Reader Response Draft 3 of Mars Rover Mobility

From the article "Mars Exploration Rover Mobility and Robotic Arm Operational Performance"(Tunstel et al., 2005), for NASA Rovers Spirit and Opportunity to traverse the uneven surface of Mars, they are equipped with multiple features to aid with their mobility. Such features include high torque, all-wheel drive, with a double-ackermann steering system for the six-wheeled robotic rovers. A rocker-bogie suspension system allows the rovers to traverse the uneven ground with a level difference of 25 centimetres without tipping over and rolling. Each rover also has multiple camera pairs. Front and rear camera pairs are mounted on the body for sensing and evading danger. While another camera pair is mounted at a fixed height of 1.3 metres above the ground and is used for global path planning and visual odometry. Visual odometry uses the images taken from the elevated camera pair to map out the terrain of Mars for autonomous control (Tunstel et al., 2005). The mobility of NASA Rovers Spirit and Opportunity was a key factor in the success of exploring the surface of Mars. 

            One of the key elements is the rocker-bogie suspension system, which allows all six wheels of the rovers to be in contact with the ground at all times. According to Lindemann et al., the center of mass of the rovers is located near the pivot of the suspension, which allows the rovers to tilt up to 45 degrees. This is a major factor in aiding the mobility of the rovers as compared to using a standard spring suspension system when traversing the uneven and rocky terrain of Mars.

            The next key element is the double-ackermann steering system. A typical ackermann steering system is used to manoeuvre a vehicle along a curve by adjusting the angle of the front wheels for the axes of all four wheels to intersect at a common center point, which is the center point of the curved trajectory. This allows the vehicle to move along the curve while having minimal wheel slippage, according to Vogel. The double-ackermann steering system that is used on Spirit and Opportunity, however, adjusts the angle of the front and rear wheels of the six-wheeled rovers. This allows for greater control of turning with the six wheels rather than controlling only the two front wheels if a standard ackermann steering system is used.

            The mounted camera pairs located at the front and back of the rovers are also essential in aiding the mobility of the rovers for hazard detection. According to Tunstel et al., the front and back-mounted camera pairs are used to detect obstacles along the paths of the rovers and relay the information of the obstacle back to the controller for the rovers to avoid a collision. This is another important factor as even though the rovers can stay stable while traversing, if they do not have the means to avoid obstacles, it would be all for naught in a collision. Therefore, this makes the front and back-mounted camera pairs essential in aiding the mobility of the rovers.

            However, even with all the features of the rovers, According to Kalita et al., Spirit and Opportunity were stuck for an extended time due to being caught in loose soil, as the wheels could not get any traction. Opportunity was able to get free and continue its mission, but Spirit was rendered immobile after having travelled 7730.50 metres, as reported by NASA, with an article aptly named “Spirit”.

            In conclusion, the mobility system of NASA rovers Spirit and Opportunity allowed for the success in the mission of exploring the surface of Mars due to the features that were added to the rovers. According to the article “NASA’S Opportunity Rover Mission on Mars Comes to End.”, both Spirit and Opportunity were expected to travel only 1000 metres and last a maximum of 90 Martian days. However, Spirit carried out its mission for 2208 Martian days and travelled 7730.50 metres, while Opportunity carried out its mission for 5352 Martian days and travelled 45.16 kilometres.

 

References

Kalita, H., Thangavelautham, J. Exploration of Extreme Environments with Current and Emerging Robot Systems. Curr Robot Rep 1, 97–104 (2020). 

https://doi.org/10.1007/s43154-020-00016-3

Lindemann, R., Bickler, D., Harrington, B., Ortiz, G. & Voorhees, C. (2006). Mars Exploration Rover Mobility Development. IEEE Robotics & Automation Magazine.

https://ieeexplore.ieee.org.singaporetech.remotexs.co/stamp/stamp.jsp?tp=&arnumber=1638012&tag=1

National Aeronautical and Space Administration. (February 13, 2019). NASA’S Opportunity Rover Mission on Mars Comes to End.

https://mars.nasa.gov/news/8413/nasas-opportunity-rover-mission-on-mars-comes-to-end/

National Aeronautical and Space Administration. (2011). Spirit

https://solarsystem.nasa.gov/missions/spirit/in-depth/

Tunstel, E., Maimone, M., Trebi-Ollennu, A., Yen, J., Petras, R., & Wilson, R. (2005). Mars exploration rover mobility and robotic arm operational performance. NASA. 

https://www-robotics.jpl.nasa.gov/publications/Mark_Maimone/MobIDDPerf90sols.pdf

Vogel, J. Tech Explained: Ackermann Steering Geometry (n.d.)

https://www.racecar-engineering.com/articles/tech-explained-ackermann-steering-geometry/

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