(Preliminary) Direct Access System User's Guide
Contents
1. lt Rate 26 25 150 210 Msps Encoder Channel Demodulator Modulator Discrete lt Error Coding Channel DAS Modulator NRZ M Channels 1 NRZ L Rates 13 125 NRZ L 75 105Mbps Rate 13 125 75 105 Mbps L Q Channels Channels Storage 13 Bits Frame Overhead Bits Bits Added Subtracted Reed Solomon Decoder lt 4 Discrete Source 9 Channel EOS Users Instruments Figure 4 EOS AM DAS Digital Satellite Communications Link Model 19 DMC201198 861I0cOING 0 H H i SPACECRAFT Differential Power Ratio Channel NL 2 20 Modulator Upconverter Amplifier Anteng S NRZ M onvolutiona never Q Channel 1 Frequency Source 8212 5 MHz p Buc USER GROUND STATION Receive2. Down Converters Channel not used SQPSK Demodulator Receiver 2 NRZ L Differential Viterbi Decod CCSDS CADUs 2 Channel P J Figure 5 Spacecraft to User Downlink Configuration for DAS Direct Broadcast Mode With Q I 4 1 8661 FOQUISAON 0 969800051 Ic 861I0COING NRZ SPACECRAFT DB Data Differential Power Ratio 13 125 Mbps Encoder Channel Q l 4 1 CCSDS CADUS Differential NRZ M DDL or DP2 Data r 105 Mbps Encoder CCSDS CADUS Q Channel 2 22 C CR M DIC CM CM CE CN RH USER GROUND STATION Receive Antenna Down Converters Channel i i NRZ L NRZ M Viterbi Channel 13 128 Mops Decoder 4 Decode DB data 1 CCSDS CADUs SQPSK Demodulator Receiver Channel NRZ L Differential NEUEM Viterbi 105 Mbps amp Decoder lt lt Decoder DDL or DP2 data 8 Q Channel CCSDS CADUs Figure 6 Spacecraft to User Downlink Configuration for DAS Direct Downlink DDL or Direct
3. E N dB 10 11 12 94 Figure 16 Theoretical Curves of The Probability of Error As A Function of Data DMC201198 Coding Methods 5 BOL bps BPSK BRF CADU CCSDS C amp DH CMD COMMS C amp T CTIU DAS dc DB dB DDL DG DP DSN EDAC EIRP EL EOC EOL EOS IS20008696 20 November 1998 APPENDIX 3 ACRONYM LIST Amplitude Modulation Azimuth Bit Error Rate Biphase Space Beginning of Life bits per second Binary Phase Shift Keyed Band Reject Filter Channel Access Data Unit Consulting Consortium of Space Data Systems Command and Data Handling Subsystem Command Communications Subsystem Command and Telemetry Command Telemetry Interface Unit Direct Access System Direct Current Direct Broadcast decibel Direct Downlink Data Group as defined in STDN 101 2 Direct Playback Deep Space Network Error Detection and Correction Effective Isotropic Radiated Power Elevation EOS Operations Center End of Life Earth Observation System 53 DMC201198 1520008696 20 November 1998 EOSDIS EPGN ESD FDIR FOT GHz GN HGA H K H amp S Hz ICD IF I O Kbps kHz KSA LHCP LNA LPC Mbps Msps MHz MO N A NASA NCO NRZ L NRZ M OCXO omni DMC201198 Earth Observation System Data Information System EOS Polar Ground Network Electrostatic Discharge Fault Detection Isolation and Recovery Flight Operations Team Giga Hertz Ground Network Hi
4. 40 degrees p p 38 degrees p p 30 degrees p p 29 degrees Note 3 Includes 0 6 degrees circular DAS Antenna pointing error total EOS system allocation 37 DMC201198 1520008696 20 November 1998 This page intentionally left blank DMC201198 38 1520008696 20 November 1998 6 DAS COMMUNICATION LINK BUDGETS The DAS system is required to achieve positive link margin with a Bit Error Rate BER of less than 1 x 107 as required by CCSDS Grade 2 level of service The DAS was designed with a goal of maintaining link margins of more than 3 dB for every link The link budgets provided in this section are based on worst case Equivalent Isotropic Radiated Power EIRP and axial ratio losses measured in tests of the DAS Engineering Test Model ETM antenna on a mockup of the Spacecraft nadir deck For each DAS operating mode link budgets are provided for four earth station elevation angles 5 409 63 and 90 The budget is based on the specified minimum end of life EOL Solid State Power Amplifier SSPA output power of 11 5 dBW i e 14 W and the minimum DAS antenna gain The rationale for estimates of the various losses in the link budget is explained in EOS DN COMM 14B Antenna performance test data is provided in Appendix 1 in order that the user can revise the following link margins as required for specific operating conditions The data shows that the DAS system EIRP drops significantly around 20 degrees off
5. IS20008696 20 November 1998 The following documents are listed for the convenience of the user These documents do not form a part of this document and are not controlled by their reference herein The EOS AM Spacecraft Communications Subsystem Specification PS20008580 controls the requirements for the DAS design and operation This specification shall govern in the event of a conflict between this DAS User s Guide and any of the documents listed below 2 1 Lockheed Martin Documents Design Documents 20054745 EOS DN COMM 014B EOS DN COMM 021 EOS DN COMM 025 EOS DN C amp DH 052 Specifications 520005396 PS20008506 PS20008573 PS20008575 PS20008580 PS20008589 PS20008590 EOS AM 1 Spacecraft Flight Systems Manual Volume III Communications Subsystem X band Design Approach Design and Breadboard Report for the KSA and DAS Modulators Design and Breadboard Report for the Convolutional Encoder Boards in the EOS KSA and DAS Modulators Command and Data Handling Subsystem Functional Description 5 Spacecraft Contract End Item Specification SEP 101 Critical Development Performance Specification Direct Access System Antenna Critical Development Performance Specification DAS Upconverter Critical Development Specification Science Data Formatting Equipment Performance Specification Communications Subsystem for EOS AM Spacecraft Critical Development Pe
