Astrometric VLBI Observation of Spacecraft with Phase DelayM.Sekido, R.Ichikawa,H.Osaki,

T.Kondo,Y.Koyama

(National Institute of Information and

Communications Technology :NICT,Japan)

M.Yoshikawa,T.Ohnishi(ISAS,Japan),

W.Cannon, A.Novikov (SGL,Canada),

M.Berube (NRCan,Canada), and

NOZOMI VLBI group(NICT,ISAS,NAOJ,GSI,Gifu Univ. Yamaguchi Univ., Hokkaido Univ., Japan)

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Spacecraft Navigation with VLBI: Motivation

Requirments for increased accuracy of orbit control for future space missions: – For landing, orbiting, & saving energy

R&RR

R01

R02

VLBI

+

SC Astrometry

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NOZOMI’s Earth Swing-by • NOZOMI was launched in July 1998.• Due to some troubles, new orbit plan with Earth

swing-by was proposed. • R&RR observations were difficult in a period.

VLB

I Observations Apr. MayMar.Jan. Feb. Jun.

May 22, 24, 27

June 4

Mizusawa(NAO)

Kashima(CRL)

Koganei(CRL)

Usuda(ISAS)

Yamaguchi(Yamaguchi Univ.)

Gifu(Gifu Univ.)

Kagoshima(ISAS)(uplink)

Tomakomai(Hokkaido Univ.)

Tsukuba(GSI)

AlgonquinSGL & NRCan

Japanese and Canadian VLBI Stations participated in NOZOMI VLBI observations.

ISAS,CRL,NAOJ, GSI,Gifu Univ, Yamaguchi Univ. Hokkaido Univ.SGL, NRCan supported.

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Tasks to be done for S.C.astrometry are

• Constructing VLBI delay mode for Finite distance radio source– Including relativity and curvature of wavefront

• Writing Data Processing and Analysis software– Observation with IP-sampler boards recording to HD– Software correlator

• Narrow band signal

– Analysis software• Group delay or Phase delay

– Delay Resolution: (nano/pico seconds)

– Ambiguity problem

VLBI delay model for finite distance radio source

VLBI for finite distance radio source

Normal VLBI

c

SB

Y-XB

BB

XX YY

SS

c

KB

YX RR 00

0Y0X RRK

(Fukuhisma 1993 A&A)

BB

XX YY

RX0

RY0

KK

Relativistic VLBI delay model for finite distance radio source

c

cccc

VUγ

ct

ττ

eeeeg

202

220222

22

12

1

2

21

2

2)1(1

VR

wVKVR

bVwVbK

c

ccc

VUγ

ct

ττe

eeeeg

)(1

21

2

2)1(1

20

022

22

0

12wVK

VKbVwVbK

CONSENSUS MODEL (M.Eubanks 1991)

Finite Distance VLBI MODEL (Sekido & Fukushima 2003)

Finite-Infinite : Delay Difference

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Analysis Procedure for SC Astometory

I. Compute a priori (delay, rate) (C) and partials– We modified “CALC9” for our use(finite VLBI).

(Thanks to GSFC/ NASA group for permission to use)

II. Extracting Observable (g, p)(O) with software correlator.

xx

y

y

CO

III. Computing O-C and least square parameter estimation

Group Delay(Post-fit Residual)

Rate residual

Delay Residual

Orbit motion

Estimated Coordinates(Group Delay)

6/4(VLBI)

6/4(R&RR)

May 27

June 4

Origin is Orbit on May 27, which was Determined by ISAS with R&RROrigin is Orbit on June 4.

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Observable: Phase Delay & Group delay

Frequency

Ph

ase

Band width

g:Group Delay

Phase Delay

0

g ~ 1/BW ~1 nano second (Spacecraft)

p ~ 1/RF ~1 pico second

2 n ambiguity

Phase delayA C

B

Closure of Phase delay(Kashima-Usuda-Tsukuba)

Kashima-Usuda-Tsukuba

Phase Delay Post fit residualP

ost

Fit

Del

ay R

esid

ual

(se

c)

Estimated CoordinatesComparison with R&RR measurement

Summary• VLBI observations for spacecraft were per

formed with domestic and intercontinental baselines.

• Formula for Finite VLBI delay model and analysis software was developed by using CALC9.

• Astrometric SC coordinates were obtained with Group/Phase delay observables by absolute astrometry.

• Nest step:– Improve coordinates accuracy by using differ

ential VLBI technique.

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Thank you for attention.

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SpaceOrbit of NOZOMI

Apr. MayMar.Jan. Feb. Jun.

Group Delay(Range signal)

ClosureObservation mode= 2MHz, 2bit

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Spacecraft Navigation with VLBI : Motivation

Required for increased accuracy for future space missions: – For landing, orbiting, & saving energy

• JPL/NASA has been employed– Japanese Space Agency (ISAS+NASDA=JAXA)

• NOZOMI(Japanese Mars Explorer)– Needs to support orbit determination with VLBI.

• Mission as our own Project

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Spacecraft Navigation

R&RR

R01

R02

VLBI

+

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Observation： IP-VLBI Sampler board

• Sampling rate:40k-16MHz• Quantization bit: 1-8bit• 4ch/board• 10MHz,1PPS inputs

K5　 VLBI　 System

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Phase Delay Analysis

4 June 2003

Predicted　 Orbit

Pos

t F

it D

elay

Res

idu

al (

sec)

DeterminedOrbit

Estimated Coordinates

Comparison with R&RR

measurement

DeterminedOrbitPredicted　

Orbit