Command and data handling
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COMMAND AND DATA HANDLING. Instructor: Roy C. Hsu Computer Science and Information Engineering Department National Chiayi University 10/30/2008. OUTLINE. Introduction Command Systems Telemetry Systems Data Processing and Storage Cases Study. INTRODUCTION. Command and Telemetry

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Command and data handling

COMMAND AND DATA HANDLING

Instructor: Roy C. Hsu

Computer Science and Information Engineering Department

National Chiayi University

10/30/2008


Outline

OUTLINE

  • Introduction

  • Command Systems

  • Telemetry Systems

  • Data Processing and Storage

  • Cases Study


Introduction

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


Introduction cont

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


Command systems

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


Generalized spacecraft command system

GENERALIZED SPACECRAFT COMMAND SYSTEM

Receiver/

Demodulator

Command

Decoder

Command

Logic

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 decoder

Command 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 cmd

Interface Circuitry: might be simple or complex functions


Complete command system

COMPLETE COMMAND SYSTEM

Ground

Support

Equipment

Modulation

Radio

Frequency

Link

Spacecraft

Command

System

Block Diagram of a complete command system


System requirements

SYSTEM REQUIREMENTS

S/C MISSION

S/C ORBIT/

TRAJECTORY

GROUND STATION

LINK ANALYSIS/COVERAGE

COMMAND LOGIC


Telemetry systems

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…

    • SpecificS/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


Spacecraft telemetry system

SPACECRAFT TELEMETRY SYSTEM

ACQUISITION

Sensors

Conditioners

Selectors

Converters

PROCESSING

Compressors

Formatters

Storage

TRANSMISSION

Encoder

Modulator

Transmitter

Antenna

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


Telemetry system of ground segment

TELEMETRY SYSTEM OF GROUND SEGMENT

RECEIPT

Antenna

Receiver

Demodulator

Decoder

PROCESSING

De-compressor

Translator

Storage

DELIVERY

Display

Printer

Plotter

Block Diagram of a ground segment telemetry system


Spacecraft data handling

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.


Spacecraft data handling system

SPACECRAFT DATA HANDLING SYSTEM

CENTRAL

PROCESSING

UNIT

PROCESSOR DATA BUS

MEMORY:

ROM, RAM,

Special-

purpose

MASS

STORAGE

INPUT/OUTPUT

PORTS

BUS

INTERFACE

SPACECRAFT DATA BUS


Central processing unit

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.


Central processing unit cont

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.


Flight software development

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 approachto the design and maintenance of the software product.


Flight software development cont

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.


Other data handling components

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.


Rocsat 1 case study

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.


Rocsat 1 command and telemetry system

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


Rocsat 1 command system

ROCSAT-1 COMMAND SYSTEM

2039 MHZ 2Kbps NRZ-L

SPECIAL COMMANDS

BILEVEL

TIE

PCU

RCVR

ADE,GPS,PCUDDC,SAR,DIE DSE

SERIAL

OUTPUT

CIRCUIT

SOFTWARE

BILEVEL

MDE,OBC,PCU TDE,DDC

RCVR

ANA

MDE

1553

OBC

TIE,RIU OCI,IPEI


Command and data handling

ROCSAT-1 Telemetry Processing Overview

GPSE

Spacecraft

Subsystems

Spacecraft

1553 BUS

RF

Assembly

Transponder

TIE

OBC

IPEI

Science Data RS 422

Recorded / Playback Data

OCI

Science Data RS 422

Serial

SSR

RIU

ECP

Downlink

FDF

SDDCs

TT&C

Station

MOC

SSC

Ground


Rocsat 1 data handling system

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


Rocsat 1 flight software

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


Rocsat 1 flight software cont

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


Rocsat 1 flight software functions

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


Rocsat 1 flight software functions cont

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)


Rocsat 1 flight software functions cont1

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


Rocsat 1 flight software functions cont2

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 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”.


Flight software initialization

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


Initialization top level structure

INITIALIZATIONTOP LEVEL STRUCTURE

Power_up/

Hardware Reset

exe_bootup

Software “Reset”

Software Restart

exe_restart

exe_main

utl_isr_load

exe _vrtx_init

VRTX


Task structure

TASK STRUCTURE

Priorities QTR=10

ONE=20

SCP=30

SXT=40

EXE=50

Startup

Code

QTR

ONE

SXT

SCP

EXE


Task control diagram

TASK CONTROL DIAGRAM

SP_TASK_INIT_EF*

EXE

SXT

SP_SCHEDULE_EF

SP_SCHEDULE_EF

SP_QTR_IEF

QTR ISR

SP_SCHEDULE_EF

QTR

C

U

B

ONE

Uplink

ISR

SP_ATC_EF

SP_RTCS_EF

SP_ALARM_EF

SP_ONE_IEF

SCP

SP_SCHEDULE_EF

ONE ISR

CUB-Command Uplink Buffer

*-set by QTR,ONE,SXT,SCP


Command input data flow

COMMAND INPUT DATA FLOW

Uplink

interrupt

OUB

CIRCULAR

BUFFER

CCSDS

codeblock

Codeblock

Status

table

Uplink

ISR

Command

frames

CCSDS

Transfer

Frame

processing

QTR

task

CCI_MAIN

CDS

Library

Real-time

command

ATC

RTCS

KPD,code and data upload

CCI_COMMAND_

PROCESSING

CCI

Library


Command execution data flow

COMMAND EXECUTION DATA FLOW

real_time

CMD

CUB

SP_rt_

Command_

Jump_table

CDS

Library

ccl_real_time_

command

Real_time

CMD

cci_command_

uploads

ATC CMD

cci_atc_

command_types

CCI_

Comand_

Jump_

table

cci_command_

processing

RTCS

CMD

CLB

cci_rtcs_load

KPD

upload

cci_memory

cci_kpd_load

SP_UPDATE_RTCS_EF

Code&data

upload

SP_update_

Rtcs_queue

cci_code_

and_data_upload

RTCS

SCP

Task

Manage

CIB

SP_schedule_

atc_queue

ACT

cci_manage_cib

SP_SCHEDULE_ATC_EF

EXE

Task


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