Frank Stocklin

1
Micro-Arcsecond Imaging Mission, Pathfinder
(MAXIM-PF)
Data Systems

• Frank Stocklin
• Ron Vento
• Bob Summers
• May 17 2002

2
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

3
OPS CONCEPT

• HUB to Free Flyers(FF)
• UHF
• Coherent for ranging/ 60 Kbps duplex data
  transfer
• CDMA
• simultaneous receive of 6 FFs
• Time share transmits to 6 FFs
• may also be able to simultaneous transmit to FFs
  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 HGAs 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

4
Data SystemsDriving Requirements Assumptions

• 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 FFs 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

5
Data SystemsDriving Requirements Assumptions

• No FF inter-communications
• Data Latency None
• Telemetry BER 10-5
• Selective redundancy appropriate

6
Selected Configuration RationaleFree 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 FFs
• Ranging enabled by use of PN code
• FFs will compute range to HUB
• 60 Kbps duplex link between HUB FFs
• Baseline approach is to time share transmissions
  from HUB to FFs
• Possible to design for simultaneous
  transmissions-needs some NRE
• Laser
• Used for range and position of the HUB to FFs
• Prototype will fly on STS this summer

7
Selected Configuration RationaleHUB

• 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)

8
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

9
Data SystemsSelected Configuration Rationale
RF
DETECTOR
RF
RF
RF
HUB
RF
Free Flyers(6)
RF
RF
LASER FFs to HUB
LASER HUB to DETECTOR
X Band
34M
MOC
DSN 34 M
Command
Science Hskpg
10
Selected Configuration and RationalFunctional
Free Flyer Block Diagram
Multi Channel UHF transponder
Hybrid
Diplexer
Omnis/ patches
CMD/TLM
CDH
LASER
To HUB
11
Selected Configuration and RationalFunctional
HUB Block Diagram
Multi CH UHF/S Band Transponder(2)
Diplexer
Hybrid
UHF Omnis/patches
CMD/TLM
6 Channels from FFs CDMA
HUB to FF communications
HPA (2)
S-Band Omnis
Hybrid
RF Switch
CDH
Diplexer
6 LASER Reflectors
0.3M S-Band Reflector
LASER
To Detector
HUB to Detector communications
12
Selected Configuration and RationalFunctional
Detector Block Diagram
S Band Transponder(2)
HPA (2)
S Band Omnis
Diplexer
Hybrid
CMD/TLM
0.3 M HGA
RF Switch
Detector to HUB communications
Hybrid
RF Switch
X Band Transponder(2)
CDH
X-Band Omnis
Diplexer
0.5M X-Band Reflector
1 LASER Reflector
Detector to Ground communications
13
Maxim_PF Signal Margins

14
Power/Mass/Cost SummaryFree Flyer
15
Mass/Cost/Power Summary HUB
16
Mass/Cost/Power Summary Detector
Includes gimbals, booms, deployment hardware
17
Data SystemsCost Summary

• FreeFlyer (6) 0.8 M
• HUB 4.5 M
• Detector 11 .7 M
• Ground station 2.4 M (4 years)
• TOTAL 19.4 M
• Laser cost included in instruments
• Includes 1 hr pre/post pass time

18
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

19
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
  FFs) is probably doable but needs to be funded
  demonstrated
• Basic design is low-medium risk

20

• Back-Up Charts

21
UHF HUB/Freeflyer - Freeflyer/Hub50 kbps
DOWNLINK
MARGIN CALCULATION
GSFC
C.L.A.S.S. ANALYSIS 1 DATE TIME 5/14/ 2 14
947 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/(HzK) -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
22
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
143644 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/(HzK) -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
23
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
121748 PERFORMED BY R. VENTO
LINKID MAXIM


FREQUENCY 2250.0 MHz RANGE
20000.0 km  
MODULATION BPSK
DATA RATE 34.000
kbps
CODINGTURBO
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/(HzK)
-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
24
-X-Band DSN 34 M BWG to Detector5 Kbps
HGA
  TABLE 0.5 S/C ANTENNA UPLINK
DATE TIME 05/14/02 15 125 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(MI1.10 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 (BERE-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 ---------------------------------------
------------------------------------
25
X-band Downlink Detector to 34M BWG5 Kbps OMNI
Mode
DOWNLINK
MARGIN CALCULATION
GSFC
C.L.A.S.S. ANALYSIS 1 DATE TIME 5/15/ 2
103922 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/(HzK)
-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
26
S-band Detector/Hub - Hub/Detector50 bits OMNIs
DOWNLINK
MARGIN CALCULATION
GSFC
C.L.A.S.S. ANALYSIS 1 DATE TIME 5/15/ 2
102954 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/(HzK) -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
27
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.

28
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.

29
WEIGHT AND POWER ESTIMATE
Using parametric model and engineering estimates
Note 10 mW transmitter will require less power
(lt 100 mW).
30
COST SCHEDULE ESTIMATE

• COST
• Based on COTS laser technology still requires a
  receiver.
• Assumes that fundamental RD 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

31
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).

32
SHARED TELESCOPE ALTERNATIVE

• EXAMPLE
• Reduced shared aperture to 2.5 cm.
• Decreased laser power to 2 mW and 10 mW.

SCALABILITY