CubeSat Communications Review and Concepts. Workshop, July 2, 2009

Transcription

1 CubeSat Communications Review and Concepts CEDAR CubeSats Constellations and Communications Workshop, July 2, 29 Charles Swenson

2 Presentation Outline Introduction slides for reference Link Budgets Data Handling Near Term Concepts Considered wild and crazy ideas involving a community effort. CEDAR CubeSat Communications Review and Concepts (7/2/9) 2

3 CubeSat Lifetime. m 2 /kg NRLMSIS model NASA/Hathaway 3. titude (km) Al Altitude Decay (4//2 Launch) 2 Sigma Sigma Nominal Predictions Year Lifetime (y years) km 45 km 4 km CubeSat Lifetime Launch date June 27, 27 CEDAR Small Satellite Workshop

4 Encode Binary Signal 2 Binary encoded as Amplitu ude % 2% 4% 6% 8% % - -2 Bit Period Binary encoded as Amp plitude 2 % 2% 4% 6% 8% % - -2 Bit Period Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 4 June CEDAR 27, Small 27 Satellite Workshop

5 Encode Binary Signal + Noise 2 Binary encoded as Amplitu ude % 2% 4% 6% 8% % - -2 Bit Period Binary encoded as Amp plitude 2 % 2% 4% 6% 8% % - -2 Bit Period Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 5 June CEDAR 27, Small 27 Satellite Workshop

6 Encode Binary Signal + More Noise 2 Binary encoded as Amplitu ude % 2% 4% 6% 8% % - -2 Bit Period Binary encoded as Amp plitude 2 % 2% 4% 6% 8% % - -2 Bit Period Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 6 June CEDAR 27, Small 27 Satellite Workshop

7 Optimal Algorithm (Is it a?) Amplitude Binary Binary 2 % - 2% 4% 6% 8% % -2 Bit Period Amplitude 2 % - 2% 4% 6% 8% % -2 Bit Period 2 Energy in Bit Period = Σ.5.46,.22, Po ower % 2% 4% 6% 8% % - Bit Period 57.57,. Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 7

8 Optimal Algorithm (Is it a?) Amplitude Binary Binary 2 % - 2% 4% 6% 8% % -2 Bit Period Amplitude 2 % 2% 4% 6% 8% % - -2 Bit Period = % 2% 4% 6% 8% % - -2 Po ower Bit Period Energy in Bit Period Σ -.5.4,.2, 58.58,. Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 8

9 Frequency of Occurrence Pow wer Bit Error 2 % 2% 4% 6% 8% % - Bit Period Bit Rate Signal to Noise Band Width Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 9

10 Required Signal to Noise Ratio Noise Spectral Density Modulation (notes) E b /N o Bandwidth For BER of -5 FSK R FSK-4 FSK R BPSK 9.6 R DPSK.3 R Energy in bit QPSK R Convolutionally Coded PSK 4.4 Link Type (notes) Margin Units Flight Termination 9 db Command & Control 6 db Space Loss Data Dump 3 db Other db Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29)

11 Link Budget Design Element Symbol Units Link Link Frequency f GHz.45 Transmitter Power P tx Watts Transmitter Power P tx dbw. Transmitter Antenna Gain G tx db. Antenna Transmitter Losses L tx db -.5 Antenna Beamwidth θ tx Deg 86.7 Antenna Misalignment α tx Deg 3 Alignment Loss L θtx db -.3 Equivalent Isotropic Radiated Power EIRP dbw -.8 Losses Propagation Path Length S Km 278. Space Loss L s db Atmospheric L a db -. Polarization Loss L p db -3 Total Losses L db Receiver Antenna Gain G r db 26.6 Antenna Receiver Loss L r db -.5 Antenna Beamwidth θ r Deg 8.6 Antenna Misalignment α r Deg Alignment Loss L θr db -.6 Total Receiver G db Sky (Antenna) Noise Temperature T a K 3 Receiver Temperature T r K. System Noise Temperature T s K 3. Receiver Merit G/T DB(/K) 4.84 Powers Power Flux Density φ db(w/m^2) Carrier Power Received P rx dbw Noise Spectral Density N o db(w/hz) Carrier to Noise Density P rx /N o db(hz) Rates Data Rate R Bps.E+5 Eb/No E b /N o db Required deb/no db Required Margin db 6 Margin db 2.6 Space Loss 4 to 5 db difference in going from VHF (~44 MHz) to S-Band (~2.2 GHz) Low Gain Antenna Omni Directional High Gain Antenna Directional Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29)

12 Data Flow Onboard Instruments º 4º R collected Spacecraft Memory R transmitted Simulate for year in STK and report contact and gap times. Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 2

13 Percentage time in Contact Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 3

14 Straw Man Telemetry Quantity Symbol Value Units Factor of Safety α.5unitless Contact t Time Percent τ.%unitless Packet Overhead 7%Unitless Velocity 7.5km/s Word odsize 6bits 6bts Now 2-3 years 3-6 years Transmitted Rate Collection Rate Data Samples Spatial Sampling kbits/s kbits/s Hz m Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 4

15 Regulations The Law The NTIA US Frequency Allocations The ITU All satellites go through international licensing Category of usage Earth to Space Space to Earth Amateur MHz 2.4 GHz ISM industrial, scientific and medical MHz GHz Government (Primary) MHz 4-42 MHz 45 MHz GHz GH 5.46 GHz Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 5

