Rovers – learning from Lunokhod
The USSR may have lost the race to the Moon, but future planetary exploration is likely to be undertaken by rovers inspired by Russian Space-Race era technology
Less than a decade after Yuri Gagarin began the human spaceflight era, the Soviet Union declared a limit on how far into space humans should go. Reacting to the US Apollo triumph, Soviet leaders indicated that sending people to the Moon was far too risky and expensive for them to compete against the Americans.
Robots were Russia's Apollo astronauts. On 20 September 1970, the Luna 16 spacecraft touched down on the Moon, retrieved 101g of soil and returned it to Earth (the first of three successful sample-return missions). On 17 November 1970 a bathtub-shaped Lunokhod ('Moonwalker') robot rolled off the Luna 17 lander to explore the Sea of Rains for almost 11 months. Later – the month after the last US moonwalkers returned to Earth aboard Apollo 17 – a second Lunokhod commenced four months of roaming.
Apollo has generally dominated the competing Moon landings. Human moonwalkers returned far more samples, took better images and covered comparable distances – thanks to the Lunar Rovers – but the Lunokhods deserve credit for sheer endurance. No Apollo lander could have survived the Moon's vast day-to-night temperature fluctuations, still less spacesuited humans.
In the end, these mechanical avatars foretold the shape of planetary exploration to come. There is a surviving rover on Mars today, with more being readied for both Mars and the Moon, but little likelihood of human bootprints marking any planetary soil for at least 15 years. Yet, the real Lunokhod history scarcely fits into the simplistic 'man versus machine' template.
Once the Cold War ended, it became obvious the Soviets had indeed competed in the manned Moon race. Their efforts were doomed by infighting and under-funding, but a telltale LK lunar lander had been designed to carry a single cosmonaut.
What is less well known is that Lunokhods were originally developed as part of this manned lunar programme. Just 40 per cent the mass of the Apollo Lunar Module, the LK lander possessed limited redundancy. Responding to this potential unreliability, the idea was to launch a spare unmanned lander first, along with a robot rover (originally designated 'Ye-8').
This rover would inspect the lander for damage, as well as serving as a radio beacon for the follow-up manned lander to home in on. However, due to irregular lunar gravity, a precision landing might prove difficult. So the rover had another purpose, transporting the cosmonaut to reach his back-up lander, if needed (carrying 24 hours' worth of life support).
Eventually, the rover was given additional tasks to prepare for a manned landing. Then, as the prospect of achieving this receded, the Ye-8 programme took on a life of its own. Its lander was also modified for sample return missions. The first Lunokhod mission launched on January 1969 – the rovers' profile would be higher, if one had beaten Neil Armstrong – but blew up a few seconds in. Lunokhod 1 finally landed 18 months later.
Form followed function for this 2.3m-long 756 kg rover. Its bathtub body was a pressurised vessel – Russian engineers liked to keep delicate electronics in air instead of vacuum. Resisting the bitter -150°C night and then the 120°C daytime heat was the key issue. So Lunokhod 1 had a clam-like lid with solar panels to catch the Sun, exposing a radiator to expel waste heat. When the fortnight-long night began, the lid closed, sealing in heat produced by a polonium-210 isotope.
Lunokhod 1 moved on eight woven-wire wheels, each independently powered. A ninth wheel served as an odometer. Four corner cameras produced high-resolution panoramic images, with a pair of front-mounted TV cameras for the rover's operators – 382,500km away at Simferopol in the Crimea- steering by remote control.
Twin five-man teams did the work – a driver, commander, navigator, engineer and radio operator – having practiced on a simulated lunar surface. They alternated every two hours on sometimes nail-biting shifts.
The sweating driver was guided not by video but a succession of still images, updated every 20 seconds. He had to contend > < with the 2.5-second signal delay, as well as a metre-wide blind spot ahead. Lunokhod 1 had two speeds: 0.8 km/h or 2km/h, plus reverse gear. Drivers recalled details from previous images to manoeuvre safely and were dependent on shadows to make out surface relief. They did not drive during the three days of lunar noon, or when the Sun was low in the sky. Each lunar night they left the rover to hibernate.
Lunokhod 1's instruments included a penetrometer to measure soil density, an X-ray spectrometer, X-ray telescope and a cosmic ray detector – in November 1970 measuring a solar flare strong enough to injure humans. The relationship between Lunokhod operators and scientists was tense – researchers had to stay in an adjacent room, to begin with. They invariably wanted closer examinations of intriguing but potentially hazardous rocks. Project chief Georgy Babakin answered: 'It is Lunokhod, not Lunostop'.
During its 10.5km travels over 310 days, Lunokhod 1 returned more than 500 panoramic images and 20,000 TV images, performed 500 surface probes and 25 X-ray examinations. Driving against jammed brakes, its power gradually declining, Lunokhod 1 failed abruptly as its isotope gave out on 4 October 1970.
Wheel-less Lunokhods served as the basis of lunar orbiters – Luna 19 launched in September 1970 and Luna 22 launched in May 1974. In the meantime, Lunokhod 2 took shape, landing inside the Le Monnier crater on 15 January 1973. This 840 kg rover moved twice as rapidly, with an extra TV camera solving the blind spot problem (square instead of round TV cameras gave Lunokhod 2 a distinctive look), with an updated image every three seconds. It carried a magnetometer to detect lunar magnetism and a photometer to measure night sky brightness.
