Module: vscmgStateEffector

Executive Summary

This dynamic effector class implements a variable speed control moment gyroscope or VSCMG device.

The module PDF Description contains further information on this module’s function, how to run it, as well as testing.

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
cmdsInMsg	VSCMGArrayTorqueMsgPayload	motor torque command input message
speedOutMsg	VSCMGSpeedMsgPayload	VSCMG speed output message
vscmgOutMsgs	VSCMGConfigMsgPayload	vector of VSCMG output messages

User Guide

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

Import the vscmgStateEffector class:

from basilisk.simulation import vscmgStateEffector

create a default VSCMG function:

def defaultVSCMG():
  VSCMG = messaging.VSCMGConfigMsgPayload()
  VSCMG.rGB_B = [[0.],[0.],[0.]]
  VSCMG.gsHat0_B = [[0.],[0.],[0.]]
  VSCMG.gtHat0_B = [[0.],[0.],[0.]]
  VSCMG.ggHat_B = [[0.],[0.],[0.]]
  VSCMG.u_s_max = -1
  VSCMG.u_s_min = -1
  VSCMG.u_s_f = 0.
  VSCMG.wheelLinearFrictionRatio = -1
  VSCMG.u_g_current = 0.
  VSCMG.u_g_max = -1
  VSCMG.u_g_min = -1
  VSCMG.u_g_f = 0.
  VSCMG.gimbalLinearFrictionRatio = -1
  VSCMG.Omega = 0.
  VSCMG.gamma = 0.
  VSCMG.gammaDot = 0.
  VSCMG.Omega_max = 6000. * macros.RPM
  VSCMG.gammaDot_max = -1
  VSCMG.IW1 = 100./VSCMG.Omega_max
  VSCMG.IW2 = 0.5*VSCMG.IW1
  VSCMG.IW3 = 0.5*VSCMG.IW1
  VSCMG.IG1 = 0.1
  VSCMG.IG2 = 0.2
  VSCMG.IG3 = 0.3
  VSCMG.U_s = 4.8e-06 * 1e4
  VSCMG.U_d = 1.54e-06 * 1e4
  VSCMG.l = 0.01
  VSCMG.L = 0.1
  VSCMG.rGcG_G = [[0.0001],[-0.02],[0.1]]
  VSCMG.massW = 6.
  VSCMG.massG = 6.
  VSCMG.VSCMGModel = 0
  return VSCMG

Create a list to store the VSCMGs:
```
VSCMGs = []
```
Create a VSCMG and append it to the list:
```
VSCMGs.append(defaultVSCMG())
```

(Optional) Adjust the VSCMG parameters:

VSCMGs[0].gsHat0_B = [[1.0], [0.0], [0.0]]
VSCMGs[0].gtHat0_B = [[0.0], [1.0], [0.0]]
VSCMGs[0].ggHat_B = [[0.0], [0.0], [1.0]]
VSCMGs[0].Omega = 2000 * macros.RPM
VSCMGs[0].gamma = 0.
VSCMGs[0].gammaDot = 0.06
VSCMGs[0].rGB_B = [[0.1], [0.002], [-0.02]]

(Optional) Create additional VSCMGs and append them to the list:

ang = 54.75 * np.pi/180
VSCMGs.append(defaultVSCMG())
VSCMGs[1].gsHat0_B = [[0.0], [1.0], [0.0]]
VSCMGs[1].ggHat_B = [[math.cos(ang)], [0.0], [math.sin(ang)]]
VSCMGs[1].gtHat0_B = np.cross(np.array([math.cos(ang), 0.0, math.sin(ang)]),np.array([0.0, 1.0, 0.0]))
VSCMGs[1].Omega =  350 * macros.RPM
VSCMGs[1].gamma = 0.
VSCMGs[1].gammaDot = 0.011
VSCMGs[1].rGB_B = [[0.0], [-0.05], [0.0]]

VSCMGs.append(defaultVSCMG())
VSCMGs[2].gsHat0_B = [[0.0], [-1.0], [0.0]]
VSCMGs[2].ggHat_B = [[-math.cos(ang)], [0.0], [math.sin(ang)]]
VSCMGs[2].gtHat0_B = np.cross(np.array([-math.cos(ang), 0.0, math.sin(ang)]),np.array([0.0, -1.0, 0.0]))
VSCMGs[2].Omega = -900 * macros.RPM
VSCMGs[2].gamma = 0.
VSCMGs[2].gammaDot = -0.003
VSCMGs[2].rGB_B = [[-0.1], [0.05], [0.05]]

Create an instantiation of the VSCMGs::
vscmgStateEffector = vscmgStateEffector.VSCMGStateEffector()

Add the VSCMGs to the vscmgStateEffector:

for item in VSCMGs:
  vscmgStateEffector.AddVSCMG(item)

The VSCMG angular states output message is speedOutMsg.
The configuration of the VSCMG is created using an output vector of messages vscmgOutMsgs.

