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Telecommunications and Navigation Strategies in NASA�s Mars Exploration Program

Chad Edwards

DESCANSO SeminarMarch 15, 2001

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Outline

• Introduction & Acknowledgments• Program Overview• Capability Trades

– Telecommunications– Navigation

• Electra - A Standardized Proximity Link Comm/Nav Payload

• Communications Protocols• Key Technologies• Summary

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Acknowledgments

• Many people & organizations have contributed over the past several years to the concepts presented here, including the Mars Network team as well as the current MGS, Odyssey, and MER project teams

• Key contributors include:– Dave Bell, Todd Ely, Tom Jedrey, Shel Rosell, Steve

Townes, Jeff Srinivasan, Jon Adams, Joe Guinn, RolfHastrup, Bob Cesarone, Stan Butman, Yoaz Bar-Sever, Steve Lichten, Polly Estabrook, Adrian Hooke, Loren Clare, Greg Kazz, Ed Greenberg, Tony Barrett, and many more...

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Mars Exploration Timeline

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

MGS

Telecom Relay

Telecom Relay

ASI/NASA Marconi Telesat

MER Twins Netlanders

MSR Lander

Competed Scout Payload

ASI/NASA Sci Orbiter

MAV

MRO

Beagle 2

Orb

iters

(on-

orbi

t)La

nder

s(s

urfa

ce o

pera

tions

)

Competed Scout Mission

CNES MSR Orbiter

Nozomi

Mars Express

Odyssey

Extended Mission Standby

CNES Orb

Smart Lander

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Program Drivers on Comm/Nav Infrastructure• Increased science data return (e.g., for multi-spectral surface

pancam imagery)• Complexity of MSR surface operations, with the resulting need for

frequent command cycles and rapid, low-latency engineering data return to support operations planning

• Robust, high-accuracy radio-based approach navigation (e.g., ~<1 km entry knowledge for aerocapture or precision landing)

• Capture of real time engineering telemetry during critical events such as EDL, aeromaneuvering, MAV launch, etc., for feed-forward fault diagnosis in the event of anomaly

• Energy-efficient relay telecommunications for energy- and mass-constrained scout-class missions

• Radio tracking of orbiting sample canister to support in-orbit sample rendezvous

• Surface position determination to support long-range rover navigation

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Mars Telecommunications: Representative Capabilities

Orbiter Direct-to-Earth Link� 10 kbps - 1 Mbps to 34m @ 2.7 AU� Example: MGS

� 25 kbps� 1.5 m HGA� 25 W TWTA

Large Lander Direct-to-Earth Link� 1 kbps - 10 kbps to 70m @ 2.7 AU� Example: MER

� 2 kbps� 28 cm HGA� 15 W SSPA

Lander Relay Link� 100 kbps - 1 Mbps� Example: MER

� 128 kbps� Omni UHF antenna� 10 W SSPA

No DTE capab ility for Scout-class landers

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Direct-to-Earth Communications

• Keys to increased DTE link capability:

– Transmit power– Transmit aperture– Frequency (Ka-band offers

~4x improvement over X-band

– Earth receive aperture (70m offers ~4x improvement over 34m)

• Mass, power constraints imply landed DTE capability will always fall well below orbital DTE capability

Mars-to-Earth Deep Space LinkMars-to-Earth Deep Space LinkMars-to-Earth Deep Space LinkMars-to-Earth Deep Space Link

0.01

0.1

1

10

100

1000

10000

0 1 2 3 4 5Antenna Diameter (m) Antenna Diameter (m) Antenna Diameter (m) Antenna Diameter (m)

3W10W30W100W300W

Range=2.67 AU, X-band, 34m DSN

MRO:MRO:MRO:MRO:- 2.5 m HGA- 100 W TWTA- 300 kbps

MER:MER:MER:MER:- 28 cm HGA- 15 W SSPA- 0.6 kbps

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Key Aspects of Relay Communications

