The Oryol program

In 1993 the Russian Space Agency initiated a research and development program called Oryol (“Eagle”) to devise a strategy for the development of reusable space transportation systems in the 21st century. While the program was mainly aimed at technology development, several design bureaus were also invited to work out poss­ible schemes for a Russian Aerospace Plane (RAKS), although it is hardly likely the intention was to actually build one. The focus was both on SSTO and two-stage-to – orbit (TSTO) concepts.

Schemes for vertically launched, partially reusable TSTO systems were devised by RKK Energiya, KB Salyut (which became part of the Khrunichev Center in 1993), and TsNIImash. All these revolved around the use of winged flyback boosters and expendable second stages, capable of placing about 25 tons into low 51° inclination orbits. All the concepts relied on the use of LOX/LH2 engines, with the RD-0120 figuring prominently in three of the four schemes. The payloads could either be traditional satellites placed under a payload fairing or spaceplanes. Primarily intended for space station support, these Reusable Orbital Ships (MOK) would have an expendable instrument and cargo compartment.

Attention was also given to air-launched systems. It would seem that NPO Molniya got some funding under Oryol to continue work on its air-launched MAKS versions. Meanwhile, the Mikoyan bureau studied a fully reusable TSTO system called MiGAKS, consisting of a turbojet/ramjet powered hypersonic carrier aircraft and a spaceplane with rocket engines. The aircraft would propel the spaceplane to Mach 6 before releasing it and would then return either to its home base or to a runway downrange. The Mikoyan bureau studied hypersonic planes burning a combination of kerosene and hydrogen (total take-off mass 420 tons) or hydrogen alone (take-off mass 350 tons). Payload capacity to a low 51° inclination orbit was 12.3 tons for the first version and 10 tons for the second version.

In the SSTO area, the Mikoyan bureau came up with an unmanned spaceplane called MiG-2000. Weighing 300 tons at take-off, the 54 m long vehicle would be accelerated to Mach 0.8 by a liquid-fueled rocket sled, with ramjets propelling it to Mach 5 before rocket engines burning LOX and subcooled liquid hydrogen took

RKK Energiya’s MKR spaceplane (source: RKK Energiya).

over to boost it to orbit. Payload capacity was 9 tons to a low 51° inclination orbit and cross-range capability was up to 3,000 km.

RKK Energiya proposed a 1,400-ton SSTO spaceplane called MKR (Reusable Space Rocket Plane). This would be launched on its own vertically, powered by seven tripropellant LOX/LH2/kerosene engines with a sea-level thrust of 250 tons each. Externally resembling a Buran orbiter, most of the mid and aft fuselage was occupied by propellant tanks, leaving room only for a 8.0 x 4.5 m payload bay. Payload capacity was anywhere from 10 to 18 tons to low 51° orbits, depending on whether the vehicle was manned (maximum crew of three) or unmanned. Missions would last no longer than seven days. Cross-range capability was 2,000 km [22].

There was other SSTO research in the 1990s apparently not funded under Oryol. Khrunichev’s KB Salyut worked on a vertical take-off/horizontal landing system reminiscent of America’s VentureStar, and the Makeyev bureau designed a vertical take-off/vertical landing system called Korona similar to the American DC-X and its Delta Clipper prototype [23]. Finally, NPO Molniya did paper studies of sled – launched SSTOs (VKS-R) as well as vertical take-off/horizontal landing systems (VKS-O) [24].

Perhaps the most exotic SSTO concept was Ajax, originally conceived in the late 1980s by Vladimir L. Frayshtadt at the holding concern Leninets in Leningrad, but not made public until the 1990s. The basic principle is that Ajax turns the kinetic energy produced by the incoming airflow into chemical energy and power. Hydrocarbon fuel circulating under the skin is decomposed into several constituents by aerodynamic heating (“endothermic fuel conversion”) and routed to a so-called magnetohydrodynamics (MHD) propulsion system, consisting of an MHD genera­tor, a scramjet, and an MHD accelerator. The MHD generator extracts energy and thereby slows down the airflow before it enters the combustion chamber, circum­venting the problems associated with mixing fuel and air at high Mach numbers.

Subsequently, the extracted energy is re-injected into the system by the MHD accel­erator (located behind the combustion chamber) which speeds up the airflow. Another novelty on Ajax is the creation of plasma at the leading and trailing edges of its body to ensure a smoother air flow across the fuselage [25].

The Oryol program was finished in 2001. The general conclusion was that the best way to go forward in the near future was to develop partially reusable TSTO systems with flyback boosters and conventional rocket engines. Including space – planes as a means of satellite deployment in TSTO systems would only be effective if they could lower launch costs by 5-7 times compared with expendable launch vehicles and if they could be made five times more reliable, both of which are unattainable goals at the present time. Therefore, preference was given to TSTO systems with conventional satellite deployment techniques. The partially reusable Angara rockets using the Baykal flyback stage were seen as a first step in that direction. SSTOs were considered worth developing only if their dry mass could be made 30 percent lower than that of systems like the Space Shuttle or Energiya – Buran, which is unrealistic for the time being. The most promising SSTO designs were considered to be vertical take-off/horizontal landing systems [26].

Under the Federal Space Program for 2001-2005 Oryol was followed by another research program called Grif (“Vulture”), focusing among other things on studies of new, heat-resistant materials, construction materials, and air-breathing engines [27]. The latest Federal Space Program (2006-2015) only envisages the development of a partially reusable TSTO system with a flyback booster, an indication that SSTO has been shelved for many years to come. A tender to develop the TSTO is to be held in 2009 and the system is supposed to be fielded in 2016, although this is subject to further review. Payload capacity should be 25-35 tons to low orbit and launch costs should be reduced 1.5 times by avoiding the expenditures associated with clearing first-stage impact zones.

A possible contender is the RN-35, a TSTO system designed by the Keldysh Research Center in 2001-2003. Having a payload capacity of 35 tons, it would have a winged flyback booster burning liquid oxygen and methane. This may eventually be followed around 2030 by the RN-70, a similar system with a 70-ton payload capacity. There may be cooperation with the French CNES space agency under a program known as Ural [28]. At any rate, given the conclusions of the Oryol studies, it is unlikely that spaceplanes will be part of the TSTO program.