Talking to the Stars Deep Space Telecommunications

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Talking to the StarsDeep Space Telecommunications

• James Lux, P.E.
• Spacecraft Telecommunications Equipment Section
• Jet Propulsion Laboratory
• james.p.lux_at_jpl.nasa.gov

29 Sep 2003, CL03-2624
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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!
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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
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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

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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!)

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Path Loss (Friis Equation)

• Loss (dB) 32.44 20 log(km) 20 log(MHz)
• (Assumes Isotropic Antenna, which isnt really
  fair!)

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Example Link Budgets

• Downlink dominates the design
• But waitare 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?

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Whats the Frequency?

• Protected spectrum
• Trend S gt X gt Ka band (more channels, more BW)
• Up and Down related by ratio for ranging

SUp2.110-2.120Dn2.290-2.300 X Up
7.145-7.190Dn8.400-8.450 KaUp 34.2-34.7Dn
31.8-32.3
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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
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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)

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Power Amplifiers

• Phase Modulation (BPSK, QPSK)
• Power Amplifiers SSPAs TWTAs
• Efficiency is real important

GD Xband SSPA
Thales X-band TWT
100W? 50-702-3 kgEPC30x5x5 cm
17 W? 291.32kg17.4x13.4x4.7 cm
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Coding

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

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Data Rates
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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

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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 09
CY 08
CY 07
CY 06
CY 05
CY 10
CY 03
CY 04
CY 11
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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)

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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.

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Flight QualifiedEquipment Design

• Environments
• Thermal
• Radiation
• Vacuum
• Mechanical

• Analyses
• Worst Case
• FMEA
• FMECA
• Parts Stress

• Testing
• Performance
• Environmental

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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.)

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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
• Dont generate heat in the first place

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Space EnvironmentsVacuum

• HV breakdown
• Multipaction
• Low pressure (e.g. Mars surface _at_ 5 Torr)
• Paschen minimum
• Outgassing vacuum compatibility
• Mechanical issues (cold weld, lubes)
• Thermal management
• Radiation conduction yes, convection no

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Testing -Thermal Vac

• Vacuum chamber thermal shroud
• Simulate cold space

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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

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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

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Testing - Vibe and Shock

• Vibration and shock
• Launch loads
• Pyro events
• Testing without breaking

Cassini
MER
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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

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Network design

• Historically s/c to earth
• Interplanetary networks

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Relay Orbiters

• Galileo its probe
• DS-2 on ill fated Mars Polar Orbiter
• Cassini Huygens
• MRO, MGS, future

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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