ENH: add structural to total mass ratio for motor and rocket

rocketpy/prints/rocket_prints.py

@@ -36,6 +36,8 @@ def inertia_details(self):
         print(f"Rocket Mass: {self.rocket.mass:.3f} kg (without motor)")
         print(f"Rocket Dry Mass: {self.rocket.dry_mass:.3f} kg (with unloaded motor)")
         print(f"Rocket Loaded Mass: {self.rocket.total_mass(0):.3f} kg")
+        mass_ratio = self.rocket.dry_mass / self.rocket.total_mass(0)
+        print(f"Rocket Structural to total mass ratio: {mass_ratio:.3f}")
         print(
             f"Rocket Inertia (with unloaded motor) 11: {self.rocket.dry_I_11:.3f} kg*m2"
         )

rocketpy/prints/solid_motor_prints.py

@@ -65,6 +65,8 @@ def motor_details(self):
         print(
             f"Total Propellant Mass: {self.solid_motor.propellant_initial_mass:.3f} kg"
         )
+        mass_ratio = self.solid_motor.dry_mass / self.solid_motor.total_mass(0)
+        print(f"Structural to total mass ratio: {mass_ratio:.3f}")
         average = self.solid_motor.exhaust_velocity.average(*self.solid_motor.burn_time)
         print(f"Average Propellant Exhaust Velocity: {average:.3f} m/s")
         print(f"Average Thrust: {self.solid_motor.average_thrust:.3f} N")