Curiosity latest, largest in series of space buggies

EPA/Micheal Nelson

A NASA engineer examines a test model of the Curiosity Mars rover.

By Paul A. Eisenstein, The Detroit Bureau

Olympian Usain Bolt might seem to be powered by lightning, but meanwhile on Mars, another epic performer this week, the Curiosity rover, draws its power from 10.6 lbs. of plutonium dioxide.

In a week dominated by the Olympics, it has taken a successful mission to the Red Plant, capped by what NASA officials earlier described as ?seven minutes of sheer terror,? to grab some headlines. The successful, if tricky, landing means a six-legged, unmanned rover packed with science gear might soon be able to offer hints as to whether life once grabbed a tenuous foothold on Mars.

Dubbed Curiosity, it is the most sophisticated in a line of rovers that date back to the days of the Apollo era when astronauts during a series of moon landings were able to extend their range with the help of a lunar equivalent of the dune buggy.

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How do the various rovers compare?

The former Soviet Union launched several primitive devices, starting with Lunokhod 1, in 1970. The first rover worked for 11 months; a second, Lunokhod 2, operated for just four months. The vehicles sent back pictures and analyzed the lunar soil, but they traveled only short distances.

The only manned models ever taken into space were known as the Lunar Roving Vehicles, or LRVs, battery-powered four-wheelers that served ?Apollo missions 15, 16 and 17. Developed in part by General Motors, they were as stripped-down as possible to permit them to be loaded onto a Saturn V rocket for launch. They were folded up inside a cargo bay inside the Apollo mission?s Lunar Excursion Modules, or LEMs.

Power was provided by what was, for the time, highly sophisticated 36-volt silver-zinc potassium hydroxide batteries. They weren?t rechargeable, which didn?t matter on the one-way missions they were sent on in the Apollo program. The key was the battery pack?s durability in the moon?s devastating environment. Maximum range was 57 miles, though the longest distance driven was 22.3 miles on Apollo 17 ? with the astronauts never getting farther than 4.7 miles from their LEM base.

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Incidentally, despite a humorous Bridgestone ad that ran last year suggesting moon buggy tires might be worth stealing, regular, inflatable rubber tires wouldn?t have worked in the zero-atmosphere environment. Instead, the LRV?s ?resilient wheels? had titanium chevrons, or plates, covering a weave of metal around an aluminum disc.

The Apollo program ended in 1972, and it took another quarter century before a rover was again to reach alien soil. In 1997, a 23-pound craft named Sojourner rolled out of a fixed base ship called the Mars Pathfinder. It boasted limited range and functionality, but showed that a vehicle operating somewhat autonomously could extend man?s reach to a planet other than Earth.

Sojourner was the proof in concept for another rover mission launched into space ? or two rovers, to be more precise ? in 2003.? Dubbed Spirit and Opportunity, these little buggies, not much bigger than the remote-controlled cars many hobbyists play with, were heading for a much more distant destination than the LRVs.

The two craft landed in January 2004 and were expected to function for just 90 days each. In fact, Spirit continued to roam the Red Planet until getting stuck in a sand pit in 2009. Opportunity continues to operate, roving the surface around Mars? equator on a series of new missions not even conceived of when it was launched.

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The two craft each boast six legs mounted to what is, for practical purposes, a little boogie board. The design allows the two rovers to skitter over surprisingly large obstacles ? though deep sand appears to have been an insurmountable hurdle. Each wheel has its own motor, and power is generated from solar panels and then stored in a set of batteries, which were originally expected to be weak links that would give out after 90 days.

While the Apollo?s LRV could move with reasonable haste, Spirit and Opportunity were designed to march forward at barely 2 inches a second. And their early autonomous object-detection software required them to stop ever 10 to 20 seconds to observe the terrain and decide how to then proceed.

While communications between the moon and Earth take only a couple seconds, communicating with Mars takes precious minutes, depending on Mars' position relative to the Earth as it revolves around the sun. So, like the little skateboardlike lunar rovers, the big Curiosity lander also had to be designed to make a series of autonomous decisions ? starting with its perilous landing.

That Rube Goldberglike process began with the spacecraft that held the rover turning its heat shield into the thin Martian atmosphere at 13,000 mph. As the spacecraft's speed decreased, the heat shield was discarded and a massive parachute was deployed. As the craft descended, it needed to slow even more, something the chute couldn?t achieve in the thin Martian atmosphere. So a rocket-powered ?backpack? fired up. The spacecraft then descended until it was just above the rust-red surface, at which point Curiosity was lowered the rest of the way on a set of cables. The cables were released, the backpack flew away and then crashed to the ground.

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NASA had good reason to be worried, considering that a string of other rover-equipped Mars landers, including the Soviet Union?s Mars 2 and 3, and America?s Beagle 2, had crashed as they attempted to land.

After traveling 352 million miles over the course of 263 days ? at speeds of up to 54,000 mph ? Curiosity will now move at a snail?s pace, barely 1.5 inches a second, or less than a tenth a mile per hour. It has an anticipated range from its landing point of barely 15 miles.

Though sized somewhere between a Smart ForTwo car and a Fiat 500, at 129 inches length, the six-wheel Mars buggy is as wide as the original Hummer H1, at 109 inches. It measures 87 inches high, or more than a Ford F-150 Raptor pickup. And its total payload is just 88 pounds. Of course, because Mars? gravity is only 38 percent of Earth?s, that?s more than you might think.

As with Spirit and Opportunity, the unmanned Curiosity has to operate autonomously. One-way communication times can reach a maximum 13.5 minutes, so it would be impossible to function effectively otherwise. But controllers on Earth can upload extensive software commands to get the craft to do their bidding.

Unlike the earlier Mars landers, Curiosity won?t have to worry about keeping its solar panels properly aimed. The craft uses 10.6 pounds of nuclear fuel to operate its six individually powered wheels, radios, cameras, science lab and a 43.3-inch robotic arm.

While America?s space program may be struggling for funds during the current fiscal belt-tightening, few expect Curiosity to be the last rover to leave Earth?s confines:

• The increasingly ambitious Chinese are looking to send the unmanned Chang?e 3 to the moon in 2013;
• India also wants to dig some lunar soil with a mobile craft it calls Chandrayaan-II that is set for a 2014 launch;
• NASA, meanwhile, is exploring several rover projects including the six-legged ATHLETE, or All-Terrain Hex-Legged Extra-Terrestrial Explorer, Scarab and SEV, or the Space Exploration Vehicle.

Beyond that? Perhaps we?ll see something from private industry. Several firms this year have announced interest in mining asteroids. They?ll need some help, and a new rover could be the answer.??

Source: http://bottomline.nbcnews.com/_news/2012/08/06/13145826-curiosity-latest-largest-in-a-series-of-space-buggies?lite

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