The rotors are 1.2m in length and spin up to 2500rpm.
This gives circa 160m/s (560km/h) linear speed of the rotor tip.
Pretty much impossible for the rotors to survive touching anything at that speed.
The rotors are probably already designed with absolute minimum margins. Not only the rotors are part of the package to deliver to surface of Mars, then they have to be lifted in thin atmosphere, but they also need to be spun up to very huge speeds and then quickly controlled to keep the craft stable. The mass of those rotors is critical to how well the craft can be controlled.
This gives circa 160m/s (560km/h) linear speed of the rotor tip.
Pretty much impossible for the rotors to survive touching anything at that speed.
The rotors are probably already designed with absolute minimum margins. Not only the rotors are part of the package to deliver to surface of Mars, then they have to be lifted in thin atmosphere, but they also need to be spun up to very huge speeds and then quickly controlled to keep the craft stable. The mass of those rotors is critical to how well the craft can be controlled.