|Spacecraft: Surface Operations: Rover
The rover´s "arm"
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.
At the end of the arm is a turret, shaped like a cross. This turret, a hand-like structure, holds various tools that can spin through a 350-degree turning range.
The four tools, or science instruments, on the robotic arm are:
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.
Protecting the arm
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.