Buran Atop Mriya Credit - © Mark Wade

Winged orbital launch vehicle. Family:

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:

• An-225 Mriya carrier aircraft, the largest in the world, originally developed to transport the Buran orbiter. The Mriya would take the 275 tonne MAKS piggy-back a launch position appropriate for the target orbit. The optimum release manoeuvre involved a dive from 7.8 km altitude to 6.8 km over a 7 km distance. The transport would then pull up, releasing MAKS at 8.6 km altitude and 900 km/hr. After release the transport nosed over, reaching a peak altitude of 8.8 km, levelling out at 8.2 km 20 km from the start of the manoeuvre.

• External tank. This carried liquid oxygen, kerosene, and liquid hydrogen propellants. It was 6.38 m in diameter and 32.1 m long, with a total mass of 248,000 kg and an empty mass of 11,000 kg.

• MAKS Orbiter. This spaceplane, designed for 100 reuses, used on-board systems based on those already developed for Energia and Buran. The orbiter had an empty mass of 18,400 kg, with a wingspan of 12.5 m and a length of 19.3 m. The aerodynamic shape was refined considerably from that of Spiral / 49 / Bizan to accommodate the main engine installation in the tail. An unmanned version could deliver 9.5 tonnes to a 200 km, 51 degree orbit in a payload bay 2.8 m diameter x 8.7 m long. The manned version took two crew and a payload of 8.3 tonnes in a bay 2.8 m diameter x 6.8 m long to the same orbit. In the orbiter's tail were two RD-701 tripropellant engines. These were designed for 15 re-uses and used dense kerosene and liquid oxygen for initial operations, then switched modes to a reduced thrust and higher specific impulse using low density liquid hydrogen and liquid oxygen. This reduced the size of the huge hydrogen tank otherwise required. The RD-701 engine assembly in the MAKS had a total mass of 3990 kg and delivered a total thrust of 400,000 kgf at separation from the An-225.

Manufacturer: Molniya. LEO Payload: 6,600 kg (14,500 lb). to: 400 km Orbit. at: 90.00 degrees. Payload: 9,500 kg (20,900 lb). to a: 200 km, 51 degree orbit in unmanned configuration trajectory. Associated Spacecraft: MAKS Orbiter. Liftoff Thrust: 3,900.000 kN (876,700 lbf). Total Mass: 275,000 kg (606,000 lb). Core Diameter: 6.38 m (20.93 ft). Total Length: 39.00 m (127.00 ft). Flyaway Unit Cost $: 113.000 million. in: 1985 unit dollars. Cost comments: Cost $ 1,000 / kg to orbit in 1992 dollars.

• Stage0: 1 x An-225. Gross Mass: 600,000 kg (1,320,000 lb). Empty Mass: 216,000 kg (476,000 lb). Motor: 6 x D-18T. Thrust (vac): 1,387.072 kN (311,826 lbf). Isp: 9,000 sec. Burn time: 3,375 sec. Length: 84.00 m (275.00 ft). Diameter: 18.07 m (59.28 ft). Propellants: Air/Kerosene.

• Stage1: 1 x MAKS Orbiter. Gross Mass: 18,600 kg (41,000 lb). Empty Mass: 18,600 kg (41,000 lb). Motor: 1 x RD-701. Thrust (vac): 3,618.771 kN (813,532 lbf). Isp: 437 sec. Burn time: 440 sec. Length: 19.30 m (63.30 ft). Diameter: 3.00 m (9.80 ft). Propellants: Lox/Kerosene/LH2.

• Stage2: 1 x MAKS Tank. Gross Mass: 248,100 kg (546,900 lb). Empty Mass: 10,820 kg (23,850 lb). Motor: 1 x None. Thrust (vac): 0 N ( lbf). Isp: 437 sec. Burn time: 440 sec. Length: 32.10 m (105.30 ft). Diameter: 6.38 m (20.93 ft). Propellants: Lox/Kerosene/LH2.

LEO Payload: 5,400 kg (11,900 lb). to: 200 km Orbit. at: 51.00 degrees. Payload: 7,000 kg (15,400 lb). to a: equatorial, 0 degree, 200 km altitude orbital trajectory. Total Mass: 275,000 kg (606,000 lb). Version:

MAKS-T. Status: Study 1988.

All cargo version of MAKS. Air-launched heavy-lift launcher would use an expendable second stage with a payload container. Release conditions: Piggy-back, 275,000 kg, 38.0 m length x 24.0 m wingspan, 900 kph at 9,500 m altitude. Effective velocity gain compared to vertical launch 270 m/s. Payload bay 13.0 m long x 5.0 m diameter.

LEO Payload: 18,000 kg (39,000 lb). to: 200 km Orbit. at: 51.00 degrees. Payload: 19,500 kg (42,900 lb). to a: equatorial, 0 degree, 200 km altitude orbital trajectory. Total Mass: 275,000 kg (606,000 lb). Version:

MAKS-D. Status: Study 1981.

NPO Molniya, Antonov, and TsAGI proposed a spaceplane demonstrator project to the European Space Agency in 1993-1994 under the RADEM project. This would be a scaled-back version of the cancelled MAKS spaceplane using existing rocket engines. An unmanned prototype of the MAKS would be fitted out with RD-120 Lox/Kerosene engines. Launched from atop the An-225, the MAKS-D would reach an altitude of 80 to 90 km and a speed of Mach 14 to 15.

The ES experimental spacecraft would have a launch mass of 56 metric tons, including 45 metric tons of propellant. It would fly at hypersonic speed out to a range of 1500 km, and then return to an automatic landing at its launching base. Three variants were proposed:

• Basic variant. Purpose of the flight tests would be to prove MAKS-M / I-HOTOL flight algorithms, materials, and engine reusability. 38.0 m length x 24.0 m wingspan

• Basic variant modified for scramjet flight tests

• Orbital vehicle with 2 metric tons payload. For the orbital vehicle the MAKS-D served as the first stage of the booster. It would release the RS rocket stage, equipped with a European HM-7B Lox/LH2 engine. The rocket stage engine would ignite five seconds after release of the aircraft from the An-225 transport and work in tandem with the RD-120 installed on MAKS-D. Following exhaustion of main stage propellants the MAKS would release the rocket stage, which would continue on to orbit. This scheme was analogous to NASA's early X-34 concepts.

1985 - During the year - An-225 project started. Spacecraft: Buran. 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.

1989 May - MAKS draft project. Spacecraft: MAKS Orbiter. MAKS draft project is completed.

1989 May 13 - First flight An-225 / Buran. Spacecraft: Buran. First flight of the An-225 super-heavy transport with the Buran spaceplane mounted atop it.

1989 June 4 - An-225 / Buran displayed at Paris Air Show. Spacecraft: Buran.

1993 - RADEM project NPO Molniya, Antonov, and TsAGI proposed a spaceplane demonstrator project to the European Space Agency in 1993-1994 under the RADEM project. This would be a scaled-back version of the cancelled MAKS spaceplane using existing rocket engines.