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Talking to the Stars Deep Space Telecommunications James Lux, P.E. Spacecraft Telecommunications Equipment Section Jet Propulsion Laboratory

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Presentation on theme: "Talking to the Stars Deep Space Telecommunications James Lux, P.E. Spacecraft Telecommunications Equipment Section Jet Propulsion Laboratory"— Presentation transcript:

1 Talking to the Stars Deep Space Telecommunications James Lux, P.E. Spacecraft Telecommunications Equipment Section Jet Propulsion Laboratory 29 Sep 2003, CL

2 Overview What is spacecraft telecom? What are the technical challenges? Whats different from the usual? How have we done it in the past Whats going to happen in the future

3 A little about Jim New technologies – Distributed Metrology and Control for Large Arrays Adaptive Optics for RF, with distributed computing – DSP Scatterometer Testbed General purpose DSP instead of custom hardware – Advanced Transponder FPGA for NCO, de/modulation, de/coding Seawinds Calibration Ground Station (CGS) – Measure time to ns, freq to Hz, pwr to 0.1dB Tornadoes and projects in the garage

4 Tornadoes, Fire Whirls, Eclipses, High Voltage, Shrunken Coins, Robots!

5 Telecom-centric View of Spacecraft Design Instrument Solar Panels Batteries Power Control Command & Data Handling Subsystem Transponders Power Amps Antennas Radioisotope Thermal Generator Power Subsystem Telecom Subsystem Telemetry Commands Mechanical Thermal Structural Subsystems RF Telemetry RF Commands Attitude Control

6 Some terminology Consultative Committee for Space Data Systems (red, green, blue books) Transponder = Radio HGA, MGA, LGA = High Gain Antenna, Medium…, Low… TWTA = Travelling Wave Tube Amplifier SSPA = Solid State Power Amplifier (tele)Commands = What we send to the spacecraft (uplink) Telemetry = What we get back from the spacecraft (downlink) Engineering, Housekeeping = what we need for operation and health monitoring Science Data = The raison dêtre for the whole exercise

7 The Technical Challenges Its a LONG way away – Path loss – Pointing – Light time We have limited power – Solar panels – Radioisotope Thermal Generator (RTG) It takes forever to get there (and we hang out there a long time too!) – Mars – 6-8 months – Outer planets Jupiter (Galileo 6 yrs getting there, 7 yrs in orbit) Saturn (Cassini 7 yrs) (Voyager 26 yrs and still going!)

8 Path Loss (Friis Equation) Loss (dB) = log(km) + 20 log(MHz) (Assumes Isotropic Antenna, which isnt really fair!) Mars 2 AU 376E6 km 172 dB Jupiter 5AU 750E6 km 178 dB Pluto 40 AU 5900E6 km 195 dB S band (2.3 GHz) 66 dB X band (8 GHz) 78 dB Ka Band (32 GHz) 90 dB

9 Example Link Budgets X band Jupiter TelecommandTelemetry Tx Power20 kW +73 dBm 35 Watts +45 dBm Tx Antenna(70 m) +77 dB (2 m) +46 dB Path Loss-288 dB Rx Antenna(2 m) +46 dB (70 m) +77 dB Rx Power-92 dBm-120 dBm Rx kT noise(300K) -174 dBm/Hz (20K) -186 dBm/Hz Rx BW1kHz +30 dBHz 100 kHz +50 dBHz SNR+52 dB!+16 dB Downlink dominates the design But wait… are these assumptions reasonable? 35W Tx Power DC power avail? 46 dBi for antenna? Surface figure Antenna efficiency 2 m ok? 300K receiver noise temp? 100 kHz enough BW for data?

10 Whats the Frequency? Protected spectrum Trend S > X > Ka band (more channels, more BW) Up and Down related by ratio for ranging S Up: Dn: X Up: Dn: Ka Up: Dn:

11 Transponders SDST – Small Deep Space Transponder Tx Syn Rx Syn Stalo USO Bit Demod Coding LNA Phase locked Tx/Rx for ranging Bit/Command decoder Multiple Bands

12 Spacecraft Antennas Accomodation – Fit in the launch vehicle shroud (few meter diameter) – Fit on the spacecraft – Gimbals? Deployment – Galileo HGA didnt Pointing – High gain is great, but youve got to point it to the Earth – 46 dB » 1º » 17 mrad (2 meter dish at X-band)

13 Power Amplifiers Phase Modulation (BPSK, QPSK) Power Amplifiers SSPAs & TWTAs Efficiency is real important 17 W η: 29% 1.32kg 17.4x13.4x4.7 cm 100W η: 50-70% 2-3 kg+EPC 30x5x5 cm GD Xband SSPA Thales X-band TWT

