# Rocket Class¶

class rocketpy.Rocket.Rocket(motor, mass, inertiaI, inertiaZ, radius, distanceRocketNozzle, distanceRocketPropellant, powerOffDrag, powerOnDrag)[source]

Keeps all rocket and parachute information.

Geometrical attributes
radius

Type

float

area

Rocket’s circular cross section largest frontal area in squared meters.

Type

float

distanceRocketNozzle

Distance between rocket’s center of mass, without propellant, to the exit face of the nozzle, in meters. Always positive.

Type

float

distanceRocketPropellant

Distance between rocket’s center of mass, without propellant, to the center of mass of propellant, in meters. Always positive.

Type

float

Mass and Inertia attributes
mass

Rocket’s mass without propellant in kg.

Type

float

inertiaI

Rocket’s moment of inertia, without propellant, with respect to to an axis perpendicular to the rocket’s axis of cylindrical symmetry, in kg*m^2.

Type

float

inertiaZ

Rocket’s moment of inertia, without propellant, with respect to the rocket’s axis of cylindrical symmetry, in kg*m^2.

Type

float

centerOfMass

Distance of the rocket’s center of mass, including propellant, to rocket’s center of mass without propellant, in meters. Expressed as a function of time.

Type

Function

reducedMass

Function of time expressing the reduced mass of the rocket, defined as the product of the propellant mass and the mass of the rocket without propellant, divided by the sum of the propellant mass and the rocket mass.

Type

Function

totalMass

Function of time expressing the total mass of the rocket, defined as the sum of the propellant mass and the rocket mass without propellant.

Type

Function

thrustToWeight

Function of time expressing the motor thrust force divided by rocket weight. The gravitational acceleration is assumed as 9.80665 m/s^2.

Type

Function

Eccentricity attributes
cpEccentricityX

Center of pressure position relative to center of mass in the x axis, perpendicular to axis of cylindrical symmetry, in meters.

Type

float

cpEccentricityY

Center of pressure position relative to center of mass in the y axis, perpendicular to axis of cylindrical symmetry, in meters.

Type

float

thrustEccentricityY

Thrust vector position relative to center of mass in the y axis, perpendicular to axis of cylindrical symmetry, in meters.

Type

float

thrustEccentricityX

Thrust vector position relative to center of mass in the x axis, perpendicular to axis of cylindrical symmetry, in meters.

Type

float

Aerodynamic attributes
aerodynamicSurfaces

List of aerodynamic surfaces of the rocket.

Type

list

staticMargin

Float value corresponding to rocket static margin when loaded with propellant in units of rocket diameter or calibers.

Type

float

powerOffDrag

Rocket’s drag coefficient as a function of Mach number when the motor is off.

Type

Function

powerOnDrag

Rocket’s drag coefficient as a function of Mach number when the motor is on.

Type

Function

Motor attributes
motor

Rocket’s motor. See Motor class for more details.

Type

Motor

Initializes Rocket class, process inertial, geometrical and aerodynamic parameters.

Parameters
• motor (Motor) – Motor used in the rocket. See Motor class for more information.

• mass (int, float) – Unloaded rocket total mass (without propelant) in kg.

• inertiaI (int, float) – Unloaded rocket lateral (perpendicular to axis of symmetry) moment of inertia (without propelant) in kg m^2.

• inertiaZ (int, float) – Unloaded rocket axial moment of inertia (without propelant) in kg m^2.

• distanceRocketNozzle (int, float) – Distance from rocket’s unloaded center of mass to nozzle outlet, in meters. Generally negative, meaning a negative position in the z axis which has an origin in the rocket’s center of mass (without propellant) and points towards the nose cone.

• distanceRocketPropellant (int, float) – Distance from rocket’s unloaded center of mass to propellant center of mass, in meters. Generally negative, meaning a negative position in the z axis which has an origin in the rocket’s center of mass (with out propellant) and points towards the nose cone.

• powerOffDrag (int, float, callable, string, array) – Rocket’s drag coefficient when the motor is off. Can be given as an entry to the Function class. See help(Function) for more information. If int or float is given, it is assumed constant. If callable, string or array is given, it must be a function of Mach number only.

• powerOnDrag (int, float, callable, string, array) – Rocket’s drag coefficient when the motor is on. Can be given as an entry to the Function class. See help(Function) for more information. If int or float is given, it is assumed constant. If callable, string or array is given, it must be a function of Mach number only.

Returns

Return type

None

evaluateReducedMass()[source]

Calculates and returns the rocket’s total reduced mass. The reduced mass is defined as the product of the propellant mass and the mass of the rocket without propellant, divided by the sum of the propellant mass and the rocket mass. The function returns an object of the Function class and is defined as a function of time.

