NASA does indeed use high-altitudes on earth to test Mars aerobraking, atmospheric entry, and supersonic parachute deployment[0]. For the actual terminal descen

NASA does indeed use high-altitudes on earth to test Mars aerobraking, atmospheric entry, and supersonic parachute deployment[0]. For the actual terminal descent and landing speeds are low enough the atmosphere is not significant, you can just test that at sea level. [0] https://en.wikipedia.org/wiki/Low-Density_Supersonic_Decelerator https://en.wikipedia.org/wiki/Low-Density_Supersonic_Deceler...