14 Coding Coding gets you closer to the Shannon Limit Deep space telecom codes wind up in other industries – Reed-Solomon – Turbo codes

15 Data Rates

16 So, now you want to build a deep space telecom system? Youre in for the long haul (5-10 years) Youre going to generate a lot of paper and go to a lot of meetings Its a different environment out there! Mission/Quality Assurance is a very different animal in space than in consumer electronics

17 How can it take so long? Lots of steps in the process Lots of interaction/integration with other subsystems C/D Launch 11/10 Concept Review 10/05 PDR 7/07 PMSR 10/06 CDR 7/08 Reach Mars 9/11 RFP 10/05 B A E 9Mos 12 Mos 40 Mos Pre Phase A Gleam in eye 10/03 CY 03 CY 09CY 08CY 07CY 06 CY 04 CY 05 CY 10 CY 11+ Contract to industry EM (Engineering Model) FM (Flight Model) ATLO NASA commits the funds

18 Some Odd Consequences of the Long Life Cycle Parts availability – Mission manager will want parts with proven heritage (i.e. they worked the last time) – 5 more years til launch Engineer retention – Youll finish the telecom system a year or two before launch – It may take 5 years after launch to get there, then what if you have a question about how something works? Development tools – Compilers, in circuit emulators, etc. Keep those old databooks! – Galileo used 1802 μP (until a week ago)

19 More Practicalities Our product is paper! – Quote from a HRCR (Hardware Review and Certification Record) submittal document: The documentation required for this submittal is not included due to its size. It is being supplied separately on a shipping pallet.

20 Flight Qualified Equipment Design Environments – Thermal – Radiation – Vacuum – Mechanical Analyses – Worst Case – FMEA – FMECA – Parts Stress Testing – Performance – Environmental

21 Space Environments Radiation Not something that commercial vendors usually care about – Radiation tolerance/hardness is process dependent Kinds of radiation – Total Ionizing Dose (TID) LEO – 25 kRad; Europa – 4 MRad – Single Event Effects SEU (bit flips) SEGR (Gate rupture) Latchup Linear Energy Transfer (LET) 65 MeV/cm – Prometheus adds something new: Neutrons! Shielding – Adds mass, scattering may make things worse etc. Design (Silicon on Insulator, TMR, etc.)

22 Space Environments Temperature Qualification vs Design vs Test – Typical test range –45ºC to 75ºC Thermal Management – Conduction Cooling no fans in space! – Radiators, Heat pipes (Mass?) – Heaters (survival, replacement) Space is very cold! – Lots of modeling – Higher efficiency designs Dont generate heat in the first place

23 Space Environments Vacuum HV breakdown – Multipaction – Low pressure (e.g. Mars 5 Torr) Paschen minimum Outgassing & vacuum compatibility Mechanical issues (cold weld, lubes) Thermal management – Radiation & conduction: yes, convection: no

24 Testing -Thermal Vac Vacuum chamber + thermal shroud Simulate cold space

25 Mission Assurance (aka 5X) Good Design – Design reviews – Lots of analysis (Faults, Worst Case, Parts Stress) Good Parts – Parts selection – Parts testing Verification – Qualification Testing – Good record keeping Traceability to sand – are the widgets were using the same as the ones we tested

26 Parts is NOT Parts Class S aka Grade 1 Class B+ aka Grade 2 (883B plus screening) Plastic Encapsulated Microcircuits (PEM) Inspectability! Traceability – e.g. GIDEP alerts If a given part fails for someone else, we can know if that part is in our system, and then we can determine if its going to cause a problem

27 Testing - Vibe and Shock Vibration and shock Launch loads Pyro events Testing without breaking Cassini MER

28 The Future More networking – Not so much point to point stovepipe Higher frequencies – More bandwidth – Optical Higher data rates – More science More functionality in the radio – Software radios

29 Network design Historically s/c to earth Interplanetary networks

30 Relay Orbiters Galileo & its probe DS-2 on ill fated Mars Polar Orbiter Cassini & Huygens MRO, MGS, & future

31 New technologies FPGAs – Reconfigurable in flight (but what if theres a bug in the upload?) – Upsets? Latchup? Power? Testability? Optical Comm – 100 Mbps – At least you have a telescope to see Earth (pointing!) Pushing the A/D closer to the antenna – Direct IF conversion – Fast, low power, wide A/Ds SSPAs – New topologies (Class E) give higher efficiency – IRFFE – self adjusting circuits

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