MNT: Point mass motor and rocket fixes

- MNT: pointmassmotor fixing the various properties.
- MNT: fixing super init and init inheritance by changing order in pointmassrocket
- MNT: pointmassrocket property setter and default value fixes

Author: aZira371

rocketpy/motors/pointmassmotor.py

@@ -1,74 +1,22 @@
 from functools import cached_property
-
 import numpy as np
-
-from typing import Callable 
-
+from typing import Callable
 from rocketpy.mathutils.function import Function, funcify_method
-from .motor import Motor 
+from .motor import Motor
 
-class PointMassMotor(Motor): 
-    """Class representing a motor modeled as a point mass.
-
-    Inherits from the Motor class and simplifies the model to a thrust-producing
-    object without detailed structural components. The total mass of the motor
-    will vary with propellant consumption, similar to a standard motor. However,
-    its inertia components and the center of propellant mass are considered zero
-    and fixed at the motor's reference point, respectively.
-    """
+class PointMassMotor(Motor):
+    """Motor modeled as a point mass for 3-DOF simulations."""
 
     def __init__(
         self,
         thrust_source,
         dry_mass,
         propellant_initial_mass,
-        burn_time = None,
-        propellant_final_mass = None,
-        reshape_thrust_curve = False,
-        interpolation_method = "linear",
+        burn_time=None,
+        propellant_final_mass=None,
+        reshape_thrust_curve=False,
+        interpolation_method="linear",
     ):
-        """Initialize the PointMassMotor class.
-
-        This motor simplifies the physical model by considering its mass to be
-        concentrated at a single point, effectively setting all its inertia
-        components to zero. Propellant mass variation and exhaust velocity
-        are still simulated and derived from the thrust and propellant consumption
-        characteristics, similar to the base Motor class.
-
-        Parameters
-        ----------
-        thrust_source : int, float, callable, str, numpy.ndarray, Function
-            Thrust source. Can be a constant value (int, float), a callable
-            function of time, a path to a CSV file, a NumPy array, or a
-            RocketPy `Function` object.
-        dry_mass : float
-            Total dry mass of the motor in kg.
-        propellant_initial_mass : float
-            Initial mass of the propellant in kg. This is a required parameter
-            as the point mass motor will still simulate propellant consumption.
-        burn_time : float, optional
-            Total burn time of the motor in seconds. Required if `thrust_source`
-            is a constant value or a callable function, and `propellant_final_mass`
-            is not provided. If `thrust_source` is a CSV, array, or Function,
-            the burn time is derived from it.
-        propellant_final_mass : float, optional
-            Final mass of the propellant in kg. Required if `thrust_source`
-            is a callable function and `burn_time` is not provided. If not
-            provided, it is calculated by the base Motor class.
-        reshape_thrust_curve : bool, optional
-            Whether to reshape the thrust curve to start at t=0 and end at
-            burn_time. Defaults to False.
-        interpolation_method : str, optional
-            Interpolation method for the thrust curve, if applicable.
-            Defaults to 'linear'.
-
-        Raises
-        ------
-        ValueError
-            If insufficient data is provided for mass flow rate calculation.
-        TypeError
-            If an invalid type is provided for `thrust_source`.
-        """
         if isinstance(thrust_source, (int, float, Callable)):
             if propellant_initial_mass is None:
                 raise ValueError(
@@ -79,14 +27,13 @@ def __init__(
                     "For constant or callable thrust, either 'burn_time' or "
                     "'propellant_final_mass' must be provided."
                 )
-        
         elif isinstance(thrust_source, (Function, np.ndarray, str)):
             if propellant_initial_mass is None:
                 raise ValueError(
                     "For thrust from a Function, NumPy array, or CSV, 'propellant_initial_mass' is required."
                 )
         else:
-             raise TypeError(
+            raise TypeError(
                 "Invalid 'thrust_source' type. Must be int, float, callable, str, numpy.ndarray, or Function."
             )
 
@@ -95,172 +42,50 @@ def __init__(
 
         super().__init__(
             thrust_source=thrust_source,
-            dry_inertia=(0, 0, 0), # Inertia is zero for a point mass
-            nozzle_radius=0, # Nozzle radius is irrelevant for a point mass model
-            center_of_dry_mass_position=0, # Pass 0 directly to the superclass
+            dry_inertia=(0, 0, 0),
+            nozzle_radius=0,
+            center_of_dry_mass_position=0,
             dry_mass=dry_mass,
-            nozzle_position=0, # Nozzle is at the motor's origin
+            nozzle_position=0,
             burn_time=burn_time,
-            reshape_thrust_curve=reshape_thrust_curve, 
+            reshape_thrust_curve=reshape_thrust_curve,
             interpolation_method=interpolation_method,
-            coordinate_system_orientation="nozzle_to_combustion_chamber", # Standard orientation
+            coordinate_system_orientation="nozzle_to_combustion_chamber",
         )
 
