Exploring Mars: An Electric-Powered Manned Rover

Grace Tang Thomas Jefferson High School for Science and Technology

This article was originally published in the 2021 print edition of Teknos Science Journal.

On Saturday, May 30, 2020, 10.3 million viewers sat behind their laptops, monitors, and TVs, as two astronauts escaped Earth’s atmosphere. On November 15, 2020, four astronauts spearheaded the first of 6 crewed missions to space. Eyes were glued to screens throughout the nation, and so were mine. This was another small step for man, closer to landing on a surface covered in rocks and red dust. NASA is gearing up for its manned mission to Mars, leaving us to wonder: What will we do once we reach the Martian surface? How do we explore the unpredictable terrain? How can we broaden the leap for mankind? In the Engineering Design Lab, I collaborated with a group of fellow researchers, brainstorming ideas for an electric-powered crewed rover.

Some cannot imagine exploring a city without buses or taxis, so imagine an attempt to explore a new planet on foot. The weaker gravity on Mars has detrimental effects on the human body, causing bones to rapidly lose density and minerals such as calcium. Our muscles lose strength and endurance as well, leading to cardiovascular ailments. Gravity only 38% as strong as on Earth will have consequences on our hand-eye coordination, vision, balance, and locomotion [1]. Such disorientation makes traveling on foot more difficult and dangerous for astronauts, creating the need for better transportation. 

In 1969, NASA began developing the Lunar Roving Vehicle (LRV) in preparation for the 1971 Apollo 15 mission. This electric-powered vehicle employs lithium-ion batteries and spans 60 square feet with a collapsible feature for astronauts to assemble on the lunar surface. The LRV utilizes an electric four-wheel-drive mechanism to transport astronauts at up to 9mph over rocky terrain. NASA had constructed two more LRVs for each subsequent Apollo mission, leaving three waiting for humans to return to the lunar surface [6]. However, technological advancements since 1970 show us  possible areas of improvement for these crewed rovers. While designing my own manned rover, I searched for a solution and incorporated certain components to better this model for future explorations to Mars.

Space missions have used robotic ground vehicles to explore vast extraterrestrial terrains. Previous missions to Mars have deployed the rovers Spirit, Curiosity and Opportunity, each powered with solar panels and rechargeable batteries. Due to limited battery capacity, Mars rovers must maximize the range covered by a battery charge. In a 2021 study, Avanzini et al developed equations to determine the most efficient speed given a battery level. At each power level, if the rover operated at the best speed, then we would maximize the residual charge at the end of the mission and minimize recharging time. These researchers later applied their findings to the three LRVs from the Apollo missions. Having considered rover weight, battery voltage/discharge data, and even various soil parameters, they modified the optimum speed to increase the LRV’s best predicted range from 10.34 km to 11.8 km. Their research did not account for environmental factors such as extreme winds or range-extending mechanisms such as regenerative braking. However, because the vehicles would be operating in such an unfamiliar environment, they would cover distances at low, uniform speeds, so breaking phases would have little to no effect on energy recovery [2]. All of these factors are areas of exploration in future research [2].

Along with battery efficiency, vehicle stability is another part of the problem. Crewed rovers need to implement a suspension system capable of adapting to unpredictable Martian terrain, in order to maximize vehicle sustainability and passenger safety. Suspension systems isolate the vehicle’s body from the terrain and keep the wheels in the correct camber [4]. Currently, the most developed and conventional suspension system for the rover is the rocker-bogie suspension system, which uses six wheels. However, researchers Bollineni et al. found an independent, rhombus-shaped arrangement that increases both energy efficiency and traction [3]. Rovers must handle steep inclines as well as uneven terrain. Bollineni et al. concluded that lowering the vehicle's center of mass can prevent tipping up to a 30-degree incline.

A popular independent suspension system found in today’s cars is the MacPherson strut. Complete with a control arm, knuckle, and strut, this system works particularly well in off-road vehicles. Previously, research into MacPherson struts only tested one factor, failing to look at the system as a whole. Dehbari and Marzbanrad simulated a more exact mathematical model of the system [4]. Because suspension systems have non-linear behavior, a multibody simulation approach is chosen to predict suspension behavior. These researchers found that ride and handling are directly affected by the suspension and, while the former improves, the latter worsens [4]. Therefore, we must consider a responsive steering system, such as the rack and pinion.

Considering all these potential enhancements, I tackled the design process with my team. For our project, we took the basic model found in the LRVs and made adjustments. The original frame design was too large for astronauts to control and maneuver easily. Thus, we opted to construct our own chassis that is approximately 20 square feet. Additionally, we plan to stack similar lithium-ion batteries found on LRVs and manufacture our own charge controller to manipulate the battery charge states. Coupled with an independent MacPherson strut suspension system and rack-and-pinion steering, not only will we improve driving stability and safety, but also mobility and maneuverability.

Launching humans towards Mars is no longer a far-off dream. Electric vehicles have seen major improvements, particularly with battery life and weight. Currently, the electric vehicle industry is racing to discover cheaper and lighter lithium-ion batteries [5]. Applying our advancements on Earth to extraterrestrial conditions will both facilitate exploration and help developers find areas of improvement with data from testing in adverse conditions. Martian weather and topography are wildly unpredictable and difficult to factor into design optimizations without proper testing [1]. Since we cannot easily test these vehicles on Mars, future researchers must rely on simulations of the gravitational and environmental differences from current robotic rover data. Despite limited resources, our team continues to refine our current models, create CAD simulations, and move towards testing and driving a physical rover.

References

[1] Abadie, L. J., Lloyd, C. W., & Shelhamer, M. J. (2020, February 6). The Human Body in Space (J. Perez, Ed.). National Aeronautics and Space Administration. Retrieved January 31, 2021, from https://www.nasa.gov/hrp/bodyinspace

[2] Avanzini, G., de Angelis, E. L., & Giulietti, F. (2021). Performance analysis and sizing guidelines of electrically-powered extraterrestrial rovers. Acta Astronautica, 178, 349-359. https://doi.org/10.1016/j.actaastro.2020.09.035

[3] Bollineni, R. K., Menon, S. S., & Udupa, G. (2020). Design of Rover and Robotic Arm. Materials Today: Proceedings, 24, 1340-1347. https://doi.org/10.1016/j.matpr.2020.04.450

[4] Dehbari, S., & Marzbanrad, J. (2018). Kinematic and Dynamic Analysis for a New MacPherson Strut Suspension System. Mechanics and Mechanical Engineering, 22(4), 1223-1238. https://doi.org/10.2478/mme-2018-0094

[5] Ewing, J. (2020, September 20). The Age of Electric Cars Is Dawning Ahead of Schedule. The New York Times. https://www.nytimes.com/2020/09/20/business/electric-cars-batteries-tesla-elon-musk.html 

[6] Klesman, A. (2019, May 31). A car for the Moon: The Lunar Roving Vehicle. Astronomy. https://astronomy.com/news/2019/05/a-car-for-the-moon-the-lunar-roving-vehicle