6. 43 6 63 24 90 0 Units Comments Received Carrier to Noise Density 94 15 98 72 92 00 98 14 dB Hz 11 14 16 Convert C to Eb 78 75 78 75 78 75 78 75 dB bps 10 log 75e6 User to Supply Note 1 oo Ground Multipath Degradation 000 0 Differential Encoder Decoder Loss 0 20 I Q Channel Power Split Loss 3 20 Link margin Without Reed Solomon Decoding 1 1 1 pwr ratio w tolerance eed qu wee ____ E 2 N 22 23 24 nk marsin Ree Somon Decode _ E User should provide a value for the Ground Multipath Degradation because this item in budget depends on the ground station design The uncertainty band for the implementation loss is 1 1 dB based on two analysis methods The actual value will depend on the ground station as well as the spacecraft segment Loss includes allowance for degradation of Reed Solomon decoding from small number of bit errors generated in spacecraft after the Reed Solomon encoding and before viterbi encoding N 22 23 27 E E E E 8661 FOQUISAON 0c 9698000 51 1520008696 20 November 1998 APPENDIX 1 ANTENNA PERFORMANCE DATA This section provides DAS system test data for reference only The measured variation in the DAS system gain and axial ratio as a function of ground antenna elevation angle are shown in Figur
7. In addition to providing a direct to user communications link the DAS serves as a backup to the TDRSS Ku band science data return communications path The DAS transmits science data via an 8 2125 GHz link directly to user ground stations on the earth at the data rates shown in Table III The DAS return link is a scheduled service which is available 10046 of the time during Spacecraft science mode and the availability of DAS services does not depend on High Gain Antenna HGA operability 3 1 DAS RF Communication Links The DAS provides three types of science data return capabilities including a real time direct downlink DDL of ASTER instrument data b real time direct broadcast DB of MODIS instrument data and Spacecraft ancillary data c direct playback DP for a backup to the Ku band science data downlink The direct playback service is described here for completeness The performance requirements for the DAS contingency direct playback service are controlled by the X band Radio Frequency Control Document RFICD 531 RFICD EOS AM 1 EPGN These services are used to downlink data from Spacecraft Instruments as shown in Table I The Spacecraft Bus will include packetized ancillary data in the DB and DP data streams which are identical to the ancillary data included with the science data for transmission via the Ku band link When DP service is used the C amp DH will include Spacecraft housekeeping telemetry in the data sent to the DAS
8. Modulator The DB and DDL services will be provided during normal Spacecraft operations The DP service will be used in contingency conditions only i e when the Spacecraftis incapable of normal recorder playback via the HGA TDRSS link Table I Science Data Downlink Service Allocations Ancillary House keeping Teleme EE NE __ _ NM RE In addition to these three science data downlinks the DAS provides Pseudo Random Stream PRBS downlink for test purposes 13 DMC201198 1520008696 20 November 1998 3 2 DAS Functional Description Figure 1 shows the block diagram of the DAS and the major components are listed in Table II Table II Major Components Subsystem Component Major Function DAS Antenna DAS Communications Links DAS SSPA DAS RF Transmission DAS Upconverter DAS IF to RF Frequency conversion DAS Modulator Science Data modulation and coding on the DAS RF link DAS Band Pass Filter RF Spectrum limiting DAS Waveguide Switch Select Prime Redundant SSPA whose output is routed to the antenna DAS Coaxial Switch Select Prime Cross strapping connections of DAS Modulator Das Upconverter The DAS is a single antenna system with 2 for 1 redundancy of the modulators upconverters and SSPAs Coaxial switches allow either modulator to provide the modulated carrier to either upconverter amplifier system This cross strapping between the primary and redundant chains of equi
9. Octets VCDUPRIMARY HEADER 48 Bits 6 Octets VCDU SIGNALLING VERSION IDENTIFIER VIRTUAL FIELD NUMBER VCDU ID CHANNEL DATA UNIT SPACECRAFT VIRTUAL COUNTER ID CHANNEL ID 701 72A 2 8 2 octets 3 octets 1 octet VCDU Data Unit Zone Randomized 1 per following equation VCDU DATA UNIT ZONE SOLOMON Randomized CHECK h x x8 7 x9 x3 1 SYMBOLS 7088 1024 886 octets 128 octets Figure 8 Format of Channel Access Data Unit CADU with Science Data DMC201198 24 1520008696 20 November 1998 FILL CADU Fill Channel Access Data Unit 8192 Bits 1024 Octets TACFFCID 32 Elie ccc CVCDU Ace e eL Coded Virtual Channel Data Unit 8160 Bits 1020 Octets VCDUPRIMARY HEADER ______ 48 Bits 6 Octets VCDU SIGNALLING VERSION IDENTIFIER VIRTUAL FIELD NUMBER VCDU ID CHANNEL DATA UNIT SPACECRAFT VIRTUAL COUNTER ID CHANNEL ID 01 2 111111 00 00 2 8 6 24 2 octets 3 octets 1 octet CVCDU VCDU Data Unit Zone Randomized REED per following equation VEDU DATA UNIT ZONE SOLOMON Randomized CHECK h x x8 x7 5 x3 1 0101 0101 SYMBOLS 7088 1024 886 octets 128 octets Figure 9 Format of CADU with Fill Data 25 DMC201198 9c Figure 10 Data Randomization 8661 FOQUISAON 0c 9698000CSI 1520008696 20 Novem
10. be available in non nominal Spacecraft operating modes such as delta V mode and the type of safe mode in which the Spacecraft Controls Computer SCC continues to function During nominal operation the DAS subsystem will provide Direct Broadcast DB service Mode 3 and for Direct Downlink DDL service Mode 4 at scheduled times when the Spacecraft passes over user earth stations Typically both Mode 3 and Mode 4 would be performed using unbalanced SQPSK modulation which provides a Q channel with 4 times the power of the Ichannel In between times when DB and DDL science data downlinks are scheduled the DAS subsystem would operate in standby mode in which RF transmission is disabled The other operating modes will be used less frequently typically during checkout or contingency conditions 4 1 Pseudo Random Bit Stream Test DAS mode 1 provides for PRBS data to be generated internal to the modulator for the purpose of biterrorrate BER checking The DAS is designed to achieve positive link margins with a Bit Error Rate BER of lt 102 prior to Reed Solomon decoding as required by CCSDS Grade 2 of service on all direct to user communications links 4 2 Direct Broadcast of MODIS Instrument Data Direct Broadcast is a service in which real time MODIS instrument science data and ancillary data is broadcast directly to earth stations Data for direct broadcast is accepted on DAS Modulator input channel 1 only The DAS transmits the DB data s
