Rosetta_CD\PR\what_is_RS_v4.ppt, 03.01.2016 10:59AM, 1 Mars Data Workshop Mars Express Radio Science...

$: Rosetta_CD\PR\what_is_RS_v4.ppt, 03.01.2016 10:59AM, 1 Mars Data Workshop Mars Express Radio Science MaRS Introduction Experiment, Operations, Observations.$
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Mars Data Workshop

Mars Express Radio Science MaRSIntroduction

Experiment, Operations, Observations

Martin Pätzold, Silvia Tellmann

Rheinisches Institut für Umweltforschung RIU

Abt. Planetare Forschung

Universität zu Köln

ESAC 9th June 2008

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Mars Express Rosetta

www.radio-science.de

3. March 2004

Venus Express

9. November 200514. April 2006

Launch: 2. June 2003 Arrival: 25. December 2003

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Rosetta Mars Express Venus Express

comets VenusMars

35-m New Norcia Antenna

Radio Science Experiments at RIU, Köln

Radio Science Experiments on interplanetary spacecraft

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What is Radio Science?

Radio Science is interested in:

Small changes in frequency (phase), signal power,polarisation of a radio carrier signal, transmitted by aspacecraft and received at a ground station on Earth


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... You may conclude on...

... the media which the radio signal propagated through

... the perturbing forces acting on the spacecraft.

Was ist Radio Science?

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In the Beginning.... the basic idea

• 1962 studies about radio propagation done at JPL• 1962 Review on Space Research, Iowa City

Von Eshleman, Stanford UniversityBistatic Radar Astronomy

„one man´s noise is the other man´s data“


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Up link_ ra d io _ sc ie nc e .c d r/D190

„Bistatic Radar Astronomy“

ground station antenna

Interplanetary spacecraft

Idea: ground station transmist radio signal

-> received by s/c-> processed and analyzed on board (radio spectrometer)-> s/c transmits results via TM to Earth


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Up link_ ra d io _ sc ie nc e .c d r/D190

realize.... Plan Boscillators, radio spectrometers withpower and mass optimized for s/cwere not available

Plan B:• s/c transmits radio signal, • G/S transmits and records, • process and analyze data at home • advantage:

• use the onboard radio subsystem• no dedicated hardware (well... Ok... later USOs)

• problem: low RF power and SNR


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well... back to... Plan APluto Kuiper – Belt (PKB) „New Horizons“

Science objectives PKB Radio Science:• Density, pressure, temperature of the neutral and ionized atmosphere of

Pluto (Charon?) • Gravity field Pluto and Charon; separation of masses, bulk density

Radio Science Experiment (REX): • powerful uplink radio signal (X-Band)• signal processing on board• radio spectrometer, USO 1kg, 1W• results via TM to Earth• cooperation with Prof. G.L. Tyler, Stanford University (Co-I contribution RIU Cologne)• launch 2006; Pluto flyby 2014

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RF Functional Block Diagram

Mars Express

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RF Functional Block Diagram

USOVenus ExpressRosetta

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Spacecraft High Gain Antennas

Rosetta Venus ExpressMars Express

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S/C High Gain Antennas (HGA)

Rosetta Venus ExpressMars Express

diameter 2,20m 1,70m 1,30 m X-band (8,4 GHz)gain 42 dBi 40 dBi 37 dBiRF Power 20 Watt 65 Watt 65 Watt EIRP 85 dBm 88dBm 85 dBm

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ESA´s New Norcia 35-m ground station

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NASA Deep Space Network

70 m

34 m HEF26 m

34 m BWG cluster, Goldstone

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Radio Science: observed parameters• radio carrier frequency shifts:

– change of the relative speed between the ground station on Earth and the spacecraft (Doppler effect)

– propagation of the radio signal in dispersive media

• Change of the signal power by

– absorption in media

– scattering (particles and surfaces)

• Change of polarisation by

– reflection at surfaces (Brewster angle)

– Faraday-Rotation in ionized media with external magnetic field


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Frequency bands

L S C X

300GHz EHF SHF UHF VHF HF

3MHz

30GHz

3GHz

300MHz

30MHz

K P

Radarbänder Uplink Downlink

S-Band 2100 MHz 2300 MHz

X-Band 7100 MHz 8400 MHz

Ka-Band 32000 MHz

UK

W (

WD

R K

öln

)

GP

S

AS

TR

A

TV

te

rre

str

isc

h

Telekomm. Sat.

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Radio Link ModesMars Express

Venus Express

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Why two downlink frequencies?

contributions to the received carrier frequency:

G /SEarth thermalr r

rec 0 0 0 bend troposphere / ionosphere f0 s / c

v v 40.31 1 dNe(t)f (t) f f f ds f f

c c c f dt

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c c c f dt

transmitted carrier frequency: X-band 8400 MHz S-band 2300 MHz

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c c c f dt

transmitted carrier frequency: X-band 8400 MHz S-band 2300 MHz

thermal noise; s/c radio subsystem G/S equipmentf ~ order of mHz

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c c c f dt

Doppler frequency term due to relative motion between s/c and G/S:vr ~ 10 km/s: Doppler shift 280 kHz @ X-band Doppler shift 77 kHz @ S-band

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c c c f dt

Doppler frequency term due to relative motion between s/c and G/S:vr ~ 10 km/s: Doppler shift 280 kHz @ X-band Doppler shift 77 kHz @ S-band

changes in Doppler frequency due to gravitational andnon-gravitational perturbing forces acting on the s/c

