Classic laundering of tax dollars on so-called "research". As private USA corporate interests want to get back in the coaxial helicopter game, what better way than fund your novo "catchup with the Russkies" project than funnelling some tax theft shekels through a something something something "NASA Mars helicopter" something... Quadcopter or hexacopter provide greater flying redundancy and power balancing flight modes (particularly important in extreme remote environment as Mars), so coaxial autonomous chopper is just a fancy way to spend (thieve) millions of sheckels. And you prolly want a light weight fixed wing craft with variable axis props (lift + rotate to pusher/puller) to maximise solar powered flight time for such remote autonomous micro flying craft blah blah blah ... Cest la (((vie)))... NASA's Mars Helicopter makes maiden flight in JPL simulator https://newatlas.com/nasa-mars-helicopter-maiden-flight/59071/ https://en.wikipedia.org/wiki/Coaxial_rotor https://en.wikipedia.org/wiki/Category:Coaxial_rotor_helicopters