11. 1520008696 CAGE No 79272 20 November 1998 Preliminary Direct Access System User s Guide for the EOS AM Spacecraft ICD 107 Prepared under Contract NAS5 32500 NASA Goddard Space Flight Center Greenbelt Maryland 20771 Prepared by Lockheed Martin Corporation Lockheed Martin Missiles amp Space Valley Forge Operations P O Box 8555 Philadelphia PA 19101 DMC112098 Sheet 1 of 55 1520008696 20 November 1998 This page intentionally left blank DMC201198 2 1520008696 20 November 1998 REVISION LOG This log identifies those portions of this document which have been revised since the original issue Revised portions of each page for the current revision only are identified by marginal striping Paragraph Number s Affected Approval Preliminary 2 Nov 20 1998 3 DMC201198 1520008696 20 November 1998 This page intentionally left blank DMC201198 4 1520008696 20 November 1998 TABLE OF CONTENTS SECTION PARAGRAPH TITLE PAGE 1 SCOPE ies ea Benet 9 2 APPLICABLE DOCUMENTS 5 2 2x23 499 EX uer nba ees 11 2 1 Lockheed Martin Documents 2 252699 oedet esus 11 2 2 NASA eut arii NP 12 3 OVERVIEW OF THE DIRECT ACCESS SYSTEM DAS 3 1 DAS RF Communication Links 13 3 2 DAS Functional De
12. Antenna Elevation Angle 48 16 Theoretical Curves of The Probability of Error Pe As A Function of Data Coding Methods gt bw wur Res 50 7 DMC201198 1520008696 20 November 1998 TABLE II DMC201198 LIST OF TABLES TITLE Science Data Downlink Service Allocations Major Components rss de o vena hou ata m aed DAS Subsystem Operating Modes X band DAS Subsystem Performance Characteristics DAS Return Link Performance Summary 1 DAS Return Downlink Budget for Direct Broadcast DB Mode with OE o uus sudes edo daha dans DAS Return Downlink Budget for Direct Downlink DDL Direct Playback 2 DP2 Modes teed E RS DAS Return Downlink Budget for Direct Playback 1 13 14 32 35 39 41 42 43 1520008696 20 November 1998 1 SCOPE This document provides the following an overview of the types of services which will be provided to the user community by the EOS AM Spacecraft Direct Access System DAS b information which provides the user community an understanding of the ground station requirements for accessing the DAS services 9 DMC201198 1520008696 20 November 1998 This page intentionally left blank DMC201198 10 2 APPLICABLE DOCUMENTS
13. Deg t 70 8661 1 9698000 51 861I0CcOING 0s ISUV uoneAo j4 euuajuy SnsJ9A ONLY PIX y 5 lt SVA ST AMJIA Axial Ratio dB DAS System Axial Ratio vs Elevation Angle A AXIAL RATIO MAX x AXIAL RATIO MEAN AXIAL RATIO MIN Elevation Angle deg 8661 FOQUISAON 0c 9698000 51 1520008696 20 November 1998 APPENDIX 2 IMPACT OF DATA CODING ON REQUIRED EB NO AND BIT ERROR RATE This appendix provides information about how the BER and required Eb No depends on the type of data coding performed by the ground system Eb No is the ratio of received energy per bit i e the received power times the bit duration to the noise spectral density The receiver noise bandwidth is determined by the data rate and the choice of modulation and coding The DAS communications link model shown in Figure 4 illustrates a concatenated coding scheme in which Reed Solomon RS coding and then convolution CONV encoding are applied on the Spacecraft prior to transmission to the earth station At the earth station it is assumed that a demodulator will employ a 3 bit soft decision Viterbi CONV decoding process and that the subsequent bit stream will be Reed Solomon decoded prior to delivery to the data users Data arrives at the DAS Modulators on the Spacecraft in an NRZ L format and is converted to an NRZ M format prior to convolutional encoding In t
14. EB NO AND BIT ERROR nee e Ne UR CBE 49 APPENDIX III 3 ACRONYM LIST aU Pies xr dodi 5 DMC201198 6 1520008696 20 November 1998 LIST OF FIGURES FIGURE TITLE PAGE 1 X band Block Diagram svat ene Ped 15 2 DAS Antenna Configuration iss csv bes a aes ways 16 3 DAS Satellite to Earth Station Geometry 18 4 EOS AM DAS Digital Satellite Communications Link Model 19 5 Spacecraft to User Downlink Configuration for DAS Direct Broadcast Mod With CE Id iue saa ERES bed 20 6 Spacecraft to User Downlink Configuration for DAS Direct Downlink DDL or Direct Playback 2 DP2 Modes With Q Iz4 1 21 7 Spacecraft to User Downlink Configuration for DAS Direct Playback 1 DP1 or Pseudo Random Bit Stream PRBS Modes with Q I 1 1 22 Format of Channel Access Data Unit CADU with Science Data 24 Format of CADU with Data 25 10 PRN GEN PING abe PEG 26 11 Functional Configuration of the Convolutional Encoder 27 12 n Parallel Data Encoder and the n Encoded Sequences 28 DAS System EIRP Minus Axial Ratio Loss 46 14 DAS System Antenna Gain dBi Versus Antenna Boresight Angle 47 15 DAS System Axial Ratio Versus Ground
15. L DP1 and DP2 data The composite serial symbol output from the n parallel encoder consists of the branch encoder output symbols interleaved every nth symbol Each branch of the n parallel encoder has the shift register representation shown in Figure 11 The n parallel encoder and the composite serial n encoded sequences are shown in Figure 12 The G2 symbol is inverted to provide an increased symbol transition density when the uncoded data signal has a low transition density The commutation rate and input data rate are coherent 3 4 2 Viterbi Decoding A phase ambiguity will occur in the carrier reference signal in the receiver whenever a suppressed carrier tracking loop is used to synthesize the coherent carrier reference The incorrect phase of the reference signal will result in an inversion of the baseband data signal at the demodulator output In addition a symbol ambiguity exists since the Viterbi decoder has no prior knowledge whether a given symbol is from the G1 or G2 generator The Viterbi decoder resolves the symbol ambiguity and decodes either the true or inverted symbol The NRZ M to NRZ L converter resolves any phase inversions that might be present in the baseband data resulting in true NRZ L output 23 DMC201198 1520008696 20 November 1998 CADE e Channel Access Data Unit 8192 Bits 1024 Octets IJACFFCID 32 Zae CVCDU Coded Virtual Channel Data Unit 8160 Bits 1020