Add the effector to your spacecraft:

scObject.addStateEffector(vscmgStateEffector)

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

Create the VSCMG torque command input message:

cmdArray = messaging.VSCMGArrayTorqueMsgPayload()

Set the torque command for each VSCMG in the array:

cmdArray.wheelTorque = [0.0, 0.0, 0.0]  # [Nm]
cmdArray.gimbalTorque = [0.0, 0.0, 0.0]  # [Nm]

Write the command message:

cmdMsg = messaging.VSCMGArrayTorqueMsg().write(cmdArray)

Subscribe the vscmgStateEffector to the command message:
```
vscmgStateEffector.cmdsInMsg.subscribeTo(cmdMsg)
```

Add the module to the task list:

unitTestSim.AddModelToTask(unitTaskName, vscmgStateEffector)

class VSCMGStateEffector : public SysModel, public StateEffector 

#include <vscmgStateEffector.h>

VSCMG state effector class.

Public Functions

VSCMGStateEffector()

~VSCMGStateEffector()

void registerStates(DynParamManager &states)

void linkInStates(DynParamManager &states)

void updateEffectorMassProps(double integTime)

void Reset(uint64_t CurrentSimNanos): Reset the module to origina configuration values.

void AddVSCMG(VSCMGConfigMsgPayload *NewVSCMG)

This method allows VSCMG devices to be added to this effector

Parameters:: NewVSCMG – VSCMG device to be added

void UpdateState(uint64_t CurrentSimNanos)

This method is the main cyclical call for the scheduled part of the VSCMG dynamics model. It reads the current commands array and sets the VSCMG configuration data based on that incoming command set. Note that the main dynamical method (ComputeDynamics()) is not called here and is intended to be called from the dynamics plant in the system

Parameters:: CurrentSimNanos – The current simulation time in nanoseconds

void WriteOutputMessages(uint64_t CurrentClock)

This method is here to write the output message structure into the specified message.

Parameters:: CurrentClock – The current time used for time-stamping the message

void ReadInputs(): This method is used to read the incoming command message and set the associated command structure for operating the VSCMGs.

void ConfigureVSCMGRequests(double CurrentTime)

This method is used to read the new commands vector and set the VSCMG torque commands appropriately. It assumes that the ReadInputs method has already been run successfully.

Parameters:: CurrentTime – The current simulation time converted to a double

void updateContributions(double integTime, BackSubMatrices &backSubContr, Eigen::Vector3d sigma_BN, Eigen::Vector3d omega_BN_B, Eigen::Vector3d g_N): [-] Back-sub contributions

void updateEnergyMomContributions(double integTime, Eigen::Vector3d &rotAngMomPntCContr_B, double &rotEnergyContr, Eigen::Vector3d omega_BN_B): [-] Energy and momentum calculations

void computeDerivatives(double integTime, Eigen::Vector3d rDDot_BN_N, Eigen::Vector3d omegaDot_BN_B, Eigen::Vector3d sigma_BN): [-] Method for each stateEffector to calculate derivatives

Public Members

std::vector<VSCMGConfigMsgPayload> VSCMGData: [-] VSCMG data structure

Eigen::MatrixXd *g_N: [m/s^2] Gravitational acceleration in N frame components

ReadFunctor<VSCMGArrayTorqueMsgPayload> cmdsInMsg: [-] motor torque command input message

Message<VSCMGSpeedMsgPayload> speedOutMsg: [-] VSCMG speed output message

std::vector<Message<VSCMGConfigMsgPayload>*> vscmgOutMsgs: [-] vector of VSCMG output messages

std::vector<VSCMGCmdMsgPayload> newVSCMGCmds: [-] Incoming torque commands

VSCMGSpeedMsgPayload outputStates: [-] Output data from the VSCMGs

std::string nameOfVSCMGOmegasState: [-] identifier for the Omegas state data container

std::string nameOfVSCMGThetasState: [-] identifier for the Thetas state data container

std::string nameOfVSCMGGammasState: [-] identifier for the Gammas state data container

std::string nameOfVSCMGGammaDotsState: [-] identifier for the GammaDots state data container

int numVSCMG: [-] number of VSCMGs

int numVSCMGJitter: [-] number of VSCMGs with jitter

BSKLogger bskLogger: [-] BSK Logging

Private Members

VSCMGArrayTorqueMsgPayload incomingCmdBuffer: [-] One-time allocation for savings

uint64_t prevCommandTime: [-] Time for previous valid thruster firing

StateData *hubOmega: [rad/s] angular velocity of the B frame wrt the N frame in B frame components

StateData *OmegasState: [rad/s] RW spin state

StateData *thetasState: [rad] RW angle

StateData *gammasState: [rad] CMG gimbal angle

StateData *gammaDotsState: [rad/s] CMG gimbal angle rate