MORE X-15S?

During the development of the X-15, many wanted to expand the program beyond the three airplanes covered under the original agreements. This opinion obviously did not prevail, but the proposals are nonetheless of passing interest. Early on, North American suggested using X-15 as part of an extensive training program for astronauts and test pilots, believing that such a program could familiarize pilots with rocket-powered aircraft, the use of reaction controls, and the physiological sensations of space flight. The Air Force did not express any particular interest.-141

Early in 1958, researchers at the HSFS wanted to procure one additional X-15 for flight-control research, but NACA Headquarters did not concur. It was the first of several such proposals.142–

In mid-1958 the first serious proposal to expand the X-15 program came when Air Force Headquarters asked the ARDC if there was any merit to expanding the X-15 program. On 8 April 1958, headquarters requested recommendations for "configuration changes, estimated costs, aircraft availability, the increased performance expected, the test results to be obtained, and a brief substantiation of their value." Headquarters wanted the results of the study at an early date because it needed to make a decision before North American disbanded the engineering team.143–

The X-15 Project Office asked the AFFTC, North American, and WADC for recommendations. By 29 April, these organizations concluded that the best approach would be to improve performance using new structural materials and an improved rocket engine instead of the XLR99. The development difficulties with the XLR99 apparently influenced the call for a new engine, although the WADC suggested that any new engine should "be obtained as a result of across the board BMD [Ballistic Missile Division] and other efforts, and not as a sole X-15 effort."144-

The Navy verbally concurred with expanding the program on 19 May, and the NACA agreed a day later. On 13 June the X-15 Project Office recommended to the ARDC that three additional airplanes be constructed using higher-temperature structural materials than those used in the original design. The ARDC forwarded this recommendation to Air Force Headquarters on 16 June.145-

Apparently, the seeming urgency in the 8 April letter from headquarters had evaporated. On 18 November 1958, Major General Marvin C. Demler, director of research and development at Air Force Headquarters, finally informed the ARDC that the X-15 program would not be expanded. In the interim, the Research Airplane Committee had met on 31 October and Hugh Dryden concluded the three original airplanes were adequate for NASA’s purposes. Ultimately, the Research Airplane Committee recommended against procuring additional airplanes.146

There was, however, another fleeting prospect. After an explosion seriously damaged the X-15-3 during an XLR99 ground test, the X-15 Project Office had to solicit additional funds from the Pentagon to rebuild the aircraft. This prompted a renewed interest in the X-15 and the data it might deliver for future use in the Air Force space program. On 12 August 1960, Air Force Headquarters ordered a complete review of the X-15 program. The X-15 Project Office presented its results at the 17-18 October 1960 X-15 program review. The briefing identified original program objectives that were no longer valid, new objectives to consider, continuing objectives, and funding requirements. Surprisingly, the general officers who were briefed agreed that the X – 15 promised to be considerably more important to the Air Force space effort than had been foreseen when the program was initially conceived in 1954, or when the program expansion was rejected in late 1958. The Pentagon advised the ARDC that it would "entertain" proposals for additional X-15s to be operated exclusively by the Air Force.

As part of the ongoing discussion, the AFFTC put together its own recommendation for the program. On 26 October 1960 the AFFTC released a report that called for three additional X-15s and one more NB-52 "to carry out R&D objectives not presently covered by the present NASA-AF – Navy X-15 program." The AFFTC expected to "own and operate" these aircraft. Based on a 1 January 1961 start, the AFFTC expected the first aircraft to be delivered (along with a third NB-52) in September 1961, with the others following in March and June 1962. The flight program was to average 60 flights per year through December 1965. Some of the research objectives for the new aircraft included flight control and guidance, aero-thermo-elasticity, supersonic boundary-layer turbulence, sonic fatigue, landing-impact data, and electromagnetic propagation. The AFFTC expected that it would need an additional 330 people to support the X-15, plus 37 more to operate the High Range during AFFTC flights.147

Another proposal, originating from Brigadier General Donald R. Flickinger at ARDC Headquarters, was for a two-place biomedical research version of the airplane.-1148!