16. Playback 2 DP2 Modes With 0 1 4 1 8661 194 0 9698000 51 861I0cOING CT PRBSData 4 L 2 SPACECRAFT 1 75 Mbps ar i bod 1 1 Formatted Science 9 Be 5 Modulator 2 Ubconverter B Amplifer 150 Mbps oM CCSDS CADUS E 8 DAS PRBS Data Frequency Source OCXO RHC x 75 Mbps NRZ L 8212 5 MHz EDU CELLULE DEI TURCA 4 USER GROUND STATION RHC Receive Down BER Test Set Converters Differential Decoder DP1 data 75 Mbps 150 Mbps Bit Interleaver CCSDS CADUS Differential Channel Decoder 75 Mbps BER Test Set a M ro J Figure 7 Spacecraft to User Downlink Configuration for DAS Direct Playback 1 DP1 or Pseudo Random Bit Stream PRBS Modes With Q I 1 1 8661 FOQUISAON 0c 9698000 51 1520008696 20 November 1998 3 4 Baseband Signal Characteristics The format of the Channel Access Data Units CADUS which are the DAS downlink data 1s shown in Figure 8 The Spacecraft Science Formatting Equipment SFE will use fill data as necessary to maintain constant data rat
17. S mode 6 provides DP2 service in which direct playback data will appear only on the Q channelata rate of 105 Mbps The I channel will be used to transmit 13 125 Mbps of DB data In this mode the Q I power ratio will be 4 1 Direct playback data is accepted on modulator input channel 2 only The DAS transmits the DP data stream via a QPSK modulated X band downlink The DP service can not be provided on a continuous basis since time must be allocated for recording before playback can occur The DP service will be utilized only as a backup in case of any interruption of the ability to transmit science data to ground users via the TDRSS Ku band return link service The DP service will not be available simultaneously with the TDRSS Ku band return link service The ancillary data transmitted in the direct playback data will be identical to that transmitted in the Ku band services Users of the DPI service should only use the VCDU data after Reed Solomon decoding due to a small number of bit errors generated in the spacecraft after the Reed Solomon encoding and before the viterbi encoding DPI mode only The anomalous conditions which would warrant DP mode service usage include a HGA pointing problem b Tracking and Data Relay Satellite System communication path outage for any length of time greater than Solid State Recorder SSR recording capabilities c EOS Data Operations System EDOS outage for any length of time greater than SSR recording capa
18. ber 1998 K STAGE SHIFT REGISTER 7 INFORMATION DATA V MODULO 2 ADDERS 2 GENERATOR COEFFICIENTS Gl 1111001 G2 1011011 COMMUTATOR 2X DATA RATE ENCODED DATA NOTE SYMBOL FROM G2 COMPLEMENTED G1 PRECEDES G2 RELATIVE TO THE INFORMATION DATA BIT PERIOD Figure 11 Functional Configuration of the Convolutional Encoder 27 DMC201198 1520008696 20 November 1998 INPUT DATA NRZ M DATA ENCODER 1 DATA ENCODER n 8 m 2 G2 G2 G1 G1 G1 Figure 12 n Parallel Data Encoder and the n Encoded Sequences DMC201198 28 1520008696 20 November 1998 3 5 DAS Management 3 5 1 Scheduling The user must schedule DAS services for a time when the Spacecraft passes over the user s ground station The scheduling of DAS services will be achieved by Relative Time Sequences RTS commands uplinked from the EOS Operations Center EOC Typically the DAS commands will be uplinked the day before the scheduled contact The instrument mode changes and commands will be controlled independently of the DAS commands There will be no automatic coordination of the start of DAS transmission with the start of a data packet That is data will be transmitted continuously from the moment that the DAS Modulator mode is selected without regard to synchronization with the beginning of a data set The user can choose to coordinate instrument operations with a scheduled contact by coordinating the timing requirements in th
19. bilities 4 5 Standby The standby mode DAS mode 7 provides a means for disabling RF output while maintaining oscillator stability for operational readiness By scheduling DB and DDL services to occur over user ground stations interference with DSN ground stations is avoided The standby mode disables the DAS subsystem RF output by switching off the IF and LO outputs from the DAS Modulator 33 DMC201198 1520008696 20 November 1998 This page intentionally left blank DMC201198 34 1520008696 20 November 1998 5 DAS RF CHARACTERISTICS The DAS RF signal parameters for all services are listed in Table IV Table IV X band DAS Subsystem Performance Characteristics Transmit Center Frequency 8212 5 0 01 MHz Axial Ratio Angle from S C Antenna Axial Ratio Boresight degrees dB 63 8 14 43 6 9 8 29 0 13 5 24 0 17 0 17 9 lt 32 5 lt 10 1 0 63 8 approximates Constant Power Density Data Modulation SQPSK USQPSK 1 Reclock Differential Encoding Rate 1 2 Convolu tional Encoding Assigned Frequency Range Bandwidth 8025 to 8400 MHz 375 MHz Gain Slope 10MHz min interval Angle from S C Antenna Gain Slope Boresight degrees dB MHz 63 8 0 057 43 6 0 085 17 9 0 23 0 0 18 90 1 1 modes 128 52 1 4 modes Data Skew with respect to 1 2 sym lt 0 375 nsec bol offset 35 DMC201198 1520008696 20 November 1998 Table IV X band DAS Subsystem Performance Characteri
