Post on 18-Jan-2016
Final Version
Frank StocklinRon Vento
Bob Summers
May 17 2002
Data Systems
Micro-Arcsecond Imaging Mission, Pathfinder (MAXIM-PF)
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LAI-Maxim-PF May 17.2002Goddard Space Flight Center
Final Version
Data SystemsTopics
Ops Concept Driving Requirements and Assumptions Selected Configuration and Rationale Signal Margin Summary Component Power/Mass/Cost Summary Risk Assessment LASER option Backup
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OPS CONCEPT
HUB to Free Flyers(FF) UHF
Coherent for ranging/ 60 Kbps duplex data transfer CDMA
simultaneous receive of 6 FF’s Time share transmits to 6 FF’s
may also be able to simultaneous transmit to FF’s if necessary-needs some NRE LASER reflector FF to HUB to determine relative position
HUB to Detector S-Band
34 kbps/5.5 Kbps using HGA’s w/omni backup Simultaneous receive/transmit with HUB to FF
LASER reflector to determine relative position
Detector to Ground X Band to DSN
5 Mbps/5 Kbps 15 minute dump/day
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LAI-Maxim-PF May 17.2002Goddard Space Flight Center
Final Version Launch Date: August 2015
Mission Life: 4 years required/5 year goal Nominal Orbit: L2 Location Stellar pointing One HUB S/C & 6 identical Free Flyers located in a spherical arc
forming a radius of 100-500 m 50 Kbps to/from
One Detector S/C located at 20 KKM from HUB 34/5.5 Kbps to/from
Distance from HUB to FF’s must be determined RF ranging will be course & LASER will be fine
Distance from HUB to Detector must be determined RF ranging will be course & LASER will be fine
Formation flying Maintained by continuous RF & LASER
Data SystemsDriving Requirements &
Assumptions
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Final Version No FF inter-communications
Data Latency: None Telemetry BER =10-5
Selective redundancy appropriate
Data SystemsDriving Requirements &
Assumptions
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Selected Configuration & Rationale
Free Flyers
UHF selected because of ease of antenna design to minimize nulls
Transponder design from current transceiver design* CDMA used to enable simultaneous communication with 6 FF’s Ranging enabled by use of PN code
FF’s will compute range to HUB 60 Kbps duplex link between HUB & FF’s Baseline approach is to time share transmissions from HUB
to FF’s Possible to design for simultaneous transmissions-needs some
NRE
Laser Used for range and position of the HUB to FF’s
* Prototype will fly on STS this summer
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Selected Configuration & Rationale
HUB
UHF/S-Band Transponders (2) S-Band
2 omnis Fixed HGA (0.3 M) 2 HPAs (10 watts) Transmit/receive 34 kbps/5.5 kbps to/from detector (operational
mode) Transmit/receive 50 bps with detector (coarse ranging and
emergency) UHF
2 omnis (or patches) Transmit 60 kbps to each of 6 FFs (time shared - effective rate
received at each FF is 10 kbps)
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Selected Configuration & RationaleDetector
S-Band 2 transponders 2 omnis Fixed HGA (0.3 M) 2 HPA (10 watts) Transmit/receive 5.5kbps/34 kbps to/from HUB (operational mode) Transmit/receive 50 bps with HUB (coarse ranging and emergency)
