Rover and Track

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March 25, 2004

The engineers at NASA's Jet Propulsion Laboratory, home of some of the best six-wheeled exo-atmospheric off-roaders anywhere, have really done it this time. Their 2004 series MERs (Mars Exploration Rovers) are jam-packed with so many cutting-edge technologies (several literally with cutting edges) it takes a stack of owner's manuals the height of a Sherman tank to do them justice. Suffice it to say, the MER design team seems to have covered all their off-road/off-planet bases: active cruise control and roll stabilization, satellite radio, multi-zone climate control system, stability management, not two but four airbags, and an advanced onboard navigation system that not only provides excellent route management but also makes parallel parking between hematite outcroppings a veritable martian breeze.

JPL first ventured into the off-planet SUV business seven years ago with the '97 Sojourner (Rover & Track, July '97). Weighing in at all of 23 pounds, the low-slung, sporty Sojourner made its name negotiating the boulder-strewn test track at Ares Vallis for two-and-a-half months at speeds approaching .02 miles-per-hour.

But as they say in the exo-atmospheric SUV trade - "that was then, this is wow!" and wow is what JPL engineers wanted out of their new red rock buggy. While the 2004 MER tips the scales at a whopping 384 pounds -- 16 times that of Sojourner - unfettered it is capable of speeds in excess of 2-inches-per-second (.1 mph) flat out, making it four-and-a-half times quicker than its microwave-oven-sized predecessor.

Normally, such a step up in performance could not be possible without sacrifices in other areas. But JPL engineers are quick to point out that the MER not only one-ups the Sojourner on red-line performance but also handling and flat-cornering, all the while providing a decent grip and a ride that's firm yet not overly harsh.

How is all this performance and handling available on one rover? The story begins under the hood which actually requires you to look under the wheels… or rather inside them.

Nested inside each of the MER's six 10.3-inch aerospace aluminum wheels is a 20-watt DC motor which hammers out 6000 rpm and, after a 1500:1 gear reduction, up to 92 foot/pounds of torque. JPL engineers claim one motor alone can lift the vehicle up and over a vertical wall twice the diameter of its wheels. Nested alongside the drive motors in the two front and two rear wheels are also individual steering actuators which provides the 2004 MER with crisp, tight turns and the capability to turn in place, a full 360 degrees.

Adding to the MER's stellar handling characteristics is its "rocker-bogie" suspension, which comes standard for 2004. Invented by the engineers at JPL, and first used with much success on its forerunner the Sojourner rover, the rocker-bogie system utilizes a series of titanium linkages to balance the load while allowing the MER's wheels to climb obstacles twice their size, conform to changing terrain, thereby imparting a very solid and squeak-free ride.

As for the 2004 MER's exterior appointments, the rover is neither objectionable nor inspiring. Instead, it is a study in utility -- straight lines, sharp angles and protruding antennas abound. This critic wants to know where is the bold yet sculptured surfaces Americans have come to expect in their off-road vehicles? Where is the aerodynamic styling?

JPL engineers dismiss these concerns explaining aerodynamics are little required in an atmosphere 1/100th that of Earth and that the MER's size and outward appearance was predicated on the dimensions of the pyramid-shaped shipping container that carried it to its current test track. They stress that performance is what its buyers value most. While overall styling may leave something to be desired, special exterior touches are noteworthy. The generous use of gold electroplated Kapton tape on the body panels is appreciated and the spiral flexure custom wheels, or "dubs", with their NASA "meatball" logos anodized into the center are easy on the eyes.

One thing is for certain, the 2004 MER commands attention. For those considering a 2004 MER I have some bad news. The entire model year (two flight, two engineering models) of the high profile vehicles is sold out. But don't fear, the design wizards at JPL are already setting their sites on their next product line, the 2010 MSL or Mars Science Laboratory - an all-terrain vehicle that designers claim will be five times the size of the 2004 MER while providing all the performance you expect from a JPL product (see the upcoming March 2010 issue of Rover & Track for in-depth coverage). For a sneak peak, see image to the right..

Media Contact: DC Agle(818) 393-9011

Images

This animation is created from still images taken by the Mars Exploration Rover Spirit

This animation is created from still images taken by the Mars Exploration Rover Spirit during its approximately 21.2-meter (69.6-foot) drive across the pebbly ground at Gusev Crater, Mars.

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Artist's concept of NASA's Mars Science Laboratory

Artist's concept of NASA's Mars Science Laboratory

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