Module MAPLEAF.ENV.launchRail

Modeling of the effects of a Launch Rail on rocket launches

''' Modeling of the effects of a Launch Rail on rocket launches '''

from MAPLEAF.Motion import (AngularVelocity, ForceMomentSystem, Quaternion,
                            Vector)

__all__ = [ "LaunchRail" ]

class LaunchRail():
    def __init__(self, initialPosition, initialDirection, length, earthRotationRate=0):
        ''' Provide initial position and direction in global inertial frame '''
        self.initialPosition = initialPosition # m
        self.initialDirection = initialDirection.normalize() # Ensure the direction is a unit vector
        self.length = length # m
        self.earthAngVel = earthRotationRate # rad/s, about z-axis

    def getPosition(self, time):
        ''' Launch Rail moves with the earth's surface '''
        rotationSoFar = Quaternion(
            axisOfRotation=Vector(0,0,1), 
            angle=(self.earthAngVel * time)
        )
        return rotationSoFar.rotate(self.initialPosition)

    def getDirection(self, time):
        ''' Launch Rail moves with the earth's surface '''
        rotationSoFar = Quaternion(
            axisOfRotation=Vector(0,0,1), 
            angle=(self.earthAngVel * time)
        )
        return rotationSoFar.rotate(self.initialDirection)

    def getVelocity(self, time):
        pos = self.getPosition(time)
        angVel = AngularVelocity(0, 0, self.earthAngVel)
        return angVel.crossProduct(pos)

    def applyLaunchTowerForce(self, state, time, unadjustedForce):
        '''
            If on launch tower, projects forces experienced onto the launch tower directions and sets Moments = 0
            Returns two values: onTower(Bool), adjustedForce(Motion.ForceMomentSystem)
        '''
        distanceTravelled = (state.position - self.getPosition(time)).length()
        if distanceTravelled < self.length:
            # Vehicle still on launch rail

            # Project total force onto the launch rail direction (dot product)
            adjustedForceMagnitude = unadjustedForce.force * self.getDirection(time)
            adjustedForceVector = self.initialDirection * adjustedForceMagnitude

            # No resultant moments while on the launch rail
            adjustedForce = ForceMomentSystem(adjustedForceVector)

            return adjustedForce
        else:
            # Vehicle has left the rail
            return unadjustedForce

    def applyLaunchTowerMotionConstraint(self, state, time):
        ''' If on launch tower, stops rocket from sliding off the bottom before engine is lit '''
        currPosition = self.getPosition(time)
        currDirection = self.getDirection(time)

        distanceTravelled = (state.position - currPosition) * currDirection
        if distanceTravelled < self.length:
            # Vehicle still on launch rail

            if distanceTravelled <= 0:
                # If vehicle has slid of the bottom of the rail
                # Reset its position to the bottom of the rail
                state.position = currPosition

                # Velocity adjustment
                velocityAlongRail = state.velocity * currDirection
                if velocityAlongRail < 0:
                    # If velocity along rail is also negative, set it to zero relative to the rail
                    state.velocity = self.getVelocity(time)

            return True, state
        else:
            # Vehicle has left the rail
            return False, state

Classes

class LaunchRail (initialPosition, initialDirection, length, earthRotationRate=0)

Provide initial position and direction in global inertial frame

Expand source code

class LaunchRail():
    def __init__(self, initialPosition, initialDirection, length, earthRotationRate=0):
        ''' Provide initial position and direction in global inertial frame '''
        self.initialPosition = initialPosition # m
        self.initialDirection = initialDirection.normalize() # Ensure the direction is a unit vector
        self.length = length # m
        self.earthAngVel = earthRotationRate # rad/s, about z-axis

    def getPosition(self, time):
        ''' Launch Rail moves with the earth's surface '''
        rotationSoFar = Quaternion(
            axisOfRotation=Vector(0,0,1), 
            angle=(self.earthAngVel * time)
        )
        return rotationSoFar.rotate(self.initialPosition)

    def getDirection(self, time):
        ''' Launch Rail moves with the earth's surface '''
        rotationSoFar = Quaternion(
            axisOfRotation=Vector(0,0,1), 
            angle=(self.earthAngVel * time)
        )
        return rotationSoFar.rotate(self.initialDirection)

    def getVelocity(self, time):
        pos = self.getPosition(time)
        angVel = AngularVelocity(0, 0, self.earthAngVel)
        return angVel.crossProduct(pos)

    def applyLaunchTowerForce(self, state, time, unadjustedForce):
        '''
            If on launch tower, projects forces experienced onto the launch tower directions and sets Moments = 0
            Returns two values: onTower(Bool), adjustedForce(Motion.ForceMomentSystem)
        '''
        distanceTravelled = (state.position - self.getPosition(time)).length()
        if distanceTravelled < self.length:
            # Vehicle still on launch rail

