Module: spaceToGroundTransmitter

Executive Summary

This module provides a model of access-dependent data downlink from a simple transmitter at a fixed baud rate. Specifically, the transmitter reads a DataStorageStatusMsgPayload from the storage unit it is subscribed to, searches for the data buffer with the maximum amount of data, and downlinks a packet of data at a fixed baud rate. The transmitter writes out a DataNodeUsageMsgPayload describing the data name and baud rate of the data it wants to downlink.

In comparison to Module: simpleTransmitter, downlink is only enabled when a AccessMsgPayload indicates that the spacecraft for which the transmitter is associated has access to an object that can provide it (such as a Module: groundLocation.)

For more information on how to set up and use this module, see the simple data system example: scenarioDataDemo

Module Assumptions and Limitations

This module makes no additional assumptions outside of those already made in the Module: dataNodeBase base class.

Message Connection Descriptions

This module uses the input and output messages of the Module: dataNodeBase base class, plus an additional DataStorageStatusMsgPayload input message subscribed to and read customRead() method.

Module I/O Messages

Msg Variable Name	Msg Type	Description
storageUnitInMsgs	DataStorageStatusMsgPayload	Vector of storage units that are connected to the transmitter. Add storage unit with the addStorageUnitToTransmitter method.
groundAccessInMsgs	AccessMsgPayload	Vector of access messages available to the transmitter. Add input messages with the addAccessMsgToTransmitter method.

User Guide

This module inherits the user guide from the Module: dataNodeBase base class, but there are several key differences from other Module: dataNodeBase child classes:

• Unlike other child classes of Module: dataNodeBase, this module does not require a user to set a nodeDataName

• The nodeBaudRate variable should be set to a negative value in order to remove data from the storage unit.

• The user must specify a packetSize variable (negative value) in addition to the nodeBaudRate variable

• The user must specify the number of buffers numBuffers variable so the transmitter knows how many buffers to search through

• The user must specify the storage unit the transmitter should subscribe to using the addStorageUnitToTransmitter()` method

To set up this module users must create a SimpleTransmitter instance:

transmitter = spaceToGroundTransmitter.SpaceToGroundTransmitter()
transmitter.ModelTag = "transmitter"

Set the nodeBaudRate, packetSize, and numBuffers variables:

transmitter.nodeBaudRate = -16000. # baud
transmitter.packetSize = -1E6 # bits
transmitter.numBuffers = 2

The next step is to attach one or more DataStorageStatusMsgPayload instances to it using the addStorageUnitToTransmitter() method:

transmitter.addStorageUnitToTransmitter(storageMsg)

Next, attach available AccessMsgPayload instances using the addAccessMsgToTransmitter() method:

transmitter.addAccessMsgToTransmitter(accessMsg)

The final step is to add the model to task:

scenarioSim.AddModelToTask(taskName, transmitter)

Follow the Module: partitionedStorageUnit or Module: simpleStorageUnit instructions to add the transmitter to a storage unit.

For more information on how to set up and use this module, see the simple data system example: scenarioDataDemo

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class SpaceToGroundTransmitter : public DataNodeBase

#include <spaceToGroundTransmitter.h>

space to ground data transmitter class

Public Functions

SpaceToGroundTransmitter()

Constructor, which sets the default nodeDataOut to zero.

~SpaceToGroundTransmitter()

void addStorageUnitToTransmitter(Message<DataStorageStatusMsgPayload> *tmpStorageUnitMsg)

Adds a dataStorageStatusMsgPayload name to be accessed by transmitter.

Parameters

tmpStorageUnitMsg – A spacecraft state message name.

Returns

void

void addAccessMsgToTransmitter(Message<AccessMsgPayload> *tmpAccessMsg)

Adds a msg name to ground location access list

Parameters

tmpAccessMsg – input name.

Returns

void

Public Members

double packetSize

Size of packet to downklink (bytes)

int numBuffers

Number of buffers the transmitter can access.

std::vector<ReadFunctor<DataStorageStatusMsgPayload>> storageUnitInMsgs

vector of input messages for storage unit messages

std::vector<ReadFunctor<AccessMsgPayload>> groundLocationAccessInMsgs

vector of input message for ground location access

std::vector<DataStorageStatusMsgPayload> storageUnitMsgsBuffer

local copy of data storage messages

uint64_t hasAccess

class variable

BSKLogger bskLogger

class variable

Private Functions

void evaluateDataModel(DataNodeUsageMsgPayload *dataUsageMsg, double currentTime)

Loads the nodeDataOut attribute into the dataUsageMessagePayload instance.

Parameters

• dataUsageSimMsg –

• currentTime –

bool customReadMessages()

Private Members

double packetTransmitted

Amount of packet downlinked (bytes)

double currentTimestep

Current timestep tracked for data packet integration.

double previousTime

Previous timestep tracked for data packet integration.

std::vector<AccessMsgPayload> groundLocationAccessMsgs

local copy of ground access messages