20. boresight NASA does not plan to use the DAS direct playback service within 24 degrees of antenna boresight i e above 63 14 degrees of ground station elevation angle Information on the impact of data coding to BER and required Eb No performance is provided in Appendix 2 Table V DAS Return Link Performance Summary 1 Channel Link Margin dB For Various Ground Elevation Angles degrees GNE EEG E Direct Broadcast with Q I 4 1 13 125 5 97 10 54 0 12 6 26 to 3 meter ground antenna 3 82 9 96 Direct Downlink or Direct Playback 105 11 56 4 84 10 98 2 DP2 with Q I 2 4 1 to 11 3 meter ground antenna Direct Playback 1 DP1 with 150 LQ 3 6 8 17 1 45 7 59 Q I 1 1 to 11 3 meter ground antenna 1 For ground system with Reed Solomon decoding 6 1 Direct Broadcast DB Link Budget The link budget for the DB mode with a Q I power ratio of 4 1 is provided in Table VI 6 2 Direct Downlink DDL Link Budget The link budget for the DDL mode with 80 of the transmit power on the channel with the ASTER data is shown in Table VII 39 DMC201198 1520008696 20 November 1998 6 3 Direct Playback Link Budgets The link budget for the the Direct Playback 1 DP1 mode is shown in Table VIII The link budget for the Direct Playback 2 DP1 mode with 8096 of the transmit power on the Q channel with the playback data is shown in Table VII DMC201198 40 Iv 861I0COING Table VI DAS Return Downlink Budget for Di
21. d 6 4 3 Direct Downlink of ASTER Instrument Data DDL service in which real time ASTER instrument science data is broadcast to earth stations with 11 3 meter dishes is provided whenever DAS mode 4 is selected Data for direct downlink is accepted on channel 2 only The DAS transmits DDL data stream in real time QPSK modulated X band downlink DDL data appears only on the Q channel for DAS mode 4 and the Q I power ratio is 4 1 DMC201198 32 1520008696 20 November 1998 The DDL service is dedicated to science data from the ASTER instrument This service will be activated only when ASTER is in operation and when a target 11 3 meter DAS ground station is within range DDL service will be scheduled by the Flight Operations Team FOT based on requests for service from user stations and it will be controlled by the Spacecraft Controls Computer SCC per Stored Command Table SCT uploads 4 4 Direct Playback of Recorded Science and Housekeeping Data Direct Playback DP service in which stored science and ancillary data is broadcast to earth stations with 11 3 meter dishes is provided whenever DAS modes 5 or 6 is selected There are two types of DP service DP1 and DP2 d DAS mode 5 provides DPI service in which data on the I and Q channels will be bit interleaved for an effective data rate of 150 Mbps In this mode the power of the I and Q channels will be balanced i e Q I power ratio 1 1 e DA
22. e instrument and DAS command instructions provided to the EOC 3 5 2 Anomalies The Flight Operations Team FOT at the EOC will not have direct visibility of DAS output performance because the science telemetry transmitted by the DAS will not be routed to the EOC The Spacecraft does not support any automated Fault Detection Isolation and Recovery FDIR for the DAS System Therefore the user must notify the EOC of any problems with DAS service in order to start an investigation of the anomaly 29 DMC201198 1520008696 20 November 1998 This page intentionally left blank DMC201198 30 1520008696 20 November 1998 4 DAS SUBSYSTEM OPERATING MODES There are seven DAS subsystem operating modes as shown in Table The DAS subsystem can be configured for only one of these seven operating modes at any time but any combination of operating modes can be used during any orbit DAS services are available all of the time and the DAS operational duty cycle can vary from 0 to 100 During mode transitions the DB DDL and DP services may be interrupted for about 5 sec If the DAS Modulator is ever turned off it will require approximately 15 minutes warmup time after turn on before meeting long term frequency stability requirements The DAS subsystem is only required to be operational during Spacecraft nominal science mode when the instruments are functioning and are producing science data It is possible that DAS services may also
23. es The format of the fill CADU is shown in Figure 9 The VCDU Data Unit Zone for Science Data is randomized to ensure data transition density in the downlink stream The following CCSDS polynomial is XOR ed with the data to randomize it h x 9 x7 ex 3 1 The random sequence generator is initialized to all One s at the beginning of each VCDU This randomizing is applied to science data and to SFE fill VCDU s This randomization is as shown in Figure 10 The DAS downlink data will have a 255 223 Reed Solomon RS outer code with interleave depth 1 4 to provide improved bit error performance The RS encoding will achieve a bit error rate BER of less than 1077 RS encoding is performed on the randomized data Convolutional encoding and Viterbi decoding with eight levels of quantization 3 61 soft decision are used to provide a performance gain for each type of DAS service as explained below 3 4 1 Convolutional Coding For the X band downlink a non systematic transparent convolutional code with a code rate of 1 2 and a constraint length of 7 is used The I and Q channel data signals are differentially formatted separately and then rate 1 2 convolutionally encoded prior to transmission to the I and Q channels Each rate 1 2 convolutional encoder is an n parallel encoder An n parallel encoder consists of n branch encoders in parallel where the quantity n is either 1 for the DB data or 8 for the DD
24. es 13 14 and 15 respectively If itis desired to evaluate the link budget for a different ground elevation angle from the ones shown in this document the EIRP and polarization loss rows 4 and 6 in the link budgets can be updated using the information in Figure 13 The DAS system tests were performed using an Engineering Test Model ETM antenna mounted on a mockup of the nadir face of the Spacecraft The data in these three figures is a weighted average of the ETM antenna measurements at five frequencies in which the data is integrated with respect to power spectral density occupancy of the DP1 150 150 Mbps I Q signal The following factors should be used to adjust the data in these figures for other data rates Symbol Rate Correction Factor 26 Mps 40 3 dB 210 Mps 0 2 dB 47 DMC201198 861I0CcOING Sr 55071 opes EXV 5 093545 SVA EIRP DBW DAS SYSTEM EIRP MINUS AXIAL RATIO LOSS EFF EIRP MAX A EFF EIRP MEAN a EFF EIRP MIN 40 50 ELEVATION ANGLE DEG 8661 FOQUISAON 0c 9698000 51 6t 861I0COING ISUV 349159104 euuajuy 6 19 euuasjuy 45 SVA Gain dBi DAS System Antenna Gain dBi vs Antenna Borsight Angle 150 Mbps Data MIN MEAN 40 50 Antenna Boresight Angle