The Air Force called a meeting at Wright Field on 14 November that brought together representatives from the ARDC, the WADC,149 the command and control division of the Air Force Cambridge Research Laboratories, and the Army Corps of Engineers.-1501 It was immediately apparent to the X-15 Project Office that if all of the stated requirements for X-15-type aircraft were to be satisfied, "several additional X-15s will be required." Two weeks earlier the government had notified North American of the meeting, and Charlie Feltz prepared a briefing outlining several advanced X-15 configurations. Feltz presented his briefing on the afternoon of 14 November and provoked further interest in a comprehensive extension program.151

Although a two-seat X-15 engineering study had been required in the original proposals, the government had not taken any action on the idea. Nevertheless, it loomed in the background during much of the early X-15 program. The variant shown during the November 1960 meeting differed somewhat from the one originally proposed. North American optimized this version for "space training and biomedical research." Instead of simply deleting the research instrumentation and extending the canopy over the second cockpit, the new configuration extended the fuselage by approximately 14 inches and added a second cockpit with a separate canopy. The company deleted the aero-thermo research equipment, but the extension provided space for a variety biomedical equipment.-1152

North American environmentally separated the second cockpit from the primary cockpit so that it could study alternate atmospheres (i. e., not nitrogen-purged). A separate set of dummy controls could be installed that would allow the second pilot to react independently from the pilot flying the aircraft. His responses would be recorded and reconstructed on the ground to evaluate performance under acceleration and weightless conditions. It was expected that flight profiles could be developed that would allow five minutes under essentially weightless conditions during flights to altitudes in excess of 500,000 feet. The change added 354 pounds to the aircraft, but the use of an uprated XLR99 would have increased performance by 120 fps.[153]

The meetings resulted in NASA rearranging the existing X-15 program slightly to accommodate the Air Force research priorities, and relegating excess work to the new research extension program. The product was a revised System 605A plan released on 1 February 1961. Essentially, the X-15 Project Office requested approval for the construction of two additional aircraft, both of them slightly stretched two-seat versions similar to one proposed by Charlie Feltz in November. For the moment, the question of additional single-seat aircraft or advanced models was not considered pressing and was deferred. The two-seat aircraft would satisfy the need for biomedical research and training of future aerospace research pilots and Dyna-Soar astronauts.-1154

The idea was short-lived. On 20 March 1961, Major General Marcus F. Cooper, chief of research and engineering at ARDC Headquarters, disapproved the development plan. Cooper instructed the X-15 Project Office to revise the existing (October 1960) development plan to reflect funding changes proposed by the Pentagon. Nevertheless, in one paragraph Cooper instructed Wright Field to "give consideration to the election of the best type of vehicle to use in training future

Aerospace Research Pilots___ The possibility of using the existing X-15s for this purpose after

completion of the test program should be explored. In addition the need for additional X-15 aircraft or other vehicles, such as Dyna-Soar, for this purpose should be considered." The concept could potentially require additional X-15s.[155]

Although this kept hopes alive for an expanded X-15 program, it essentially buried the two-seat X-15. As Cooper explained, funding shortages for FY61 and FY62 would prevent "the additional heavy funding required in those years to support the proposed additional X-15 aircraft." It had also become apparent that the existing X-15s, with some additional equipment and telemetry installations, could acquire the majority of the desired biomedical data at far less cost. The X-15 Project Office had also begun to worry that stretching the X-15 fuselage might involve more engineering and development work than anticipated, although the subsequent development of X – 15A-2 proved this concern to be unfounded.-156

The ARDC Commanders Program Management Review in March 1961 tasked the X-15 Project Office to review "identified problem areas which might require investigation by X-15 type aircraft with particular attention given to the relationship between the problem areas and presently authorized advanced aerospace programs and studies." The response indicated that two additional single-place X-15s would be useful for investigating a variety of Air Force-specific areas of interest. The ARDC rejected this recommendation on 2 August 1961, and all thoughts of additional X-15s seemed to fade.-152