The solar-powered (but nuclear-heated) 756-kilogram rover, measuring 1.35 meters tall and 2.15 meters across its tub-shaped equipment compartment, rolled on eight metal wheels with cleats at a top speed of 0.1 kilometers per hour. A hinged, bowl-shaped lid lined with electricity-generating solar cells opened to expose a thermal radiator atop the tub; as night approached, Lunokhod 1's operators commanded it to close the lid to hold in heat and protect its delicate electronics.
|Lunokhod 1. Image credit: Lavochkin Association/NASA.|
The rover would then have stood by until a lander bearing a single cosmonaut arrived. If his lander became damaged during touch-down so that it could not return him to lunar orbit, the Lunokhod operator team on Earth would drive the rover to pick him up for transfer to a waiting, pre-landed backup lander. The United States had, incidentally, in the early 1960s considered launching site-survey rovers to Apollo landing sites, and had studied long-range automated rovers that visiting astronauts could board and drive.
Even before the successful Apollo 11 landing (20 July 1969), the Soviets claimed that they never intended to land cosmonauts on the Moon. This was, of course, untrue, but it found a receptive audience among those who opposed piloted lunar exploration on the basis of cost or who favored the Soviet Union in the Cold War.
Through their official media, the Soviets declared that they had opted instead for robot explorers that cost much less than Apollo and placed no human life at risk. This message was particularly potent in the months following the near-disaster of Apollo 13 (11-17 April 1970). They told the world that Lunokhod 1 and its cousins, the Luna automated sample returners, presaged a new era of extensive and intensive robotic lunar and planetary exploration.
Billed as a "logical follow-on" to the Viking landings planned for mid-1976, JPL's 1127-pound rover would include six wire wheels akin to those on the Apollo Lunar Roving Vehicle, which at the time was scheduled to be driven by astronauts on the Moon for the first time in 1971. Mobility would enable "extended" Viking objectives: for example, while Viking would land on a safe, flat plain and seek living organisms only within reach of its three-meter-long robot arm, the 1979 rover could land in a flat area, then enter rugged terrain to seek out biologically promising sites.
|Viking 1 launch on a Titan III-E rocket on 20 August 1975. Image: NASA.|
Assuming a 3 November 1979 launch, Earth-Mars transfer would need 268 days. During the voyage, a door would open in the top of the aeroshell and the rover's cylindrical electricity-generating Radioisotope Thermal Generators (RTGs) would extend into space on a boom. The plutonium-powered RTGs would continually generate heat; if kept sealed within the aeroshell during the flight to Mars, heat build-up would damage the rover.
Mars arrival would occur in August 1980. The orbiter's rocket motor would slow the spacecraft so that the planet's gravity could capture it into orbit. Two days later, it would tweak its orbit so that it would pass over the rover's primary landing site. The JPL team estimated that its Mars rover could reach sites between 30° north and 30° south latitude.
The JPL engineers described the rover landing sequence in considerable detail. Two hours after separation from the orbiter and 300 seconds before landing (that is, at L minus 300 seconds), the aeroshell would encounter the thin upper atmosphere of Mars. Entry deceleration would peak at about 12 times the force of Earth's gravity.
At L minus 80 seconds, moving at a speed of Mach 2.5, the aeroshell would deploy a compact ballute ("balloon-parachute") 21,000 feet above Mars. Three seconds later, at 19,000 feet and a speed of Mach 2.2, a single parachute would deploy and the ballute would separate.
At L minus 73 seconds, with the rover streaking through the martian sky at Mach 2, the parachute would fill with thin martian air. Six seconds later, the lower aeroshell would separate, exposing the rover's underside and twin landing radars.
|JPL's 1979 Mars rover in its landed configuration. Arrows point to the three terminal descent rocket motors. Image credit: JPL/NASA.|
JPL's rover would comprise a train of three compartments, each with one wheel pair. Flexible connectors would link the compartments. The forward compartment (the "science bay") would include a Viking-type soil sampler arm with an attached soil magnetic properties experiment, a new-design "chisel and claw" arm, four biology experiment packages (the number NASA planned to launch on the Viking landers at the time JPL completed its rover report), a mass spectrometer, a weather station, and a seismometer. The forward compartment wheel hubs would carry one terminal descent rocket motor each, and the front wheel pair would be steerable.
The middle compartment (the "electronics bay") would house the 95-pound dual-purpose (science & rover control) computer. A telescoping stalk would support a dish-shaped high-gain antenna, a low-gain antenna, a facsimile camera capable of generating a 360° panorama, and a vidicon camera with rangefinder.
The rear compartment (the "power bay") would include the twin externally-mounted RTGs, landing radars on its wheel hubs, and a rear-mounted terminal descent rocket motor. The rear wheel pair would, like the front pair, be steerable.
From some time before Earth launch until its second day on Mars, the three compartments would be squeezed together tightly with their wheels touching. This would enable the rover to fit within the confines of its Viking-type aeroshell.
Controllers on Earth would check out the rover during its first day after touchdown on Mars. On Day 2, they would spread out its compartments, deploy its appendages, and discard the terminal descent motors and landing radars. The JPL design team looked briefly at retaining the terminal descent rockets to enable the rover to "hop" over obstacles, but rejected this capability as being too fraught with risk.
Science operations would commence on Day 3. Mars surface operations would span one Earth year, from August 1980 to August 1981.