X-Band 2 Transponders 2 omnis 2 gimbaled HGAs (0.5 M) Transmit/Receive 50 Kbps/5 kbps with DSN 34 M (using S/C HGA) Transmit/Receive 50 bps/5 kbps with DSN 34 M (using S/C omni) Ranging available
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Data SystemsSelected Configuration &
Rationale
MOCDSN 34 M
Science & Hskpg
Command
HUB
34M
Free Flyers(6)
DETECTOR
LASER FF’s to HUB
RF
RFRF
RFRFRF
RF
LASER HUB to DETECTOR
X Band
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Final Version
Selected Configuration and Rational
Functional Free Flyer Block Diagram
C&
DH
LASER
CMD/TLM
Multi Channel UHF transponder HybridDiplexer Omnis/
patches
To HUB
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Selected Configuration and Rational
Functional HUB Block Diagram
C&
DH
UHF Omnis/patche
s
0.3M S-Band
ReflectorLASER
Multi CH UHF/S BandTransponder(2)
CMD/TLM
Diplexer Hybrid
S-Band Omnis
Hybrid
HUB to FF communications
HUB to Detector communications
6 Channels from FF’s
CDMA
RF SwitchDiplexer
To Detecto
r
6 LASER
Reflectors
HPA(2)
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Selected Configuration and Rational
Functional Detector Block Diagram
C&
DH
S Band Omnis
0.5M X-Band
Reflector
S BandTransponder(2)
CMD/TLM
Diplexer Hybrid
X-Band Omnis
Hybrid
Detector to HUB communications
Detector to Ground communications
RF SwitchDiplexer
1 LASER
Reflector
RF Switch
HPA(2)
X BandTransponder(2)
0.3 M
HGA
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Final Version
Maxim_PF Signal Margins
Mode Data Rate Margin (dB) Max Range
Antennas
UHF HUB/ Freeflyer Freeflyer/ HUB
60 kbps 22.3 Omnis at 1 milliwatt
S-band Hub to Detector
34 kbps 4.7 0.3 M HGA
X-Band Tlm Detector to 34 M
5 Mbps 0.7 0.5 M HGA
X-Band Uplink 34 M Detector
5 kbps 20.9 S/ C 0.5 HGA 34 M at 200 watts
S-Band Detector to HUB
5.5 kbps 9.6 0.3 M HGA
S-band Hub to Detector to HUB
50 bps 0.0 Omnis
X-Band Tlm Detector to 34 M
5 kbps 0.9 Omni
X-Band Uplink 34 M Detector
5 kbps 2.5 S/ C Omni 34 M at 2000 watts
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Power/Mass/Cost SummaryFree Flyer
Component Power (Peak/ Average)
Mass Cost
UHF Omni Antenna (2)
----- 2 kg $ 100 k
UHF xpndr
10/ 10 watts 3.5 kg $ 500 k
Diplexer , hybrid , Misc
----- 2 kg $ 200 k
Laser I ncluded in instruments
TOTALS 10/ 10 watts 7.5 kg $800 k
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Mass/Cost/Power Summary HUB
Component Power
Peak/ Average Mass Cost
S/ UHF-band Omni Antennas (4)
----- 4kg $200 k
S/ UHF-band Xpndr (2)
22 / 22watts 7 kg $1.0 M
S-Band HPA (2) 40/ 40 watts 8 kg $1.0 M
S-Band HGA (fi xed)
---- 4 kg $2.0 M
Diplexers ,Hybrids Miscellaneous
----- 6kg $ 300 k
Laser Reflectors (6) ----- TBD TBD
Laser I ncluded in instruments
Total 62/ 62 watts 29 kg $4.5 M
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Mass/Cost/Power Summary Detector
*Includes gimbals, booms, deployment hardware
ComponentPower
(peak/Average)Mass Cost
S/X-band Omni Antennas (2 each)
4 kg $200K
X-Band xpndr (2) 42/25 watts 8 kg $1.0 M
S-Band xpndr (2) 22/22 watts 7 kg $1.0 M
S-Band HPA (2) 40/40 watts 8 kg $1.0 M
S-Band HGA (fixed) 4 kg $2.0 M
X-Band HGA (2)( gimbaled)
