Talking to the StarsTalking to the StarsDeep Space TelecommunicationsDeep Space Telecommunications

James Lux, P.E.

Spacecraft Telecommunications Equipment Section

Jet Propulsion Laboratory

james.p.lux@jpl.nasa.gov

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