User:- Transmit power- Antenna gain/steering- Power/energy constraints

Proximity Link:- Frequency band- Comm protocols- Multiple Access

Scheme

Orbiter Deep Space Link:- Data rate (~power x gain)- Frequency (X, Ka)- Range variation (25x comm performance)

Orbiter Proximity Link:

- Data Rate- Antenna gain/steering

Orbit:- Slant range- Connectivity- Global Coverage

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Proximity Link Characterisitics• Omni-to-omni links

– Simple ops for lander and orbiter– Link performance scales as 1/freq2

– Current ~400 MHz UHF band represents balance between link performance and RF component size

• Omni-to-directional links– Increased orbiter antenna gain can significantly improve link performance – To first order, for fixed orbiter aperture size, link performance is

frequency-independent– However, orbiter antenna pointing requirements scale with frequency

• Directional-to-directional links– Opens possibility for very high link performance, event over long slant-

range links– Requires antenna pointing at both ends of link

– Link performance scales as freq2

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Proximity Link Communications

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

100 1000 10000 100000

Range (km)Range (km)Range (km)Range (km)

UHF Omni Txmt/Omni Rcv

UHF Omni Txmt/10 dBi Rcv

MARSAT UHF Omni Txmt/17 dBi Rcv

MARSAT X 20 cm Txmt/1.3 m Rcv

Areostationary

Pre-aerobraking elliptical orbit

Continuous link from areostationaryorbit

Normalized Data RateNormalized Data RateNormalized Data RateNormalized Data RateAssumes 1 W Transmit Power(at output of power amplifier)

400kmTwo 5-10 min

passes/sol forlow-lat sites

4450km

4-5 hrs/sol@ all latitudes

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Critical Event Communications

Sun SPK

Mars01

To Earth

Orbiter

Lander

• Program policy is to ensure realtime communications for critical mission events– Entry, Descent, and Landing– Mars Ascent Vehicle Launch– Aerocapture MOI

• Options:– DTE “semaphores” can

provide ~ 1 bps capability– High-rate prox link (will be

required to characterize more complex 2nd-gen systems)

• Infrastructure orbiters• Converted cruise stage• Black box

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Orbit Changes for EDL SupportOrbit Changes for EDL SupportOrbit Changes for EDL SupportOrbit Changes for EDL Support

0.01

0.1

1

10

100

1000

10000

100000

0100200300400500600700

Time Interval (days)Time Interval (days)Time Interval (days)Time Interval (days)

180 deg In-OrbitPhasing6-hr Local TimeNodal Plane Change

Orbital Changes to Support EDL Communications

NodalPlaneChange

OrbitPhasing

• Use of low-altitude science orbiter for EDL comm relay requires orbit adjustment to ensure EDL visibility

• Preliminary analysis of ∆V partial derivatives

– In-plane orbit phasing: ~0.26 m/s per deg/day– Nodal plane change: ~326 m/s per deg/day

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Key Aspects of Relay Navigation

Precision Approach Navigation� X-band Doppler on HGA link

between approach s/c and orbiter� Capability: <0.5 km B-plane error

@ E-1 day

Orbiting Sample Canister Tracking� 1-way or 2-way Doppler

tracking on UHF link� Open-loop recording for weak

signals� Capability: <100 km 1-way

<100 m 2-way

Surface Positioning� 1-way or 2-way Doppler/range

tracking on UHF link� Capability: <10 m position

uncertainty within 1 sol

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Mars Approach Navigation

0

5

10

15

20

25

Mars Lander Approach Navigation

5 Days Before Entry1 Day Before Entry

0

0.2

0.4

0.6

0.8

1

B-PlaneMagnitude

Uncertainty(km)1σσσσ

DSN Doppler & Range Only

NearPolar

NearEquatorial ∆∆∆∆VLBI Proximity

Orbiter Optical

Atmospheric Entry Performance

FlightPath

Angle*Uncertainty

(deg)1σσσσ

All �best� cases assume 10% unmodelled dynamicsAll �worst� cases assume 30% unmodelled dynamicsDSN Only Near Polar 'worst' case driven by low declination conditions∆VLBI assumes DOR tones used with no system biasesProximity Orbiter in low Mars polar orbitOptical �best� assumes 12cm aperture camera (mass -1kg),Optical �worst� assumes 5cm aperture camera