25. gh Gain Antenna Housekeeping Telemetry Health and Safety Telemetry Hertz Interface Control Drawing Intermediate Frequency Input Output kilobits per second Kilohertz Ku band Single Access Left Hand Circularly Polarized Low Noise Amplifier Load Power Conditioner Mode as defined in STDN 101 2 Megabits per second Megasymbols per second Megahertz Master Oscillator Not Applicable National Aeronautics and Space Administration Numerically Controlled Oscillator Non Return to Zero Level Non Return to Zero Mark Ovenized Crystal Oscillator omnidirectional 54 PLL PM PN pps PBSG PRBS PWM QPSK RFI RHCP RT SCC SFE SQPN SQPSK SSR STDN TCXO TDRSS TLM VCO VSWR WGS WPS WSGT X band RFICD 1520008696 20 November 1998 Printed Circuit Board Phase Lock Loop Phase Modulation Pseudorandom Noise pulses per second Pseudorandom Bit Stream Generator Pseudo Random Bit Stream Phase Width Modulated Quadrature Phase Shift Keying Radio Frequency Radio Frequency Interference Right Hand Circularly Polarized Remote Terminal Spacecraft Control Computer Science Formatting Equipment Staggered Quadriphase Pseudorandom Noise Staggered Quadrature Phase Shift Keying Solid State Recorder Spaceflight Tracking and Data Network Temperature Compensated Drystal Oscillator Tracking and Data Relay Satellite System Telemetry Voltage Controlled Oscillator Voltage Standing Wave Ratio Waveguide Switc
26. h Wallops Island Station White Sands Ground Tracking NASA document 5310 RFICD EOS AM 1 EPGN 55 DMC201198
27. h Reed Solomon Decoding 27 Required 1 2 CONV RS 2 40 2 40 28 SYSTEM LINK MARGIN 1 2 CONV RS 5 97 10 54 382 996 29 LINK MARGIN ABOVE 3DB GOAL 1 2 2 97 7 54 0 82 CONV RS 1 User should provide a value for the Ground Multipath Degradation because this item in budget depends on the ground station design 2 The uncertainty band for the implementation loss is 0 3 dB based on two analysis methods The actual value will depend on the ground station as well as the spacecraft segment Note 2 N 21 22 23 21 22 26 E NE EX gt 8661 1 0c 9698000 51 861I0COING Table VII DAS Return Downlink Budget for Direct Downlink DDL or Direct Playback 2 DP2 Modes Ground Station Antenna Gain 3m 56 1 dBi Eff 2 0 55 Range at Ground Elevation Angle of 5 degrees 2574 5 BB Lue T mm T Gnd Station Elev Angle DAS Ant Boresight Angle degrees Parameter 5 63 8 40 43 6 63 24 90 0 Units Comments 13 pue free pa or 6m Wr feoeo respon pe sw am we we vm ww pam a LT pum ume es pon um psoas oan nm Ground Station Antenna Gain 57 30 5730 57 30 57 30 11 3m eff 55 Received Carrier Power 109 89 3107 31 114 37 108 54
28. he NRZ M format data values are defined by either a change in value from the Nth to the N 1st bit logic 1 or by no change in value from the Nth to the 3 150 bit logic 0 The differential encoding process in which the format is changed from NRZ M to NRZ L doubles the bit error rate because a single bit error in the NRZ M data stream produces two adjacent errors after conversion to the NRZ L data format Figure 16 illustrates the significant benefits of data coding by showing the probability of error Pe as a function of Eb No performance associated with several types of data coding For a BER of 1 x 105 the required Eb No values range from 9 6 dB for the case of no coding to 4 2 dB for convolution encoding only to greater than 2 4 dB for convolution plus Reed Solomon coding with 1 4 The link budgets provided in Section 6 are provided for two points on Figure 16 a Point A Convolutional Encoding length 7 rate 1 2 Only requires a Eb No of 4 2 dB to achieve a BER of 1 x 10 b Point Reed Solomon plus Convolutional Encoding requires a Eb No of greater than 2 4 dB to achieve a BER of 1 x 1075 51 DMC201198 1520008696 20 November 1998 107 10 2 10 3 10 10 5 1078 1077 1078 1079 10 19 0 1 2 THEORETICAL CURVES IDEAL NO CODING Ns CONV CODING 7 1 2 R S CODING 255 223 CONV R S IDEAL INTERLEAVE gt 5 L CONV R S NO INTERLEAV
29. ion Contact with the user ground stations is achieved through the DAS antenna The DAS antenna is composed of a cup and dipole feed with a shaped reflector which transmits in as shown in Figure 2 The antenna operates with right hand circularly polarized signals The reflector is shaped to provide approximately constant power density on the earth for a subtended angle of 63 8 about the Spacecraft earth pointing axis DMC201198 14 SI 861I0CcOING RECORDER EM pese NT DAS PANEL Science Formatting LCL Equipment SFE Part of Part of C amp DHS CMD TLM Signals 120V DAS Equipment Figure 1 X band Block Diagram 8661 0C 9698000 51 861I0cOING 91 Vitron Absorber Cup Dipoles Graphite Feed Assembly Reflector WR112 Waveguide Input SSS ISS SJ IY SA eee Aluminum Boom Adapter Graphite Sandwich Panel ribs Interface to DAS Support Tripod Figure 2 DAS Antenna Configuration 8661 FOQUISAON 0c 9698000 51 1520008696 20 November 1998 Figure 3 shows the DAS satellite to earth station geometry The boresight of the DAS antenna will continuously point toward the center of the earth User ground stations which are assumed to be either 3 meter 11 3 meter receiver dishes should be programmed to track in X band as the satellite passes overhead The Spacecraft to ear