16/1 watts 24 kg * $6.0 M
Hybrids, diplexers, switches, misc
10 kg $500K
Laser reflectorIncluded in instruments
Total 120/88 watts 65 kg $11.7 M
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Data SystemsCost Summary
FreeFlyer (6) $0.8 MHUB $4.5 MDetector $11 .7 MGround station $2.4 M (4 years)**
TOTAL $19.4 M*
*Laser cost included in instruments ** Includes 1 hr pre/post pass time
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LASER OPTION
Laser data link between the HUB and Detector Eliminates two 0.3 M antennas
4 kg and $2 M savings on both HUB and Detector. RF transponders and HPAs still required for coarse ranging and
emergency modes Requires 1.9 kg,and 1.9 watts on both HUB and Detector $1 M NRE and $0.5 M per flight unit
Net difference from RF -2.1 kg, + 2 watts, -$0.5 M (Detector-Includes all NRE) -2.1 kg, + 2 watts, -$1.5 M (HUB)
** Exact details are given in the backup charts
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Data SystemsRisk Assessment
Some NRE to make current transceiver design to transponder
Multi channel receive for HUB is an evolving capability but is not a concern for the time frame of this mission
Simultaneous transmission of 2 independent signals (HUB to FF & Detector) is also doable but should be encouraged(funded) to make it happen
Simultaneous transmission of 6 signals (HUB to FF’s) is probably doable but needs to be funded & demonstrated
Basic design is low-medium risk
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Back-Up Charts
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UHF HUB/Freeflyer - Freeflyer/Hub50 kbps
*** DOWNLINK MARGIN CALCULATION*** GSFC C.L.A.S.S. ANALYSIS #1 DATE & TIME: 5/14/ 2 14: 9:47 PERFORMED BY: R. VENTO LINKID: MAXIM FREQUENCY: 400.0 MHz RANGE: 0.5 km MODULATION: BPSK DATA RATE: 50.000 kbps CODING: RATE 1/2 CODED BER: 1.00E-05 OMNIS AT 300 DEG 1 MILLIWATT PARAMETER VALUE REMARKS --------------------------------------------------------------------------------------------- 01. USER SPACECRAFT TRANSMITTER POWER - dBW -30.00 0.0 WATTS 02. USER SPACECRAFT PASSIVE LOSS - dB 5.00 NOTE A 03. USER SPACECRAFT ANTENNA GAIN - dBi 0.00 NOTE A 04. USER SPACECRAFT POINTING LOSS - dB 0.00 NOTE A 05. USER SPACECRAFT EIRP - dBWi -35.00 06. POLARIZATION LOSS - dB 0.30 NOTE A 07. FREE SPACE LOSS - dB 78.46 NOTE B 08. ATMOSPHERIC LOSS - dB 0.00 NOTE A 09. RAIN ATTENUATION - dB 0.00 NOTE A 10. MULTIPATH LOSS - dB 0.00 NOTE A 11. GROUND STATION ANTENNA GAIN - dB 0.00 NOTE A 12. GROUND STATION PASSIVE LOSS - dB 5.00 NOTE A 13. GROUND STATION POINTING LOSS - dB 0.00 NOTE A 14. SYSTEM NOISE TEMPERATURE - dB-DEGREES-K 24.77 NOTE A 15. GROUND STATION G/T - dB/DEGREES-K -29.77 16. BOLTZMANN'S CONSTANT - dBW/(Hz*K) -228.60 CONSTANT 17. RECEIVED CARRIER TO NOISE DENSITY - dB/Hz 85.07 18. MODULATION LOSS - dB 0.00 NOTE A 19. DATA RATE - dB-bps 46.99 NOTE A 20. DIFFERENTIAL ENCODING/DECODING LOSS - dB 0.00 NOTE A 21. USER CONSTRAINT LOSS - dB 0.00 NOTE A 22. RECEIVED Eb/No - dB 38.08 23. IMPLEMENTATION LOSS - dB 3.00 NOTE A 24. REQUIRED Eb/No - dB 4.25 NOTE B 25. REQUIRED PERFORMANCE MARGIN - dB 0.00 NOTE A 26. MARGIN - dB 30.83 * MAXI04 * Minus 7.8 dB when supporting 6 Freeflyers simultaneously
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Final Version
