Module: spiceInterface

Executive Summary

The SPICE interface class gets time and planetary or spacecraft body information from the JPL ephemeris library

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 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
spiceTimeOutMsg	SpiceTimeMsgPayload	spice time sampling output message
epochInMsg	EpochMsgPayload	(optional) input epoch message
planetStateOutMsgs	SpicePlanetStateMsgPayload	vector of planet state output messages
scStateOutMsgs	SCStatesMsgPayload	vector of spacecraft state messages
attRefStateOutMsgs	AttRefMsgPayload	vector of spacecraft attitude reference state output messages
transRefStateOutMsgs	TransRefMsgPayload	vector of spacecraft translation reference state output messages

User Guide

This module uses the JPL Spice software to determine the position and orientation of both a celestial body, or a spacecraft. The appropriate Spice kernel must be loaded up to provide the state information for the selected body names.

To setup a celestial body, use the module method addPlanetNames(vector<string>) in python. Multiple object names can be provided by providing a list of names. With each module update cycle, the corresponding celestial body states are provided in the vector of output messages planetStateOutMsgs[]. Note that the vector elements are in the order that the celestial body names were added.

To use this module to read in spacecraft states from a spice kernel, then the spacecraft Spice name is added using the method addSpacecraftNames(vector<string>). The module provides a vector out corresponding spacecraft state output messages in three different formats.

scStateOutMsgs[]: these are the SCStatesMsgPayload state output messages that the Module: spacecraft module provides
attRefStateOutMsgs[]: these are the attitude reference messages AttRefMsgPayload. These are useful to only prescribe the spacecraft attitude motion.
transRefStateOutMsgs[]: these are the translational reference message TransRefMsgPayload. These are useful to only prescribe the translational motion and leave the attitude motion free.

class SpiceInterface : public SysModel 

#include <spiceInterface.h>

spice interface class

Public Functions

SpiceInterface(): This constructor initializes the variables that spice uses. Most of them are not intended to be changed, but a couple are user configurable.

~SpiceInterface(): The only needed activity in the destructor is to delete the spice I/O buffer that was allocated in the constructor

void UpdateState(uint64_t CurrentSimNanos)

This method is the interface point between the upper level simulation and the SPICE interface at runtime. It calls all of the necessary lower level methods.

Parameters:: CurrentSimNanos – The current clock time for the simulation
Returns:: void

int loadSpiceKernel(char *kernelName, const char *dataPath)

This method loads a requested SPICE kernel into the system memory. It is its own method because we have to load several SPICE kernels in for our application. Note that they are stored in the SPICE library and are not held locally in this object.

Parameters:

kernelName – The name of the kernel we are loading
dataPath – The path to the data area on the filesystem

Returns:

int Zero for success one for failure

int unloadSpiceKernel(char *kernelName, const char *dataPath)

This method unloads a requested SPICE kernel into the system memory. It is its own method because we have to load several SPICE kernels in for our application. Note that they are stored in the SPICE library and are not held locally in this object.

Parameters:

kernelName – The name of the kernel we are unloading
dataPath – The path to the data area on the filesystem

Returns:

int Zero for success one for failure

std::string getCurrentTimeString(): class method

void Reset(uint64_t CurrentSimNanos)

Reset the module to origina configuration values.

Returns:: void

void initTimeData()

This method is used to initialize the zero-time that will be used to calculate all system time values in the Update method. It also creates the output message for time data

Returns:: void

void computeGPSData()

This method computes the GPS time data for the current elapsed time. It uses the total elapsed times at both the GPS epoch time and the current time to compute the GPS time (week, seconds, rollovers)

Returns:: void

void pullSpiceData(std::vector<SpicePlanetStateMsgPayload> *spiceData)

This method gets the state of each spice item that has been added to the module and saves the information off into the array.

Returns:: void

void writeOutputMessages(uint64_t CurrentClock)

This method takes the values computed in the model and outputs them. It packages up the internal variables into the output structure definitions and puts them out on the messaging system

Parameters:: CurrentClock – The current simulation time (used for time stamping)
Returns:: void

void clearKeeper(): class method

void addPlanetNames(std::vector<std::string> planetNames): take a vector of planet name strings and create the vector of planet state output messages and the vector of planet state message payloads

void addSpacecraftNames(std::vector<std::string> spacecraftNames): take a vector of spacecraft name strings and create the vectors of spacecraft state output messages and the vector of spacecraft state message payloads

Public Members

Message<SpiceTimeMsgPayload> spiceTimeOutMsg: spice time sampling output message

ReadFunctor<EpochMsgPayload> epochInMsg: (optional) input epoch message

std::vector<Message<SpicePlanetStateMsgPayload>*> planetStateOutMsgs: vector of planet state output messages

std::vector<Message<SCStatesMsgPayload>*> scStateOutMsgs: vector of spacecraft state output messages

std::vector<Message<AttRefMsgPayload>*> attRefStateOutMsgs: vector of spacecraft attitude reference state output messages

std::vector<Message<TransRefMsgPayload>*> transRefStateOutMsgs: vector of spacecraft translational reference state output messages

std::string SPICEDataPath: — Path on file to SPICE data

std::string referenceBase: — Base reference frame to use

std::string zeroBase: — Base zero point to use for states

std::string timeOutPicture: — Optional parameter used to extract time strings

bool SPICELoaded: — Boolean indicating to reload spice

int charBufferSize: — avert your eyes we’re getting SPICE

uint8_t *spiceBuffer: — General buffer to pass down to spice

std::string UTCCalInit: — UTC time string for init time

std::vector<std::string> planetFrames: — Optional vector of planet frame names. Default values are IAU_ + planet name

bool timeDataInit: — Flag indicating whether time has been init

double J2000ETInit: s Seconds elapsed since J2000 at init

double J2000Current: s Current J2000 elapsed time

double julianDateCurrent: s Current JulianDate

double GPSSeconds: s Current GPS seconds

uint16_t GPSWeek: — Current GPS week value

uint64_t GPSRollovers: — Count on the number of GPS rollovers

BSKLogger bskLogger: — BSK Logging

Private Members

std::string GPSEpochTime: — String for the GPS epoch

double JDGPSEpoch: s Epoch for GPS time. Saved for efficiency

std::vector<SpicePlanetStateMsgPayload> planetData

std::vector<SpicePlanetStateMsgPayload> scData