Module: linearTranslationOneDOFStateEffector

Executive Summary

The linear translation body class is an instantiation of the state effector abstract class. The integrated test is validating the interaction between the linear translation body module and the rigid body hub that it is attached to. In this case, a 1-DoF linear translation body has an inertia tensor and is attached to the hub by a single degree of freedom axis. The spinning axis is fixed in the body frame and the effector is rigid, which means that its center of mass location does not move in the F frame. An optional motor force can be applied on the spinning axis, and the user can also lock the axis through a command.

Message Connection Descriptions

The following table lists all the module input and output messages. The module msg variable name is set by the user from python. The msg type contains a link to the message structure definition, while the description provides information on what this message is used for.

Module I/O Messages

Msg Variable Name

Msg Type

Description

translatingBodyOutMsg

LinearTranslationRigidBodyMsgPayload

Output message containing the linear translation body state displacement and displacement rate

motorForceInMsg

ArrayMotorForceMsgPayload

(Optional) Input message of the motor force value

motorLockInMsg

ArrayEffectorLockMsgPayload

(Optional) Input message for locking the axis

translatingBodyRefInMsg

LinearTranslationRigidBodyMsgPayload

(Optional) Input message for prescribing the displacement and displacement rate

translatingBodyConfigLogOutMsg

SCStatesMsgPayload

Output message containing the translating body inertial position and attitude states

Detailed Module Description

A 1 DoF translating body has 2 states: rho and rhoDot. The displacemet and displacement rate can change due to the interaction with the hub, but also because of applied forces (control, spring and damper). The displacement remains fixed and the displacement rate is set to zero when the axis is locked.

Mathematical Modeling

See the following tech report for a detailed description of this model.

Note

P. Johnson and J. Vaz Carneiro, “Single Axis Translating Effector,” Technical Note, University of Colorado, Autonomous Vehicle Systems (AVS) Lab, Boulder, CO, March 9, 2024.

User Guide

This section is to outline the steps needed to setup a Translating Body State Effector in Python using Basilisk.

  1. Import the linearTranslatingBodyOneDOFStateEffector class:

    from Basilisk.simulation import linearTranslatingBodyOneDOFStateEffector

  2. Create an instantiation of a Translating body:

    translatingBody = linearTranslatingBodyOneDOFStateEffector.linearTranslatingBodyOneDOFStateEffector()

  3. Define all physical parameters for a Translating Body. For example:

    translatingBody.setMass(20.0)
translatingBody.setFHat_B([[3.0 / 5.0], [4.0 / 5.0], [0.0]])
translatingBody.setR_FcF_F([[-1.0], [1.0], [0.0]])
translatingBody.setR_F0B_B([[-5.0], [4.0], [3.0]])
translatingBody.setIPntFc_F([[50.0, 0.0, 0.0],
                             [0.0, 80.0, 0.0],
                             [0.0, 0.0, 60.0]])
translatingBody.setDCM_FB([[0.0, -1.0, 0.0],
                           [0.0, 0.0, -1.0],
                           [1.0, 0.0, 0.0]])

  4. (Optional) Define initial conditions of the effector. Default values are zero states:

    translatingBody.setRhoInit(1.0)
translatingBody.setRhoDotInit(0.05)

  5. (Optional) Define spring and damper coefficients. Default values are zero:

    translatingBody.setK(100.0)
translatingBody.setC(0.0)

  6. (Optional) Define a unique name for each state. If you have multiple translating bodies, they each must have a unique name. If these names are not specified, then the default names are used which are incremented by the effector number:

    translatingBody.nameOfThetaState = "translatingBodyRho"
translatingBody.nameOfThetaDotState = "translatingBodyRhoDot"

  7. (Optional) Connect a command force message:

    cmdArray = messaging.ArrayMotorForceMsgPayload()
cmdArray.motorForce = [cmdForce]  # [Nm]
cmdMsg = messaging.ArrayMotorForceMsg().write(cmdArray)
translatingBody.motorForceInMsg.subscribeTo(cmdMsg)

  8. (Optional) Connect an axis-locking message (0 means the axis is free to move and 1 locks the axis):

    lockArray = messaging.ArrayEffectorLockMsgPayload()
lockArray.effectorLockFlag = [1]
lockMsg = messaging.ArrayEffectorLockMsg().write(lockArray)
translatingBody.motorLockInMsg.subscribeTo(lockMsg)

  9. (Optional) Connect a displacement and displacement rate reference message:

    translationRef = messaging.LinearTranslationRigidBodyMsgPayload()
translationRef.rho = 0.2
translationRef.rhoDot = 0.0
translationRefMsg = messaging.LinearTranslationRigidBodyMsg().write(translationRef)
translatingBody.translatingBodyRefInMsg.subscribeTo(translationRefMsg)

  10. The linear states of the body are created using an output message translatingBodyOutMsg.

  11. The translating body config log state output message is translatingBodyConfigLogOutMsg.

  12. Add the effector to your spacecraft:

    scObject.addStateEffector(translatingBody)

    See Module: spacecraft documentation on how to set up a spacecraft object.