X-band Downlink Detector to 34M BWG5 Mbps HGA
*** DOWNLINK MARGIN CALCULATION*** GSFC C.L.A.S.S. ANALYSIS #1 DATE & TIME: 5/14/ 2 14:36:44 PERFORMED BY: R. VENTO LINKID: 11 FREQUENCY: 8475.0 MHz RANGE: 1800000.0 km MODULATION: BPSK DATA RATE: 5000.000 kbps CODING: TURBO BER: 1.00E-05 S/C 0.5 METER ANTENNA 99% AVAILABILITY PARAMETER VALUE REMARKS --------------------------------------------------------------------------------------------- 01. USER SPACECRAFT TRANSMITTER POWER - dBW 6.99 5.0 WATTS 02. USER SPACECRAFT PASSIVE LOSS - dB 3.00 NOTE A 03. USER SPACECRAFT ANTENNA GAIN - dBi 30.35 NOTE A 04. USER SPACECRAFT POINTING LOSS - dB 0.50 NOTE A 05. USER SPACECRAFT EIRP - dBWi 33.84 06. POLARIZATION LOSS - dB 0.50 NOTE A 07. FREE SPACE LOSS - dB 236.11 NOTE B 08. ATMOSPHERIC LOSS - dB 0.50 NOTE A 09. RAIN ATTENUATION - dB 1.00 NOTE A 10. MULTIPATH LOSS - dB 0.00 NOTE A 11. GROUND STATION ANTENNA GAIN - dB 68.20 NOTE A 12. GROUND STATION PASSIVE LOSS - dB 0.00 NOTE A 13. GROUND STATION POINTING LOSS - dB 0.00 NOTE A 14. SYSTEM NOISE TEMPERATURE - dB-DEGREES-K 20.79 NOTE A 15. GROUND STATION G/T - dB/DEGREES-K 47.41 16. BOLTZMANN'S CONSTANT - dBW/(Hz*K) -228.60 CONSTANT 17. RECEIVED CARRIER TO NOISE DENSITY - dB/Hz 71.74 18. MODULATION LOSS - dB 0.00 NOTE A 19. DATA RATE - dB-bps 66.99 NOTE A 20. DIFFERENTIAL ENCODING/DECODING LOSS - dB 0.00 NOTE A 21. USER CONSTRAINT LOSS - dB 0.00 NOTE A 22. RECEIVED Eb/No - dB 4.75 23. IMPLEMENTATION LOSS - dB 3.00 NOTE A 24. REQUIRED Eb/No - dB 1.00 NOTE A 25. REQUIRED PERFORMANCE MARGIN - dB 0.00 NOTE A 26. MARGIN - dB 0.75 MAXI06 NOTE A: PARAMETER VALUE FROM USER PROJECT - SUBJECT TO CHANGE NOTE B: FROM CLASS ANALYSIS IF COMPUTED
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Final Version
S-band Detector/Hub - Hub/Detector5.5 Kbps - 34 Kbps HGAs
*** DOWNLINK MARGIN CALCULATION*** GSFC C.L.A.S.S. ANALYSIS #1 DATE & TIME: 5/14/ 2 12:17:48 PERFORMED BY: R. VENTO LINKID: MAXIM FREQUENCY: 2250.0 MHz RANGE: 20000.0 km MODULATION: BPSK DATA RATE: 34.000 kbps CODING:TURBO BER: 1.00E-05 S/C ANTENNAS ARE 0.3 METERS AT 300 DEG TURBO CODES PARAMETER VALUE REMARKS ----------------------------------------------------------------------------------------------------------- 01. USER SPACECRAFT TRANSMITTER POWER - dBW 6.99 5.0 WATTS 02. USER SPACECRAFT PASSIVE LOSS - dB 3.00 03. USER SPACECRAFT ANTENNA GAIN - dBi 14.51 04. USER SPACECRAFT POINTING LOSS - dB 0.00 05. USER SPACECRAFT EIRP - dBWi 18.50 06. POLARIZATION LOSS - dB 0.30 07. FREE SPACE LOSS - dB 185.51 08. ATMOSPHERIC LOSS - dB 0.00 09. RAIN ATTENUATION - dB 0.00 10. MULTIPATH LOSS - dB 0.00 11. GROUND STATION ANTENNA GAIN - dBi 14.51 0.3 M, EFF: 55.0% 12. GROUND STATION PASSIVE LOSS - dB 0.00 13. GROUND STATION POINTING LOSS - dB 0.00 14. SYSTEM NOISE TEMPERATURE - dB-DEGREES-K 24.77 15. GROUND STATION G/T - dB/DEGREES-K -10.26 16. BOLTZMANN'S CONSTANT - dBW/(Hz*K) -228.60 CONSTANT 17. RECEIVED CARRIER TO NOISE DENSITY - dB/Hz 51.04 18. MODULATION LOSS - dB 0.00 19. DATA RATE - dB-bps 45.31 20. DIFFERENTIAL ENCODING/DECODING LOSS - dB 0.00 21. USER CONSTRAINT LOSS - dB 0.00 22. RECEIVED Eb/No - dB 5.72 23. IMPLEMENTATION LOSS - dB 3.00 24. REQUIRED Eb/No - dB 1.00 25. REQUIRED PERFORMANCE MARGIN - dB 0.00 26. MARGIN - dB 1.72 MAXI02
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Final Version