Mapping between Flight Path Angle and B-Plane Magnitude Uncertainties depends on entry conditions.All cases assume equavalent mapping for -15 deg Flight Path Angle and -5345km B-Plane Magnitude

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Trade Space: Relay Orbits

Orbit Pros ConsLow-altitude polar Global coverage; low slant-

range for energy-efficient relaycomm, even with simple omniantennas

Very limited connectivity,particularly in equatorial band

Low-altitude equatorial Frequent contact to equatorialregion (can complement polarorbiters); low slant range

No coverage to mid-lat andpolar regions

Mid-altitude (e.g., alt =4450 km, incl = 130deg)

Global coverage with uniformconnectivity from pole to pole;longer and more frequent passdurations

Larger slant range (can becompensated to some extentby increasing orbiter antennagain)

Areostationary (alt =17,000 km)

Continuous contact to oneregion of planet

Large slant range; hi-rate linkswill require directivity fromsurface user; no globalcoverage

ÒHigh-NoonÓ ellipticalorbits

Several orbits exist withprecession such that apoapseis fixed near local noon,resulting in long daytimepasses

Large slant range at apoapse;hi-rate links will requiredirectivity from surface user;variable slant range over orbitincreases ops complexity

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Low-Altitude Relay Orbiters

• Polar orbit provides global coverage but limited coverage of low-latitude sites

• Equatorial orbit provides frequent contact, increased data return for low-latitude sites, but no coverage beyond +- 30 deg

Telesat Coverage vs. Mars Surface Latitude

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Latitude

Hou

rs p

er S

ol

400 km, Inc. 93 deg, Nadir Pointed 2.8 dBi


Telesat Data Return vs. Mars Surface LatitudeNadir Pointed S/C Antenna

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Latitude

Mbi

ts/s

ol/w

att



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Mid-Altitude Orbiters

• 4450 km altitude provides increased coverage– Large ground track– 4-5 hrs contact per sol, nearly

uniform in latitude– Multi-Gb/sol with steered

orbiter antenna

Telesat Data Return vs. Mars Surface Latitude

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90Latitude

Mbi

ts/s

ol/w

att

400 km, 93° Polar Orbiter, Nadir Pointed 2.8 dBi

4450 km, 130.2° Polar Orbiter, Nadir Pointed 10.4 dBi

4450 km, 130.2° Polar Orbiter, Steered 13 dBi

Telesat Coverage vs. Mars Surface Latitude

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90Latitude

Hou

rs p

er S

ol

400 km, 93° Polar Orbiter

4450 km, 130.2° Inclined Orbiter

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Areostationary and Highly Elliptical Orbiters• Areostationary

– 17,000 km altitude– Continuous view of one region of planet (~25% of planet centered

about sub-satellite point; no view of polar regions)– High-rate (~1 Mbps) continuous relay to Earth with directional

surface antenna (satellite at fixed point on sky w.r.t. surface user)– Lower-rate (~10 kbps) continuous relay to Earth with simple omni

surface antenna

• HEO– Several “sun-sync” orbits exist with apoapse at a fixed local time

(e.g., local noon); long daytime passes– Large slant range at apoapse -> similar link considerations as for

areo: directional surface antenna req’d for high rate (but now satellite moves on sky w.r.t. surface user)

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2007 Marconi Comm/Nav Orbiter

• Joint ASI/NASA mission– ASI provides:

• Spacecraft• ATLO• S/C flight engineering

– NASA provides:• Launch vehicle• Prox link comm/nav payload• Deep space-specific engineering support• Mission ops

• First dedicated Mars telecommunications and navigation orbiter

– Mid-altitude orbit optimized for comm/nav role, improving performance relative to low-altitude science orbiters

– Will provide comm (EDL and surface relay) and nav (approach nav, surface position, orbital rendezvous) services to other elements of Mars program

