NPO ENERGIYA’S OK-M SPACEPLANES

Between 1984 and 1993 NPO Energiya studied several relatively small spaceplanes that were primarily intended to replace Soyuz and Progress for space station support. These had the general designator OK-M (Small-Size Orbital Ship).

The basic OK-M was a 15-ton spaceplane launched by the Zenit rocket. The interface between the vehicle and the rocket was an adapter equipped with four 25-ton solid-fuel motors that could be used to either pull the ship away from the

rocket in an emergency or to provide extra thrust during launch by being activated shortly after second-stage ignition. Aerodynamically, OK-M was a mini-version of Buran, having delta wings with elevons and a vertical stabilizer with rudder/speed brake. The outer surface was covered with Buran-type heat-resistant tiles. The ship could carry a crew of two in the cabin and—if required—four more cosmonauts in a pressurized module inside its 20 m3 cargo bay. The nosecap of the vehicle would be retracted to expose an androgynous docking port. OK-M had two orbital maneuver­ing engines and 34 thrusters, all burning nitrogen tetroxide/UDMH. Power was to be provided by 16 batteries, although solar panels were also considered. Payload capacity was 3.5 tons to a 51.6°, 200 km orbit and just 2 tons to a 450 km Mir-type orbit.

Better satisfying the logistics requirements of space stations were two heavier spaceplanes called OK-M1 (31.8 tons) and OK-M2 (30 tons). Jointly developed with NPO Molniya, they were very similar to the air-launched MAKS-OS spaceplane.

However, NPO Energiya felt that such vehicles should be launched with conventional rocket systems until various mass-related and other technical issues associated with the air-launch technique were solved.

The main difference between OK-M1 and OK-M2 was the launch profile. For OK-M1 Energiya studied a rather unwieldy-looking two-stage-to-orbit configuration known as the Reusable Multipurpose Space Complex (MMKS). This consisted of a huge external fuel tank with the small spaceplane strapped to one side and a Buran look-alike vehicle to the opposite side. The external tank contained liquid oxygen, liquid hydrogen, and kerosene to power tripropellant engines in both vehicles. The Buran-sized vehicle was to act as the system’s first stage. It essentially was a Buran without a crew compartment carrying extra liquid oxygen and kerosene tanks in the cargo bay to feed four main engines in the tail section. After separating from the external tank, it would return to Earth using two jet engines mounted on either side of the mid fuselage. Next the OK-M1 would fire its two main engines to reach orbit. Safety features for OK-M1 included ejection seats for the crew and an emergency separation system.

OK-M2 was to be launched atop an Energiya-M rocket with conventional strap – on boosters or winged flyback boosters. The adapter connecting it to the rocket was virtually identical to that in the Zenit/OK-M configuration and also included solid – fuel motors that could be used either in a launch abort or for final orbit insertion. Another option was to install ejection seats in the vehicle, which would allow the use of a much simplified and lighter adapter section.

Because of the different launch technique, OK-M2 required no main engines, which translated into a higher payload capacity—namely, 10 tons to a 250 km, 51.6° inclination orbit vs. 7.2 tons for OK-M1 (6 and 5 tons, respectively, for Mir-type altitudes). Other differences were a LOX/kerosene orbital maneuvering/reaction control system for OK-M1 (2 OMS engines and 18 thrusters) vs. LOX/ethanol for OK-M2 (3 OMS engines, 27 thrusters). Both vehicles could accommodate four crew members in the crew compartment and another four in a pressurized module in the 40 m3 cargo bay. The power supply system relied on a combination of fuel cells and batteries. Just like MAKS-OS, both ships had foldable wings [13]. In 1994 a proposal was made to launch OK-M2 with a European Ariane-5 booster outfitted with Energiya strap-on boosters [14].

Concurrently with the OK-M studies, NPO Energiya worked out plans for a ballistic reusable spacecraft called Zarya (“Dawn”). This looked like an enlarged Soyuz descent capsule with a small expendable instrument section attached to it. Weighing 15 tons, it would be launched by Zenit and make a vertical landing using a cluster of 24 liquid-fuel braking engines rather than parachutes. The heat shield would be similar to that of Buran. Zarya was mainly intended for space station support, but also was to fly autonomous missions in the interests of the Ministry of Defense and the Academy of Sciences. Maximum crew capacity was eight.

Indications are that Zarya was considered a much more likely contender to replace or complement Soyuz/Progress than the OK-M spaceplanes. While OK-M was no more than a conceptual study, Zarya development was sanctioned by a government decree in January 1985 and even went beyond the “preliminary design’’ phase. Zarya was eventually canceled in January 1989 due to a lack of financing, although Valentin Glushko’s death that same month may have contributed to the decision [15].