How do you control attitude with just two contra-rotating rotors? I've Googled, but can't find an answer.
Extra points for why NASA chose this mode, and terrestrial drones don't?
Extra points for why NASA chose this mode, and terrestrial drones don't?
https://www.youtube.com/watch?v=GhsZUZmJvaM
explains it: they can change the attack angle of rotor blades for different positions, which produces a torque, though you have to compensate for the gyroscopic effect, which lags behind.
Humans cannot fly this, but computers can.
The video also explains why the chose two contra-rotating rotors instead of a quad-copter design.
[1] https://hackaday.com/2020/09/02/an-up-close-look-at-the-firs...