Status: Cancelled 1963.
Weldon Worth at Wright-Patterson AFB (WPAFB) initiated this first attempt at development of an air-breathing single-stage-to-orbit manned spaceplane. WPAFB issued Department of Defense study requirement SR-89774 in 1957, for a reusable space booster. By 1959 this had developed into the ROLS (Recoverable Orbital Launch System), a single-stage-to-orbit horizontal-take-off-and-landing vehicle. The aircraft would use a LACES (Liquid Air Collection System) engine. This would liquefy air scooped up during ascent, and then use it as oxidizer for rocket feel at high altitude.
Later testing showed that it would be possible to obtain pure liquid oxygen, not just liquid air, through differential liquefaction techniques. An aircraft equipped with such an ACES (Air Collection and Enrichment System) could fly as early as 1967, it was believed. Research contracts were issued, with Marquardt and General Dynamics responsible for the overall engine system, and Garret AirResearch building the heat exchanger. ACES circulated the aircraft's liquid hydrogen fuel through thin tubes in the air intake, which liquefied the air. The liquid air was first shunted to low pressure collection tanks, then pumped to high pressure tanks for the separation process. In late 1960 and early 1961 a 125 kgf demonstrator engine was being operated for up to five minutes using liquid air obtained with the Garrett hear exchanger.
Study contracts were let to Boeing, Douglas, Convair, Lockheed, Goodyear, North American, and Republic. The USAF Aerospaceplane specification called for a horizontal takeoff / horizontal landing, single-stage-to-orbit vehicle that would carry three crew from any airfield to orbit and back. Payload would be accommodated in a 12 m long x 7.6 m wide x 3.0 m deep payload bay The spaceplane was to be operational by 1970 at a total development cost of $5 billion. Despite development work done on ACES, most contractors suggested use of a scramjet propulsion system. This had first been described publicly in a NACA paper in early 1958. Marquardt was already developing such an engine for the Air Force, with Alexander Katveli at Republic Aircraft working closely with Antonio Ferri at the General Electric Applied Sciences Laboratory in New York.
All of the study contractors reported back that such an aircraft would require a lot of basic technology development before it was even determined to be feasible or not. In December 1960 the USAF SAB concluded that too much emphasis was being placed on operational aspects of an aerospaceplane, and not enough on the basic research and development required to create and mature the technology needed.
The study contractors saw weight problems, with all potential designs being very sensitive to any increase in weight growth during development. This could result in a useless vehicle, not capable of reaching orbit. As studies progressed, various schemes were proposed to overcome this difficulty. One of the more outrageous was HIRES (Hypersonic In-flight Refueling System) - a plan to top up the Aerospaceplane's fuel tanks with a hypersonic tanker. It was proposed that test flights be conducted with two X-15's flying in formation at Mach 4-6 to test the feasibility of such maneuvers. Finally in late 1962 the technical realities forced the USAF to change the project baseline to a two-stage-to-orbit vehicle.
On 21 June 1963 Douglas, General Dynamics, and North American each received from USAF ASD $500,000 contracts for further Aerospaceplane development planning. Martin received a contract from the USAF Flight Dynamics Laboratory (FDL) to build a full-scale wing-fuselage structure. Air Force SR-651 set requirements for follow-on propulsion development and studies - ACES, a Mach 8.0 subsonic combustion ramjet, LACES, turboramjet designs, scramjets, structure concepts, and so on. Despite this renewed activity, the USAF SAB concluded in October 1963 that the existing state of the art was insufficient to realize an Aerospaceplane in any reasonable time scale. The Aerospaceplane was deleted from the USAF FY 1964 budget request. Only basic propulsion research under SR-651 would be continued, although this too would wither away or pass into the black world. It was not until 1992 that the Japanese renewed basic research and development on a LACES concept.
|Astroplane American winged orbital launch vehicle. Martin concept of 1961 for a horizontal takeoff / horizontal landing, single-stage-to-orbit vehicle that would be powered by nuclear magnetohydrodynamic engines.|