Module: thrOnTimeToForce

Executive Summary

The thrOnTimeToForce module converts commanded thruster on times into thruster force outputs to be used in a MuJoCo simulation. If a new commanded on-time is received for a thruster that on-time replaces any remaining on-time for that thruster.

Note

This module uses a zero-order-hold approach to convert on-time commands to forces and is designed to be used with fixed thruster force magnitudes. This module additionally assumes that the on-time commands are built using some external logic and this module is not responsible for enforcing any minimum off-time or maximum duty cycle limits on the thrusters.

The module only latches a new on-time command when the input message has a new timeWritten value. If a Python user rewrites the command without advancing timeWritten (or only writes once and expects it to be interpreted as a new command later), the module treats it as stale and does not re-latch it.

Message Connection Descriptions

The following table lists all the module input and output messages. The module msg connection 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
onTimeInMsg	THRArrayOnTimeCmdMsgPayload	input on-time command array
thrusterForceOutMsgs	SingleActuatorMsgPayload	vector of thruster force output messages

User Guide

This section is to outline the steps needed to set up the thrOnTimeToForce module in Python using Basilisk.

Import the thrOnTimeToForce class:

from Basilisk.simulation import thrOnTimeToForce

Create an instance of thrOnTimeToForce:

module = thrOnTimeToForce.ThrOnTimeToForce()

set the fixed thruster force magnitudes for the module:
```
thrMag = [2.0, 3.0]
module.setThrMag(thrMag)
```
For each thruster in the system, add a thruster to the module:
```
module.addThruster()
```

Add the module to the task list:

sim.AddModelToTask(unitTaskName, module)

class ThrOnTimeToForce : public SysModel 

#include <thrOnTimeToForce.h>

Converts thruster on-time commands into per-thruster force messages.

Public Functions

ThrOnTimeToForce() = default: This is the constructor for the module class.

~ThrOnTimeToForce() = default: This is the destructor for the module class.

void Reset(uint64_t CurrentSimNanos): This method is used to reset the module and checks internal consistency.

void UpdateState(uint64_t CurrentSimNanos): This is the main method that gets called every time the module is updated. It decrements firing timers and writes one force command per thruster.

void setThrMag(const std::vector<double>&): setter for thrMag property

inline std::vector<double> getThrMag() const: getter for thrMag property

void addThruster(): method for adding a new thruster force output channel

Public Members

ReadFunctor<THRArrayOnTimeCmdMsgPayload> onTimeInMsg: input on-time command array

std::vector<Message<SingleActuatorMsgPayload>*> thrusterForceOutMsgs: vector of thruster force output messages

BSKLogger bskLogger: BSK Logging.

Private Members

int numThr = 0: number of thrusters

std::vector<double> thrMag: [N] fixed force magnitude for each thruster

std::vector<double> firingTimeRemaining: [s] remaining commanded firing time for each thruster

uint64_t prevCommandWriteNanos: [ns] last processed command message time stamp

double previousUpdateTimeSec: [s] previous module update time