Parameters

None

Returns

self.reducedMass – Function of time expressing the reduced mass of the rocket, defined as the product of the propellant mass and the mass of the rocket without propellant, divided by the sum of the propellant mass and the rocket mass.

Return type

Function

evaluateTotalMass()[source]

Calculates and returns the rocket’s total mass. The total mass is defined as the sum of the propellant mass and the rocket mass without propellant. The function returns an object of the Function class and is defined as a function of time.

Parameters

None

Returns

self.totalMass – Function of time expressing the total mass of the rocket, defined as the sum of the propellant mass and the rocket mass without propellant.

Return type

Function

evaluateStaticMargin()[source]

Calculates and returns the rocket’s static margin when loaded with propellant. The static margin is saved and returned in units of rocket diameter or calibers.

Parameters

None

Returns

self.staticMargin – Float value corresponding to rocket static margin when loaded with propellant in units of rocket diameter or calibers.

Return type

float

addTail(topRadius, bottomRadius, length, distanceToCM)[source]

Create a new tail or rocket diameter change, storing its parameters as part of the aerodynamicSurfaces list. Its parameters are the axial position along the rocket and its derivative of the coefficient of lift in respect to angle of attack.

Parameters
• topRadius (int, float) – Tail top radius in meters, considering positive direction from center of mass to nose cone.

• bottomRadius (int, float) – Tail bottom radius in meters, considering positive direction from center of mass to nose cone.

• length (int, float) – Tail length or height in meters. Must be a positive value.

• distanceToCM (int, float) – Tail position relative to rocket unloaded center of mass, considering positive direction from center of mass to nose cone. Consider the point belonging to the tail which is closest to the unloaded center of mass to calculate distance.

Returns

• cl (Function) – Function of the angle of attack (Alpha) and the mach number (Mach) expressing the tail’s lift coefficient. The inputs are the angle of attack (in radians) and the mach number. The output is the tail’s lift coefficient. In the current implementation, the tail’s lift coefficient does not vary with mach.

• self (Rocket) – Object of the Rocket class.

addNose(length, kind, distanceToCM)[source]

Creates a nose cone, storing its parameters as part of the aerodynamicSurfaces list. Its parameters are the axial position along the rocket and its derivative of the coefficient of lift in respect to angle of attack.

Parameters
• length (int, float) – Nose cone length or height in meters. Must be a positive value.

• kind (string) – Nose cone type. Von Karman, conical, ogive, and lvhaack are supported.

• distanceToCM (int, float) – Nose cone position relative to rocket unloaded center of mass, considering positive direction from center of mass to nose cone. Consider the center point belonging to the nose cone base to calculate distance.

Returns

• cl (Function) – Function of the angle of attack (Alpha) and the mach number (Mach) expressing the nose cone’s lift coefficient. The inputs are the angle of attack (in radians) and the mach number. The output is the nose cone’s lift coefficient. In the current implementation, the nose cone’s lift coefficient does not vary with mach

• self (Rocket) – Object of the Rocket class.

addFins(n, span, rootChord, tipChord, distanceToCM, radius=0, cantAngle=0, airfoil=None)[source]

Create a fin set, storing its parameters as part of the aerodynamicSurfaces list. Its parameters are the axial position along the rocket and its derivative of the coefficient of lift in respect to angle of attack.

Parameters
• n (int) – Number of fins, from 2 to infinity.

• span (int, float) – Fin span in meters.

• rootChord (int, float) – Fin root chord in meters.

• tipChord (int, float) – Fin tip chord in meters.

• distanceToCM (int, float) – Fin set position relative to rocket unloaded center of mass, considering positive direction from center of mass to nose cone. Consider the center point belonging to the top of the fins to calculate distance.

• radius (int, float, optional) – Reference radius to calculate lift coefficient. If 0, which is default, use rocket radius. Otherwise, enter the radius of the rocket in the section of the fins, as this impacts its lift coefficient.

• cantAngle (int, float, optional) – Fins cant angle with respect to the rocket centerline. Must be given in degrees.

• airfoil (tuple, optional) – Default is null, in which case fins will be treated as flat plates. Otherwise, if tuple, fins will be considered as airfoils. The tuple’s first item specefies the aifoil’s lift coefficient by angle of attack and must be either a .csv, .txt, ndarray or callable. The .csv and .txt files must contain no headers and the first column must specify the angle of attack, while the second column must specify the lift coefficient. The ndarray should be as [(x0, y0), (x1, y1), (x2, y2), …] where x0 is the angle of attack and y0 is the lift coefficient. If callable, it should take an angle of attack as input and return the lift coefficient at that angle of attack. The tuple’s second item is the unit of the angle of attack, accepting either “radians” or “degrees”.

Returns

• cl (Function) – Function of the angle of attack (Alpha) and the mach number (Mach) expressing the fin’s lift coefficient. The inputs are the angle of attack (in radians) and the mach number. The output is the fin’s lift coefficient.

