In the 1960s, the topic of spaceplanes was very popular. In various countries, these programs have evolved in many ways. One of them was the American START program - Spacecraft Technology and Advanced Re-entry Tests. START was launched in August 1964 at the initiative of the US Air Force and incorporated the results of the X-15 and X-20 missile glider programs. In addition, work was used to study the entry into the dense layers of the atmosphere of the warheads of ballistic missiles. The US military has set a global goal - to combine previous developments and develop a space plane that can deliver a payload into Earth's orbit. Since the customers were the military, of course, nuclear weapons were meant as a "payload".
By 1966, the SV-5D experimental spaceplane project was ready. The development of this device was carried out by the Baltimore branch of the Martin company. The hull design was quite original. Three vertical stabilizers were equipped with rudders. The spaceplane was a double cone with a flat bottom surface and a pair of short stabilizer wings, which were mounted at a large angle. The third stabilizer was mounted at right angles to the aft fuselage. Pitch control was carried out by elevons, which were differentially coupled to control the roll maneuver. The structure at the front of the fuselage is almost spherical. The models weighed 399-408 kg. The dimensions were also small: the wingspan was 1.22 mm, the length was 4.22 m.
Model SV = 5D "Prime"
It was assumed that the SV-5D spaceplane would be launched into orbit by the carrier and, after completing the flight mission, it would independently descend with an airplane-like landing. Having experience in flights in the modes of entry into the atmosphere, when the ablation protection is partially destroyed, and the control of aerodynamic rudders loses its effectiveness, it was proposed to use jet nozzles.
At the first stage of testing, the SV-5D was supposed to include only unmanned launches with a load of 0.5-0.9 tons. Simultaneously with hypersonic tests, it was decided to conduct flight tests of a large manned SV-5D for controllability and stability in subsonic flight modes and for landing training.
The first prototype SV-5D (also known as "Prime") was unmanned on December 21, 1966. In fact, the car was a model for aerodynamic tests weighing 405 kg. The first launch of the apparatus ended in an accident. The spaceplane, launched by the Atlas SLV-3 launch vehicle along a suborbital ballistic trajectory, crashed into the ocean after entering the atmosphere. The device could not be saved. The cause of the disaster was not disclosed. The launch of the second apparatus, which took place on March 5, 1967, also ended in failure. Only the third unmanned model launched on April 19, after being badly burned, landed at the calculated location. Despite this, the results obtained were quite encouraging. The spaceplane, after separation from the carrier, reached a speed of 28157 km / h without any serious consequences. During the descent, at an altitude of 45,000 feet, the speed decreased to M = 2, the braking parachute opened. The SV-5D splashed down and was picked up by a C-130 transport aircraft.
While the tests were being carried out, Martin, on its own initiative, developed two more variants of the spaceplane - the SV-5J, a training one equipped with an air-jet engine and the SV-5P, a manned one designed for orbital flight. But, at the end of 1967, the START program changed a lot, which became the reason for the change in designations. As a result, the SV-5D received the designation X-23, and the modified SV-5P was given the index X-24. An attempt was made to link the further development of the program with the design of the Manned Orbiting Laboratory (MOL) orbital station, which was planned to be launched into orbit in 1969.
The X-24 has undergone a number of improvements. The changes were not of a global nature. They were mainly related to the improvement of equipment and aerodynamic qualities. The updated project was given the designation X-24A. Overall dimensions were: length - 7, 5 meters, diameter - 4, 2 meters. The flight weight was equal to 5192 kg of which 2480 kg fell on fuel. The fuel consisted of liquid oxygen and alcohol. The maximum thrust of the XLR-11 rocket engine installed on the Kh-24A was 3845 kg. Time of continuous work - 225 seconds.
