1. From you host … Dr. H

2. Introduction In the present project, communications design forces us to think about the overall arrangement of the system and its technological underpinnings. In the present project, communications design forces us to think about the overall arrangement of the system and its technological underpinnings. How many pieces of infrastructure need to communicate over long distances? How many pieces of infrastructure need to communicate over long distances? What do they need to communicate & how often? What do they need to communicate & how often? How much command, control and decision making is local and how much is centered on Earth? (autonomy vs. centralized human control) How much command, control and decision making is local and how much is centered on Earth? (autonomy vs. centralized human control) “A communications architecture is the arrangement, or configuration, of satellites and ground stations in a space system, and the network of communication links that transfer information between them.” L & W, SMAD

3. Steps in Defining a Communications Architecture 1. Identify communication links A. Define mission objectives B. Define mission requirements C. Determine the architecture 2. Determine data rates for each link A. Specify accuracy required B. Determine sampling rates, quantization levels. 3. Design each link A. Select frequency band B. Select modulation, coding C. Determine antenna size, beamwidth constraints D. Determine transmitter power constraints E. Estimate received noise, interference powers F. Calculate antenna gains & transmitter power 4. Size the comm system A. Select antenna configuration B. Calculate antenna size C. Estimate antenna masses D. Estimate transmitter masses

4. Conventional – Apollo-like Lunar transfer orbit insertion Lunar Transit M.B.  Powered landing at MB Step 1: Comm. Architecture flows from the chosen systems layout. Example: This configuration… … might give rise to…

5. Conventional – Apollo-like M.B.   Centralized ground control  Comm. System clustered near earth or on supply vehicle  Long comm. Links used for all activity

6. Second example: Distributed, Cooperative System M.B.  On-Orbit Assembly Lunar Transit Lunar Base Manufacturing and Assembly

7. M.B.  LEO assembly formation  More numerous, but shorter links.  C 3 more local. Long links used lightly, short links used heavily  System distributed over both Earth and Moon  Extensive lunar comm. infrastructure Distributed, Cooperative System

8. Link function Data Dissemination Architecture Point-to-pointBroadcast Tracking Telemetry & Command Data Collection Data Relay Comm. Architecture Defined by Function SpacecraftRelay Spacecraft

9. Step 2: Determine Data Rates for Each Link What info must be communicated and how fast? Analog-to-digital conversion: Sample frequency >2.2 x (max input frequency) Divide the range of the analog signal into M =2n levels – n = no. of bits per sample Mean-square noise power = (V)2/12, where V = Vfull-scale/M Signal-to-quantization noise power ratio = (M2-1). So you need smaller steps for weaker signals.

10. Step 2: Determine Data Rates No. of bits per sample determined by mission requirements No. of bits per sample determined by mission requirements Data rate = (No. samples/sec.) X (No. of bits/sample) Abbreviated: bps Data rate = (No. samples/sec.) X (No. of bits/sample) Abbreviated: bps Analog info. Max inpur freq (Hz) Sampling freq. (Hz) No. bits per sample Data rate (bps) Voice (PCM) 36008000764K Voice (delta PCM) 36008000656K DS1 Multiplexer 24 voice channels ---1,544M Original picturephone 900K2M36M Color Television (Commercial quality) 4.0M8.8M544M Color Television (Broadcast quality) 4.2M9.25M1092.5M

11. Step 2: Data Rates for TT&C Monitoring: Monitoring: Several hundred functions might be sampled, but at a low rate Several hundred functions might be sampled, but at a low rate Typical data rate ~ 50bps Typical data rate ~ 50bps Transmitting commands: Transmitting commands: Usually ~ 1/sec. Usually ~ 1/sec. Command message is typically ~ 48 to 64 bits Command message is typically ~ 48 to 64 bits Tracking: Tracking: Grnd station measures range or range rate for computing orbit ephemeris Grnd station measures range or range rate for computing orbit ephemeris For typical parameters of existing TT&C systems see table on next slide For typical parameters of existing TT&C systems see table on next slide

