THE SPACESHIP FOR ORBITING THE MOON: THE LUNIY ORBITALNY KORABL, LOK

The Soviet moon ship was the LOK (Luniy Orbitalny Korabl). Unlike the L-1 Zond, the LOK had a direct point of comparison with American hardware – the Apollo command-and-service module. Sixteen began construction, seven were completed and parts of four can still be found in museums. The LOK flew only once, on the fourth N-1 launch in November 1972, when it was destroyed, although the descent module was saved by the escape system. The traditional engineering view of the LOK is that it was a beefed-up Soyuz able to fly to the moon, but it was much more capable than that – a versatile lunar spaceship in its own right, a worthy contemporary to Apollo [17].

The descent module was the same as the normal Soyuz – but designed for a crew of two, not three; and with a thicker heat shield for the high reentry speed. The LOK weighed more, 3,050 kg, rather than 2,850 kg. The orbital module was similar to the normal Soyuz, but with different instrumentation, controls and many additional portholes for lunar orbit observations. The spacesuit for the moonwalk would be housed here, and it was from this module that the spacesuited cosmonaut would leave on his moonwalk to climb into the lunar module (LK) and begin the descent to the lunar surface. The orbital module had a large hatch, 90 cm, sufficiently wide to permit the cosmonaut to exit in the Kretchet lunar suit. The orbital module had a control unit for masterminding the link-up in lunar orbit after the landing and a forward-looking porthole. Rendezvous and docking would be controlled from there, not from the descent module.

Compared with Soyuz, it had a much larger skirt at the base, an additional small forward module and a docking system at the front, called Kontakt. A series of antennae and helices were used to zone in on the returning landing module, the LK, for rendezvous and docking. The LOK’s probe, called Aktiv, would penetrate an aluminium plate on the top of the LK. It had 108 recessed honeycomb hexagons on a plate 100 cm across and entry to only one of these would be sufficient to achieve a firm capture.

The most visible differences from Soyuz were in the instrument-and-propulsion module at the rear and the small extra module at the front. The 800 kg front module contained six fuel tanks, each with 300 kg of UDMH, four engines for attitude control in lunar orbit, an orientation engine and the Kontakt docking unit. On Apollo, there was a small conical docking unit on the front of the command module, but the other elements were made an integral part of the service module. For rendezvous, the LOK closed in on the LK in lunar orbit, the flight engineer peering through the forward­looking porthole, using television and handling an adjacent control panel. The front module of the LOK had four attitude control thruster units, each with two main nozzles and two small ones. The engine system was made by the Arsenal Design Bureau in Leningrad.

At the rear, the LOK carried two propulsion sets. The biggest was the main engine for the return to Earth, the equivalent of the Service Propulsion System of Apollo. The LOK’s engine had a thrust of 3,388 kg and a specific impulse of 314 and its primary purpose was to make the trans-Earth injection burn out of lunar orbit. The engine, called the S5.51, was built by the Isayev design bureau. The LOK also carried the standard Soyuz engine, to be used as a rendezvous motor, with a thrust of 417 kg, a specific impulse of 296 and capable of 35 restarts. The LOK carried 2,032 kg of nitrogen tetroxide and 1,120 kg of UMDH. The LOK was the first Soviet spacecraft to carry the fuel cells pioneered by the Americans in the Gemini programme: 20 Volna cells, weight 70 kg, able to supply 1.5 kW for ten days. They were made by the Ural Electrochemical Enterprise. The only other Soviet spaceship to carry fuel cells was the Buran space shuttle in 1988. The rear section carried radiator shutters to shed heat. At the junction with the descent module were star trackers.

LOK’s arrival in lunar orbit followed a different procedure from Apollo. The mid­course manoeuvre and lunar orbit insertion were done by block D, not by the LOK’s main engine. Block D would again be used to lower the orbit of the LOK and LK over the lunar surface to its final orbit dipping to 16 km and, finally, for all but the final part of the powered descent of the LK. On Apollo, the Service Propulsion System carried out the mid-course correction moonbound, lunar orbit insertion and lunar orbit corrections.

With the LK down on the surface, the profile of the LOK now closely approxi­mated that of the Apollo command-and-service module. The LOK would orbit the moon, a sole cosmonaut flight engineer aboard, like the single astronaut on the Apollo. For half of each orbit, it would be around the farside of the moon, out of contact with the Earth. Once the LK blasted off from the lunar surface, it was the task of the LOK to locate the rising LK, close in and dock. The Kontakt system was designed in such a way that a simple contact would join the spacecraft together, so there was no question of hard and soft dockings. Unlike Apollo, the LK cosmonaut would transfer externally back to the LOK by spacewalk. The LK would, like the American LM, then be jettisoned. The LOK would then make the crucial burn out of lunar orbit, make the three day coast back to Earth, carry out two mid-course corrections (one at mid-point, one just before reentry) and then make a Zond-type skip reentry.

Source: RKK Energiya (2001)