Presentation is loading. Please wait.

Presentation is loading. Please wait.

Talking to the Stars Deep Space Telecommunications

Similar presentations

Presentation on theme: "Talking to the Stars Deep Space Telecommunications"— 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? 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!
From top left, clockwise: Exploding Cadillac for a movie of the week Small Tesla coil 1991 Total Eclipse in La Paz, Baja California 8 foot high Fire vortex 40 foot artificial tornado for Volvo (U.K.) commercial Quarter shrunk by electromagnetic forces Roger the robot

5 Telecom-centric View of Spacecraft Design
Telecom Subsystem Command & Data Handling Subsystem Instrument Telemetry Transponders RF Telemetry Instrument Commands Power Amps RF Commands Antennas Power Subsystem There’s really a lot more to spacecraft design than shown here, however, we’re just talking about telecom. Power is really, really important for most deep space designs. Typically, you have a hundred watts DC, or so, to work with. (although, Prometheus will certainly change things, with 100 kWe available from the reactor) Attitude control is important, because that’s how we point the antenna, and it’s always a tradeoff between antenna gain and pointing. 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 CCSDS – - all the specs can be downloaded as PDF files.

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!) Path loss of hundreds of dB Pointing is a problem: you’ve got to find Earth, and high gain antennas have narrow beamwidths. Light time has a lot of weird side effects. For instance, you might be transmitting from a different DSN station than you receive from, because Earth has turned in the intervening time. Long life and reliability is a very important aspect. If you only have one widget, that MTBF of 50,000 hours starts looking awfully short.

8 Path Loss (Friis Equation)
Loss (dB) = log(km) + 20 log(MHz) (Assumes Isotropic Antenna, which isn’t 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 271 277 295 X band (8 GHz) 78 dB 282 288 306 Ka Band (32 GHz) 90 dB 294 300 318 Isotropic antennas are scaled to the wavelength, so the “receiver capture area” gets smaller as the frequency gets higher. In real life, you’re constrained by a physical size of the antenna, more than some artificial “isotropic”. However, if you don’t know which direction to transmit (or receive), you do need to approach isotropic patterns.

9 Example Link Budgets Downlink dominates the design
X band Jupiter Telecommand Telemetry Tx Power 20 kW +73 dBm 35 Watts +45 dBm Tx Antenna (70 m) +77 dB (2 m) +46 dB Path Loss -288 dB Rx Antenna Rx Power -92 dBm -120 dBm Rx kT noise (300K) -174 dBm/Hz (20K) -186 dBm/Hz Rx BW 1kHz +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? Recall that the entire s/c may only have 100W DC power available. If your transmitter PA is 20% efficient, and you’ve only got 50W allocated to you, then you’re limited to 10W RF power.

10 What’s 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 Phase locked Tx/Rx for ranging Bit/Command decoder
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 Deployment Pointing
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 TWTA = Travelling Wave Tube Amplifier Composed of TWT (the tube) and a High Voltage Power Supply (HVPS) (or Electronic Power Converter – EPC) Tubes have been around for decades. State of the art for tubes is steadily advancing, as people spend money to develop the next one. EPC is a challenge: High Voltage (8 kV) and thermal dissipation are challenges in space. Two flavors of tubes: conduction cooled (shown) and radiation cooled (big fins or a “can” that radiates to “cold space”) SSPAs are steadily gaining efficiency with new devices. GaAs, GaN, etc. Limited gain/power from one device means that SSPA design has a lot of work with (low-loss) power dividers and combiners. 100W η: 50-70% 2-3 kg+EPC 30x5x5 cm 17 W η: 29% 1.32kg 17.4x13.4x4.7 cm

14 Coding Coding gets you closer to the “Shannon Limit”
Deep space telecom codes wind up in other industries Reed-Solomon Turbo codes Eb/No = Energy in a bit divided by Noise density

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 Long, long development schedules + long, long missions Paper and meetings because spacecraft are very complex systems with lots of interactions and interfaces…and… Paper is important for traceability and mission assurance QA for space concentrates on making sure QTY:1 works forever, as opposed to the consumer model of “yield management”

17 How can it take so long? Lots of steps in the process
Lots of interaction/integration with other subsystems Contract to industry RFP 10/05 EM (Engineering Model) Pre Phase A FM (Flight Model) A 12 Mos “Gleam in eye” 10/03 9Mos B ATLO Concept Review 10/05 A/B is also called “formulation” C/D is “implementation” E is operations RFP = Request for Proposal PMSR = PDR= Preliminary Design Review CDR = Critical Design Review ATLO = Assembly Test and Launch Operations (final assy, attach to launch vehicle (LV), and light the fuse) C/D 40 Mos PMSR 10/06 E NASA commits the funds PDR 7/07 CDR 7/08 Launch 11/10 Reach Mars 9/11 CY 03 CY 04 CY 05 CY 06 CY 07 CY 08 CY 09 CY 10 CY 11+

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.” We are moving to electronic records, but, format compatibility is always a problem. Viewing a D-size sheet on your computer isn’t all that easy.

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.) Radiation susceptibility is more complex than you can imagine. Scattering, direction of travel, 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 Don’t 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 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 Higher frequencies Higher data rates
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 Optical Comm
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 IRFFE = DARPA’s Intelligent RF Front Ends program from DARPA MTO

Download ppt "Talking to the Stars Deep Space Telecommunications"

Similar presentations

Ads by Google