LiquidMotor Class#

class rocketpy.LiquidMotor[source]#

Class to specify characteristics and useful operations for Liquid motors. This class inherits from the Motor class.

See also

Motor

Variables:

LiquidMotor.coordinate_system_orientation (str) – Orientation of the motor’s coordinate system. The coordinate system is defined by the motor’s axis of symmetry. The origin of the coordinate system may be placed anywhere along such axis, such as at the nozzle area, and must be kept the same for all other positions specified. Options are “nozzle_to_combustion_chamber” and “combustion_chamber_to_nozzle”.
LiquidMotor.nozzle_radius (float) – Radius of motor nozzle outlet in meters.
LiquidMotor.nozzle_position (float) – Motor’s nozzle outlet position in meters, specified in the motor’s coordinate system. See Positions and Coordinate Systems for more information.
LiquidMotor.positioned_tanks (list) – List containing the motor’s added tanks and their respective positions.
LiquidMotor.dry_mass (float) – Same as in Motor class. See the Motor docs.
LiquidMotor.propellant_initial_mass (float) – Total propellant initial mass in kg, includes fuel and oxidizer.
LiquidMotor.total_mass (Function) – Total motor mass in kg as a function of time, defined as the sum of propellant mass and the motor’s dry mass (i.e. structure mass).
LiquidMotor.propellant_mass (Function) – Total propellant mass in kg as a function of time, includes fuel and oxidizer.
LiquidMotor.total_mass_flow_rate (Function) – Time derivative of propellant total mass in kg/s as a function of time as obtained by the tanks mass flow.
LiquidMotor.center_of_mass (Function) – Position of the motor center of mass in meters as a function of time. See Positions and Coordinate Systems for more information regarding the motor’s coordinate system.
LiquidMotor.center_of_propellant_mass (Function) – Position of the motor propellant center of mass in meters as a function of time. See Positions and Coordinate Systems for more information regarding the motor’s coordinate system.
LiquidMotor.I_11 (Function) – Component of the motor’s inertia tensor relative to the e_1 axis in kg*m^2, as a function of time. The e_1 axis is the direction perpendicular to the motor body axis of symmetry, centered at the instantaneous motor center of mass.
LiquidMotor.I_22 (Function) – Component of the motor’s inertia tensor relative to the e_2 axis in kg*m^2, as a function of time. The e_2 axis is the direction perpendicular to the motor body axis of symmetry, centered at the instantaneous motor center of mass. Numerically equivalent to I_11 due to symmetry.
LiquidMotor.I_33 (Function) – Component of the motor’s inertia tensor relative to the e_3 axis in kg*m^2, as a function of time. The e_3 axis is the direction of the motor body axis of symmetry, centered at the instantaneous motor center of mass.
LiquidMotor.I_12 (Function) – Component of the motor’s inertia tensor relative to the e_1 and e_2 axes in kg*m^2, as a function of time. See LiquidMotor.I_11 and LiquidMotor.I_22 for more information.
LiquidMotor.I_13 (Function) – Component of the motor’s inertia tensor relative to the e_1 and e_3 axes in kg*m^2, as a function of time. See LiquidMotor.I_11 and LiquidMotor.I_33 for more information.
LiquidMotor.I_23 (Function) – Component of the motor’s inertia tensor relative to the e_2 and e_3 axes in kg*m^2, as a function of time. See LiquidMotor.I_22 and LiquidMotor.I_33 for more information.
LiquidMotor.propellant_I_11 (Function) – Component of the propellant inertia tensor relative to the e_1 axis in kg*m^2, as a function of time. The e_1 axis is the direction perpendicular to the motor body axis of symmetry, centered at the instantaneous propellant center of mass.
LiquidMotor.propellant_I_22 (Function) – Component of the propellant inertia tensor relative to the e_2 axis in kg*m^2, as a function of time. The e_2 axis is the direction perpendicular to the motor body axis of symmetry, centered at the instantaneous propellant center of mass. Numerically equivalent to propellant_I_11 due to symmetry.
LiquidMotor.propellant_I_33 (Function) – Component of the propellant inertia tensor relative to the e_3 axis in kg*m^2, as a function of time. The e_3 axis is the direction of the motor body axis of symmetry, centered at the instantaneous propellant center of mass.
LiquidMotor.propellant_I_12 (Function) – Component of the propellant inertia tensor relative to the e_1 and e_2 axes in kg*m^2, as a function of time. See LiquidMotor.propellant_I_11 and LiquidMotor.propellant_I_22 for more information.
LiquidMotor.propellant_I_13 (Function) – Component of the propellant inertia tensor relative to the e_1 and e_3 axes in kg*m^2, as a function of time. See LiquidMotor.propellant_I_11 and LiquidMotor.propellant_I_33 for more information.
LiquidMotor.propellant_I_23 (Function) – Component of the propellant inertia tensor relative to the e_2 and e_3 axes in kg*m^2, as a function of time. See LiquidMotor.propellant_I_22 and LiquidMotor.propellant_I_33 for more information.
LiquidMotor.thrust (Function) – Motor thrust force, in Newtons, as a function of time.
LiquidMotor.total_impulse (float) – Total impulse of the thrust curve in N*s.
LiquidMotor.max_thrust (float) – Maximum thrust value of the given thrust curve, in N.
LiquidMotor.max_thrust_time (float) – Time, in seconds, in which the maximum thrust value is achieved.
LiquidMotor.average_thrust (float) – Average thrust of the motor, given in N.
LiquidMotor.burn_time (tuple of float) – Tuple containing the initial and final time of the motor’s burn time in seconds.
LiquidMotor.burn_start_time (float) – Motor burn start time, in seconds.
LiquidMotor.burn_out_time (float) – Motor burn out time, in seconds.
LiquidMotor.burn_duration (float) – Total motor burn duration, in seconds. It is the difference between the burn_out_time and the burn_start_time.
LiquidMotor.exhaust_velocity (Function) – Propulsion gases exhaust velocity in m/s.

