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Talking to the Stars Deep Space Telecommunications
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Transcript of Talking to the Stars Deep Space Telecommunications
Talking to the StarsTalking to the StarsDeep Space TelecommunicationsDeep Space Telecommunications
James Lux, P.E.
Spacecraft Telecommunications Equipment Section
Jet Propulsion Laboratory
29 Sep 2003, CL03-2624
OverviewOverview
What is spacecraft telecom?What are the technical challenges?What’s different from the usual?How have we done it in the pastWhat’s going to happen in the future
A little about JimA 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
Tornadoes, Fire Whirls, Eclipses, High Voltage, Tornadoes, Fire Whirls, Eclipses, High Voltage, Shrunken Coins, Robots!Shrunken Coins, Robots!
Telecom-centric View ofTelecom-centric View ofSpacecraft DesignSpacecraft Design
Instrument
Instrument
Solar Panels
Batteries
Power Control
Command & Data Handling
Subsystem
Transponders
Power Amps
Antennas
Radioisotope Thermal Generator
Power Subsystem
Telecom Subsystem
Telemetry
Commands
MechanicalThermal
StructuralSubsystems
RF Telemetry
RF Commands
AttitudeControl
Some terminologySome 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
The Technical ChallengesThe 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 (Friis Equation)Path Loss (Friis Equation)
Loss (dB) = 32.44 + 20 log(km) + 20 log(MHz)(Assumes Isotropic Antenna, which isn’t really fair!)
Mars
2 AU
376E6 km
172 dB
Jupiter5AU
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
Example Link BudgetsExample Link BudgetsX 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 -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 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?
What’s the Frequency?What’s the Frequency?
Protected spectrum Trend S > X > Ka band (more channels, more BW) Up and Down related by ratio for ranging
Potential Spectral Occupancy of Mars Missions in 2007
-30
-20
-10
0
8400 8405 8410 8415 8420 8425 8430 8435 8440 8445 8450
Frequency, MHz
Rel
ativ
e P
SD
, dB
Odyssey(160ksps, ch.8)Mars07Lander (300 ksps, ch.12)Mars Scout Orbiter(9 ksps, ch.15)ME(586 ksps, ch.18)CNES07Orbiter(60 ksps, ch.22)Telesat( 360 ksps, ch.26)Mars05( 4.4Msps, ch. 33, f iltered)
-Only Mars Express and Odyssey have been assigned a frequency channel. Others are possibilities.-The center frequency of the n th channel is given by 8400.06 + (n-3)*1.36 MHz
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
TranspondersTransponders
SDST – Small Deep Space TransponderTx Syn
Rx SynStaloUSO
Bit Demod
Coding
LNA
•Phase locked Tx/Rx for ranging
•Bit/Command decoder
•Multiple Bands
Spacecraft AntennasSpacecraft 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)
Power AmplifiersPower Amplifiers
Phase Modulation (BPSK, QPSK) Power Amplifiers SSPAs & TWTAs Efficiency is real important
17 Wη: 29%1.32kg17.4x13.4x4.7 cm
100Wη: 50-70%2-3 kg+EPC30x5x5 cm
GD Xband SSPAThales X-band TWT
CodingCoding
Coding gets you closer to the “Shannon Limit” Deep space telecom codes wind up in other industries
– Reed-Solomon– Turbo codes
Data RatesData Rates
So, now you want to build So, now you want to build a deep space telecom a deep space telecom
system?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 meetingsIt’s a different environment out there!Mission/Quality Assurance is a very
different animal in space than in consumer electronics
How can it take so long?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 Review10/05
PDR7/07
PMSR10/06
CDR7/08 Reach Mars
9/11
RFP10/05
B
A
E
9Mos
12 Mos
40 Mos
Pre Phase A
“Gleam in eye”10/03
CY 03 CY 09CY 08CY 07CY 06CY 04 CY 05 CY 10 CY 11+
Contract to industry
EM (Engineering Model)
FM (Flight Model)
ATLO
NASA commitsthe funds
Some Odd Consequences Some Odd Consequences of the Long Life Cycleof 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)
More PracticalitiesMore 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.”
““Flight Qualified”Flight Qualified”Equipment DesignEquipment Design
Environments– Thermal– Radiation– Vacuum– Mechanical
Analyses– Worst Case– FMEA– FMECA– Parts Stress
Testing– Performance– Environmental
Space EnvironmentsSpace EnvironmentsRadiationRadiation
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.)
Space EnvironmentsSpace EnvironmentsTemperatureTemperature
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
Space EnvironmentsSpace EnvironmentsVacuumVacuum
HV breakdown– Multipaction– Low pressure (e.g. Mars surface @ 5 Torr)
Paschen minimum
Outgassing & vacuum compatibilityMechanical issues (cold weld, lubes)Thermal management
– Radiation & conduction: yes, convection: no
Testing -Thermal VacTesting -Thermal Vac
Vacuum chamber + thermal shroud Simulate “cold space”
Mission AssuranceMission Assurance(aka 5X)(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
Parts is NOT PartsParts 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
Testing - Vibe and ShockTesting - Vibe and ShockVibration and shockLaunch loadsPyro eventsTesting without breaking
Cassini
MER
The FutureThe 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
Network designNetwork design
Historically s/c to earthInterplanetary networks
Relay OrbitersRelay Orbiters
Galileo & its probe
DS-2 on ill fated Mars Polar Orbiter
Cassini & Huygens
MRO, MGS, & future
New technologiesNew 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