COMMAND AND DATA HANDLING

Instructor: Roy C. HsuComputer Science and Information Engineering

DepartmentNational Chiayi University

10/30/2008

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OUTLINE

Introduction Command Systems Telemetry Systems Data Processing and Storage Cases Study

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INTRODUCTION

Command and Telemetry providing information to and from the

spacecraft, respectively computer-based components in the

spacecraft (S/C) and at terrestrial sites commands are used to provide the info

to change the state of the S/C subsystems and to set to S/C clock

telemetry subsystem collects and processes a variety of data to be transmitted from the S/C

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INTRODUCTION (Cont.)

Data Processing and Handling 3 major tasks on board

to help control and configure the S/C to optimize the overall system performance to 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 system

S/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

Purpose to permit the spacecraft or its subsystem to be

reconfigured in response to radio signals send up to the S/C from ground

Operation receive 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 signal message 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 circuitry by executing the cmdInterface Circuitry: might be simple or complex functions

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COMPLETE COMMAND SYSTEM

Ground Support

EquipmentModulation

Radio Frequency

Link

SpacecraftCommand

System

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 distance Functions: to provide remote indication of what the

desired measurements are Telemetry data:

Status data - S/C resources, health, attitude, operation mode

Scientific 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 vehicles

Image data - captured by onboard camera Other data - locations of other objects, relayed

telemetry data from other satellites

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SPACECRAFT TELEMETRY SYSTEM

ACQUISITION

SensorsConditioners

SelectorsConverters

Block Diagram of a spacecraft telemetry system

PROCESSING

CompressorsFormatters

Storage

TRANSMISSION

EncoderModulator

TransmitterAntenna

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

Block Diagram of a ground segment telemetry system

PROCESSING

De-compressorTranslatorStorage

DELIVERY

DisplayPrinterPlotter

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SPACECRAFT DATA HANDLING衛星本體的資料處理

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

MEMORY:ROM, RAM,

Special-purpose

MASS STORAGE

INPUT/OUTPUTPORTS

BUSINTERFACE

PROCESSOR DATA BUS

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 devices

Job 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 electrodyna

mics /IPEI, experiments using Ka-band (20-30 GHz) communicati

on payloads/ECP.

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ROCSAT-1 COMMAND AND TELEMETRY SYSTEM

S-band Consultative Committee for Space Data S

ystems (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

RCVR

RCVR

TIESOFTWARE

OUTPUTCIRCUIT

OBC

SPECIAL COMMANDS BILEVEL

PCU

SERIAL

BILEVEL

ANA

1553

ADE,GPS,PCUDDC,SAR,DIE DSE

MDE,OBC,PCU TDE,DDC

MDE

TIE,RIU OCI,IPEI

2039 MHZ 2Kbps NRZ-L

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TIETransponderRF

AssemblyOBC

GPSESpacecraft

Subsystems

ECPRIUSSR

TT&CStation

MOC

FDF

SSC

SDDCs

Ground

Downlink

Spacecraft 1553 BUS

Recorded / Playback Data

Serial

Science Data RS 422

Science Data RS 422

ROCSAT-1 Telemetry Processing Overview

OCI

IPEI

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ROCSAT-1 DATA HANDLING SYSTEM

On Board Computer（ OBC） : 80C186 CPU

Real-time operation system: Versatile Real-Time eXecutive (VRTX32/86), a real-time multi-tasking OS

Employing 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 OBC No floating point co-processor Written in C, some assembly required Multi-tasking implementation Software is organized into 8 CSCs

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ROCSAT-1 FLIGHT SOFTWARE (cont.)

ACS = Attitude Deter. & Control Subsystem EPD = Electrical & Power Distribution CCI = Command and Communication Interface SCP = Stored Command Processor CDS = Command Dispatcher Subsystem UTL = Utilities DAQ = 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 me

mory - 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, 15

53B - 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 RTCSs command frame

s 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 SOFTWARE INITIALIZATION

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

exe_bootup

exe_restart

exe_main

exe _vrtx_initutl_isr_load VRTX

Power_up/Hardware Reset

Software “Reset”

Software Restart

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TASK STRUCTURE

StartupCode

QTR SXTONE SCP EXE

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

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TASK CONTROL DIAGRAM

EXE

QTR

SCP

ONE

SXT

QTR ISR

UplinkISR

CUB

ONE ISR

SP_ONE_IEF

SP_SCHEDULE_EF

SP_SCHEDULE_EF

SP_TASK_INIT_EF*

SP_SCHEDULE_EF

SP_SCHEDULE_EF

SP_QTR_IEF

SP_ATC_EFSP_RTCS_EFSP_ALARM_EF

CUB-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_MAINQTRtask

UplinkISR

CCSDScodeblock

Uplinkinterrupt

Command

frames

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COMMAND EXECUTION DATA FLOW

CUB

cci_command_processing

CCI_Comand_

Jump_table

ccl_real_time_command

cci_command_uploads

cci_kpd_load

cci_manage_cib

cci_memory

SP_schedule_atc_queue

EXETask

CLB

SCPTask

cci_atc_command_types

cci_rtcs_load

cci_code_and_data_upload

SP_rt_Command_Jump_table

CDSLibrary

ATC CMD

RTCSCMD

KPDupload

Code&dataupload

ManageCIB

Real_timeCMD

real_timeCMD

SP_update_Rtcs_queue

SP_UPDATE_RTCS_EF

SP_SCHEDULE_ATC_EF

RTCS

ACT