COMMAND AND DATA HANDLING

Instructor: Roy C. HsuComputer Science and Information

Engineering DepartmentNational Chia-Yi University

11/24/2005

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OUTLINE

IntroductionCommand SystemsTelemetry SystemsData Processing and Storage Cases Study

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INTRODUCTION

Command and Telemetryproviding information to and from the spacecraft, respectivelycomputer-based components in the spacecraft (S/C) and at terrestrial sitescommands are used to provide the info to change the state of the S/C subsystems and to set to S/C clocktelemetry subsystem collects and processes a variety of data to be transmitted from the S/C

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INTRODUCTION (Cont.)

Data Processing and Handling3 major tasks on board

to help control and configure the S/Cto optimize the overall system performanceto process data for transmission

a major onboard processor and possibly multiple dedicated processors for various subsystems are used to enhance S/C performance and reliability.ROM and RAM are used with RAM changeable through the command systemS/C data storage media: flash memory, SSR, etc software written in machine, assembly, or high level language I/O and other peripherals

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COMMAND SYSTEMS

Purposeto permit the spacecraft or its subsystem to be reconfigured in response to radio signals send up to the S/C from ground

Operationreceive the signals, decide what they mean, and then respond accordingly so that the desired reconfiguration takes place

The command system has a vital role in the overall operation of the S/C

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GENERALIZED SPACECRAFT COMMAND SYSTEM

Receiver/Demodulator

Command Decoder

CommandLogic

Interface Circuitry

Block Diagram of a generalized command system

Receiver/Demodulator: amplify the signal captured, demodulate the command (cmd) message, deliver the encoded subcarrier signalmessage to the cmd decoderCommand Decoder: decode the message to reproduce the original cmd message, which consists of a serial digital binary of 1s’ & 0s’

Command Logic: validate the cmd message, drive the I/F circuitryby executing the cmd

Interface Circuitry: might be simple or complex functions

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COMPLETE COMMAND SYSTEM

Ground Support

Equipment

Radio Frequency

Link

SpacecraftCommand

SystemModulation

Block Diagram of a complete command system

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SYSTEM REQUIREMENTS

S/C MISSION

S/C ORBIT/TRAJECTORY

GROUND STATION

LINK ANALYSIS/COVERAGE

COMMAND LOGIC

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TELEMETRY SYSTEMS

Telemeter: to measure from a distanceFunctions: to provide remote indication of what the desired measurements areTelemetry data:

Status data - S/C resources, health, attitude, operation modeScientific data gathered by onboard sensor-magnetometers, thermometers, etc…Specific S/C orbit and timing data – used for guidance and navigation by ground, sea or air vehiclesImage data - captured by onboard cameraOther data - locations of other objects, relayed telemetry data from other satellites

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SPACECRAFT TELEMETRY SYSTEM

ACQUISITION

SensorsConditioners

SelectorsConverters

PROCESSING

CompressorsFormatters

Storage

TRANSMISSION

EncoderModulator

TransmitterAntenna

Block Diagram of a spacecraft telemetry system

Acquisition: The acquisition of data is accomplished using sensors, signal conditioners, data selectors and A/D converters.

Processing: The data are processed in the telemetry system processor or in the smart sensor instrument’s resident processor.Transmission: as discussed in TT&C

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TELEMETRY SYSTEM OF GROUND SEGMENT

RECEIPT

AntennaReceiver

DemodulatorDecoder

PROCESSING

De-compressorTranslatorStorage

DELIVERY

DisplayPrinterPlotter

Block Diagram of a ground segment telemetry system

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SPACECRAFT DATA HANDLING

Spacecraft data processing and storage require the use of space-qualified microcomputers, memories, and interface devices. Unlike the devices that are used in desk-top PC, S/C applications impose design constrains that are much more severe.Low power dissipation, volume, and mass must be achieved without sacrificing overall performance. S/C systems must exhibit excellent reliability and should be able to tolerate many kind of faults.

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SPACECRAFT DATA HANDLING SYSTEM

CENTRAL PROCESSING

UNIT

PROCESSOR DATA BUS

INPUT/OUTPUTPORTS

BUSINTERFACE

MEMORY:ROM, RAM,

Special-purpose

MASS STORAGE

SPACECRAFT DATA BUS

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CENTRAL PROCESSING UNIT

One or more processing units have access to various kinds of memory, mass storage, and input/output devicesJob of the processing unit

execute the program that is stored in memory, interpret and execute commands received from the S/C command system.maintain system status and health data (housekeeping data) and format the data for transmission to the S/C telemetry system.