Controllers on Earth would guide the rover through its daily program. Operations would occur only during the martian daylight hours, when line-of-sight radio contact with Earth was possible.
Time available for operations during each 24-hour, 39-minute martian day would vary over the rover's one-Earth-year mission, as would radio-signal travel time. On 9 August 1980, for example, a rover at a site on the martian equator would remain in contact with Earth for 10.93 hours, while radio signals would need about 21 minutes to cross the gulf between the planets. In May 1981, Earth and Mars would be far apart — on opposite sides of the Sun — and radio-signal travel time would reach its maximum value of 41 minutes.
Typically, the rover would move from 50 to 100 meters at a time, then halt, image its surroundings, perform one of its science experiments, transmit its data to Earth, and then await new commands. JPL assumed that high-interest science sites would occur on average about 14 kilometers apart along its traverse route, and estimated that early in its mission the rover would travel about 300 meters per day, enabling it to traverse the distance between two science sites in 47 days. Distance traversed would, JPL optimistically assumed, rapidly increase as controllers gained confidence in their remote driving ability: the team estimated that in one Earth year its rover might traverse up to 500 kilometers.
Inspired, perhaps, by Lunokhod 1, the JPL team concluded its study by looking briefly at a lunar variant of its Mars rover design. The team found that the basic design of both rovers could be much the same, though the lunar rover launch vehicle would not need to be as large and powerful (a Titan III/Centaur without strap-on solid-propellant boosters would suffice) and a solid-propellant braking rocket would need to replace the Mars rover's aeroshell, ballute, and parachute because the moon has no atmosphere. In addition, the lunar version could tote an additional 150 pounds of science payload.
As the team's study circulated to a limited JPL audience, Lunokhod 1 continued its slow traverse over dusty Mare Imbrium. The Soviet rover was designed to function for three months, but did not officially cease operations until the 14th anniversary of the launch of Sputnik 1 on 4 October 1971, some 10 months after JPL completed its report (radio contact with Lunokhod 1 was, however, lost on 14 September 1971). During its 10.54-kilometer traverse, it beamed to Earth more than 20,000 images of its surroundings and analyzed lunar surface composition at 25 locations.
On 9 May 1973, after traversing some 37.5 kilometers in less than three months, Lunokhod 2 rolled accidentally into a dark-floored crater. Its open bowl-shaped solar array/thermal cover apparently brushed against the crater wall, becoming partly filled with lunar dirt.
When, shortly thereafter, controllers in the Crimea commanded the array/thermal cover to shut at lunar sunset, the dirt fell on Lunokhod 2's thermal radiator. Two weeks later, as the Sun rose again at Le Monnier, controllers commanded the array/thermal cover to hinge open in preparation for a new day of lunar driving.
The dirt-covered radiator could no longer reject heat adequately, so Lunokhod 2 rapidly overheated in the harsh lunar sunlight. The Soviets declared its mission ended on 3 June 1973. Lunokhod 2 was the last rover to operate on another world until Mars Pathfinder's Sojourner mini-rover in 1997.
In March 2010, NASA released high-resolution Lunar Reconnaissance Orbiter (LRO) images of the Moon's surface showing the Lunokhod 1 and Lunokhod 2 rovers and the Luna 17 and Luna 21 landers. In the intervening years, LRO has orbited lower over the Lunokhod landing sites, enabling higher-resolution imaging. LRO images clearly show the extended Luna 17 and Luna 21 ramps and the tracks Lunokhod 1 and Lunokhod 2 left on the lunar surface.
Competition with the Soviet Union was rarely mentioned as a motive for robotic exploration after the early 1970s. When it was, it lacked its old punch: for example, it utterly failed to move lawmakers when comet scientists sought to use it as a justification for funding a U.S. mission to Comet Halley during its 1985/1986 apparition.
JPL's proposed 1979 rover bears a passing resemblance to the Mars Science Laboratory (MSL) rover Curiosity launched on 26 November 2011, almost exactly 41 years after Lunokhod 1. Both the JPL 1979 rover design and Curiosity have six wheels, rear-mounted nuclear power sources, stalk-mounted cameras, and front-mounted arms.
|The nuclear-powered Mars Science Laboratory Curiosity captured a selfie on 3 February 2013. Image credit: NASA.|
Perhaps the most profound difference between the 1979 and 2011 rovers has to do with expectations. JPL engineers in 1970 assumed that their rover might cover half a thousand kilometers in a single Earth year. Curiosity, by contrast, cautiously traversed about 7.9 kilometers during its first 687-day martian year, which ended on 24 June 2014.
Although it has suffered wheel damage, Curiosity continues to climb the foothills of Aeolus Mons, an immense geologic layer-cake that fills much of Gale crater. Curiosity is expected to continue exploring until it suffers a catastrophic failure or until its electricity-generating nuclear source runs down, whichever comes first.
An Exploratory Investigation of a 1979 Mars Roving Vehicle Mission, JPL Report 760-58, J. Moore, Study Leader, Jet Propulsion Laboratory, 1 December 1970.
Challenge to Apollo: The Soviet Union and the Space Race, 1945-1974, NASA-SP-2000-4408, Asif Siddiqi, NASA, 2000, pp. 532-533, 740-743.
Press Kit, Mars Science Laboratory Landing, NASA, July 2012.
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