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SojournerThe most notable of the Microrovers was Sojourner – the descendant of Rocky 4, which captured the public’s imagination when it traveled to Mars aboard the Mars Pathfinder Mission in 1997. Sojourner’s function was to, explore the terrain of Mars within sight of the Pathfinder Lander, conducting atmospheric, geographic, and scientific experiments. Sojourner was about the size of a child's small wagon, had six wheels, and could move at speeds up to 0.6 meters (1.9 feet) per minute and travel up to three meters a day. (This isn't very fast or far, but enough to accomplish many tasks during a day.)


    Sojourner on the surface of Mars
    Sojourner on the Martian surface

All equipment on board Sojourner, computers, lasers, motors, and radio was powered by a lightweight solar array. The array was mounted on top of the rover so it would collect as much light a posible. Limited back up battery power was available and was primarily used for night time experiments and early morning operations on Mars.

Sojourner communicated with Earth via a two-way radio link. The radio link was used to send commands from Earth to the rover and receive images and data from the rover. Communications with Sojourner was not instantaneous because of the vast distance between Earth and Mars. Radio Signals took 18 minutes to reach the rover. A whole days worth of instructions were uploaded in a single transmission. Sojourner would then autonomously carry out these commands using its on-board software and sensors.


Lego Rover

Sojourner's wheels and suspension use a rocker-bogie system that is unique in that it does not use springs. Rather, its joints rotate and conform to the contour of the ground, providing the greatest degree of stability for traversing rocky, uneven surfaces. A six-wheel chassis was chosen over a four-wheel design because it provided greater stability and obstacle-crossing capability. A Six-wheeled vehicle can overcome obstacles three times larger than those crossable by four-wheeled vehicles. For example, one side of Sojourner could tip as much as 45 degrees as it climbed over a rock without tipping over.

Mechanical System
Mobility configuration and general size are drawn from the Rocky 4 prototype.

Mobility System
Six wheel rocker bogey with four corner steering. Total of ten motors (actuators).

Navigation System
Black and white CCD cameras, and five laser stripe projectors on front side of the Rover. Quartz rate gyro. Accelerometers (3). Wheel optical encoders. Bump detector switches.

Motor Control System
Bang-Bang on/off control of motor actuation is used based on motor position monitored by optical encoders. No variable rate motion is possible.

11.5 kilograms (24.3 lbs.) on Earth (about 9 lbs. on Mars).

60 x 40 x 35 centimeters.

Up to 0.6 meters (1.9 feet) per minute. Sojourners average daily distance was about 3 meteres, travling no more than 10 meters away from the Pathfinder Lander.

Sojourner Home Page
TeleComunications Systems
Control & Navigation Systems
Power & Control Systems


Pathfinder Lander

The Mars Pathfinder (formerly known as the Mars Environmental Survey, or MESUR) was the second of NASA's low-cost planetary Discovery missions. The mission consisted of a stationary lander and a surface rover. The mission had the primary objective of demonstrating the feasibility of low-cost landings on Mars, and exploration of the Martian surface. The tradition of using small robotic rovers for planetary exploration is contiuned with NASA/JPL's Mars Exploration Rover Project

Pathfinder Home Page
JPL Robotics Home Page

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