0

1

2

3

4

5

400 kmscienceorbiter

Marconi

0

20

40

60

80

100

120

140

160

180

200

400 kmscienceorbiter

Marconi

(results for +-30 deg latitude band)

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Electra Proximity Link Payload

• Effort is underway to develop a next-generation standardized Mars proximity link payload– To be flown on all Mars orbiters, starting with MRO’05 - provides

de facto interoperability and enables gradual implementation of Mars orbital comm/nav infrastructure at low incremental cost

– Flight reconfigurable/reprogrammable over long mission lifetime– Greater flexibility (wider range of supported data rates; swappable

txmt/rcv bands, multi-channel operation)– Addition of X-band (8.4 Ghz) proximity comm/nav capability– Improved navigation/timing performance– Improved performance (coding, low-loss half-duplex mode,

reduced NF, increased PA efficiency, …)– Modularity to allow scaling for low-mass lander/scout applications– Portability to facilitate integration with variety of orbiters– Self-contained relay functionality (including relay data

management) for improved testability

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Electra Physical Configuration

SDSTA

SDSTB

C&DHA

C&DHB

DATA / CMD

DATA / CMD

DATA / CMD

DATA / CMD

USOA

USOB

HYB

RID

XCVR A

XCVR B70

.X M

Hz

70.X

MH

z

XX.X

MH

zXX

.X M

Hz

DATA / CMD

DATA / CMD

DATA / CMD

DATA / CMD

UHF XCV

X RCV

UHF XCV

X RCVNADIR X-BAND

LOW GAIN

DTE X-BANDMEDIUM GAIN

DTE X-BANDHIGH GAIN

ELECTRA PAYLOAD

S RCV

S RCV

NADIR S-BANDLOW GAIN

NADIR UHFMEDIUM GAIN

ZENITH UHFLOW GAIN

NADIR UHFLOW GAIN

BOOM MOUNTED(S/C SUPPLIED BOOM)

HYB

RID

LEGEND

Spacecraft Supplied

Electra Supplied

Jet Propulsion Laboratory4800 Oak Grove DrivePasadena, California 91109

Project: Mars Technology ProgramDesign: Electra PayloadPage Description: Redundant Payload/SC IntegrationDesigned By: T. JedreyUpdated By:

Rev1.0

Size Date01/29/01

Document NumberSheet 1 of 1

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Electra Functional Block Diagram

3 WAYSWITCH

NADIR OMNI

ZENITH OMNI

NADIR MEDIUM GAIN

UHF ANTENNAPACKAGE

DUPLEXER 2x2SWITCH

NADIR

HGA

X-BAND ANTENNAPACKAGE

2 WAYSWITCH BPF X-BAND

DOWNCONVERTER

UHFUPCONVERTER

2 WAYSWITCH

LNA

LNADUAL CHANNEL UHFDOWNCONVERTER

PHYSICAL LAYERPROCESSOR

LINK LAYERPROCESSOR

PAYLOADCONTROLLER

TRANSMIT DATA

RECEIVE DATA

CO

NTR

OL

BU

S

TRAN

SM

IT D

ATA

REC

EIVE

DAT

A

SPACECRAFTINTERFACE

(LVDS)

PROGRAMMEMORY

PROGRAMMEMORY

PROGRAMMEMORY

MASSMEMORY

PA

SPLITTER

PAYLOADCONTROL

2 WAYSWITCH

NADIR

S-BAND ANTENNAPACKAGE

BPF S-BANDDOWNCONVERTER

LNA

ANTENNA SUBSYSTEM RF SUBSYSTEM BASEBAND SUBSYSTEM

NC

O ϕ

CO

STAS

I/Q

POW

ER E

STIM

ATE

DIG

ITAL

BAS

EBAN

D

NC

O ϕ

TRAN

SMIT

DAT

AR

EC

EIVE

DAT

A

USO SUBSYSTEM

USO

USO DISTRIBUTION

POWER SUBSYSTEM

POWERCONVERSION

SPACECRAFTINTERFACE

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Protocols

• CCSDS Proximity-1 Space Link Protocol – Provides standards for the physical and data link layers for Mars

proximity communications– First implementation on Mars Odyssey– Will be key for achieving interoperability among MER A/B,