Lunokhod 2 covered more ground than its predecessor – 37 km – and performed daring manoeuvres, scaling slopes and edging along between craters. Four months in though, the mission came to a premature conclusion.
The Sun behind them, the drivers missed a crater that the rover plunged into. Old hands at this, they drove straight out – but lunar crater edges accumulate loose soil. This tipped onto the solar lid. The resulting power dip was survivable – but not this thermally-insulating material falling onto the radiator. While the first Lunokhod died of cold, this one perished from overheating during the June 1973 lunar dawn.
End of the line
The last Soviet sample-return mission flew in 1976, but the Lunokhod programme was over. A third Lunokhod with a moveable arm was built, but the Soviet leadership had lost interest in lunar exploration now because the Americans had. The rover never made it beyond Moscow's Lavochkin company museum.
Lunokhod 2 continued scientific service – its French-built retro reflector is used to this day to measure the Earth-Moon distance to a matter of centimetres. In 1993, videogame mogul (and eventual space tourist) Richard Garriott bought ownership of both Lunokhods. Lunokhod 1 was pinpointed last year by Nasa's high-resolution Lunar Reconnaissance Orbiter and is now also employed for laser reflection.
Two decades on, Lunokhod designer Alexander Zemurdzhian fielded a robot for the Chernobyl rooftop clean-up. High radiation levels limited the robot's effectiveness while Zemurdzhian suffered radiation burns. Other Lunokhod veterans – including wheel-designer Mikhail Malenkov and chief operator Vyacheslav Dovgan have since joined a Russian team, contesting the $30m Google Lunar X-Prize, to send a privately-funded rover to the Moon.
Nasa tends to downplay the Lunokhods' influence – 'there was nothing we could use there' sniffed JPL's Jeff Pickler, designer of 1997's microwave-sized Mars Pathfinder rover. But however much technology has progressed, Lunokhods established the very concept of mobile robot exploration.
And with the current generation of astronauts and cosmonauts languishing not much higher than Gagarin's orbit, their descendants will be the ones doing all the exploring.
A driver's guide to Mars
Beneficiaries of three decades worth of Moore's Law, Nasa's currently-operating Mars Exploration Rovers are golf-cart-sized six-wheelers with a 185kg mass. They have to be smart, explains principal investigator Steve Squyres: 'You can't real-time joystick with a typical one-way delay time of 10 minutes. Instead we have a set of imaging systems that the vehicle uses to build up a 3D topography, autonomously negotiating its way past obstacles.'
Mars is in some ways a milder environment than the Moon – its nights are much shorter and not as cold, while average daytime temperatures tend to be below zero. The terrain is more varied, however, and weather, notably wind and dust storms, is a wild card. Both rovers have had problems with dust build-ups that, thankfully, later blew off again. Though because Mars dust is weathered, it is not as abrasive or statically chargeable as lunar soil.
The Spirit rover is currently silent and irretrievably stuck in soil, while Opportunity is still mobile, having chalked up 26.6km in seven years. Lunokhod 2's record still has 10km on its modern rival.
Rovers: The next generation
Rivalry between India and China has sparked a new Moon rover race. Meanwhile, Nasa and ESA rovers will share a ride to the Red Planet in 2018. But first, Nasa has an even bigger rover than the Lunokhods, launching before the year is out.
Mars Science Laboratory This car-sized Mars vehicle is the largest and most expensive rover yet. Weighing 900kg, it costs $2.5bn and counting. It launches on an Atlas V rocket this November to arrive on Mars in August 2012. Named Curiosity, the MSL's payload includes a HD 3D video camera, designed by James Cameron, and a laser-based spectrometer examining targets of interest from 7m. MSL foregoes solar panels entirely for a plutonium power source that should keep it roaming Mars for at least 14 years, with 60m of heat pipes to radiate away excess heat.
Chandrayaan-2 Designed by India with Russian assistance, this solar-powered rover will be landed near the Moon's south pole by Russia's Luna-Resurs lander in 2013. Equipped with laser- and X-ray spectrometers, the compact 15kg rover will search out water ice, but without radioactive heating is unlikely to endure the lunar night.
Chang'e-3 rover China's 2013-launched rover will be eight times larger than its Indian rival and will be powered by a radioisotope. Standing 1.5m high, the rover will have an arm to dig up soil samples for analysis. Its landing site is uninspiring: the Sinus Iridium ('Bay of Rainbows') is a flat lava plain – making for an easier touchdown, but comparatively uninteresting scientifically.
ExoMars ESA's first planetary rover will make its way to the Red Planet via a Nasa skycrane. Solar panels will keep its batteries topped up, relying on a radioisotope for night-time heating. Its mass will be 295kg. Currently being put through its paces in a simulated Martian environment, ExoMars will create 3D maps of its surroundings for largely autonomous operations. ExoMars will carry a ground-penetrating radar system to guide a 2m-deep drill. It will also illuminate surfaces with UV to detect fluorescing biomarkers.
MAX-C Mars Astrobiology Explorer-Cacher is a small Nasa rover. Just 65kg in mass, the solar-powered and radio-isotope-heated rover will search out scientifically interesting rocks, using a drill, if necessary, then securely store them. These cached samples could then be the target of a future Mars Sample Return mission.
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