Lunar Self-Propelled Vehicle

an unmanned or manned vehicle designed to travel on and study the moon.

In designing and building such a vehicle, Soviet scientists and designers were faced with solving a number of complex problems. It was necessary to develop a totally new type of vehicle, one capable of functioning for a prolonged period under the unusual conditions of open space on the surface of another celestial body. The principal tasks included (1) the development of an optimal propelling device with high crosscountry capability but low weight and power consumption that would ensure reliable operation and safety of motion, (2) the design of systems for the remote control of the vehicle, (3) the provision of the necessary thermal conditions by means of a heat control system that would maintain within prescribed limits the temperature of the gas in instrument sections and of structural elements and equipment located inside and outside (in open space during the lunar days and nights) hermetically sealed compartments, (4) the selection of a power source and materials for the structural elements, and (5) the development of lubricants and lubricating systems that could be used under vacuum conditions.

The scientific equipment of the lunar vehicle had to make possible the study of the topographic and selenomorphological features of the terrain; the determination of the chemical composition and the physical and mechanical properties of the soil; the investigation of the radiation conditions en route to the moon, in the space near the moon, and on the lunar surface, as well as cosmic X-radiation; and the conducting of experiments on the laser ranging of the moon.

The first lunar vehicle—the Soviet Lunokhod 1, which was designed to conduct numerous scientific studies on the surface of the moon—was placed on the moon by the Luna 17 unmanned spacecraft and functioned on the lunar surface from Nov. 17, 1970, through Oct. 4, 1971, traveling a total of 10,540 m. Lunokhod 1 weighed 756 kg and consisted of two parts: an instrument module and a wheeled chassis. The sealed instrument module was shaped like a frustum of a cone. Its body was made of magnesium alloys, which ensured sufficient strength and lightness. The upper part of the module’s body was used as a radiator-cooler in the temperature control system and was covered by a lid. During the lunar night the lid covered the radiator, thus preventing the radiation of heat from the module. During the lunar day the lid was open, and the elements of the solar battery located on the inner side recharged the storage cells that fed electric power to the on-board equipment.

The instrument module contained the temperature control and electrical systems, the receiving and transmitting devices of the radio system, the remote control instruments, and the instruments of the electronic data conversion unit for the scientific equipment. The front section contained television camera illuminators, the electric drive for a movable high-directional antenna used for transmitting television images of the lunar surface to the earth, a broadly directional antenna for receiving radio commands and transmitting telemetry information, scientific instruments, and an optical corner reflector manufactured in France. Two panoramic telephoto cameras (one of the cameras in each pair was structurally connected to a local-vertical finder) and four rod aerials for receiving radio commands from the earth over different frequency bands were mounted on the port and starboard sides. An isotopic source of thermal energy was used to heat the gas circulating within the vehicle. Alongside this was placed an instrument for determining the physical and mechanical properties of the lunar soil.

The abrupt temperature variations resulting from the alternation of day and night on the lunar surface and the large temperature differences between parts of the vehicle in the sun and shade necessitated the development of a special temperature control system. At the low temperatures of the lunar night, the circulation of the heat-transfer gas through the cooling circuit was automatically stopped, and the gas was directed into the heating circuit in order to heat the instrument module.

The Lunokhod’s electrical power supply system consisted of a solar battery with chemical buffer batteries and automatic control devices. Control of the solar battery actuator was effected from the earth; the lid could be set at any angle from 0° to 180° to ensure maximum use of solar energy.

The on-board radio system received commands from the control center and transmitted data from the vehicle to the earth. A number of elements of the radio system were used not only for operations on the lunar surface but also during the flight from the earth. The Lunokhod’s two television systems were used to carry out independent tasks. A half-frame television system was designed to transmit to the earth television images of the terrain required by the team controlling the Lunokhod’s movement from the earth. The possibility and expediency of employing such a system, which is characterized by a lower rate of image transmission than the broadcasting television standard, were dictated by specific lunar conditions, particularly by the slow changing of the landscape as the Lunokhod traveled. The second television system was used to obtain a panoramic view of the surrounding terrain and to survey sections of the stellar sky, the sun, and the earth for celestial navigation purposes. This system consisted of four panoramic telephoto cameras.

