Transcript Satellite Command And Data Handling Subsystem

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
2
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
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
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COMPLETE COMMAND SYSTEM
Ground
Support
Equipment
Modulation
Radio
Frequency
Link
Spacecraft
Command
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 sensormagnetometers, 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
PROCESSING
TRANSMISSION
Sensors
Conditioners
Selectors
Converters
Compressors
Formatters
Storage
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
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TELEMETRY SYSTEM OF
GROUND SEGMENT
RECEIPT
PROCESSING
DELIVERY
Antenna
Receiver
Demodulator
Decoder
De-compressor
Translator
Storage
Display
Printer
Plotter
Block Diagram of a ground segment telemetry system
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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
PROCESSOR DATA BUS
MEMORY:
ROM, RAM,
Specialpurpose
MASS
STORAGE
INPUT/OUTPUT
PORTS
BUS
INTERFACE
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.
15
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), RandomAccess 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
BILEVEL
PCU
SERIAL
RCVR
SOFTWARE
TIE
OUTPUT
CIRCUIT
RCVR
OBC
ADE,GPS,PCU
DDC,SAR,DIE
DSE
BILEVEL MDE,OBC,PCU
TDE,DDC
ANA
1553
MDE
TIE,RIU
OCI,IPEI
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ROCSAT-1 Telemetry Processing Overview
GPSE
Spacecraft
Subsystems
Spacecraft
RF
Assembly
1553 BUS
Transponder
TIE
OBC
IPEI
Science Data RS 422
Recorded /
Playback Data
Serial
Science Data RS 422
SSR
RIU
OCI
ECP
Downlink
FDF
TT&C
Station
Ground
MOC
SDDCs
SSC
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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 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 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”.
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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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INITIALIZATION
TOP LEVEL STRUCTURE
Power_up/
Hardware Reset
Software “Reset”
exe_bootup
Software Restart
exe_restart
exe_main
utl_isr_load
exe _vrtx_init
VRTX
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TASK STRUCTURE
Priorities
QTR=10
ONE=20
SCP=30
SXT=40
EXE=50
SCP
EXE
Startup
Code
QTR
ONE
SXT
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TASK CONTROL DIAGRAM
SP_TASK_INIT_EF*
EXE
SXT
SP_SCHEDULE_EF
SP_SCHEDULE_EF
QTR ISR
SP_QTR_IEF
QTR SP_SCHEDULE_EF
Uplink
ISR
C
U
B
ONE
SP_ATC_EF
SP_RTCS_EF
SP_ALARM_EF
SP_ONE_IEF
SCP SP_SCHEDULE_EF
CUB-Command Uplink Buffer
*-set by QTR,ONE,SXT,SCP
ONE ISR
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COMMAND INPUT
DATA FLOW
Uplink
interrupt
QTR
task
Uplink
ISR
CCI_MAIN
CCSDS
codeblock
Codeblock
Status
table
OUB
CIRCULAR
BUFFER
Command
CCSDS
Transfer
Frame
processing
Real-time
command
CCI_COMMAND_
PROCESSING
frames
CDS
Library
ATC
RTCS
KPD,code and data upload
CCI
Library
34
COMMAND EXECUTION
DATA FLOW
CUB
ccl_real_time_
command
Real_time
CMD
ATC CMD
cci_command_
processing
CCI_
Comand_
Jump_
table
RTCS
CMD
KPD
upload
Code&data
upload
real_time
CMD
SP_rt_
Command_
Jump_table
CDS
Library
cci_command_
uploads
cci_atc_
command_types
cci_rtcs_load
CLB
cci_memory
cci_kpd_load
SP_update_
Rtcs_queue
cci_code_
and_data_upload
Manage
CIB
RTCS
ACT
SP_schedule_
atc_queue
cci_manage_cib
SP_UPDATE_RTCS_EF
SCP
Task
SP_SCHEDULE_ATC_EF
EXE
Task
35