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Rovers on sand in the Simulation-Based Engineering Lab. (Joel Hallberg \/ UW\u2013Madison via SWNS)<\/p>\n
By Stephen Beech<\/strong><\/p>\n Robotic space rovers keep getting stuck because the surface of the moon<\/a> is “fluffier\u201d than on Earth, suggests a new study.<\/p>\n Researchers reckon they’ve finally worked out why the multi-million dollar extraterrestrial vehicles get bogged down in soft sand or gravel on the lunar surface and Mars.<\/p>\n They say it’s because gravity on Earth, where the rovers are tested, pulls down on sand much more strongly than the gravity on the red planet or the moon<\/a> does.<\/p>\n When a space rover gets stuck in soft sand or gravel – such as the Mars rover Spirit in 2009 \u2014 engineers issue a series of commands that move its wheels or reverse its course in a delicate, time-consuming effort to free it and continue its exploratory mission.<\/p>\n While Spirit remained permanently stuck, it is now hoped that better pre-mission terrain testing on Earth could help avert future problems.<\/p>\n Using computer simulations, mechanical engineers at the University of Wisconsin\u2013Madison<\/a> in the United States uncovered a flaw in how rovers are currently tested on Earth.<\/p>\n They say that error leads to “overly optimistic” conclusions about how rovers will behave once they’re deployed on extraterrestrial missions.<\/p>\n An important element in preparing for these missions is an accurate understanding of how a rover will traverse extraterrestrial surfaces in low gravity to prevent it from getting stuck in soft terrain or rocky areas.<\/p>\n On the moon<\/a>, the gravitational pull is six times weaker than on Earth.<\/p>\n Mechanical engineering professor Dan Negrut poses with a space rover used for testing. (Joel Hallberg \/ UW\u2013Madison via SWNS)<\/p>\n By Talker<\/p>\n For decades, researchers testing rovers have accounted for that difference in gravity by creating a prototype that is a sixth of the mass of the actual rover.<\/p>\n They test the lightweight rovers in deserts, observing how it moves across sand to gain insights into how it would perform on the moon.<\/p>\n But it turns out that the standard testing approach “overlooked” a seemingly inconsequential detail: the pull of Earth\u2019s gravity on the desert sand.<\/p>\n Through simulation, Wisconsin\u2013Madison Professor Dan Negrut and his team determined that Earth’s gravity pulls down on sand much more strongly than the gravity on Mars or the moon does.<\/p>\n He explained that, on Earth, sand is more rigid and supportive – reducing the likelihood it will shift under a vehicle\u2019s wheels.<\/p>\n But Negrut says the moon\u2019s surface<\/a> is \u201cfluffier\u201d and therefore shifts more easily – meaning rovers have less traction, which can hinder their mobility.<\/p>\n He said: \u201cIn retrospect, the idea is simple: we need to consider not only the gravitational pull on the rover but also the effect of gravity on the sand to get a better picture of how the rover will perform on the moon.<\/p>\n A rover’s operation is simulated in Project Chrono, an open-source physics simulation engine developed at UW-Madison. (Dan Negrut \/ UW\u2013Madison via SWNS)<\/p>\n By Talker<\/p>\n \u201cOur findings underscore the value of using physics-based simulation to analyse rover mobility on granular soil.\u201d<\/p>\n The researchers\u2019 discovery resulted from their work on a NASA-funded project to simulate the VIPER rover, which had been planned for a lunar mission.<\/p>\n The team utilised Project Chrono, an open-source physics simulation engine developed at UW\u2013Madison in collaboration with scientists from Italy.<\/p>\n The software allows researchers to quickly and accurately model complex mechanical systems – such as full-size rovers operating on “squishy” sand or soil surfaces.<\/p>\n While simulating the VIPER rover, they noticed “discrepancies” between the Earth-based test results and their simulations of the rover\u2019s mobility on the moon.<\/p>\n Digging deeper with Chrono simulations revealed the testing flaw.<\/p>\n<\/p>\n
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