16 Drinking the Kool-Aid CONCEPS Optical Communications Retro modulators Lasers and Telescopes Advantages/Disadvantages CubeSat Pointing Requirements No Licensing Concerns Ground Station Networks European GENSO (Amateur Frequencies) Real Time data from constellations ti Power (Tx on time) High Gain Ground Stations SRI 2 meter dish, etc Facility Costs Spectrum Requirements (Licensing Concerns) Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 6

17 Example - Summary of Ground Station Network Data from 28 survey of station capability Cubesat community stations Maximum capacity estimates kbps (UHF): 5 GB 2kbps (S-Band): 273GB Assessing Global Ground Station Capacity James Cutler, Dylan Boone University of Michigan

18 Constellation Data Flow for HiDEF 9 Small Satellites km spatial sampling 55 Mbits/day 2 GBytes onboard storage

19 Big Ear On the Ground Image courtesy of g g _ UxZmP// _ 4s3Ag Regulations on 46 to 47 MHz CEDAR CubeSat Communications Review and Concepts (7/2/9) 9

20 Regulations on 46 to 47 MHz Earth exploration-satellite service applications, other than the meteorological-satellite service, may also be used in the bands MHz and MHz for space-to-earth transmissions subject to not causing harmful interference to stations operating in accordance with the Table. US2 In the band MHz, space stations ti in the Earth exploration-satellite service may be authorized for space-to-earth transmissions on a secondary basis with respect to the fixed and mobile services. When operating in the meteorological-satellite service, such stations shall be protected from harmful interference from other applications of the Earth exploration-satellite service. The power flux-density produced at the Earth s surface by any space station in this band shall not exceed -52 dbw/m²/4 khz. MHz Bandwidth! CEDAR CubeSat Communications Review and Concepts (7/2/9) 2

21 Straw Man Concept Power on ground limited -52 dbw/m²/4 khz -58 dbw / m² khz CubeSat at reentry 25 km altitude Entire bandwidth, MHz. Isotropic antenna on CubeSat Max Power Tx -watt RF Design Element Symbol Units Link Link Frequency f GHz.465 Transmitter Power P tx Watts Transmitter Power P tx dbw. Transmitter Antenna Gain G tx db. Antenna Transmitter Losses L tx db -.5 Antenna Beamwidth θ tx Deg 8. Antenna Misalignment α tx Deg 5 Alignment Loss L θtx db -.8 Equivalent Isotropic Radiated Power EIRP dbw -.58 Losses Propagation Path Length S Km 25. Space Loss L s db Atmospheric L a db -. Polarization Loss L p db -3 Total Losses L db Receiver Antenna Gain G r db 35.9 Antenna Receiver Loss L r db -.5 Antenna Beamwidth θ r Deg 2.5 Antenna Misalignment α r Deg Alignment Loss L θr db -.9 Total Receiver G db Sky (Antenna) Noise Temperature T a K 6 Receiver Temperature T r K 2. System Noise Temperature T s K 8. Receiver Merit G/T DB(/K).89 Powers Power Flux Density φ db(w/m 2 ) Power Flux Spectral Density φ f db(w/m 2 /khz) Power Flux Spectral Density Limit φ f db(w/m 2 /khz) Carrier Power Received P rx dbw Noise Spectral Density N o db(w/hz) Carrier to Noise Density P rx /N o db(hz) 2.5 Rates Data Rate R Bps.E+7 Eb/No E b/n o db 32.5 Required Eb/No db 9.6 Required Margin db 3 Margin db 9.45 Directions In Ionosphere-Thermosphere-Mesosphere Research (2//29) 2

22 What can you do with -Watt Tx Assumptions 465 MHz frequency Isotropic antenna s on CubeSat Watt RF power (~4mW orbit average power) 8 K system noise temperature 36 dbi ground station gain (8 meter dish) BSPK or QPSK (E b /N o 9.6 db) Results Mbits/s for spacecraft at 6 km circular orbit Continuous.36 m on orbit sampling with 6 bit words Science CEDAR CubeSat Communications Review and Concepts (7/2/9) 22

23 Last Thoughts Dishes 8 Meter at Wallops 2 Meter at SRI and MoreHead University Develop an array of antennas and create multiple sites. Code division Multiple Access Give each satellite their own spread spectrum code Develop Custom ASIC for CubeSats Some engineering at this point would be useful The big advantage Isotropic antenna. Low impact on spacecraft. CEDAR CubeSat Communications Review and Concepts (7/2/9) 23

24 Misc Slides

25 Data Flow CEDAR CubeSat Communications Review and Concepts (7/2/9) 25

26 Small Satellites Class Mass (kg) Cost ($M) Large satellite > > Small satellite Mini-satellite Micro-satellite Nano-satellite Pico-satellite < < 2.2 University Nanosatellite Program (25 kg) NOAA-N Prime (4 kg) TIMED (58 kg) Cubesats ( to 3 kg) ST5 AIM SSTL MicroSat-7 (2 kg) (7 kg) CEDAR CubeSat Communications Review and Concepts (7/2/9) 26

27 CubeSat Low mass, low volume, low power, low cost 3-U -U.5-U Low, but increasing science capabilities Enables missions not cost effective e with larger spacecraft CEDAR CubeSat Communications Review and Concepts (7/2/9) 27