Beagle 2, Mars Exp, Odyssey

• CCSDS File Delivery Protocol– Provides reliable end-to-end file delivery– Addresses unique aspects of deep space communications

• Long RTLT• Intermittent connectivity• High BER links• Multi-hop store-and-forward relays• Custody transfer to minimize onboard storage rqmts

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Key Technologies

• The Mars Technology Program is funding a number of important comm/nav technology task:– Deep Space Communications

• High-EIRP RF Technologies (B. Lovick)• Optical Comm Flight Demo (K. Wilson)

– Mars Proximity Communications• Electra Advanced Development (T. Jedrey)• UHF Antennas (K. Kelly)

– Radio-Based Navigation• ST5 Flight Demo (W. Bertiger)• In Situ Navigation (J. Guinn)

– Communications Protocols and Coding• Proximity Link Protocols (L. Clare)

010315 cde-26

Evolution of Mars Telecommunications Capability

1

10

100

0.1

0.01

Dat

a R

etur

n (G

b/so

l)

Direct to Earth:• High Mass, Power• 0.01 - 0.1 Gb/sol• Energy-constrained

contact time

Direct to Earth:• High Mass, Power• 0.01 - 0.1 Gb/sol• Energy-constrained

contact time

Comm Relay w/Low-Alt Sci S/C:

• Simple omni-omni UHF comm

• 0.1 - 1 Gb/sol• Very limited contact

Comm Relay w/Low-Alt Sci S/C:

• Simple omni-omni UHF comm

• 0.1 - 1 Gb/sol• Very limited contact

Dedicated Telesats:• Telecom-optimized orbit

(e.g., 4200 km)• 1 - 10 Gb/sol• Increased connectivity

Dedicated Telesats:• Telecom-optimized orbit

(e.g., 4200 km)• 1 - 10 Gb/sol• Increased connectivity

AreostationaryRelay Sat:• 10-100 Gb/sol• Continuous or near-

continuous connectivity

AreostationaryRelay Sat:• 10-100 Gb/sol• Continuous or near-

continuous connectivity

(Pathfinder era) (Limited roving Era) (Outpost era)(Extensive roving era)

ContinuousMb/s StreamingVideo

Full-resPANCAMIn 1 Sol

Full-resPANCAMIn 1 Week

Full-resPANCAMIn 1 hr

010315 cde-27

Evolution of Mars Radio-Based Navigation Capability

100 m

1 km

10 km

10 m

1 m

Posi

tion

Unc

erta

inty

DSN-only Initial Orbiting Infrastructure

(1-2 sci orb w/ comm/nav payload)

2nd-Gen Orbiting Infrastructure

(Dedicated telesats, on-board proc)

Precision Approach Navigation(B-plane error at data cut-off)

Surface Positioning(within 1 sol)

DSN� Doppler� Range� ∆VLBI

� 1-way X-band Doppler between approach s/c and orbiter(s)

� Earth-in-the-loop processing

� Improved X-band & UHF Doppler and range between approach s/c and orbiter(s)

� Autonomous on-board processing

� 2-way UHF Doppler between surface asset and orbiter

� Earth-in-the-loop processing

� Improved X-band & UHF Doppler/range between surface asset and orbiters

� Autonomous on-board processing� More frequent contacts/updates

010315 cde-28

Some Parting Questions...• How do we manage and operate a heterogenous collection of

orbital relay spacecraft as an integrated Mars comm/nav infrastructure?

• What is the science value of increased bandwidth and connectivity? – How would a continuous high-rate areostationary relay change our surface

operations concepts?• When is it cost-effective to transition to:

– Demand access proximity service concept?– On-board radiometric data processing?– Higher-frequency directional lander links?