__init__(thrust_source, dry_mass, dry_inertia, nozzle_radius, center_of_dry_mass_position, nozzle_position=0, burn_time=None, reshape_thrust_curve=False, interpolation_method='linear', coordinate_system_orientation='nozzle_to_combustion_chamber')[source]#

Initialize LiquidMotor class, process thrust curve and geometrical parameters and store results.

Parameters:

thrust_source (int, float, callable, string, array, Function) –
Motor’s thrust curve. Can be given as an int or float, in which case the thrust will be considered constant in time. It can also be given as a callable function, whose argument is time in seconds and returns the thrust supplied by the motor in the instant. If a string is given, it must point to a .csv or .eng file. The .csv file can contain a single line header and the first column must specify time in seconds, while the second column specifies thrust. Arrays may also be specified, following rules set by the class Function. Thrust units are Newtons.

See also

Thrust Source Details
dry_mass (int, float) – Same as in Motor class. See the Motor docs.
dry_inertia (tuple, list) – Tuple or list containing the motor’s dry mass inertia tensor components, in kg*m^2. This inertia is defined with respect to the the center_of_dry_mass_position position. Assuming e_3 is the rocket’s axis of symmetry, e_1 and e_2 are orthogonal and form a plane perpendicular to e_3, the dry mass inertia tensor components must be given in the following order: (I_11, I_22, I_33, I_12, I_13, I_23), where I_ij is the component of the inertia tensor in the direction of e_i x e_j. Alternatively, the inertia tensor can be given as (I_11, I_22, I_33), where I_12 = I_13 = I_23 = 0.
nozzle_radius (int, float) – Motor’s nozzle outlet radius in meters.
center_of_dry_mass_position (int, float) – The position, in meters, of the motor’s center of mass with respect to the motor’s coordinate system when it is devoid of propellant. See Positions and Coordinate Systems
nozzle_position (float) – Motor’s nozzle outlet position in meters, specified in the motor’s coordinate system. See Positions and Coordinate Systems for more information.
burn_time (float, tuple of float, optional) – Motor’s burn time. If a float is given, the burn time is assumed to be between 0 and the given float, in seconds. If a tuple of float is given, the burn time is assumed to be between the first and second elements of the tuple, in seconds. If not specified, automatically sourced as the range between the first and last-time step of the motor’s thrust curve. This can only be used if the motor’s thrust is defined by a list of points, such as a .csv file, a .eng file or a Function instance whose source is a list.
reshape_thrust_curve (boolean, tuple, optional) – If False, the original thrust curve supplied is not altered. If a tuple is given, whose first parameter is a new burn out time and whose second parameter is a new total impulse in Ns, the thrust curve is reshaped to match the new specifications. May be useful for motors whose thrust curve shape is expected to remain similar in case the impulse and burn time varies slightly. Default is False.
interpolation_method (string, optional) – Method of interpolation to be used in case thrust curve is given by data set in .csv or .eng, or as an array. Options are ‘spline’ ‘akima’ and ‘linear’. Default is “linear”.
coordinate_system_orientation (string, optional) – Orientation of the motor’s coordinate system. The coordinate system is defined by the motor’s axis of symmetry. The origin of the coordinate system may be placed anywhere along such axis, such as at the nozzle area, and must be kept the same for all other positions specified. Options are “nozzle_to_combustion_chamber” and “combustion_chamber_to_nozzle”. Default is “nozzle_to_combustion_chamber”.

exhaust_velocity#

Computes the exhaust velocity of the motor from its mass flow rate and thrust.

Returns:: self.exhaust_velocity – Gas exhaust velocity of the motor.
Return type:: Function

Notes

The exhaust velocity is computed as the ratio of the thrust and the mass flow rate. Therefore, this will vary with time if the mass flow rate varies with time.

propellant_mass#

Evaluates the total propellant mass of the motor as the sum of fluids mass in each tank, which may include fuel and oxidizer and usually vary with time.

Returns:: Mass of the motor, in kg.
Return type:: Function

property propellant_initial_mass#

Property to store the initial mass of the propellant, this includes fuel and oxidizer.

Returns:: Initial mass of the propellant, in kg.
Return type:: float

mass_flow_rate#

Evaluates the mass flow rate of the motor as the sum of mass flow rate from each tank, which may include fuel and oxidizer and usually vary with time.

Returns:: Mass flow rate of the motor, in kg/s.
Return type:: Function