30. plied within the DAS modulator prior to transmission to the earth station At the earth station it is assumed that the demodulator will employ a 3 bit soft decision Viterbi decoding process code rate of 1 2 and constraint length of 7 and that the bit stream will be Reed Solomon decoded prior to delivery to the data users The specific Spacecraft to user downlink configurations for the various DAS services are shown in the following figures a Figure 5 Direct Broadcast DB with Q I 4 1 b Figure 6 Direct Downlink DDL or Direct Playback 2 DP2 with Q I24 1 c Figure 7 Direct Playback 1 DP1 or Pseudo Random Bit Stream PRBS Test with Q I 1 1 The user is encouraged to review the X band RFICD for a detailed description of NASA s approach to preparing the direct playback data at EPGN 17 DMC201198 861I0cOING EOS AM orbit Horizon 64 degrees 705 Km DAS Antenna Horizon Earth center Figure 3 DAS Satellite to Earth Station Geometry Dm e the link distance is 2575 Km at the min imum ground station elevation angle of 5 degrees 8661 J9qui9 0N 0c 9698000 51 1520008696 20 November 1998 11 3M or 3M 8212 5 MHz Earth Station SSPA DAS Antenna Receiver DAS pconverter Waveform amp 4 Continuous Rate 1 2 7 Viterbi Convolutional Decoder
31. pment provides 4 paths for X band transmission through the DAS subsystem ensuring that no credible single point failure can cause the loss of the DAS communication link Upon command 4 bit wide data is delivered on either or both data channels to the DAS modulator from the Science Formatting Equipment SFE which is part of the Command and Data Handling C amp DH Subsystem The signal from the SFE 15 differential emitter coupled logic ECL in a non return to zero level NRZ L format The DAS Modulator reclocks the data and differentially encodes it to convert the data to non return to zero mark NRZ M format The modulator then encodes the NRZ M signal using a convolutional encoder at a rate of 1 2 and a constraint length of 7 The output symbol rate from the convolutional encoder is two times the input bit rate The I and Q channel data is Staggered Quadrature Phase Shift Keying SQPSK modulated onto the X band carrier at the intermediate frequency IF The Q I power ratio is either 1 1 or 4 1 depending on the mode as shown in Table The upconverter converts the IF frequency to X band and delivers this signal to the solid state power amplifier SSPA The SSPA provides the final amplification required to provide adequate RF power at X band to close the communication link The output of the SSPA is routed to the DAS antenna via a waveguide transfer switch and transmit filter 3 3 DAS to Earth Station Communication Link Interface Descript
32. provide a value for the Ground Multipath Degradation because this item in budget depends on the ground station design 2 The uncertainty band for the implementation loss is 1 9 dB based on two analysis methods The actual value will depend on the ground station as well as the spacecraft segment N EX E gt 8661 1 0c 9698000 51 861I0COING Table VIII DAS Return Downlink Budget for Direct Playback 1 DP1 Mode Ground Station Antenna Gain 3m 56 1 dBi Eff 2 0 55 Range at Ground Elevation Angle of 5 degrees 2574 5 Baar IM Data Type NRZ L M NRZ L M Gnd Station Elev Angle DAS Ant Boresight Angle degrees Parameter 5 63 8 40 43 6 63 24 90 0 Units Comments oue fam pow free oem rjesmsomum ue 5 owe oom pas FS 0 ome pass pem pas pssamcmsm pum Ground Station Antenna Gain 57 30 57 30 57 30 57 30 10m eff 55 Received Carrier Power 10974 10716 11422 108 39 sum of 4 through 10 8661 J9qui9 0N 0 969800051 861I0cOING Table VIII DAS Return Downlink Budget for Direct Playback 1 DP1 Mode continued Gnd Station Elev Angle DAS Ant Boresight Angle degrees Parameter 5 63 8 40
33. rect Broadcast DB Mode with Q I 4 1 Ground Station Antenna Gain 3m 45 6 dBi Eff 0 55 Range at Ground Elevation Angle of 5 degrees 2574 5 Data Rate Mbps 13 125 13 125 Data Type NRZ L M NRZ L M Gnd Station Elev Angle DAS Ant Boresight Angle degrees Parameter 5 63 8 40 43 6 63 24 90 0 Units Comments e pas pas oe 38 w feos Tuis arii reso aen an soras D iroster eorpore oso finnen fo oa mm oo ferne _ Ground Station Antenna Gain 45 60 45 60 45 60 45 60 3m eff 55 Received Carrier Power 121 14 118 56 125 62 119 79 sum of 4 through 10 8661 1 0 9698000 51 861I0cOING cr Table VI DAS Return Downlink Budget for Direct Broadcast DB Mode with Q I 4 1 continued Gnd Station Elev Angle DAS Ant Boresight Angle degrees Parameter 5 63 8 40 43 6 63 24 90 0 Units Comments 14 24 71 22 72 296 187 173 161 deg K 5 20 89 22 88 G T degraded by rain Received Carrier to Noise Density Ration C No 82 75 87 32 80 60 86 74 dB Hz 11 14 16 Convert C to Eb 71 18 71 18 71 18 71 18 dB bps 10 log 13 125e6 mE m m oo 1 20 4 1 power ratio with tolerance Link margin Wit
34. rformance Specification DAS Modulator Critical Development Performance Specification DAS SSPA 11 DMC201198 1520008696 20 November 1998 PS20008745 1520008658 Source 2 2 NASA Documents Design Documents Specifications Critical Development Performance Specification Command and Data Handling Communications Equipment Module Interface Control Document Data Format Control Book for EOS Spacecraft ICD 106 Lockheed Martin Missiles and Space P O Box 8555 Philadelphia PA 19101 8555 Memo to J Deskevich GSFC Code 502 from J Hart STel EOS AMI Interference to DSN at X band March 20 1995 531 RFICD EOS X band Radio Frequency Interface Control Document Source CCSDS 101 0 2 Jan 1987 Source DMC201198 RFICD Between the EOS AM 1 Spacecraft and the EOS Polar Ground Network EPGN NASA Goddard Space Flight Center Code 531 1 Greenbelt MD 20771 Consulting Consortium of Space Data Systems Telemetry Channel Coding Issue 2 Blue Book CCSDS Secretariat Communications and Data Systems Div Code TS National Aeronautics and Space Administration Washington DC 20546 12 1520008696 20 November 1998 3 OVERVIEW OF THE DIRECT ACCESS SYSTEM DAS The Direct Access System DAS provides real time science data from the EOS AM 1 Spacecraft Instruments directly to the science community independent of the EOS Data and Information System EOSDIS
