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LUNOKHOD

At lunar coordinates 38¿18'N, 35¿W, at 0647 hours Moscow time, November 17, 1971, the Soviet Union's Luna 17 landed on the Moon carrying the first remote-controlled wheeled lunar vehicle, Lunokhod I.


Figure 19, Lunokhod I [from Gatland, 1972].

Lunokhod I, shown in Figure 19, was structurally a magnesium alloy container on eight motorized wheels. Its mission was to investigate the lunar environment, and was equipped with instruments to measure lunar soil chemical and mechanical properties, as well as a laser retroreflector for lunar ranging experiments. The vehicle was controlled remotely by a team of five operators; commander, driver, engineer, navigator, and radio operator [Gatland, 1972]. The details of Lunokhod navigation have been difficult to verify, but much can be inferred from the vehicle's equipment and the general sequence of activity during traverses.

Two separate imaging systems were used; one system for scientific purposes and the other for vehicle guidance. The science imagers consisted of panoramic scanners producing high-quality images at a very slow rate, so they could only be used while the vehicle was stationary. Images were built up much as on a facsimile machine. Two such scanners were mounted on each side of Lunokhod, one for producing horizontal panoramas over more than 180¡, and the other for scanning 360¡ in the vertical plane. The latter provided images of the position of the Sun and Earth in the sky, the local horizon, and included the wheels in their scanning plane. These cameras were actually imaging systems adopted from earlier Soviet lunar probes, Lunas 9 and 13. They consisted of a rotating drum that could scan images with 6000 line vertical resolution [Wilson, 1987].

Two front mounted TV cameras were used to steer the vehicle while it was moving, providing stereo imagery of a 50¡ field of view ahead. The cameras captured an image in 1/25th of a second, and then transmitted the image to Earth over a period that varied from 3 to 20 seconds [Gatland, 1972].

Each of the eight drive wheels were equipped with an odometer, but because of wheel slippage, a free rolling odometer wheel was installed at the rear of the vehicle. This wheel was also used for speed calculations [Wilson, 1987]. It is not known whether velocity or distance was used to dead reckon, or what criteria was used to select or discard input from each wheel. Given that Soviet spacecraft of the era lacked sophisticated computer systems, it may be that the navigator was simply presented with telemetry from each wheel, and selected one or more of the wheels as a distance reference. The ninth odometer wheel was likely the primary reference. It is known that the difference in range measurement between the drive wheels and the odometer wheel was used to determine soil mechanical properties.

Lunokhod was equipped with an "inertial platform", but available sources describe it as a set of three orthogonal gyroscopes, there is no indication that it included accelerometers [Smolders, 1974; Wilson, 1987]. No mention is made of an independent heading reference system, and it may be that the platform was only used for attitude and directional information, but this is unverified.

Apparently, the operators would start a traverse by using panoramic cameras to determine initial position. Measurements were made of the Earth and Sun, as well as the shadows cast by the vehicle. This data, along with measurements from an internal vertical sensor, were used to establish a fix [Gatland, 1972; Smolders, 1974]. From that point, the vehicle was guided by the television cameras. The vehicle must have employed a form of dead reckoning while underway, though this is not specifically stated.

Specific navigation experiments were performed by the Lunokhod I team, the first being to determine if navigation on the Moon was possible using a single reference point. The team attempted to direct the vehicle to a point 26¿ away from a conspicuous double mountain peak. They accomplished this despite having to maneuver around craters and boulders. After traveling over 1500 feet in this mode, it was concluded that it was "possible to navigate on the moon's surface using a single reference point" [Aviation Week, 1971]. Another experiment was to navigate back to the landing module. This was accomplished using the inertial platform and measurement of shadows of the vehicle to fix position and determine the initial direction to go [Smoulders]. Here we see the use of following previously laid tracks as a practical navigation method. On January 17, Lunokhod I crossed its old tracks and the controllers used them as final guidance for about a half mile back to the lander [Aeronautics and Astronautics, 1971].

Lunokhod I operated on the lunar surface for 11 lunar days, until on September 15 the vehicle failed. Its route from November 17 through January 20 is shown in Figure 20.

Lunokhod II landed on the Moon on 12 January 1973 at 12.85¡N, 30.45¡W, about 180 km north of the Apollo 17 landing site in the Taurus Littrow valley. Lunokhod II was an improved version of Lunokhod I, equipped with an extra TV camera for guidance, and more powerful electric motors [Wilson, 1987]. Its mission, however, was cut short at about five lunar days, when It was announced that operations were terminated. What exactly happened is still unpublished, but there is speculation that an accident occurred [Astronautics and Aeronautics, 1973]. During that time, Lunokhod covered 37 km in Lemonier crater and the nearby Taurus Mountain foothills.


Figure 20. Lunokhod I route from November 17, 1971 to January 17 1972. [from Smolders, 1974].

No specific mention is made of navigational experiments with Lunokhod II, but a "complex relief map" was used by the ground crew, and Earth observatories used the vehicle's laser retroreflector to confirm position [Astronautics and Aeronautics, 1973]. This is significant in providing another possible fixing mode for lunar navigation.

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