You can calculate the hover power required out of ground effect by using the following formulas:
Given m, the mass of the helicopter, the required lift force is $L = g_{mars}*m$
The required shaft power is:
$Power (Watts) = (L^{3/2} / R * \sqrt{( 2 / (\pi * density) )})/FM$
where $R$ is rotor diameter and FM is the "figure of Merit". For a small helicopter the FM is smaller than 0.66, say 0.55.
The density at low altitude on Mars is 0.0152 kg/m^3
The gravitational acceleration $g_{mars}$ is 3.8 m/sec^2.
Example
- mass = 2 kg
- Lift = 7.6 Newton
- FM = 0.55
- Rotor diameter = 1 meter
- density = 0.0152 kg/m^3
- pi = 3.1416
The result is 264 Watts.
The fact that the counter rotating rotors are coaxial does not significantly reduce the hover power. The effective diameter is nearly the same.
Note that, when the mass is reduced to 1 kg the required power would be only 87 Watts !
In summary: Power required is proportional to (Lift to the 3/2 power exponent), inversely proportional to rotor diameter and inversely proportional to the square root of the density.
When flying forward instead of hovering the required power goes down significantly for a well shaped streamlined fuselage.
In 1929 Glauert came up with an approximate formula (the solution of a quartic) which is still used today. A good reference text book is: B W McCormick: Aerodynamics of V/STOL Flight