|Buran Atop Mriya|
Buran atop its An-225 Mriya carrier, as displayed at the Paria Air show shortly after its spaceflight.
Credit: © Mark Wade. 22,168 bytes. 538 x 262 pixels.
The MAKS spaceplane was the ultimate development of the air-launched spaceplane studies conducted by NPO Molniya. The draft project for MAKS was completed in 1988 and consisted of 220 volumes, generated by NPO Molniya and 70 sub-contractors and government institutes. Development of MAKS was authorised but cancelled in 1991. At the time of the cancellation, mock-ups of both the MAKS orbiter and the external tank had been finished. A 9,000 kgf experimental engine with 19 injectors was tested. There were 50 test burns proving the separate modes and a smooth switch between them. Since it was expected that MAKS could reduce the cost of transport to earth orbit by a factor of ten, it was hoped in the 1990's that development funding could be found. However this did not materialise. MAKS was to have flown by 1998.
In 1976-1981 it was realised that launch of Spiral from a large transport was feasible and of much lower development cost than the previous approach using a supersonic launcher. Further it was realised that a smaller orbital spaceplane would have many advantages compared to the Buran space shuttle then in development. These included quicker turnaround, more launch flexibility, and a wider range of achievable orbits. The MAKS approach would allow launch of payloads into orbit; working on satellites in orbit; and return of payloads to earth.
The MAKS design was superior to the earlier System 49 and Bizan designs in several ways. The single-stage-to-orbit allowed the propellant tank to be dropped safely into the antipodal ocean after launch, whereas the '49' with separate rocket stages was constrained to launch points where a first stage impact point 2000 km away was available. MAKS was more reusable than Bizan since all of the engines would be recovered; only the propellant tank was expendable. Finally., the availability of the An-225 transport meant that a larger spacecraft could be designed.
The MAKS draft project used 3 x NK-45 Kuznetsov Lox/LH2 engines with 90 tonnes thrust each. This design had 250 tonne flight mass and a 7 tonne net payload. Switch during development to the RD-701 tripropellant engine improved the design. The higher-density propellants allowed a smaller, lighter tank with an increase of the net payload to 8.4 tonnes.
Studies indicated that the optimum launch angle for MAKS was 45 degrees. But to attain this with the An-225 transport a rocket engine would have to be installed in the launch aircraft, which was undesirable from a development standpoint and would also cut into the gross mass of the MAKS vehicle. Finally a tank geometry, and engine/orbiter arrangement was found that allowed the proper release conditions without requiring a supplemental rocket engine in the transport.
The mix and arrangement of propellant tanks changed during development. At first the oxidiser cell was placed at the front of the drop tank. This was aerodynamically stable but resulted in excessive static loads. Other locations posed insurmountable problems with the vehicle's aerodynamic moment and separation from the carrier aircraft. Putting the entire vehicle under the launch aircraft was considered, but this would require redesign of the An-225. There were finally two choices: either an unstable design, with the wings of the MAKS orbiter pitching the vehicle up 45 degrees immediately at release; or three cylindrical tanks arranged under the orbiter in a 'Siamese' arrangement. This last solution was favoured by TsAGI Central Hydrodynamics Institute, but the design bureau felt the weight penalty was too great.
The final layout had a complex form, with the thrust vector running below the axis of the drop tank. This 'tug' arrangement basically turned the drop tank into a barge with the orbiter pushing it into orbit. This solution had the lowest mass, was the best for a variety of abort situations, produced the best separation of the orbiter from the tank, and allowed a clear field for use of the crew ejection seats in an emergency.
The MAKS expendable-tank solution also produced a higher payload fraction to orbit than competing integrated vehicle approaches (such as I-HOTOL / MAKS-M or VKS-O). This provided a better margin in case of vehicle weight growth. The drop-tank / lightweight orbiter approach also reduced the amount of orbital manoeuvring propellant required, which allowed heavier payloads to be placed into high altitude orbits than pure single-stage-to-orbit designs.
The MAKS air-launched manned space system weighed 620 tonnes on takeoff and consisted of three elements:
LEO Payload: 6,600 kg. to: 400 km Orbit. at: 90.0 degrees. Payload: 9,500 kg. to a: 200 km, 51 degree orbit in unmanned configuration trajectory. Liftoff Thrust: 400,000 kgf. Total Mass: 275,000 kg. Core Diameter: 6.4 m. Total Length: 39.0 m. Flyaway Unit Cost $: 113.00 million. in 1985 unit dollars. Cost comments: Cost $ 1,000 / kg to orbit in 1992 dollars.
System specification issued for An-225 heavy transport, which will replace 3M-T for transport of Energia core stage components and the Buran spaceplane. The aircraft will also be the launcher for the MAKS spaceplane.
MAKS draft project is completed.
First flight of the An-225 super-heavy transport with the Buran spaceplane mounted atop it.