  13. Add the module to the task list:

    unitTestSim.AddModelToTask(unitTaskName, translatingBody)
class linearTranslationOneDOFStateEffector : public StateEffector, public SysModel
#include <linearTranslationOneDOFStateEffector.h>

linear spring mass damper state effector class

Public Functions

linearTranslationOneDOFStateEffector()

Constructor.

~linearTranslationOneDOFStateEffector()

Destructor.

void setMass(double mass)

setter for mass property

void setK(double k)

setter for k property

void setC(double c)

setter for c property

inline void setRhoInit(double rhoInit)

setter for rhoInit property

inline void setRhoDotInit(double rhoDotInit)

setter for rhoDotInit property

void setFHat_B(Eigen::Vector3d fHat_B)

setter for fHat_B property

inline void setR_FcF_F(Eigen::Vector3d r_FcF_F)

setter for r_FcF_F property

inline void setR_F0B_B(Eigen::Vector3d r_F0B_B)

setter for r_F0B_B property

inline void setIPntFc_F(Eigen::Matrix3d IPntFc_F)

setter for IPntFc_F property

inline void setDCM_FB(Eigen::Matrix3d dcm_FB)

setter for dcm_FB property

inline double getMass() const

setter for mass property

inline double getK() const

setter for k property

inline double getC() const

setter for c property

inline double getRhoInit() const

setter for rhoInit property

inline double getRhoDotInit() const

setter for rhoDotInit property

inline Eigen::Vector3d getFHat_B() const

setter for fHat_B property

inline Eigen::Vector3d getR_FcF_F() const

setter for r_FcF_F property

inline Eigen::Vector3d getR_F0B_B() const

setter for r_F0B_B property

inline Eigen::Matrix3d getIPntFc_F() const

setter for IPntFc_F property

inline Eigen::Matrix3d getDCM_FB() const

setter for dcm_FB property

Public Members

Message<LinearTranslationRigidBodyMsgPayload> translatingBodyOutMsg

state output message

Message<SCStatesMsgPayload> translatingBodyConfigLogOutMsg

translating body state config log message

ReadFunctor<ArrayMotorForceMsgPayload> motorForceInMsg

(optional) motor force input message

ReadFunctor<LinearTranslationRigidBodyMsgPayload> translatingBodyRefInMsg

(optional) reference state input message

ReadFunctor<ArrayEffectorLockMsgPayload> motorLockInMsg

(optional) lock flag input message

Private Functions

void Reset(uint64_t CurrentClock) override
void registerStates(DynParamManager &states) override
void linkInStates(DynParamManager &states) override
void writeOutputStateMessages(uint64_t CurrentSimNanos) override
void updateEffectorMassProps(double integTime) override
void updateContributions(double integTime, BackSubMatrices &backSubContr, Eigen::Vector3d sigma_BN, Eigen::Vector3d omega_BN_B, Eigen::Vector3d g_N) override
void updateEnergyMomContributions(double integTime, Eigen::Vector3d &rotAngMomPntCContr_B, double &rotEnergyContr, Eigen::Vector3d omega_BN_B) override
void computeDerivatives(double integTime, Eigen::Vector3d rDDot_BN_N, Eigen::Vector3d omegaDot_BN_B, Eigen::Vector3d sigma_BN) override
void UpdateState(uint64_t CurrentSimNanos) override
void computeTranslatingBodyInertialStates()
void computeBackSubContributions(BackSubMatrices &backSubContr, const Eigen::Vector3d &F_g)
void readInputMessages()

Private Members

double mass = 1.0

[kg] mass of effector

double k = 0

[N/m] linear spring constant

double c = 0

[N-s/m] linear damping term

double rhoInit = 0

[m] initial displacement offset

double rhoDotInit = 0

[m/s] Initial displacement rate offset

Eigen::Vector3d fHat_B = {1.0, 0.0, 0.0}

unit vector axis of translation in B frame components.

