Transcript Talking to the Stars

Talking to the Stars
Deep Space Telecommunications
James Lux, P.E.
Spacecraft Telecommunications
Equipment Section
Jet Propulsion Laboratory
[email protected]
29 Sep 2003, CL03-2624
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
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
Tornadoes, Fire Whirls, Eclipses, High Voltage,
Shrunken Coins, Robots!
Telecom-centric View of
Spacecraft Design
Telecom Subsystem
Instrument
Instrument
Command &
Data Handling
Subsystem
Telemetry
RF Telemetry
Transponders
Commands
Power Amps
RF Commands
Antennas
Power Subsystem
Solar Panels
Radioisotope
Thermal Generator
Power Control
Batteries
Mechanical
Thermal
Structural
Subsystems
Attitude
Control
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
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 (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
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
Example Link Budgets
X band
Jupiter
Telecommand
Telemetry
Tx Power
20 kW
35 Watts
+73 dBm
+45 dBm
Tx Antenna
(70 m)
Path Loss
Rx Antenna
Rx Power
(2 m)
+77 dB
+46 dB
-288 dB
-288 dB
(2 m)
(70 m)
+46 dB
+77 dB
-92 dBm
-120 dBm
Rx kT noise
(300K)
(20K)
-174 dBm/Hz
-186 dBm/Hz
Rx BW
1kHz
100 kHz
+30 dBHz
+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?



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
X
Up: 7.145-7.190
Dn:8.400-8.450
Ka
Up: 34.2-34.7
Dn: 31.8-32.3
Relative PSD, dB
0
S
Up:2.110-2.120
Dn:2.290-2.300
-10
-20
-30
8400
8405
8410
8415
8420
8425
8430
8435
8440
8445
8450
Frequency, MHz
-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
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, filtered)
Transponders
Coding
SDST – Small Deep Space
Transponder
Tx Syn
Stalo
USO
Rx Syn
•Phase locked Tx/Rx for
ranging
Bit Demod
•Bit/Command decoder
LNA
•Multiple Bands
Spacecraft 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 Amplifiers



Phase Modulation (BPSK, QPSK)
Power Amplifiers SSPAs & TWTAs
Efficiency is real important
GD Xband SSPA
Thales X-band TWT
100W
η: 50-70%
2-3 kg+EPC
30x5x5 cm
17 W
η: 29%
1.32kg
17.4x13.4x4.7 cm
Coding


Coding gets you closer to the “Shannon Limit”
Deep space telecom codes wind up in other industries
– Reed-Solomon
– Turbo codes
Data Rates
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

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
Pre Phase A
“Gleam in eye”
10/03
FM (Flight Model)
A
B
Concept
Review
10/05
CY 04
9Mos
ATLO
40 Mos
C/D
NASA commits
the funds
CY 03
12 Mos
PMSR
10/06
CY 05
E
PDR
7/07
CY 06
CDR
7/08
CY 07
CY 08
Launch
11/10
CY 09
CY 10
Reach Mars
9/11
CY 11+
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)
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.”
“Flight Qualified”
Equipment Design


Environments
Analyses
– Thermal
– Worst Case
– Radiation
– FMEA
– Vacuum
– FMECA
– Mechanical
– Parts Stress

Testing
– Performance
– Environmental
Space Environments
Radiation

Not something that commercial vendors usually care about
–

Radiation tolerance/hardness is process dependent
Kinds of radiation
–
Total Ionizing Dose (TID)

–
Single Event Effects




–

SEU (bit flips)
SEGR (Gate rupture)
Latchup
Linear Energy Transfer (LET) 65 MeV/cm
Prometheus adds something new: Neutrons!
Shielding
–

LEO – 25 kRad; Europa – 4 MRad
Adds mass, scattering may make things worse etc.
Design (Silicon on Insulator, TMR, etc.)
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
Space Environments
Vacuum

HV breakdown
– Multipaction
– Low pressure (e.g. Mars surface @ 5 Torr)
 Paschen minimum

Outgassing & vacuum compatibility
 Mechanical issues (cold weld, lubes)
 Thermal management
– Radiation & conduction: yes, convection: no
Testing -Thermal Vac

Vacuum chamber + thermal shroud
 Simulate “cold space”
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
Parts is NOT Parts




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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 Shock

Vibration and shock
 Launch loads
 Pyro events
 Testing without breaking
Cassini
MER
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
Network design

Historically s/c to earth
 Interplanetary networks
Relay Orbiters

Galileo & its
probe
 DS-2
on ill fated Mars
Polar Orbiter

Cassini &
Huygens
 MRO,
MGS, &
future
New 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