• How should our proximity link standards evolve?– Physical layer– Modulation and coding– Higher layers of data management– Ultimate interface with IPN vision

A Real-World Example: MER EDL Communications

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EDL Sequence of Events Overview

1) Direct Entry from Hyperbolic Approach

2) Cruise Stage Separation: E- 15 minutes

3) Atmospheric Entry: ~125 km altitude

4) Parachute Deploy: ~10 km A.G.L., ~E+ TBD s

5) Heatshield Jettison: 20 s after chute deploy

6) Bridle Descent: 20 s after heatshield jett., 10 s to complete

7) Radar Acquisition of Ground: ~2.4 km A.G.L

8) Airbag Inflate: ~4 s prior to retrorocket ignition

9) Rocket Ignition: ~160 meters A.G.L

10) Bridle Cut: ~15 meters A.G.L, 0 m/s vertical velocity

11) First Contact w/ Ground: ~E+ TBD s

1

2

3

4

5

6

8

7

9

10

11

010315 cde-31

MERA EDL: Pt/No for Backshell LGA and Rover LGA

(2 sigma dynamics and min. measured antenna gain on MPF mockup)

No dynamics

010315 cde-32

No dynamics

MERB EDL: Pt/No for Backshell LGA and Rover LGA

(2 sigma dynamics and min. measured antenna gain on MPF mockup)

010315 cde-33

MER-A Approach Geometry

Approach Trajectory� V∞ = 2.77 km/s � Declination of V∞

= 2.04 deg (MME)


= 4.38 deg (MME)

MER-A Open

Launch 5/30/03Arrival 1/4/04

MER-A Open


MER-A Close


MER-A Close


VIEW FROM MARS NORTH POLE

EARTH

Earth Terminator

Mars Express

Mars Odyssey

V-infinity

SUN

TICK MARKS EVERY 5 MIN

MGSMars Express

Mars Odyssey

Ground TrackV-infinity

SUN


VIEW FROM EARTH

Target landing site: -14.5deg, 175deg E

MGS

VIEW FROM MARS NORTH POLE

EARTH

Earth Terminator

Mars Express

Mars Odyssey

V-infinity

SUN


MGS Mars Express

Mars Odyssey

Ground Track

V-infinity

SUN


VIEW FROM EARTH

Target landing site: -14.5deg, 175deg E

MGS

Landing

Landing

010315 cde-34

MER-B Approach Geometry


= -4.69 deg (MME)


= 1.45 deg (MME)

MER-B Open


MER-B Open


MER-B Close


MER-B Close


VIEW FROM MARS NORTH POLE EARTH

Earth Terminator

Mars Express

V-infinity

SUN


Mars Odyssey

MGS

Mars ExpressMars Odyssey

Ground Track

V-infinity

SUN


VIEW FROM EARTH

Target landing site: -2.25deg,354deg E

MGS

VIEW FROM MARS NORTH POLE EARTH

Earth Terminator

Mars Express

V-infinity

SUN


Mars Odyssey

MGS Mars Express

Mars Odyssey

Ground Track

V-infinity

SUN


VIEW FROM EARTH

Target landing site: -2.25deg,354deg E

MGS

Landing

Landing

010315 cde-35

Mars Program Assessment of Available Assets to Support MER EDL

Mars ProgramSelection

Potential EDLCommunications

Assets

Pros Cons

Odyssey Mars2001 Orbiter

• Odyssey aerobraking willbe complete• UHF radio compatibility iswell understood (same UHFradios on both vehicles)

• Requires change in orbitwhich significantly reducesthe science return of the GRSinstrument

Mars GlobalSurveyor (MGS)

� Currently at Mars andoperational� Prime science mission willbe completed� Orbit provides goodgeometry for both MEREDL events

� Extended lifetime willrequire careful propellantmanagement and opsstrategy

Mars Express ESAOrbiter

• Planned to be at Marsduring MER landings

• Arrives only 10 days prior toMER-A EDL• The potential large rangesdue to orbit geometry mayprevent MER EDL support• More complex inter-agencyinterface

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