12. Step 2: Existing TT&C Systems Network Command (Uplink) Telemetry (Downlink) DL/UL Carrier Frequency Ratio Range Measurement Frequency(GHz) Data Rate (bps)Frequency(GHz) (bps) Air Force SCN (SGLS) 1.76 – 1.84 1000, 2000 2.2 – 2.3 125 -1.024M 256/205 1 Mbps PN code NASA DSN (Near Earth) 2.025 - 2.120 7.8 - 2000 2.2 – 2.3 5.6 – 500k 240/221 PN code at 1 Mbps Plus 8 Ranging Tones 8Hz to 500Hz Intelsat/COMSAT 5.92 – 6.42 14.0 – 14.5 100 – 250 100 - 250 3.9 – 4.2 12.2 or 17.7 1000 – 4800 1000 - 4800 N/A 4Ranging Tones TDRSS (user satellite below 12,000 km) MA, S-band 2.1064 SA S-band 2.025-2.120 SA K-band 13.775 10 kbps max 300k max 25M max MA, S-band 2.2875 SA S-band 2.2-2.3 SA K-band 15.0034 1k to 1.5M 1k o 12M 1k to 300M (S) 240/221 (K) 1600/1469 3 Mbps PN Code

13. Step 2: Data Rates for Data Collection Example: A geostationary satellite with a radiometer which scans the entire Earth in 20 min. with 1 km resolution Example: A geostationary satellite with a radiometer which scans the entire Earth in 20 min. with 1 km resolution Parameter Geostationary satellite Orbit altitude (km) Ground track velocity (m/s) Ground resolution (m) Scan width (deg) In-track scan (deg) Scan time No. of samples/pixel No. bits/sample Frame efficiency Data Rate (bps) 35,78601,0001818 20 min/Earth image 1.680.95 1.42 X 10 6

14. Step 2: Data Rates for Data Relay Data relay systems typically re-transmit data with a receiver/transmitter combination called a transponder Data relay systems typically re-transmit data with a receiver/transmitter combination called a transponder Transponder bandwidths of commercial communication satellites are usually 36 MHz or 72 MHz. Transponder bandwidths of commercial communication satellites are usually 36 MHz or 72 MHz. Maximum data rate can be several times the bandwidth, depending on the modulation and the receiving station size Maximum data rate can be several times the bandwidth, depending on the modulation and the receiving station size

15. Step 3: Link Design ~Electromagnetic Signal Propagation~ r Isotropic antenna: Point source with total power, P o Total power flowing through any spherical surface of radius r remains = P o Therefore, power per unit area flowing to a receiver distance r away is proportional to 1/r 2

16. Step 3: Link Design ~Electromagnetic Signal Propagation~ But real transmit antennas have directionality. o They radiate preferentially toward the axial direction o As a result, the power per unit area transmitted along the axis is: G t x (power radiated by an isotropic antenna) And this defines the transmitting antenna gain, G t

17. Step 3: Link Design P =transmitter power P L l = transm.- to-anten. line loss x G r A r G r = receive anten. Gain A r = effective receive antenna area Noise x G t L s L a Gt = transm, anten. Gain Ls = space loss =( /4  r) 2 La = transm. path loss r

18. Step 3: Link Design – Link Equation Derivation

19. Step 3: Link Equation Derivation - Continued

20. Step 3: Link Design Equations in dB

21. Step 3: Link Design Equations in dB Typical Noise Temperatures In s/c Comm Links Noise Temperature Frequency (GHz) DownlinkCrosslinkUplink 0.22-1220600.2-2040 Antenna Noise (K) Line Loss (dB) Line Loss Noise (K) Receiver Noise figure (dB) Receiver Noise (K) System Noise (K) 1500.5352.0190375250.5354.04925521000.5354.5592727200.5358.0172817832900.5356.097012952900.5357.515041830 System Noise (dB-K) 25.727.428.632.531.132.6

22. Step 3: Detailed Procedure for Link Design

23. Step 3: Detailed Procedure for Link Design - Continued

24. Step 4: Sizing the Communications System Estimated transmit power + aperture size  System mass Type Freq. Band (GHz)Gain(dB)Beamwidth(deg)Mass(kg)SatelliteSize(m) Quad helix L(1.5)16-19181.8Intelsat-V 0.4 x 0.4 x 0.47 Conical log spiral S(2.2) 0 to -3 2201.2FLTSATCOM Parabola (fixed) S(1.7)16-19183.9 GOES I, J, K 0.7 dia HornC(4)16-19183.1Intelsat-V 0.3 dia, 0.65 L Parabola w/Feed Array C(4)21-25-29.4Intelsat-V 2.44 dia Parabola w/Feed Array C(6)21-25-15.2Intelsat-V 1.56 dia Parabola – Steerable Ku(11)361.65.8Intelsat-V 1.1 dia Parabola w/Feed Array KA(20/3045-52-47.1SUPERBIRD 1.7 dia