to be having some favorable effect on the progress of the XLR99, and Rocketdyne's supplementary efforts got off to a promising start, the Air Force was not convinced that everything was proceeding as rapidly as possible. The Propulsion Laboratory, in an effort to stimulate Reaction Motors to even greater efforts, undertook the preparation of two letters. The first, dated 17 June 1958, was from General Wray to General Anderson. Its tenor was not obscure:

For sometime General Haugen and I have been concerned by the poor progress made by Reaction Motors Division on the development of the XLR99 rocket engine for the X-15 airplane program.
This engine was one that had been recommended … on the strength of a supposed advanced state of development of the LR30 rocket engine …
… in spite of this state of development, Reaction Motors Division has experienced continual schedule slippage and financial overruns …
It is by their own admission as well as the conclusions of our project engineers a fact that Reaction Motors Division has used poor judgment and management during the early stages of the engine development program.
Inability to meet performance and original Preliminary Flight Rating Test initiation date, which was a contractor deficiency, has resulted in submission of supplemental proposals. This by acceptance or rejection has placed the Air Force in the undesirable position of making program decisions which we would have preferred the contractor, through better management, to have made at a much earlier date.

General Wray also advised that a decision as to whether Rocketdyne's or Reaction Motors' chamber and injector designs should be continued was scheduled for July. 55

The second letter, prepared by the Propulsion Laboratory, was enclosed with the first and was directed to Mr. J. W. Crosby, president of the Thiokol Chemical Corporation. General Wray felt that this second letter would have a greater impact if it went forward over General Anderson's signature. General Anderson's staff shortened the four-page draft letter to two pages which, suitably signed, went to Mr. Crosby on 27 June. The general tone of the revision was somewhat milder than the original, but the statements that ”… the results of the next few weeks … development effort will be extremely crucial in determining the direction of this engine procurement” and ”I recognize the possible impact which pending Air Force decisions may have on Reaction Motors Division” could have left little doubt as to its meaning. 56 The Air Force had quite lost patience with Reaction Motors. The implication of contract cancellation was not difficult to derive.

Mr. Crosby replied to General Anderson's letter on 3 July 1958 with the admission that a ”… decision to take this development work away from Reaction Motor(s) Division would have a serious effect on the organization.” He defended Reaction Motors' conduct of the program by emphasizing that the safety and reliability requirements of an engine intended for a manned aircraft had created unusually difficult development problems. He also offered to arrange a presentation of the current status of the XLR99 program for General Anderson. 57

As it happened, progress at Reaction Motors began to improve while General Anderson and Mr. Crosby were exchanging letters and, as a consequence, no presentation was made. In a letter of 1 August 1958, General Anderson thanked Mr. Crosby for his reply of 3 July and declined the offered presentation. 58

The threat that the engine delays would seriously impair the value of the X-15 program had generated a whole series of actions during the first half of 1958: personal visits by general officers to the contractor's plant, numerous conferences between the contractor and representatives of the government agencies involved in the program, increased support from the WADC Propulsion Laboratory and NASA, an increase in funds, an increase in effort within Reaction Motors' plant, the composition of letters containing severe censure of the company's conduct of the program, and the introduction of another contractor (Rocketdyne). Whether any of these actions, or even the threat of XLR99 cancellation implied in General Anderson's letter of June, had any real effect on the program was difficult to determine. An emergency situation had been encountered, emergency remedies were used, and by midsummer improvements began to be noted.

Reaction Motors accumulated more engine test time in the first two weeks of July than during the entire program prior to that date. Performance was somewhat low but was high enough to offer reasonable encouragement that the specification performance could be met. 59 By 7 August 1958, performance had been raised to within two and one-half 'percent of specifications. By August, it was also apparent that the Rocketdyne proposal, rather enthusiastically endorsed by the North American project group was rather optimistic. By that time, Reaction Motors' subcontract with Rocketdyne had cost $3,125,000, which the Propulsion Laboratory felt was ”particularly unreasonable since the Rocketdyne program was initiated on the basis that little development effort would be required.” The Rocketdyne chamber had failed to start on two attempts and a review of Rocketdyne's progress indicated a six to twelve month delay in the delivery schedule. The improvement at Reaction Motors and the lack of success at Rocketdyne led the Propulsion Laboratory in August 1958 to ask for the termination of the Rocketdyne program ”as soon as possible.” 60

North American and Rocketdyne officials were notified of the Air Force's intention to terminate the backup program during a visit of Generals Wray and Haugen to the contractor's Inglewood plant. Major Arthur Murray, the X-15 project officer, took the opportunity of the visit to express his opinion that Rocketdyne's failure to achieve a suitable backup chamber within the sixty days and for the few hundred thousand dollars originally contemplated came because ”… no amount of optimism or salesmanship” could change the total effort required to develop advanced equipment. 61