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c c c f dt

„plasma term“ due to the propagation of the radio signal through ionized media (solar wind, ionosphere)

depends on the change of electron density along the ray pathdepends inversely on carrier frequency

looks like noise => „plasma noise term“ f ~ order of mHz to Hz

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c c c f dt

bending of the ray path in media:depends on carrier frequency in the ionosphereindependent on frequency in the neutral atmosphereIonosphere: fbend,max ~ 1 HzAtmosphere: fbend,max ~ -10 Hz (Mars); -4500 Hz (Venus)

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c c c f dt

bending of the ray path in the Earth´s troposphere and ionosphere:a constant or slight trend for the duration of observationwill be corrected by models (GPS, Klobuchar)

bending of the ray path in media:depends on carrier frequency in the ionosphereindependent on frequency in the neutral atmosphereIonosphere: fbend,max ~ 1 HzAtmosphere: fbend,max ~ -10 Hz (Mars); -4500 Hz (Venus)

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c c c f dt

there are contributions which are• proportional to carrier frequency

• invers proportional to carrier frequency

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contributions to the received carrier frequency:G /S

Earth thermalr rrec 0 0 0 bend troposphere / ionosphere f

0 s / c


c c c f dt

there are contributions which are• proportional to carrier frequency

• invers proportional to carrier frequency

a matter of fact:

(it is not only designed like this, it is also a good idea)

X

S

f 8400MHz 880 11

f 2300MHz 240 3

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c c c f dt

compute: fS,rec – 3/11 fX,rec (differential Doppler) and apply baseline fit

G /S

S,rec X,rec S2 2S X s / c

1G /S

S,rec X,rec 2 2S S Xs / c

3 40.31 1 1 dNe(t)f (t) f (t) f ds

11 c f f dt

dNe(t) 3 c 1 1 1ds f (t) f (t)

dt 11 40.31 f f f

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c c c f dt

compute: fS,rec – 3/11 fX,rec (differential Doppler) and apply baseline fit

G /S

S,rec X,rec S2 2S X s / c

1G /S

S,rec X,rec 2 2S S Xs / c

3 40.31 1 1 dNe(t)f (t) f (t) f ds

11 c f f dt

dNe(t) 3 c 1 1 1ds f (t) f (t)

dt 11 40.31 f f f

The differential Doppler is the frequency shift due tothe propagation of the radio wave in a plasma relativeto a one-way downlink at S-band

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single frequency experiment feasible?

• Is the experiment feasible at a single downlink frequency?• In principle, yes, but...

- for gravity: at the cost of higher noise caused by the plasma- Higher plasma noise at S-band and lower Doppler SNR

- Lower plasma noise at X-band and higher Doppler SNR compared to S-band

- for the ionosphere: at the cost of a potential (small) bias in the electron density; refractivity and SNR stronger at S-band than at X-band

- for the atmosphere: no effect (independent of frequency)

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comparison differential Doppler atopposition & conjunction

DOY 338, 2005

DOY 243, 2004

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comparison differential Doppler atopposition & conjunction

DOY 338, 2005

DOY 243, 2004

solar opposition: rms ~ 4.8 mHz

solar conjunction: rms ~ 58 mHz

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Earth occultation

• What is an Earth occultation?– As seen from the Earth, the s/c is disappearing behind the

planetary disk and reappears at opposite hemisphere or opposite limb

– Occurs at specific constellations between Earth & Mars location and orbit plane orientation

– Occurs in „seasons“– The radio signals propagate through the ionosphere and the

atmosphere before the s/c is occulted– The radio link is interrrupted during the occultation proper– Mars Express can only observe the INGRESS into occultation

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bending of the radio wave

ionosphere

Earth occultation

Ionosphere refractive index < 1

Neutral atmosphere refractive index > 1

Change of the propagation path!

Mars

neutral atmosphere

: bending angle

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Data Pipeline

ESA NNO 35m DSN 35m, 70m

ESOC, Darmstadt, GE JPL, Pasadena, CA

Stanford U, CAIGM, Cologne, GE

Observables:Frequency

RangeSignal powerPolarization

Data types:Closed-loopOpen-loop

DSN data processingNNO data processing, archiving

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Data processing – the road to useful data

Level 1a: raw data from the ground stations Binary or ASCII, in specific format

Level 1b: extracted data from Level 1a ASCII, in defined format by radio science group

Translation from L1a -> L1b

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Reconstructed orbit, frequency prediction from UniBw Munich

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frequency prediction by Radio Science Simulator

• Based on flown orbit => reconstructed orbit file• Compute expected received frequency at the ground station feed:

– considering all motions: Earth, Mars, spacecraft, Earth rotation, plate tectonics

– Consider relativistic frequency shifts– Correct for light times– Assume that Mars (Venus) has no atmosphere

• Compute frequency residuals (received frequency minus predicted frequency)

• Frequency residuals are precise up to 50 mHz (worst case); to be compared with 8400 MHz or 2300 MHz

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Frequency residuals

DOY 354, 2005

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Frequency residuals

DOY 354, 2005

start of obs. occultation lost radio linkreceiver noise

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Frequency residuals

DOY 354, 2005

bias of 29 mHzdifference between observation and prediction

1-sigma standard deviation 32 mHz

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Frequency residuals

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Frequency residuals

2 minutes

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Frequency residuals

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Frequency residuals

ionopause

main peak M2 M1

neutralatmosphere

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Occultation observed by a 70-m station

same scale as before.... 1-sigma standard deviation: 3 mHz

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Level 2: frequency, Doppler residuals, differential Doppler, range, signal power; each frequency ASCII, timely ordered, calibrated; in defined format to be archived

Reconstructed orbit, frequency prediction from UniBw Munich

Rosetta_CD\PR\what_is_RS_v4.ppt, 03.01.2016 10:59AM, 1 Mars Data Workshop Mars Express Radio Science...

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