A sizable number of aeronautical experts in industry, government research agencies, and the Air Force believe they can achieve the marriage of airplane and space vehicle in the decade ahead. The result would be a gigantic step forward . THE SPACEPLANE . TOWARD A SPACE-AGE KITTY HAWK J. S. Butz, Jr. TECHNICAL EDITOR, AIR FORCE MAGAZINE F, AS Air Force planners logically contend, the national priority in a crash development program. atmosphere and space are a single operating con- These critics point to the host of separate vehicles I tinuum called aerospace, the inexorable pressure now under development, which considered in the of operational requirements on technology must event- aggregate could accomplish all of the missions Space- ually marry the airplane to the space vehicle. plane can and perhaps better. An example is the fact The object of the wedding is to conceive a winged that large boosters such as Nova can put more weight offspring which can fly into orbit, rather than being into orbit in much less time. The reconnaissance and shot there with large rocket boosters, and which can early-warning satellites, such as Samos and Midas, take off from and land on conventional airfields. The can accomplish these missions as well and perhaps as first successful flight of such a vehicle, into orbit and cheaply as Spaceplane. It is also probable that the return, will truly mark the Kitty Hawk milestone of Spaceplane, which will need a very large volume to man's conquest of space. carry its load of hydrogen fuel, will never be able to The "Spaceplane" concept has an awesome set of maneuver as well during reentry as a heavier-for-its- general requirements. It is envisioned as a self-con- size Dyna-Soar-type hypersonic glider. tained, one-stage vehicle which uses air-breathing In effect, it is the multipurpose aircraft require- engines to maneuver in the atmosphere and to ac- ment carried over into the space field. It is very diffi- celerate itself to satellite speed of about 18,000 mph. cult to say whether it is better to have a group of It must either carry enough fuel into orbit to maneuver high-performance specialized vehicles or a multipur- extensively in space or be able to collect this fuel as (Continued on page 50) it orbits in the upper atmosphere. Finally, the Space- plane must be able to withstand the heat of reentry, Shown at right is an artist's conception of four possible maneuver at very high speeds in the atmosphere as it Spaceplane configurations using hypersonic air-breathing engines which burn hydrogen fuel externally. Technically, returns to the earth's surface, and land under power the key to the Spaceplane concept—a one-stage aircraft at relatively low speeds at any desired airfield. which can fly into orbit after a conventional takeoff from a Militarily, the attractiveness of Spaceplane is un- normal-sized airfield—is to use hydrogen fuel and external. burning engines. The hydrogen fuel contains about three questionable. However, the first glance from the tech- times more energy per pound than gasoline and other hydro- nical viewpoint indicates defiance of many of the carbon fuels. External burning must be used rather than physical laws which govern the design of aircraft, conventional enclosed engines so that the exposed hot parts can be cooled by radiation to withstand the very high air-breathing engines, booster rockets, and reentry operating temperatures at hypersonic speeds. Several types vehicles. It certainly pushes current technology to its of aerodynamic configurations are now considered possible for Spaceplane use. The vehicle at top right is a modified limits, and in many areas the concept cannot be cone with its upper half removed and a small wing added. proved or disproved until more research is completed. The next is a simple delta wing with a flat bottom with As with all vehicles which strain existing knowledge, fuselage on top. The next two midwing arrangements might employ submerged canard control surfaces for Spaceplane has both strong proponents and strong use at low speeds. Podded external-burning engines critics. The argument is primarily over where Space- are a distinct possibility on the Spaceplane. Dur- ing hypersonic flight at very high altitudes the exhaust plane fits into the time schedule. plume from any engine—rocket as well as external Few people contend that Spaceplane could never burner—balloons to several times its original diameter be built, but many question whether it could fly in the (much greater than is indicated here), and it might prove necessary to get this plume away from the aircraft. next ten years, even if it were given the highest Drawing by Robert Kirwan 48 AIR FORCE Magazine • January 1961 r - P Al11' 04" , , • r • ,4 ' , ..... ° , , jel"' SPACEPLANE CONTIN pose vehicle which can do many of the necessary