-
X-Band DSN 34 M BWG to Detector5 Kbps HGA
TABLE 0.5 S/C ANTENNA UPLINK DATE & TIME: 05/14/02 15: 1:25 MAXIM PF FREQUENCY - 7200.000 MHZ GROUND ANTENNA - - - 34 BWG POWER - 0.2000 K WATTS --------------------------------------------------------------------------- PARAMETERS UNITS VALUES ESTIMATED TOLERANCES (MAX RNG: (MIN RNG: DB 1805260. KM 1800000. KM 10.0 EL) 90.0 EL) FAV ADV --------------------------------------------------------------------------- EFFECTIVE RADIATED POWER DBM 120.0 120.0 1.0 -1.0 FREE SPACE DISPERSION LOSS DB -234.7 -234.7 0.0 0.0 ATMOSPHERIC LOSS DB -0.5 0.0 0.0 0.0 POLARIZATION LOSS DB -3.0 -3.0 0.0 0.0 SPACECRAFT ANTENNA GAIN DBI 28.5 28.5 0.0 0.0 SPACECRAFT PASSIVE LOSS DB -5.0 -5.0 0.5 -0.5 MAXIMUM TOTAL RECEIVED POWER DBM -94.7 -94.2 1.1 -1.1 SPACECRAFT ANTENNA NULL DEPTH DB 0.0 0.0 0.0 0.0 MINIMUM TOTAL RECEIVED POWER DBM -94.7 -94.2 1.1 -1.1 SYSTEM NOISE DENSITY DBM/HZ -171.6 -171.6 0.0 0.0 IF NOISE BANDWIDTH( 3000.000 KHZ) DB-HZ 64.8 64.8 0.0 0.0 IF NOISE POWER DBM -106.8 -106.8 0.0 0.0 IF SNR (MIN) DB 12.1 12.6 1.1 -1.1
--------------------------------------------------------------------------- CARRIER CHANNEL ------- ------- CARRIER/TOTAL POWER DB -2.9 -2.9 0.3 -0.3 RECEIVED CARRIER POWER DBM -97.6 -97.1 1.2 -1.2 CARRIER LOOP NOISE BW( 800. HZ) DB-HZ 29.0 29.0 0.0 0.0 NOISE POWER DBM -142.6 -142.6 0.0 0.0 CARRIER/NOISE DB 45.0 45.5 1.2 -1.2 REQUIRED CARRIER/NOISE DB 15.0 15.0 0.0 0.0 AVAILABLE CARRIER MARGIN DB 30.0 30.5 1.2 -1.2 REQUIRED PERFORMANCE MARGIN DB 3.0 3.0 0.0 0.0
NET MARGIN DB 27.0 27.5 1.2 -1.2 --------------------------------------------------------------------------- COMMAND CHANNEL (PCM/PSK/PM) ------- ------- ------------ COMMAND/TOTAL POWER(MI=1.10 RAD) DB -3.5 -3.5 0.3 -0.3 RECEIVED COMMAND POWER DBM -98.2 -97.7 1.2 -1.2 PREDETECTION (PSK) NOISE BW(80.000 KHZ) DB-HZ 49.0 49.0 0.0 0.0 PREDETECTION (PSK) NOISE POWER DB -122.6 -122.6 0.0 0.0 PREDETECTION (PSK) SNR DB 24.4 24.9 1.2 -1.2 COMMAND DATA RATE ( 5.000KBPS) DB-BPS 37.0 37.0 0.0 0.0 AVAILABLE ENERGY PER BIT/NOISE DENSITY DB 36.4 36.9 1.2 -1.2 DECODER DEGRADATION DB -2.0 -2.0 0.0 0.0 REQUIRED ENERGY PER BIT/NOISE DENSITY (BER=E-5) DB 10.5 10.5 0.0 0.0 AVAILABLE COMMAND MARGIN DB 23.9 24.4 1.2 -1.2 REQUIRED PERFORMANCE MARGIN DB 3.0 3.0 0.0 0.0 NET MARGIN DB 20.9 21.4 1.2 -1.2 ---------------------------------------------------------------------------
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Final Version *** DOWNLINK MARGIN CALCULATION***