            # Project total force onto the launch rail direction (dot product)
            adjustedForceMagnitude = unadjustedForce.force * self.getDirection(time)
            adjustedForceVector = self.initialDirection * adjustedForceMagnitude

            # No resultant moments while on the launch rail
            adjustedForce = ForceMomentSystem(adjustedForceVector)

            return adjustedForce
        else:
            # Vehicle has left the rail
            return unadjustedForce

    def applyLaunchTowerMotionConstraint(self, state, time):
        ''' If on launch tower, stops rocket from sliding off the bottom before engine is lit '''
        currPosition = self.getPosition(time)
        currDirection = self.getDirection(time)

        distanceTravelled = (state.position - currPosition) * currDirection
        if distanceTravelled < self.length:
            # Vehicle still on launch rail

            if distanceTravelled <= 0:
                # If vehicle has slid of the bottom of the rail
                # Reset its position to the bottom of the rail
                state.position = currPosition

                # Velocity adjustment
                velocityAlongRail = state.velocity * currDirection
                if velocityAlongRail < 0:
                    # If velocity along rail is also negative, set it to zero relative to the rail
                    state.velocity = self.getVelocity(time)

            return True, state
        else:
            # Vehicle has left the rail
            return False, state

Methods

def applyLaunchTowerForce(self, state, time, unadjustedForce)

If on launch tower, projects forces experienced onto the launch tower directions and sets Moments = 0 Returns two values: onTower(Bool), adjustedForce(Motion.ForceMomentSystem)

Expand source code

def applyLaunchTowerForce(self, state, time, unadjustedForce):
    '''
        If on launch tower, projects forces experienced onto the launch tower directions and sets Moments = 0
        Returns two values: onTower(Bool), adjustedForce(Motion.ForceMomentSystem)
    '''
    distanceTravelled = (state.position - self.getPosition(time)).length()
    if distanceTravelled < self.length:
        # Vehicle still on launch rail

        # Project total force onto the launch rail direction (dot product)
        adjustedForceMagnitude = unadjustedForce.force * self.getDirection(time)
        adjustedForceVector = self.initialDirection * adjustedForceMagnitude

        # No resultant moments while on the launch rail
        adjustedForce = ForceMomentSystem(adjustedForceVector)

        return adjustedForce
    else:
        # Vehicle has left the rail
        return unadjustedForce

def applyLaunchTowerMotionConstraint(self, state, time)

If on launch tower, stops rocket from sliding off the bottom before engine is lit

Expand source code

def applyLaunchTowerMotionConstraint(self, state, time):
    ''' If on launch tower, stops rocket from sliding off the bottom before engine is lit '''
    currPosition = self.getPosition(time)
    currDirection = self.getDirection(time)

    distanceTravelled = (state.position - currPosition) * currDirection
    if distanceTravelled < self.length:
        # Vehicle still on launch rail

        if distanceTravelled <= 0:
            # If vehicle has slid of the bottom of the rail
            # Reset its position to the bottom of the rail
            state.position = currPosition

            # Velocity adjustment
            velocityAlongRail = state.velocity * currDirection
            if velocityAlongRail < 0:
                # If velocity along rail is also negative, set it to zero relative to the rail
                state.velocity = self.getVelocity(time)

        return True, state
    else:
        # Vehicle has left the rail
        return False, state

def getDirection(self, time)

Launch Rail moves with the earth's surface

Expand source code

def getDirection(self, time):
    ''' Launch Rail moves with the earth's surface '''
    rotationSoFar = Quaternion(
        axisOfRotation=Vector(0,0,1), 
        angle=(self.earthAngVel * time)
    )
    return rotationSoFar.rotate(self.initialDirection)

def getPosition(self, time)

Launch Rail moves with the earth's surface

Expand source code

def getPosition(self, time):
    ''' Launch Rail moves with the earth's surface '''
    rotationSoFar = Quaternion(
        axisOfRotation=Vector(0,0,1), 
        angle=(self.earthAngVel * time)
    )
    return rotationSoFar.rotate(self.initialPosition)

def getVelocity(self, time)

Expand source code

def getVelocity(self, time):
    pos = self.getPosition(time)
    angVel = AngularVelocity(0, 0, self.earthAngVel)
    return angVel.crossProduct(pos)