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CENTRAL PROCESSING UNIT (cont.)

The processing unit receives its instructions from a program stored in memory and communicates with its data sensors and other processors in the S/C through various kinds of I/O channels or over the S/C data bus.The processing unit may elect to delegate some of its tasks to special purpose peripheral processors that then execute the delegated subtasks in parallel with the execution of its own tasks.

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FLIGHT SOFTWARE DEVELOPMENT

Code development for embedded real-time processor using assembly and high-level language.The program must be error-free for the S/C data handling system.Employing computer science to design and implement the algorithms and data structure.Applying software engineering approach to the design and maintenance of the software product.

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FLIGHT SOFTWARE DEVELOPMENT (cont.)

The quality of the up-front conceptual design of the flight software will determine the success of software engineering.The problem introduced early in the design phase will be the most expensive problem.The costly problem is caused by correct implementation of a poor conceptual design, not by an incorrectly implementation of a good conceptual design.

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OTHER DATA HANDLING COMPONENTS

Memory: Read-Only-Memory (ROM), Random-Access Memory (RAM), Flash Memory.Mass Storage: disk, digital tape, solid state memory, magneto-optical disks, memory IC.Input/Output: I/O Ports, direct memory access (DMA), multi-port memory, interrupts, timers, bus interface.Fault Tolerance: radiation harness, single event upsets, CMOS latch-up, parity, error detection/correction, watchdog timer, etc…Custom, Special-Purpose Peripherals: data acquisition, data compression, image processing.Spacecraft Autonomy: the ability to monitor S/C internal functions and take appropriate actions without direct intervention from the ground.

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ROCSAT-1 CASE STUDY

A low-earth orbiting (LEO) satellite jointly developed by TRW of U.S. with a resident team of NSPO engineers. Launched on January 27, 1999 into an orbit of 600 kilometers altitude and 35 degrees inclination. Three scientific research missions/Payloads:

ocean color imaging/OCI,experiments on ionospheric plasma and electrodynamics /IPEI, experiments using Ka-band (20-30 GHz) communication payloads/ECP.

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ROCSAT-1 COMMAND AND TELEMETRY SYSTEM

S-band Consultative Committee for Space Data Systems (CCSDS) Packet Telcommand and Telemetry Uplink data rate: 2 kbps Downlink data rate: 1.4 mbps Data storage: 2 gb

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ROCSAT-1 COMMAND SYSTEM

2039 MHZ 2Kbps NRZ-L

SPECIAL COMMANDS BILEVELPCU

RCVR

RCVR

SOFTWARE

OUTPUTCIRCUIT

OBC

ADE,GPS,PCUDDC,SAR,DIE DSE

MDE,OBC,PCU TDE,DDC

MDE

TIE,RIU OCI,IPEI

SERIAL

TIE BILEVEL

ANA

1553

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ROCSAT-1 Telemetry Processing OverviewSpacecraft

SubsystemsGPSE

Spacecraft

RIU

Science Data RS 422 OCI

IPEI

1553 BUS

RFAssembly Transponder TIE OBC

Science Data RS 422Recorded / Playback Data

SerialSSR ECP

Downlink

FDF SDDCsTT&CStation

MOC SSCGround

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ROCSAT-1 DATA HANDLING SYSTEM

On Board Computer（OBC）: 80C186 CPUReal-time operation system: Versatile Real-Time eXecutive (VRTX32/86), a real-time multi-tasking OSEmploying software engineering approach for the development of the flight software.A real-time embedded system

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ROCSAT-1 FLIGHT SOFTWARE

Software executes on an 80C186 OBCNo floating point co-processorWritten in C, some assembly requiredMulti-tasking implementationSoftware is organized into 8 CSCs

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ROCSAT-1 FLIGHT SOFTWARE (cont.)

ACS = Attitude Deter. & Control Subsystem EPD = Electrical & Power DistributionCCI = Command and Communication Interface SCP = Stored Command ProcessorCDS = Command Dispatcher Subsystem UTL = UtilitiesDAQ = Data Acquisition EXE = Executive

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ROCSAT-1 FLIGHT SOFTWARE FUNCTIONS

EPD CSC- Controls battery charging and maintain battery state of charge data.- Detects anomalous power subsystem behavior- Collects sensor data for solar array on ground command- Uses ground station control for long term operation

>> Battery trending and trickle charge timing monitoring

EXE CSC- Creates tasks and determines initial spacecraft operational mode- Provides multitasking and floating point software routines- Memory scrubs and memory uploads as background processing

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ROCSAT-1 FLIGHT SOFTWARE FUNCTIONS (cont.)