The Martin X-24A
The X-24A spaceplane was a mock-up ship - the Americans were not going to launch it into space. The aircraft was intended to study the possibilities of landing at high speeds from high altitudes and to study the characteristics of supersonic flights in the upper atmosphere. On April 17, 1969, the first flight of the rocket plane prototype was carried out. The first flight with the engine turned on was carried out on March 19, 1970.
Like other cruise vehicles equipped with rocket engines, the Kh-24A could not take off on its own. In this regard, the spaceplane was delivered to a given height under the wing of a B-52 bomber. After dropping from the carrier, the pilot switched on the rocket engine and made an independent landing at the airfield. Despite its minimal number of protruding parts and futuristic design, the Kh-24A was able to reach a speed of only M = 1, 6 and reach a ceiling of 21, 8 km. These characteristics, even for a prototype, are rather modest.
Only three pilots were involved in piloting the X-24A: Jerold Gentry, John Menkey and Cecil Powell. The X-24A spaceplane flew 28 flights to the AFFTC (Air Force Flight Research Center) at Edwards Air Force Base, California. 18 flights were carried out with engine start. The last flight was carried out on June 4, 1971. Further work on the SV-5 and its upgrades was curtailed in favor of a more promising project.
X-24A specifications:
Wingspan - 4, 16 m;
Length - 7, 47 m;
Height - 3, 15 m;
Aircraft weight - 2964 kg;
Maximum takeoff weight - 4833 kg;
Engine type - Thiokol XLR11-RM-13;
Thrust - 3620 kgf;
Maximum speed - 1670 km / h;
Service ceiling - 21764 m;
Crew - 1 person.
The X-24V aerospace vehicle was significantly different from the prototypes SV-5, X-24 and X-24A. The appearance was distinguished by more "sharp" forms. The aerodynamic concept was redesigned thanks to the efforts of the Air Force Flight Dynamics Laboratory. The result is a kind of "flying iron" with a "bubble" in the cockpit canopy in the middle part of the fuselage. The length of the apparatus was 11.4 meters, the diameter was 5.8 meters. Flight weight increased to 6258 kg (fuel weight 2480 kg). The engine operating time did not change, but the thrust increased to 4444 kg. In addition to the main engine, two special LLRV landing rocket engines (thrust 181 kgf) were installed.
On August 1, 1973, Bill Dana made the first gliding flight in the X-24B. Previously, he took part in tests of the Kh-15A rocket plane. besides him, the test program was attended by: John Mankey (16 sorties), Macle Love (12 sorties), William Dana, Einar Enevoldson, Thomas McMurty, Francis Scobie (2 sorties).
X-24B
In total, the Kh-24V made 36 flights of which 12 were planning. The last flight took place on November 26, 1975. Unfortunately, the results obtained during the tests did not live up to expectations. The maximum speed did not exceed 1873 km / h, the ceiling was 22,590 m. The Kh-24V, like its predecessors, climbed to the height using the B-52 bomber.
Specifications X-24B:
Wingspan - 5, 80 m;
Length - 11, 43 m;
Height - 3, 20 m;
Empty weight - 4090 kg;
Maximum takeoff weight - 5900 kg;
Engine type - Thiokol XLR11;
Thrust - 3630 kgf;
Maximum speed - 1872 km / h;
Service ceiling - 22,600 m;
Crew - 1 person.
The test program was not completed, since at that time the Space Shuttle reusable spacecraft program was initiated, as well as the project of the X-24 plus Titan III two-stage vertical launch aerospace system.
They also stopped the development program for the improved X-24C model. Its development was carried out in 1972-1978. One of the X-24C models was planned to be equipped with a pair of ramjet engines, the other - with an XLR-99 liquid propellant rocket engine, previously used for the X-15 rocket plane. The designers of the Martin company planned to conduct tests with 200 flights. It was assumed that the X-24C will reach a speed of M = 8, but the $ 200 million demanded for research has not been allocated.
Until now, only one apparatus of the program has survived - the prototype X-24V, exhibited at the National Museum of the United States Air Force at Wright-Patterson Air Force Base.
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