Eigen::Vector3d r_FcF_F = Eigen::Vector3d::Zero()

[m] vector pointing from location F to FC in F frame components

Eigen::Vector3d r_F0B_B = Eigen::Vector3d::Zero()

[m] vector pointing from body frame B origin to point to F0 origin of F frame in B frame components

Eigen::Matrix3d IPntFc_F = Eigen::Matrix3d::Identity()

[kg-m^2] Inertia of pc about point Fc in F frame component

Eigen::Matrix3d dcm_FB = Eigen::Matrix3d::Identity()

DCM from the F frame to the body frame.

std::string nameOfRhoState = {}

Identifier for the rho state data container.

std::string nameOfRhoDotState = {}

Identifier for the rhoDot state data container.

bool isAxisLocked = false

flag for locking the translation axis

double rho = 0.0

[m] displacement from equilibrium

double rhoDot = 0.0

[m/s] time derivative of displacement from equilibrium

double rhoRef = 0.0

[m] translating body reference position

double rhoDotRef = 0.0

[m/s] translating body reference velocity

double motorForce = 0.0

[N] optional motor force

Eigen::Vector3d r_FcB_B = Eigen::Vector3d::Zero()

[m] position vector from B to center of mass location of effector

Eigen::Vector3d r_FcF0_B = Eigen::Vector3d::Zero()

[m] vector pointing from point p0 origin of F frame to center of mass location of effector in B frame components

Eigen::Matrix3d rTilde_FcF_B = Eigen::Matrix3d::Zero()

[m] tilde matrix of r_FcF_B

Eigen::Vector3d rPrime_FcF_B = Eigen::Vector3d::Zero()

[m/s] Body time derivative of r_FcF_B

Eigen::Matrix3d rPrimeTilde_FcF_B = Eigen::Matrix3d::Zero()

[m/s] Tilde matrix of rPrime_FcF_B

Eigen::Matrix3d rTilde_FcB_B = Eigen::Matrix3d::Zero()

[m] tilde matrix of r_FcB_B

Eigen::Vector3d rPrime_FcB_B = Eigen::Vector3d::Zero()

[m/s] Body time derivative of r_FcB_B

Eigen::Matrix3d rPrimeTilde_FcB_B = Eigen::Matrix3d::Zero()

[m/s] Tilde matrix of rPrime_FcB_B

Eigen::Matrix3d IPntFc_B = Eigen::Matrix3d::Identity()

[kg-m^2] Inertia of Fc about point B in B frame components

Eigen::Matrix3d dcm_BN = Eigen::Matrix3d::Identity()

DCM from the B frame to the N frame.

Eigen::Vector3d omega_BN_B = Eigen::Vector3d::Zero()

[rad/s] angular velocity of the B frame wrt the N frame in B frame components.

Eigen::Matrix3d omegaTilde_BN_B = Eigen::Matrix3d::Zero()

[rad/s] tilde matrix of omega_BN_B

Eigen::Vector3d aRho = Eigen::Vector3d::Zero()

Term needed for back-sub method.

Eigen::Vector3d bRho = Eigen::Vector3d::Zero()

Term needed for back-sub method.

double cRho = 0.0

Term needed for back-sub method.

StateData *rhoState = nullptr

state data for displacement from equilibrium

StateData *rhoDotState = nullptr

state data for time derivative of rho;

Eigen::MatrixXd *g_N = nullptr

[m/s^2] gravitational acceleration in N frame components

Eigen::MatrixXd *inertialPositionProperty = nullptr

[m] r_N inertial position relative to system spice zeroBase/refBase

Eigen::MatrixXd *inertialVelocityProperty = nullptr

[m] v_N inertial velocity relative to system spice zeroBase/refBase

Eigen::Vector3d r_FcN_N = Eigen::Vector3d::Zero()

[m] position vector of translating body’s center of mass Fc relative to the inertial frame origin N

Eigen::Vector3d v_FcN_N = Eigen::Vector3d::Zero()

[m/s] inertial velocity vector of Fc relative to inertial frame

Eigen::Vector3d sigma_FN = Eigen::Vector3d::Zero()

MRP attitude of frame F relative to inertial frame.

Eigen::Vector3d omega_FN_F = Eigen::Vector3d::Zero()

[rad/s] inertial translating body frame angular velocity vector

Private Static Attributes

static uint64_t effectorID = 1

ID number of this panel.