Rover Robotic Arm

Rovers robotic arm
Rovers Robotic Arm
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The rover arm (also called the instrument deployment device, or IDD) holds and maneuvers the instruments that help scientists get up-close and personal with Martian rocks and soil.

Much like a human arm, the robotic arm has flexibility through three joints: the rover's shoulder, elbow, and wrist. The arm enables a tool belt of scientists' instruments to extend, bend, and angle precisely against a rock to work as a human geologist would: grinding away layers, taking microscopic images, and analyzing the elemental composition of the rocks and soil.

The rover arm has an overall reach of 90 centimeters (3 feet).

It has three joints (like the human arm, a shoulder, elbow, and wrist) with five geared motors to enable the following movement capabilities:

Drawing of the mars rover arm Credit: NASA/JPL-Caltech.
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Two motors are in the shoulder for side-to-side (horizontal) and up and down (vertical) movements. The shoulder can move in the horizontal plane 160°. If the arm moved farther from left to right, it would hit the front rocker-bogie "leg" portion of the wheel suspension. The shoulder can also move the arm through 70° in the vertical plane.


The elbow joint, midway down the arm, is powered by another motor and can move through 290°, folding the arm up or out.


Two motors reside in the wrist to twist the "handful" of instruments vertically and horizontally to place the chosen instrument perpendicular to the target surface. The wrist can rotate vertically through 340°, more motion than the human wrist. Functioning similar to a Lazy Susan, the turret handles the horizontal wrist rotation, and can spin through 350°.

The arm works in conjunction with the Hazcams, which take pictures of the intended rock targets. The computer software uses these pictures to position crosshairs on the surface of the target. The arm can then adjust its approach angle to safely line up and deploy one of its four science instruments.

At the end of each instrument are contact sensors, sophisticated "curb-feelers" that tell the arm motors to shut off when the instrument has made contact with the surface of the target.


Four tools of the robotic arm Credit: NASA/JPL-Caltech.
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The Microscopic Imager provides close-up images of rocks and soil

The Mössbauer Spectrometer analyzes the iron in rocks and soil

The Alpha Particle X-Ray Spectrometer analyzes the elemental composition of rocks and soil

The Rock Abrasion Tool (RAT) grinds away the outer surface of rock to expose fresh material

The forearm also holds a small brush so that the Rock Abrasion Tool can spin against it to "brush its teeth" and rid the grinding tool of any leftover pieces of rock before its next bite.

Thirty percent of the mass of the titanium robotic arm comes from the four instruments it holds at the end of the arm. This weight makes maneuvering the lightweight arm a bit of a challenge -- like controlling a bowling ball at the end of a fishing rod. The arm must be as lightweight as possible for the overall health of the mission, and holes are even cut out in places where there is no need for solid titanium.

Once the arm and instruments have succeeded in one location but before the rover begins another traverse, the arm stows itself underneath the "front porch" of the rover body. The elbow hooks itself back onto a pin, and the turret has a T-bar that slides back into a slotted ramp. The fit is almost as tight as a necklace clasp, and it can withstand shocks of 6 G's while roving along the rocky terrain. "Six G's" is roughly equivalent to dropping a box onto a hard floor from a height of 20 centimeters (almost 8 inches). During launch and landing, the arm is restrained by a retractable pin restraint, and can withstand even higher loads of 42 G's.