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Talking to the Stars Deep Space Telecommunications

Talking to the Stars Deep Space Telecommunications. James Lux, P.E. Spacecraft Telecommunications Equipment Section Jet Propulsion Laboratory james.p.lux@jpl.nasa.gov. 29 Sep 2003, CL03-2624. Overview. What is spacecraft telecom? What are the technical challenges?

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Talking to the Stars Deep Space Telecommunications

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  1. Talking to the StarsDeep Space Telecommunications James Lux, P.E. Spacecraft Telecommunications Equipment Section Jet Propulsion Laboratory james.p.lux@jpl.nasa.gov 29 Sep 2003, CL03-2624

  2. Overview • What is spacecraft telecom? • What are the technical challenges? • What’s different from the usual? • How have we done it in the past • What’s 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 ofSpacecraft Design Telecom Subsystem Command & Data Handling Subsystem Instrument Telemetry Transponders RF Telemetry Instrument Commands Power Amps RF Commands Antennas Power Subsystem Solar Panels Power Control Mechanical Thermal Structural Subsystems Attitude Control Batteries Radioisotope Thermal Generator

  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 d’être for the whole exercise

  7. The Technical Challenges • It’s 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) = 32.44 + 20 log(km) + 20 log(MHz) (Assumes Isotropic Antenna, which isn’t really fair!)

  9. Example Link Budgets • 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. What’s the Frequency? • Protected spectrum • Trend S > X > Ka band (more channels, more BW) • Up and Down related by ratio for ranging SUp:2.110-2.120Dn:2.290-2.300 X Up: 7.145-7.190Dn:8.400-8.450 KaUp: 34.2-34.7Dn: 31.8-32.3

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

  12. Spacecraft Antennas • Accomodation • Fit in the launch vehicle shroud (few meter diameter) • Fit on the spacecraft • Gimbals? • Deployment • Galileo HGA didn’t • Pointing • High gain is great, but you’ve 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 GD Xband SSPA Thales X-band TWT 100Wη: 50-70%2-3 kg+EPC30x5x5 cm 17 Wη: 29%1.32kg17.4x13.4x4.7 cm

  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? • You’re in for the long haul (5-10 years) • You’re going to generate a lot of paper and go to a lot of meetings • It’s a different environment out there! • Mission/Quality Assurance is a very different animal in space than in consumer electronics

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

  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 • You’ll 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 EnvironmentsRadiation • 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 EnvironmentsTemperature • 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 • Don’t generate heat in the first place

  23. Space EnvironmentsVacuum • HV breakdown • Multipaction • Low pressure (e.g. Mars surface @ 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 we’re 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 it’s 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 there’s 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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