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| |  | | | | Rover and Track
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03.25.04
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Image Right: Vroom! MERs make the cover of "Rover and Track." Click for larger image. NASA/JPL artist's concept.
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.
Image left: Artist's rendering of Spirit on a test drive at Gusev Crater.
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 peek, click here.
DC Agle
NASA's Jet Propulsion Laboratory
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