-    # Removed the thrust method. It will now be inherited directly from the Motor base class,
-    # which already correctly handles the conversion of thrust_source to a Function
-    # and exposes it as a cached property.
-
-    # Removed the total_mass override. The base Motor class's total_mass property
-    # will now correctly calculate dry_mass + propellant_mass(t), which is the desired
-    # varying mass behavior for the point mass motor.
-
-    # Removed the center_of_dry_mass_position override. It is now passed directly
-    # to the super().__init__ as 0.
     @property
     def propellant_initial_mass(self):
-        """Returns the initial propellant mass for a point mass motor.
-
-        This property retrieves the value set during initialization. This implementation
-        is required as 'propellant_initial_mass' is an abstract method in the parent Motor class.
-
-        Returns
-        -------
-        float
-            Propellant initial mass in kg.
-        """
         return self._propellant_initial_mass
-    
+
     @funcify_method("Time (s)", "Exhaust velocity (m/s)")
     def exhaust_velocity(self):
-        """Exhaust velocity by assuming it as a constant. The formula used is
-        total impulse/propellant initial mass.
-
-        Returns
-        -------
-        self.exhaust_velocity : Function
-            Gas exhaust velocity of the motor.
+        """Assume constant exhaust velocity: total impulse / propellant mass"""
+        v_e = self.total_impulse / self.propellant_initial_mass
+        return Function(v_e).set_discrete_based_on_model(self.thrust)
 
-        Notes
-        -----
-        This corresponds to the actual exhaust velocity only when the nozzle
-        exit pressure equals the atmospheric pressure.
-        """
-        return Function(
-            self.total_impulse / self.propellant_initial_mass
-        ).set_discrete_based_on_model(self.thrust)
-    
     @cached_property
-    @funcify_method("Time (s)", "Mass flow rate (kg/s)", extrapolation="zero")
     def total_mass_flow_rate(self) -> Function:
-        """Time derivative of the propellant mass as a function of time.
-
-        It calculates mass flow rate as the negative of thrust divided by exhaust velocity,
-        consistent with the fundamental rocket equation.
-
-        Returns
-        -------
-        Function
-            Time derivative of total propellant mass a function of time.
-        """
-
-        exhaust_vel_func = self.exhaust_velocity
-        return -self.thrust / exhaust_vel_func
+        """Mass flow rate: -thrust / exhaust_velocity"""
+        return -self.thrust / self.exhaust_velocity
 
     @cached_property
-    @funcify_method("Time (s)", "Propellant Mass (kg)")
     def center_of_propellant_mass(self):
-        """Returns the position of the center of mass of the propellant.
-
-        For a point mass motor, the propellant's center of mass is considered
-        to be at the origin (0) of the motor's coordinate system.
+        """Center of propellant mass is always zero"""
+        return Function(0.0)
 
-        Returns
-        -------
-        Function
-            A Function object representing the center of propellant mass (always 0).
-        """
-        return 0
+    # Propellant inertias: always zero, but return as Function objects
+    def _zero_inertia_func(self):
+        return Function(0.0)
 
     @cached_property
-    @funcify_method("Time (s)", "Inertia (kg·m²)")
-    def propellant_I_11(self):
-        """Returns the propellant moment of inertia around the x-axis.
-
-        For a point mass motor, this is always zero.
-
-        Returns
-        -------
-        Function
-            A Function object representing zero propellant inertia.
-        """
-        return 0
-
+    def propellant_I_11(self): return self._zero_inertia_func()
     @cached_property
-    @funcify_method("Time (s)", "Inertia (kg·m²)")
-    def propellant_I_12(self):
-        """Returns the propellant product of inertia I_xy.
-
-        For a point mass motor, this is always zero.
-
-        Returns
-        -------
-        Function
-            A Function object representing zero propellant inertia.
-        """
-        return 0
-
+    def propellant_I_12(self): return self._zero_inertia_func()
     @cached_property
-    @funcify_method("Time (s)", "Inertia (kg·m²)")
-    def propellant_I_13(self):
-        """Returns the propellant product of inertia I_xz.
-
-        For a point mass motor, this is always zero.
-
-        Returns
-        -------
-        Function
-            A Function object representing zero propellant inertia.
-        """
-        return 0
-
+    def propellant_I_13(self): return self._zero_inertia_func()
     @cached_property
-    @funcify_method("Time (s)", "Inertia (kg·m²)")
-    def propellant_I_22(self):
-        """Returns the propellant moment of inertia around the y-axis.
-
-        For a point mass motor, this is always zero.
-
-        Returns
-        -------
-        Function
-            A Function object representing zero propellant inertia.
-        """
-        return 0
-
+    def propellant_I_22(self): return self._zero_inertia_func()
     @cached_property
-    @funcify_method("Time (s)", "Inertia (kg·m²)")
-    def propellant_I_23(self):
-        """Returns the propellant product of inertia I_yz.
-
-        For a point mass motor, this is always zero.
-
-        Returns
-        -------
-        Function
-            A Function object representing zero propellant inertia.
-        """
-        return 0
-
+    def propellant_I_23(self): return self._zero_inertia_func()
     @cached_property
-    @funcify_method("Time (s)", "Inertia (kg·m²)")
-    def propellant_I_33(self):
-        """Returns the propellant moment of inertia around the z-axis.
-
-        For a point mass motor, this is always zero.
-
-        Returns
-        -------
-        Function
-            A Function object representing zero propellant inertia.
-        """
-        return 0
+    def propellant_I_33(self): return self._zero_inertia_func()