GSFC C.L.A.S.S. ANALYSIS #1 DATE & TIME: 5/15/ 2 10:39:22 PERFORMED BY: R. VENTO LINKID: 11 FREQUENCY: 8475.0 MHz RANGE: 1800000.0 km MODULATION: BPSK DATA RATE: 5.000 kbps CODING: TURBO BER: 1.00E-05 S/C 0.5 METER ANTENNA 99% AVAILABILITY PARAMETER VALUE REMARKS --------------------------------------------------------------------------------------------- 01. USER SPACECRAFT TRANSMITTER POWER - dBW 6.99 5.0 WATTS 02. USER SPACECRAFT PASSIVE LOSS - dB 3.00 NOTE A 03. USER SPACECRAFT ANTENNA GAIN - dBi 0.00 NOTE A 04. USER SPACECRAFT POINTING LOSS - dB 0.00 NOTE A 05. USER SPACECRAFT EIRP - dBWi 3.99 06. POLARIZATION LOSS - dB 0.50 NOTE A 07. FREE SPACE LOSS - dB 236.11 NOTE B 08. ATMOSPHERIC LOSS - dB 0.50 NOTE A 09. RAIN ATTENUATION - dB 1.00 NOTE A 10. MULTIPATH LOSS - dB 0.00 NOTE A 11. GROUND STATION ANTENNA GAIN - dB 68.20 NOTE A 12. GROUND STATION PASSIVE LOSS - dB 0.00 NOTE A 13. GROUND STATION POINTING LOSS - dB 0.00 NOTE A 14. SYSTEM NOISE TEMPERATURE - dB-DEGREES-K 20.79 NOTE A 15. GROUND STATION G/T - dB/DEGREES-K 47.41 16. BOLTZMANN'S CONSTANT - dBW/(Hz*K) -228.60 CONSTANT 17. RECEIVED CARRIER TO NOISE DENSITY - dB/Hz 41.89 18. MODULATION LOSS - dB 0.00 NOTE A 19. DATA RATE - dB-bps 36.99 NOTE A 20. DIFFERENTIAL ENCODING/DECODING LOSS - dB 0.00 NOTE A 21. USER CONSTRAINT LOSS - dB 0.00 NOTE A 22. RECEIVED Eb/No - dB 4.90 23. IMPLEMENTATION LOSS - dB 3.00 NOTE A 24. REQUIRED Eb/No - dB 1.00 NOTE A 25. REQUIRED PERFORMANCE MARGIN - dB 0.00 NOTE A 26. MARGIN - dB 0.90 MAXI12 NOTE A: PARAMETER VALUE FROM USER PROJECT - SUBJECT TO CHANGE NOTE B: FROM CLASS ANALYSIS IF COMPUTED
X-band Downlink Detector to 34M BWG5 Kbps OMNI Mode
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Final Version
S-band Detector/Hub - Hub/Detector50 bits OMNIs
*** DOWNLINK MARGIN CALCULATION*** GSFC C.L.A.S.S. ANALYSIS #1 DATE & TIME: 5/15/ 2 10:29:54 PERFORMED BY: R. VENTO LINKID: MAXIM PF FREQUENCY: 2250.0 MHz RANGE: 20000.0 km MODULATION: BPSK DATA RATE: 0.050 kbps CODING: TURBO BER: 1.00E-05 PARAMETER VALUE REMARKS --------------------------------------------------------------------------------------------- 01. USER SPACECRAFT TRANSMITTER POWER - dBW 10.00 10.0 WATTS 02. USER SPACECRAFT PASSIVE LOSS - dB 5.00 NOTE A 03. USER SPACECRAFT ANTENNA GAIN - dBi 0.00 NOTE A 04. USER SPACECRAFT POINTING LOSS - dB 0.00 NOTE A 05. USER SPACECRAFT EIRP - dBWi 5.00 06. POLARIZATION LOSS - dB 0.30 NOTE A 07. FREE SPACE LOSS - dB 185.51 NOTE B 08. ATMOSPHERIC LOSS - dB 0.00 NOTE A 09. RAIN ATTENUATION - dB 0.00 NOTE A 10. MULTIPATH LOSS - dB 0.00 NOTE A 11. GROUND STATION ANTENNA GAIN - dB 0.00 NOTE A 12. GROUND STATION PASSIVE LOSS - dB 2.00 NOTE A 13. GROUND STATION POINTING LOSS - dB 0.00 NOTE A 14. SYSTEM NOISE TEMPERATURE - dB-DEGREES-K 24.77 NOTE A 15. GROUND STATION G/T - dB/DEGREES-K -26.77 16. BOLTZMANN'S CONSTANT - dBW/(Hz*K) -228.60 CONSTANT 17. RECEIVED CARRIER TO NOISE DENSITY - dB/Hz 21.02 18. MODULATION LOSS - dB 0.00 NOTE A 19. DATA RATE - dB-bps 16.99 NOTE A 20. DIFFERENTIAL ENCODING/DECODING LOSS - dB 0.00 NOTE A 21. USER CONSTRAINT LOSS - dB 0.00 NOTE A 22. RECEIVED Eb/No - dB 4.03 23. IMPLEMENTATION LOSS - dB 3.00 NOTE A 24. REQUIRED Eb/No - dB 1.00 NOTE A 25. REQUIRED PERFORMANCE MARGIN - dB 0.00 NOTE A 26. MARGIN - dB 0.03 MAXI10 NOTE A: PARAMETER VALUE FROM USER PROJECT - SUBJECT TO CHANGE NOTE B: FROM CLASS ANALYSIS IF COMPUTED
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Final Version
HUB - DETECTOR LASER COMMUNICATIONS
Concept: A low power laser communications link can exploit the precision alignment of the spacecraft to provide low rate data links with simple, low power, lightweight equipment.
