inertial3DSpin

Executive Summary

Module to compute the Inertial-3D spinning pointing navigation solution. This spin can be relative to an inertial frame or relative to an input reference frame message.

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
attRefOutMsg	AttRefMsgPayload	attitude reference output message
attRefInMsg	AttRefMsgPayload	(optional) attitude reference input message, if not connected then a zeroed input reference state is set

Module Description

This module generates an attitude reference frame state output message where the reference frame is rotating at a constant angular velocity vector relative to the input frame \(R_0\). If the input attitude frame message is not connected, then a zero’d input message is assumed.

The input reference frame \(R_0\) (user defined input message or default zero’d message) contains the state information in the form \(\pmb\sigma_{R_0/N}\), \(\pmb\omega_{R_0/N}\) and \(\dot{\pmb\omega}_{R_0/N}\). The constant spin vector is constant with respect to \(R_0\) and given by \({}^{R_0}{\pmb\omega}_{R/R0}\).

The angular velocity of the of the output reference frame \(R\) is then given by

\[\pmb \omega_{R/N} = \pmb\omega_{R/R_0} + \pmb\omega_{R_0/N}\]

As the spin vector \({}^{R_0}{\pmb\omega}_{R/R0}\) is constant with respect to \(R_0\), then the output frame angular acceleration is

\[\dot{\pmb\omega}_{R/N} = {\pmb\omega}_{R_0/N} \times {\pmb\omega}_{R/R0} + \dot{\pmb\omega}_{R_0/N}\]

Finally, the output frame MRP orientation is computed using

\[\dot{\pmb\sigma}_{R/N} = \frac{1}{4} [B(\pmb\sigma_{R/N})]\ {}^{R}{\pmb\omega}_{R/N}\]

where

\[[B(\pmb\sigma_{R/N})] = (1-\sigma_{R/N}^{2}) [I_{3\times 3}] + 2 [\tilde{\pmb\sigma}_{R/N}] + 2 \pmb\sigma_{R/N} \pmb\sigma_{R/N}^{T}\]

with \(\sigma_{R/N} = |\pmb\sigma_{R/N}|\).

User Guide

The only parameter that must be set is omega_RR0_R0 representing the \(R_0\)-constant spin axis \({}^{R_0}{\pmb\omega}_{R/R0}\).

Class Inertial3DSpin

class Inertial3DSpin : public SysModel

module configuration structure definition.

Public Functions

void reset(uint64_t callTime) override

This method performs a complete reset of the module. Local module variables that retain time varying states between function calls are reset to their default values.

Parameters:

callTime – The clock time at which the function was called (nanoseconds)

Returns:

void

void updateState(uint64_t callTime) override

This method performs all the main computations of the module

Parameters:

callTime – The clock time at which the function was called (nanoseconds)

Returns:

void

Public Members

double sigma_RN[3]

MPR of reference frame relative to inertial N frame

double omega_RR0_R0[3]

[r/s] constant angular velocity spin vector of the spinning R frame relative to the input frame R0

uint64_t priorTime

[ns] last time the guidance module is called

Message<AttRefMsgPayload> attRefOutMsg

reference attitude output message

ReadFunctor<AttRefMsgPayload> attRefInMsg

(optional) reference attitude input message

AttRefMsgPayload attRefOutBuffer

[-] structure for the output data

BSKLogger bskLogger = {}

BSK Logging.