35. sctplal 2 2222225024 Ray RE ERA RARE E 14 3 3 DAS to Earth Station Communication Link Interface Description 14 3 4 Baseband Signal Characteristics 23 3 4 1 Convolutional Coding ss 23 3 4 2 Viterbi Decoding RERO E 23 35 DAS Management 20 3541 29 3 5 2 PON 22 444 koe awe eae 29 4 DAS SUBSYSTEM OPERATING MODES 31 4 1 Pseudo Kandom Bit Stream Test 31 42 Direct Broadcast of MODIS Instrument Data 31 4 3 Direct Downlink of ASTER Instrument Data 32 4 4 Direct Playback of Recorded Science and Housekeeping Data 33 4 5 Standby MEET EI 33 5 DAS RF CHARACTERISTICS RR RR eR xe 35 6 DAS COMMUNICATION LINK BUDGETS 39 6 1 Direct Broadcast DB Link Budget 39 6 2 Direct Downlink DDL Link Budget 39 6 3 Direct Playback Link Budgets RR XXe OE Yee 40 5 DMC201198 1520008696 20 November 1998 TABLE OF CONTENTS Continued SECTION PARAGRAPH TITLE PAGE APPENDIX I 1 ANTENNA PERFORMANCE DATA 45 APPENDIX II 2 IMPACT OF DATA CODING ON REQUIRED
36. stics Continued Data Bit Jitter DB and DP mode 0 37 Radians for BER 0 37 radians for BSR DDL mode 0 85 Radians for BER 0 37 radians for BSR In Band Flux Density 0 lt OgL lt 5 lt 150 dBW m2 4 kHz 5 lt OEL lt 25 lt 150 0gL 5 2 dBW m 4 kHz 25 lt lt 90 140 dBW m 4 kHz Spurious Output Out of band lt 39dBm per Hz outside 5 of transmit freq 72 dBm per Hz 2106 4 to 2112 5 MHz Phase Noise 1 10 Hz 1 0 RMS 10 100 Hz 2 0 RMS 100 Hz 1 kHz 3 0 RMS 1 kHz 150 MHz 2 0 RMS Frequency Stability 1 Second Average 55 10 5 Hour Average 3 x 10 1 48 Hour Average 3 x 10 10 System Bit Error Rate BER 1 x 102 Goal link margin gt 3dB DAS Space Segment BER lt 0 5x1077 DB DDL DP2 lt 8x10 DPI Untracked Spurious PM 1 kHz to 150 2 degrees mHz Carrier Suppression gt 30 dB Service Interruption lt 5 seconds during mode transitions Gain Flatness dBp p over 112 MHz Antenna Boresight Gain Flatness Angle degrees dB p p 0 5 0 dBp p 17 9 3 7 dBp p 43 6 19 dBp p 63 8 2 0 dBp p DMC201198 36 1520008696 20 November 1998 Table IV X band DAS Subsystem Performance Characteristics Continued Phase Nonlinearity degrees p p over Antenna Boresight Phase Nonlinearity 112 MHz Angle degrees degrees p p 0 17 9 43 6 63 8 Note 1 SQPSK Staggered QPSK USQPSK Unbalanced Staggered QPSK Note 2 Resultant transmitted phasors
37. sum of 4 through 10 8661 J9qui9 0N 0c 9698000 51 861I0CcOING Table VII DAS Return Downlink Budget for Direct Downlink DDL or Direct Playback 2 DP2 Modes continued Gnd Station Elev Angle DAS Ant Boresight Angle degrees Parameter 5 63 8 40 43 6 63 24 90 0 Units Comments 12 Ground Station Noise Temperature 180 00 15500 15500 155 00 clear sky 3 Noise Temperature Increase Due to Rain K 116 00 32 00 18 00 estimate aj gt Total Noise Temp in dB 24 71 22 72 22 38 22 07 296 187 173 161 deg K Ground Station G T 32 59 34 58 34 58 35 23 dB K G T degraded by rain Received Carrier to Noise Density Ration C No 94 00 98 57 91 85 97 99 dB Hz 11 14 16 Convert C to Eb 80 21 80 21 80 21 80 21 dB bps 10 log 105e6 9 Ground Multipath Degradation 000 User to supply Note 11 N 1 4 pwr ratio w tolerance ww fow om 7 ieena ess es pe 1 30 38 39 s wer p 9m m 3m ww sw m mexm em Link margin With Reed Solomon Decoding __ _____ 35 SYSTEMENE MARGIN ns mw een om m m ym pom o 1 User should
38. th station link distance ranges from 2575 km at a ground station elevation angle of 5 degrees to 705 km at a station elevation angle of 90 degrees Ground antenna support is dependent on favorable radio line of sight conditions when the ground antenna angle is greater than 5 degrees i e above the local mask The ground station location determines the orbits and portions of orbits in which contacts can be made and the ground station acquisition cone determines the duration of the contact for the given orbit The ground antenna will be selected by the user to provide the performance needed for satisfactory link performance The ground antenna which meets the user s requirements may be different from the antennas assumed in the link budget tables in Section 6 Note that 3 meter dishes are suitable only for the lower data rates of DB service not for the high data rates of DDL and DP service which require dishes of approximately 11 3 meters diameter The DAS transmits all data at the fixed frequency of 8 2125 GHz The frequency reference is generated by an Ovenized Crystal Oscillator OCXO The center carrier frequency derived from the OCXO is 912 5 MHz 300 Hz The frequency stability of the OCXO are as shown in Table IV Figure 4 illustrates the overall DAS communications link Onboard the Spacecraft instrument data undergoes a concatenated encoding process in which Reed Solomon coding is applied by the SFE and then convolutional encoding is ap
39. tream in real time via a QPSK modulated X band downlink In normal operation DAS mode 3 will be used for the direct broadcast service In DAS mode 3 DB data is provided with positive link margin on the higher powered channel Q I 4 1 and 15 encoded in a single convolutional encoder DB data is provided on channel I in DAS modes 2 3 4 and 6 and the I channel data is uncoded in modes 2 and 3 and is encoded in a single convolutional encoder in modes 4 and 6 31 DMC201198 1520008696 20 November 1998 Table III DAS Subsystem Operating Modes Mode Description Input Data Output Data Rate and Maximum Data Mbps Rate Mbps Pseudo Random Bit Stream Test DB DDL and DP off DB only Q I 1 1 13 125 13 125 not used uncoded serial encoded DB only Q 1 4 1 13 125 Direct Downlink DDL _ uncoded serial encoded 13 125 105 DB serial DDL encoded parallel encoded DP1 only bit interleaved for effective rate of 150 Direct Playback 2 DP2 13 125 DB serial DP2 encoded parallel encoded 7 Standby N A Notes 1 The final output is 1 2 rate encoded data at symbol rates two times the data rates shown 2 The IF and LO outputs of the DAS Modulator are switched off in Standby mode providing a means of disabling RF output while maintaining oscillator stability for operational readiness 3 The DB link is not required for modes 4 an
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