Assumptions: Operates only when both spacecraft are in operational attitude. A low bandwidth RF link is used to control Hub and Detector
spacecraft positioning into the operational attitude. Approach:
Use low power “laser pointer” technology for the transmitters. Use a different frequency from the beacon to avoid interference. Simplify layout by using separate optics from beacon and star
tracker. Use simple modulation without forward error correction.
Requirements: Operate at a range of 20,000 kilometers between spacecraft. Communicate Forward data continuously from the Detector to
the Hub at 5500 bps. Communicate Return data from continuously from the Hub to the
Detector at 34,000 bps.
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Laser communications links
Transmitters: 671 nm, 10 & 50 mW GaAs diode lasers. 500 microradian beam divergence (simple lens). Higher power version of 5 mW “laser pointer.”
Receivers: 10 cm (4”) spacecraft telescope. 3.5 dB Implementation Loss; 2.0 dB Pointing Loss. Limited motion gimbal.
Det-to-Hub Hub-to-DetPtransmit -20.0 -13.0 dBWTx Gain (net) 75.6 75.6 dBRange Loss -291.5 -291.5 dB
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WEIGHT AND POWER ESTIMATE
Using parametric model and engineering estimates:
Mass (kg) Power (W)Telescope 0.17 0.4Solar Filter 0.10Gimbal 0.40 0.5Optics 0.20Laser Transmitter 0.10 0.2Sensor & Detector Assembly 0.20 0.2Support Electronics 0.20 0.2Mechanical & Cabling 0.20Power Conditioning 0.30 0.4
TOTAL (without margin) 1.87 1.88
Note: 10 mW transmitter will require less power (< 100 mW).
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COST & SCHEDULE ESTIMATE
COST Based on COTS laser technology; still requires a receiver. Assumes that fundamental R&D is completed; designs
exist. NRE to adapt existing designs to specific spacecraft:
~$1M. Recurring engineering for flight units: $0.2M to $0.5M.
SCHEDULE ESTIMATE (FLIGHT EQUIPMENT) NRE: ~ 6-12 months Recurring Build & Test: ~ 6-12 months
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Final Version
SUMMARY
Simple, low power “laser pointer” transmitter still requires a receiver with a telescope.
Eliminating gimbals requires precise co-alignment, though
Gimbals, if needed, can be very limited motion. Fixed geometry of spacecraft eliminates need for “look
ahead.”
Therefore Sharing the telescope for both transmit and receive
could be better: Increased transmitter gain allows smaller telescope, or Can use even lower power lasers, and Would allow much higher data rates. Little impact on mass and power.
Scalability very good (either alternative) through: Changing transmitter power (first choice up to about 100 mW). Use coding and/or better modulation (second choice). Increasing receiver telescope aperture (last choice).
Data SystemsPage 32
LAI-Maxim-PF May 17.2002Goddard Space Flight Center
Final Version
SHARED TELESCOPE ALTERNATIVE
EXAMPLE Reduced shared aperture to 2.5 cm. Decreased laser power to 2 mW and 10 mW.
SCALABILITY
DATA RATE LASER POWER MOD’N & CODING APERTURE 5 kbps 1 mW Simple; No FEC 2.5 cm
500 kbps 100 mW “ “ 1 Mbps “ Coherent; FEC “
10 Mbps “ “ 5.0 cm
Det-to-Hub Hub-to-DetPtransmit -10.0 -20.0 dBWTx Gain (net) 101.9 95.9 dBRange Loss -291.5 -291.5 dBRx Gain (net) 99.1 93.1 dBPower(receive) -100.5 -122.5 dBWPower(required) -104.9 -126.6 dBWMargin 4.4 4.0 dB