In the article “Moving on Mars” (2019), the European Space Agency (ESA) documented the locomotion system of Rosalind Franklin that was created for the ExoMars mission in 2023. The system combines several different components to traverse the various terrain of Mars.
From past experiences, the wheels of other rovers tend to get stuck while carrying out their mission on Mars, thus ESA implemented Wheel-walking on the Rosalind Franklin. Wheel-walking mimics leg motion and solves the recurring issue of stuck wheels. The system can drive individual wheels and independently rotate the axes to change the rover’s height and angle according to the surrounding terrain.
On top of the wheel-walking method, the Triple-bogie locomotion system is utilised to conquer large obstacles, while it’s adaptable metal wheels allow for more fluid control and motion when the rover meets obstacles. The motion control of the rover is further aided by inclinometers and gyroscopes.
The Triple-bogie locomotion system is key to the success of the Rosalind Franklin rover’s exploration of the Martian terrain.
During the conceptualisation of the ExoMars locomotion configuration and design, the Triple-bogie system and a list of six other favourable locomotion wheel design concepts were analysed, they were all six-wheeled designs that aimed to stabilise the rover via the positioning of the suspension bogies.
These concepts include the RCL Concept-C, RCL Concept-D, RCL Concept-E, CRAB, V-Bogie, Rocker-Bogie.
During testing, it was discovered that the central wheels of the RCL-Concept C lifted and locked out the linkages while climbing obstacles. The RCL-Concept-E, RCL-D and CRAB that were initially contrived to counter the issues faced by RCL-C, faced poor static stability problems below 40-degree angles. The complexity of the number of pivot points also resulted in a mass unsuitable for the ExoMars mission. The V-Bogie and Rocker-Bogie concept improved the static stability issues faced by the RCL-E design. However, the V-bogie had lower efficiency at climbing steps when compared to the Triple-bogie due to a rotating motion that caused the wheels to reduce traction, while the Rocker-Bogie had a larger mass than the Triple-Bogie.
As the Triple-bogie locomotion system was the simplest, lightest, and had a Stable footprint (wheelbase x wheel track), it offered a more efficient climbing performance when compared with other locomotion concepts (Patel et al., 2010).
The triple-bogie locomotion system was then developed and put through a test, with the intention of comparison between the wheel-walking locomotion mode and normal-wheel rolling.
The test contained different scenarios in various ESA test sites, ranging from entrapment, slope performance and egress stability tests. The wheel-walking mode enabled by the triple-bogie was concluded to surpass normal-wheel rolling on the variable Mars terrain, based on the evaluation of qualitative and quantitative statistics from the tests (European Space Agency, 2015). Wheel-walking outperformed normal rolling due to the increase in dynamic stability when the front wheels of the rover are tilted, which allows the rover to go down the maximum possible slope of 34-degree with consistent stability. In normal rolling, the rover loses its stability and almost overturned when the ramp was set at 29-degree.
These tests have shown that the Rosalind Franklin Mars rover will have an advantage from the increased locomotion benefits of wheel-walking and navigate smoothly on the unsteady soil of Mars (Azkarate et al., 2015).
Three aeronautical and space technology companies, MacDonald Dettwiler (MDA), Airbus and Thales Alenia Space, developed the triple-bogie system for the ESA and put the system through test environments that simulated the Martian environment as realistically as possible, taking into account the extreme temperatures, dust storms, and the difference in gravity pressure. Although there were challenges associated with replicating the martian environment, the triple-bogie system passed the acceptance screening and was deemed capable of functioning on Mars (Kanji & Buratynsky, 2019).
Despite the various benefits of the triple-bogie system, the lander platform restrictions have forced the usage of small wheels that have weak traction. However, to counter that restriction, adaptable metal wheels have been implemented in the early phases of the ExoMars project. (Poulakis et al., 2015).
In conclusion, the triple-bogie system is an essential locomotion system for the Rosalind Franklin Mars rover to succeed due to its features and functions. Possessing the most efficient, simplest and lightest locomotion system, the ability to wheel-walk, and the capability to function well in the Martian environment, will allow the Rosalind Franklin Rover to travel the perilous surface of Mars and achieve mission success.
References
Azkarate, M., Zwick, M., Hidalgo-Carrio, J., Nelen, R., Wiese, T., Poulakis, P., Joudrier, L., & Visentin, G. (2015). FIRST EXPERIMENTAL INVESTIGATIONS ON WHEEL-WALKING FOR IMPROVING TRIPLE-BOGIE ROVER LOCOMOTION PERFORMANCES. https://www.researchgate.net/profile/Pantelis-Poulakis/publication/290445721_First_Experimental_Investigations_on_Wheel-Walking_for_Improving_Triple-Bogie_Rover_Locomotion_Performances/links/56990b4b08aeeea985945307/First-Experimental-Investigations-on-Whe
European Space Agency. (2015). First Experimental investigations on Wheel-Walking for improving Triple-Bogie rover locomotion performances. https://robotics.estec.esa.int/ASTRA/Astra2015/Presentations/Session%202A/95665_Azkarate.pdf
European Space Agency. (2019). Moving on Mars. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/ExoMars/Moving_on_Mars
Kanji, S., & Buratynsky, M. (2019). Challenges associated with testing mechanisms for a Martian environment. https://www.esmats.eu/esmatspapers/pastpapers/pdfs/2019/kanji.pdf
Patel, N., Clemmet, J., & Slade, R. (2010, March 19). The ExoMars rover locomotion subsystem. Journal of Terramechanics, 47(4), 227-242. https://www.sciencedirect.com/science/article/pii/S0022489810000182
Poulakis, P., Vago, J.L., Loizeau, D., .Vicente-Arevalo, C., Hutton, A., McCoubrey, R., Arnedo-Rodriguez, J., Smith, J., Boyes, B., Jessen, S., Otero-Rubio, A., Durrant, S., Gould, G., Joudrier, L., Yushtein, Y., Alary, C., Zekri, E., Baglioni, P., Cernusco, A., Ravera, F. (2015). OVERVIEW AND DEVELOPMENT STATUS OF THE EXOMARS ROVER MOBILITY SUBSYSTEM. https://www.researchgate.net/profile/Pantelis-Poulakis/publication/290445739_Overview_and_Development_Status_of_the_ExoMars_Rover_Mobility_Subsystem/links/56990cae08ae748dfaff3900/Overview-and-Development-Status-of-the-ExoMars-Rover-Mobility-Subsystem.pdf
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