On 15 August 1958, another management meeting was held at Reaction Motors. Among those in attendance were General Haugen, Brigadier General W. A. Davis of the Air Materiel Command, Mr. Soule of NASA, and representatives from Air Force headquarters, ARDC and WADC. After evaluating the status of the XLR99 and of Rocketdyne's thrust chamber, the participants decided that the engine design should be frozen immediately and that it should incorporate Reaction Motors' chamber for purposes of the Preliminary Flight Rating Test. The Air Force and NASA urged Reaction Motors to continue its efforts to reach specification performance by minor changes of the injector design, but not at the expense of reliability or of further delaying the development schedule. A final decision on the continuation of the Rocketdyne program was postponed until October. 62

During September, the progress of Reaction Motors continued to be encouraging as engine and injectors were subjected to increased testing. The Rocketdyne program continued to lag, primarily because of difficulties in mating Reaction Motors' ignition system to the Rocketdyne chamber. By the end of the month, the X-15 project office was convinced that the Rocketdyne program was not going to be a success, calling it an ”expensive and apparently fruitless” effort. 63

On 7 October, the Technical Advisory Group met at Reaction Motors Division for a review of Reaction Motors' and Rocketdyne's progress. The review convinced the group that, while Rocketdyne's program might eventually lead to a higher performance engine, Reaction Motors' program would provide an acceptable engine at an earlier date. As a result of the group's recommendations and subsequent discussions at WADC, the Propulsion Laboratory recommended (on 10 October 1958) termination of Rocketdyne's development program. Headquarters of WADC and the X-15 project office agreed to the termination shortly thereafter. 64

Engine progress continued to be reasonably satisfactory during the remainder of 1958. A destructive failure that occurred on 24 October was traced to components that had already been recognized as inadequate and that were in the process of being redesigned. The failure, therefore, was not considered of major importance. 65

By the end of November, the X-15 project office could report that an engineering inspection on 18 November and a Technical Advisory Group meeting the same day had revealed promising progress. 66

Although the emergency actions of 1958 appeared to have produced a considerable improvement in the engine development program, all of the difficulties had not been resolved. At a Technical Advisory Group meeting of 20 January 1959, it became apparent that there were still some minor system leakage problems; that injector tests were still producing failures, particularly under low thrust and idle conditions; and that excessive heating was being encountered during idle. On 23 January, a fuel manifold failed because of excessive vibration. Reaction Motors also reported encountering difficulties in obtaining satisfactory delivery from its suppliers. 67

On 12–13 February, the project office and the Propulsion Laboratory made two presentations at WADC, one to brief General Wray on the current status of the XLR99 program, and the second to a number of the contractor's management personnel-including the president of Reaction Motors Division. The purpose of the second presentation was to reemphasize the ”Air Force's concern over the problems and delays which have been encountered.” One result of the presentations was a decision to send several of WADC's technical personnel to the contractor's plant to investigate instrumentation, vibration, materials, and fluid flow. The Air Force hoped that the investigation of these problem areas would assist the contractor in overcoming the difficulties being encountered. The new group made its initial visit during the last week of February and the first week of March. 68

A long-sought goal was finally reached on 18 April 1959 with completion of acceptance tests of the first Preliminary Flight Rating Test (PFRT) engine. The flight rating program began at once. 69

At the end of April, representatives of ARDC, WADC, AMC and Reaction' Motors met at the contractor's plant to decide on a ”realistic” schedule for the remainder of the program. They agreed that the performance flight rating test should be completed by 1 September 1959. The first engine equipped with the final flight-type injector was to be ready for running in the latter part of May, the first ground test engine was to be delivered to Edwards Air Force Base by the end of May, and the first flight engine was to be delivered by the end of July. The conferees also decided that an additional engine should be subjected to the flight rating program in order to test a 30-second idle feature which had not been included in the original test engine. 70

At the time these decisions emerged, it was quite impossible to determine whether the ”realistic” schedule could actually be achieved, but delays in the overall X-15 test program, imposed by other factors, had reduced the air of urgency which surrounded the engine program throughout 1958. Some of the factors contributing to the less-than-perfect record of engine development were obvious.

Others were relatively obscure. Early in 1959 the X-15 project officer, Major Murray, summarized some of the development difficulties, and their causes. He stated quite bluntly that prior to the stimulus provided by the Russian satellite achievements of late 1957, there had been inadequate support for programs that did not lead directly to weapons. In his view, this lack of R&D support was not the result of the policies of individuals or even of commands, but was an inherent Air Force-wide phenomenon that was only overcome by the existence of a few ”crusaders” at all levels and by the intensive efforts of those directly concerned with the individual projects. Major Murray considered that the original development schedule had been tight, that the funds had only been marginally sufficient at some stages in the program, and that personnel shortages, particularly a propulsion-expert vacancy within the project office, had all contributed to the contractor's repeated failures to meet the proposed development schedules. He also' pointed out that the entire project was in advance of the state-of-the-art and that there was a tendency on the part of scientists engaged in such projects to postpone any commitment to a final design because of recurrent hopes of finding something just a little bit better. 71 (This latter problem – leading to the cynical expression ”… best is the enemy of better” – one that still afflicts both the scientific and technical communities).

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