14 December 2015

The Russians are Roving! The Russians are Roving! A 1970 JPL Plan for a 1979 Mars Rover

1984: A Proton-K rocket very similar to those that launched Luna 17/Lunokhod 1 in 1970 and Luna 21/Lunokhod 2 in 1973 lifts off from Baikonur Cosmodrome bearing one of a pair of Vega probes destined for Venus and Halley's Comet. Image credit: Lavochkin Association/NASA
As night fell at Baikonur Cosmodrome in Soviet Kazakhstan on 10 November 1970, a Proton rocket thundered to life and began its climb toward space. Six days later, the rocket's payload, the automated Luna 17 moon lander, soft-landed on broad, flat Mare Imbrium. A team of six operators in the Soviet Crimea - five main operators plus a spare - remotely drove the Lunokhod 1 rover down ramps lowered from the lander onto the moon's dusty surface.

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
Lunokhod 1 originated in the abortive Soviet piloted moon program, though this would not be revealed until the late 1980s. Its initial role was to have been to certify as safe the landing site selected for the piloted lunar landing.

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.

U.S. space planners took note. In a report called An Exploratory Investigation of a 1979 Mars Roving Vehicle Mission, completed a timely three weeks after Luna 17 landed on Mare Imbrium and Lunokhod 1 began its traverse, a 12-man design team at the Jet Propulsion Laboratory (JPL) in Pasadena, California, described a NASA Mars rover mission in 1979.

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-C rocket on 20 August 1975. Image: NASA
The Mars rover would leave Earth between late October and mid-November 1979 on a Titan III-C rocket with a Centaur upper stage - the same rocket/upper stage combination that would launch the Vikings in 1975. It would lift off sealed within a Viking-type lander aeroshell and bioshield cap attached to a Viking-type orbiter. The orbiter's rocket motor would perform a course correction burn 10 days after launch.

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.

Cutaway of JPL's proposed 1979 Mars rover packed into its Viking-type aeroshell. The arrow points to the rover's twin RTGs, which are extended beyond the aeroshell on a boom to prevent them from overheating the rover's electronic systems during the flight to Mars. Image credit: JPL/NASA
Five days after Mars orbit arrival, the rover would cast off its bioshield cap to expose the aeroshell. Shortly before separation from the orbiter, the rover would retract its RTGs. The aeroshell would then separate and fire thrusters to slow down and fall toward Mars.

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 Mars's thin upper atmosphere. 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
Three terminal descent rocket motors on the rover would begin firing at L minus 33 seconds. Three seconds later, at an altitude of 4000 feet and a speed of 300 feet per second, the parachute and upper aeroshell would separate from the rover. The rover would then touch down gently on Mars directly on its wheels.

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's 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 fascimile 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.

Lunokhod 2 included new cameras and instruments and was designed to travel over the lunar surface more quickly than had Lunokhod 1. In this image, the dual-purpose dish-shaped solar array/thermal cover is shown folded open, as it would have been during lunar daytime. Image credit: Lavochkin Association/NASA
The Soviets followed up Lunokhod 1's success a few weeks after Apollo 17 (7-19 December 1972), the final piloted lunar mission. On 17 January 1973, Luna 21 landed inside rugged Le Monnier Crater bearing the Lunokhod 2 rover. The new rover was, the Soviets stated, superior to its predecessor. It would, for example, scuttle across the lunar surface much more rapidly than could Lunokhod 1.

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 minirover in 1997.

In March 2010, NASA released high-resolution Lunar Reconnaissance Orbiter Camera (LROC) 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, the Lunar Reconnaissance Orbiter has orbited lower over the Lunokhod landing sites, enabling higher-resolution imaging. LROC images clearly show the extended Luna 17 and Luna 21 ramps and the tracks Lunokhod 1 and Lunokhod 2 left on the lunar surface.

The last journey of Lunokhod 2: the black arrow points to the crater where the rover accidentally collected a load of lunar dirt. Soon afterwards, the rover parked for the lunar night. The white arrows running up the center of the image highlight tracks Lunokhod 2 left as the Sun rose and the dirt on its radiator caused it to overheat. The white arrow near the top of the image points to Lunokhod 2 in its final resting place. This image from NASA's Lunar Reconnaissance Orbiter shows an area of Le Monnier crater roughly 400 meters square. Image credit: NASA
Proposals for a Viking follow-on robot rover mission would be put forward throughout the 1970s and 1980s, but none would move beyond the stage of proposals and studies. In part, this was because the Soviet Union failed to follow through on its promise (or threat) to launch robot sample returners and rovers to the planets.

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
Curiosity, however, has a single body, solid wheels, and a more elaborate suspension system. Curiosity is also larger and heavier (about 2000 pounds) and depended on a more complex (and, to many observers, more worrisome) landing system known as the Sky Crane. The new system functioned as advertised, however, gently lowering Curiosity onto its wheels in Mars's equatorial Gale crater late in the evening U.S. Pacific Time on 5 August 2012.

Perhaps the most profound difference between the two 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.

Sources

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

More Information

Centaurs, Soviets, and Seltzer Seas: Mariner 2's Venusian Adventure (1962)

A 1974 Plan for a Slow Flyby of Comet Encke

Making Propellants from Martian Air (1978)

7 comments:

  1. I would love to see a lunar rover program again.

    In addition to the Lunokhod type (large rover with onboard heating system) has anyone ever looked at either

    a) rovers that would depart their lander at lunar dawn, roam for a lunar day, and then return to the lander at sunset where they would shelter for the night?

    b) rovers that would be cheap enough to be 'disposable' (survival of a single lunar night is possible, but no promises made)

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    1. The Lunar X Prize (http://lunar.xprize.org/about/overview) could well result in a rover like that. Also, as most/all of the teams are commercial, some of them may allow people to drive a rover in exchange for a donation.

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  2. Tom:

    It would be fun - in fact, I think it is a form of space tourism that could work. (I'm not convinced that space tourism involving paying passengers will pay for itself.) Sign up to pilot a rover on the moon. I imagine there'd be lots of software built in to prevent folks from damaging the rovers.

    As for your proposition "A," I haven't heard of such a thing. Some Surveyor rovers were to have operated at the end of a power cord attached to the lander. I don't know whether they were meant to return to the lander at night or just park where they were.

    As for "B," the Surveyor rovers were that way - unlikely to survive a lunar night but possible, and out of necessity built relatively cheaply. For the most part, however, as best I can tell, rovers have been intended to last for as long as possible. So, for example, Sojourner was "waranteed" for 30 days but folks at JPL weren't going to shut it off if it exceeded that goal.

    dsfp

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    Replies
    1. Proposition B (the Mini-rover) would be cheap to build, the only question is can you do enough exploring in two weeks to justify it? There is the possibility that if several rovers are near to one another and some suffer damage from freezing, rovers could work in pairs to assist each other and get one more lunar day out of them.

      Example: 4 mini-rovers are dropped, and spend two weeks on the Moon working fine. They shut down for the lunar night. At lunar dawn, an attempt is made to wake them

      Rover A doesn't respond- the cold wrecked the power/computer/communications system

      Rover B wakes up, but the wheels are shot. So B spend the next two weeks doing a detailed analysis of the regolith and every rock within the reach of it's arm.

      Rover C & D also wake, and their wheels work, but D's cameras are gone, while C has damage to the sample arm and some sensors. C drives over to D, and spends the next two weeks as D's eyes while D does the real work.

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  3. Happy Christmas David, & a productive, satisfying New Year

    ReplyDelete

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