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