Perseverance on Mars
Is it possible to move in a straight line without a compass?
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Title 4
Learning objectives :
This activity allows students to develop strategies for maintaining a straight trajectory without external cues such as GPS or the magnetic field. It simulates the autonomous navigation challenges encountered by robots on Mars.
Concepts covered
Autonomous navigation; Inertial systems; Sensor drift; Space robotics; Data integration
What students will do :
The student explores different methods for moving in a straight line using only the sensors available in a smartphone. By successively testing different FizziQ instruments (gyroscope accelerometer) while moving over 150 steps, the student evaluates the effectiveness of each method and thinks about emergency solutions that can be used by a robot like Perseverance on Mars.
What is required :
Smartphone with the FizziQ application; A clear outdoor space for walking in a straight line; FizziQ experience notebook
Scientific background :
Autonomous navigation without external cues is one of the major challenges of space robotics. On Mars, robots like Perseverance cannot rely on a global magnetic field (Mars does not have one) nor on a GPS system. This experiment simulates these constraints by exploring the sensors that can be used to maintain a straight heading. Three main approaches can be tested with FizziQ: 1) The accelerometer: in theory, maintaining zero acceleration perpendicular to the direction of travel should guarantee a straight line. In practice, the double integration required to go from acceleration to position amplifies errors, causing significant drift. 2) The gyroscope: by measuring the rotation around the vertical axis, we can detect any deviation from the straight line. More accurate than the accelerometer for short movements, it also suffers from long-term drift. 3) The light meter or camera: in the absence of a magnetic field, Mars rovers often use the position of the Sun or the stars as a directional reference, supplemented by visual cues. This “celestial” navigation is particularly reliable but depends on lighting conditions. These methods are complementary and generally combined in Martian navigation systems. Perseverance uses advanced visual navigation called “Visual Odometry” which compares successive images to determine its movement, supplemented by an inertial unit (accelerometer and gyroscope). The main difficulty remains cumulative drift: even a minimal error of 1° can cause a deviation of 2.6 meters after 150 steps (approximately 100 meters). This experiment illustrates why Martian missions progress relatively slowly: Perseverance travels only 100-200 meters per Martian day to maintain its navigational precision.