jobs engine designers that it would work through the hig. but none of them at top performance. But the increas- Mach number range right on up to orbital speeds am ing cost and complexity of individual weapon systems at very high altitudes. make the multipurpose approach an attractive one. The external-burning effort was not continue. The Spaceplane proponents do not suggest that the however, and it was abandoned along with all oth- current space programs be canceled and that all effort air-breathing engine research when the NACA be- I be put on the all-purpose vehicle. They do believe came the National Aeronautics and Space Administra emphatically that a single-stage vehicle capable of tion. The decision to drop all other air-breathing wor aircraft-type takeoffs and landings, which can carry was perhaps the most controversial one yet made b men and a sizable payload in between the atmosphere NASA. It raised strong protests from within industry, and space almost at will, will be the foundation of the military, European aeronautical circles, and within the space-vehicle program during the 1970s. NASA itself. It forced the professional reorientation The best indication available today that the Space- of the research scientists at Lewis Laboratory who plane is feasible and can be flown before 1970 is that had achieved worldwide eminence for their effor a sizable group of aeronautical experts sprinkled with air-breathing engines. The decision not only through industry, government research agencies, and weakened any Spaceplane or air-breathing booste the Air Force not only believe that it can be done but development but limited hypersonic aircraft con are enthusiastic about it. figurations to the essentially one-shot, rocket-powere Several manufacturers have already submitted pre- boost-glide type. liminary type Spaceplane proposals to the USAF. During the past couple of years theoretical wor These have been evaluated and considered in the with external burning has continued, primarily in in light of proposals from government laboratories and dustry. Further experimentation is needed immedi from within the Air Force. The USAF budget for ately, however, to obtain detailed design data and t t. fiscal 1962 contains money for more detailed Space- bring the Spaceplane onto more solid ground tech plane studies and for state-of-the-art experiments. nically. Not even the enthusiasts, however, claim that Space- The development problems of a Spaceplane exten. plane will be an easy technical development. Much of far beyond external burning, and they occur in . the current US research and development effort, such three of its basic modes of operation, which are as Dyna-Soar, the X-15, and state-of-the-art work in flight into orbit, maneuvering in space, and reentry inti high-temperature structures, high-speed stability and the atmosphere. control, etc., will feed valuable information into the When the Spaceplane takes off in the convention. Spaceplane project. But one field of experimental re- manner and accelerates to a speed of around 18,111 search vital to the project has been virtually abandoned mph while climbing to an altitude of 200 miles o in recent years, and there can be no sensible hope for more, its flight will resemble much that of a larg. a true one-stage Spaceplane unless large-scale research rocket as of an airplane. An analysis of this flight int, in this area is revived. orbit must be made from the standpoint of both type The missing technical link in the Spaceplane con- of vehicles. cept is the air-breathing engines that can operate at Fundamentally, the rocket vehicle is much easie hypersonic speeds. Air-breathing propulsion systems to analyze than the hypersonic airplane. There an theoretically can eliminate the need for high-thrust two basic factors which influence the ability of thr rocket boosters by drawing their oxidizer supply from ICBM-type rocket or a large space booster to ac- the atmosphere. Since the weight of oxygen needed celerate to orbital speed, and they are just as impor- is much larger than the fuel weight, hypersonic air- tant to the Spaceplane as they are to the rocket. These breathers offer the hope of very light, orbital propul- factors are the vehicle's mass ratio and the specific sion systems. impulse of its propellants. The key to hypersonic air-breathing engines is the The mass ratio is the total takeoff weight of th. ability to burn the fuel externally. In effect, the en- vehicle divided by its weight after all fuel has bee. gines must be turned inside out so that their hot parts consumed and the engines stop. Mass ratio is an indi will be exposed and can be cooled by radiation. The cation of the lightness and efficiency of the vehicle' air entering a conventional enclosed engine at hyper- structure, and it is a dimensionless number.