The self-propelled chassis was able to overcome a fundamentally new problem of astronautics—the movement of an automatic laboratory over the surface of the moon. The chassis was designed so that the Lunokhod had high crosscountry capability and could operate reliably for a long period with minimal weight and power consumption. The vehicle could move forward, at two speeds, and in reverse and could turn in place or while moving. It consisted of an undercarriage, a control unit, a safety system, and a device and set of sensors for determining the mechanical properties of the soil and evaluating the crosscountry capability of the chassis. Turns were made by using different rates of rotation of the wheels on the port and starboard sides and by changing the direction of rotation. Braking was accomplished by switching the electric drive motors of the chassis into the electrodynamic braking mode. Electromagnetically controlled disk brakes were incorporated to hold back the Lunokhod on slopes and to bring it to a full stop. The control unit regulated the movement of the Lunokhod on radio commands from the earth and measured and controlled the main parameters of the self-propelled chassis and the automatic operation of the instruments used to study the mechanical properties of the lunar soil. The safety system could effect automatic stopping at limiting angles of roll and trim and in case of overloading of the electric motors driving the wheels.

The device for determining the mechanical properties of the lunar soil made it possible to obtain prompt information on the soil conditions of movement. The distance traversed was determined by the number of rotations of the drive wheels. To allow for slipping of the wheels, a correction determined by means of a free-turning ninth wheel, which was lowered to and raised from the ground by a special drive, was introduced. The vehicle was controlled from the deep-space communications center by a team consisting of a commander, driver, navigator, operator, and flight engineer.

The mode of travel was selected upon evaluation of televised information and incoming telemetry data concerning the magnitude of the roll, the trim of the path traversed, and the conditions and modes of operation of the wheel drives. All systems and scientific instruments of the Lunokhod functioned normally under the conditions of space vacuum, radiation, large temperature variations, and the complexity of the terrain. Their successful operation ensured completion of both the primary and supplementary programs for scientific investigation of the moon and outer space, as well as engineering and design tests.

Lunokhod 1 examined in detail 80,000 sq m of lunar surface. For this purpose, more than 200 panoramic shots and more than 20,000 photographs of the surface were taken by the television systems. The physical and mechanical properties of the surface layer of soil were studied at more than 500 sites along the route; the chemical composition of the soil was analyzed at 25 locations. Operation of Lunokhod 1 ended as a result of depletion of the reserves of the vehicle’s isotopic source of heat. At the conclusion of its work, the vehicle was left at a nearly horizontal site in such a position that its corner light reflector would allow many years of laser ranging from the earth.

On Jan. 16, 1973, Lunokhod 2 was placed near the eastern edge of the Mare Serenitatis (Sea of Serenity), in the ancient Le Monnier crater, by the Luna 21 spacecraft. The selection of this landing site was dictated by the desirability of acquiring new data on the complex zone where the sea and continent meet. Improvement of the design and of the flight systems, installation of additional instruments, and expansion of the capabilities of the equipment made it possible to increase greatly the vehicle’s maneuverability and to perform a great deal of scientific research. In five lunar days Lunokhod 2 traversed a distance of 37 km over complex terrain.

During the flights of the Apollo 15, Apollo 16, and Apollo 17 spacecraft, American astronauts used the Lunar Rover, a two-seat self-propelled vehicle. It had four wheels, each of which had a diameter of 81 cm and a width of 23 cm. The wheel suspension was of the torsion-bar type. Each wheel was a drive wheel and was equipped with an individual motor. The vehicle had an aircraft-type control stick that permitted the astronauts to regulate their speed, to brake, and to make turns. The Rover’s control system, which included a small shutoff device, made it possible to determine the direction of motion, the total distance traveled, and the straight-line distance from and the direction to the lunar module. Special radio equipment (the lunar radio-relay unit) allowed direct communication between the astronauts and the earth. The Rover was folded and stowed in the descent stage of the lunar module. Removal of the Rover and its assembly can be accomplished by one astronaut.

The Rover weighed 725 kg including the Rover proper, 211 kg; the astronauts with portable life-support systems, 364 kg; scientific instruments 54 kg; photography and communications equipment 69 kg; and the remaining weight accounted for by lunar rock samples and miscellaneous items. The Rover was 3.1 m long, 2.1 m wide, and 1.1 m high and had a track width of 1.83 m, a range of 65 km, and a maximum speed of 13 km/hr. The Rover was designed to negotiate slopes inclined up to 20°, obstacles up to 30 cm high, and crevasses up to 70 cm wide. The maximum permissible roll and trim were 45°. The distance traveled by the Lunar Rovers was 27.2 km for the Apollo 15 flight, 27.1 km for the Apollo 16 flight, and 35.7 km for the Apollo 17 flight. The Rover greatly facilitated the astronauts’ work on the moon.