SCP CSC- Inserts validated RTCS uploads and ATC uploads into memory- Manages the RTCS and ATC areas:

>> Cancel ATC, Execute, RTCS, Inhibit RTCS, Enable RTCS, Delete RTCS, Cancel RTCS- Schedules the execution of each command in a RTCS by assignment of an absolute execution time

UTL CSC- Common routines; delay, crc, error handling, etc.- Hardware interface routines; serial, analog, GPS, GSE, 1553B- Interrupt Service Routines (ISR)

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ROCSAT-1 FLIGHT SOFTWARE FUNCTIONS (cont.)

CDS CSC- Execute each command in the Command Allocation Document

DAQ CSC- Reads sensor data from the hardware- Formats state of health data into 1 of 3 Telemetry formats

>> Normal>> Programmable>> Dump

- 32 minor frames (0-31) per major frame, 212 bytes per minor frame- 1, 2, and 4 byte quantities supported

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ROCSAT-1 FLIGHT SOFTWARE FUNCTIONS (cont.)

ADCS CSC- Processes data from the gyros, earth sensor assemblies, fine sun sensors, coarse sun sensor assemblies, and three axis magnetometer- Generates commands for the scan wheels, reaction wheels, thrusters, and torque rods.- Controls the orientation of the spacecraft in all of its operational modes.- Performs ephemeris determination based on the onboard clock and periodic uploads of orbital elements from the ground

CCI CSC- Validates and processes command frames from the CUB- Validates command type field, ATCs, and RTCSscommand frames before placing them into the CIB- Validates real-time command frames- Manages the CIB with special parameter commands “Clear CIB”, “Transfer CIB”, and “Restart CIB Load”.

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FLIGHT SOFTWAREINITIALIZATION

Initialization-Disable interrupts-RAM initialization-Copy Flight Software from EEPROM to RAM-Resets the watchdog timer-Initializes hardware-Initializes Interrupt Vector Table (IVT)-Initializes VRTX-Creates the EXE task-Passes control to VRTX

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INITIALIZATIONTOP LEVEL STRUCTURE

Power_up/Hardware Reset

exe_bootupSoftware “Reset”

exe_restart

exe_main

exe _vrtx_initutl_isr_load

Software Restart

VRTX

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TASK STRUCTURE

StartupCode

QTR SXTONE SCP

Priorities QTR=10ONE=20SCP=30SXT=40EXE=50

EXE

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TASK CONTROL DIAGRAM

EXE

QTR

SCP

ONE

SXT

SP_ONE_IEF

SP_SCHEDULE_EF

SP_SCHEDULE_EF

SP_SCHEDULE_EF

SP_QTR_IEF

SP_ATC_EFSP_RTCS_EFSP_ALARM_EF

SP_TASK_INIT_EF*

SP_SCHEDULE_EF

QTR ISR

CUBUplink

ISR

ONE ISRCUB-Command Uplink Buffer*-set by QTR,ONE,SXT,SCP

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COMMAND INPUT DATA FLOW

OUBCIRCULAR

BUFFER

CodeblockStatustable

CCI_COMMAND_PROCESSING

CDSLibrary

CCILibrary

Real-timecommand

ATCRTCSKPD,code and data upload

CCSDSTransferFrameprocessing

CCI_MAIN

UplinkISR Command

frames

Uplinkinterrupt

CCSDScodeblock

QTRtask

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COMMAND EXECUTION DATA FLOW

real_timeCMDCUB

cci_command_processing

CCI_Comand_

Jump_table

cci_kpd_loadcci_memory

SP_schedule_atc_queue

cci_atc_command_types

cci_rtcs_load

cci_code_and_data_upload

ATC CMD

RTCSCMD

Code&dataupload

ManageCIB

Real_timeCMD

SP_update_Rtcs_queue

SP_UPDATE_RTCS_EF

SP_SCHEDULE_ATC_EF

RTCSACT

SP_rt_Command_Jump_table

ccl_real_time_command

CDSLibrary

cci_command_uploads

CLBKPDupload

SCPTask

cci_manage_cibEXETask