• self (Rocket) – Object of the Rocket class.

addParachute(name, CdS, trigger, samplingRate=100, lag=0, noise=(0, 0, 0))[source]

Creates a new parachute, storing its parameters such as opening delay, drag coefficients and trigger function.

Parameters
• name (string) – Parachute name, such as drogue and main. Has no impact in simulation, as it is only used to display data in a more organized matter.

• CdS (float) – Drag coefficient times reference area for parachute. It is used to compute the drag force exerted on the parachute by the equation F = ((1/2)*rho*V^2)*CdS, that is, the drag force is the dynamic pressure computed on the parachute times its CdS coefficient. Has units of area and must be given in squared meters.

• trigger (function) – Function which defines if the parachute ejection system is to be triggered. It must take as input the freestream pressure in pascal and the state vector of the simulation, which is defined by [x, y, z, vx, vy, vz, e0, e1, e2, e3, wx, wy, wz]. It will be called according to the sampling rate given next. It should return True if the parachute ejection system is to be triggered and False otherwise.

• samplingRate (float, optional) – Sampling rate in which the trigger function works. It is used to simulate the refresh rate of onboard sensors such as barometers. Default value is 100. Value must be given in hertz.

• lag (float, optional) – Time between the parachute ejection system is triggered and the parachute is fully opened. During this time, the simulation will consider the rocket as flying without a parachute. Default value is 0. Must be given in seconds.

• noise (tuple, list, optional) – List in the format (mean, standard deviation, time-correlation). The values are used to add noise to the pressure signal which is passed to the trigger function. Default value is (0, 0, 0). Units are in pascal.

Returns

parachute – Parachute containing trigger, samplingRate, lag, CdS, noise and name. Furthermore, it stores cleanPressureSignal, noiseSignal and noisyPressureSignal which are filled in during Flight simulation.

Return type

Parachute

setRailButtons(distanceToCM, angularPosition=45)[source]

Adds rail buttons to the rocket, allowing for the calculation of forces exerted by them when the rocket is sliding in the launch rail. Furthermore, rail buttons are also needed for the simulation of the planar flight phase, when the rocket experiences 3 degrees of freedom motion while only one rail button is still in the launch rail.

Parameters
• distanceToCM (tuple, list, array) – Two values organized in a tuple, list or array which represent the distance of each of the two rail buttons to the center of mass of the rocket without propellant. If the rail button is positioned above the center of mass, its distance should be a positive value. If it is below, its distance should be a negative value. The order does not matter. All values should be in meters.

• angularPosition (float) – Angular postion of the rail buttons in degrees measured as the rotation around the symmetry axis of the rocket relative to one of the other principal axis. Default value is 45 degrees, generally used in rockets with 4 fins.

Returns

Return type

None

addCMEccentricity(x, y)[source]

Moves line of action of aerodynamic and thrust forces by equal translation amount to simulate an eccentricity in the position of the center of mass of the rocket relative to its geometrical center line. Should not be used together with addCPEccentricity and addThrustEccentricity.

Parameters
• x (float) – Distance in meters by which the CM is to be translated in the x direction relative to geometrical center line.

• y (float) – Distance in meters by which the CM is to be translated in the y direction relative to geometrical center line.

Returns

self – Object of the Rocket class.

Return type

Rocket

addCPEccentricity(x, y)[source]

Moves line of action of aerodynamic forces to simulate an eccentricity in the position of the center of pressure relative to the center of mass of the rocket.

Parameters
• x (float) – Distance in meters by which the CP is to be translated in the x direction relative to the center of mass axial line.

• y (float) – Distance in meters by which the CP is to be translated in the y direction relative to the center of mass axial line.

Returns

self – Object of the Rocket class.

Return type

Rocket

addThrustEccentricity(x, y)[source]

Moves line of action of thrust forces to simulate a disalignment of the thrust vector and the center of mass.

Parameters
• x (float) – Distance in meters by which the line of action of the thrust force is to be translated in the x direction relative to the center of mass axial line.

• y (float) – Distance in meters by which the line of action of the thrust force is to be translated in the x direction relative to the center of mass axial line.

Returns

self – Object of the Rocket class.

Return type

Rocket

info()[source]

Prints out a summary of the data and graphs available about the Rocket.

Parameters

None

Returns

Return type

None

allInfo()[source]

Prints out all data and graphs available about the Rocket.

Parameters

None

Returns

Return type

None

addFin(numberOfFins=4, cl=6.283185307179586, cpr=1, cpz=1, gammas=[0, 0, 0, 0], angularPositions=None)[source]

Hey! I will document this function later

class railButtonPair(distanceToCM, angularPosition)

Create new instance of railButtonPair(distanceToCM, angularPosition)

angularPosition

Alias for field number 1

distanceToCM

Alias for field number 0