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ASTROMETRY OBSERVATION OF SPACECRAFT WITH VERY
LONGBASELINE INTERFEROMETRY
---- A STEP OF VLBI APPLICATION FOR SPACECRAFT NAVIGATION ----
M.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
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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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For astrometry of S.C.Tasks to be done are
• VLBI delay mode for Finite distance radio source– A New VLBI delay Model corresponding to the CONS
ENSUS model.
• Narrow band width of the signal – Group delay or Phase delay
• Delay Resolution: (nano/pico seconds)• Ambiguity problem
• Data Processing and Analysis software– IP-sampler boards recording to HD– Software correlation & Analysis software
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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
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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)
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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.
III. Computing O-C and least square parameter estimation
xx
y
y
CO
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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
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Group Delay(Post-fit Residual)
Rate residual
Delay Residual
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Orbit motion
Group Delay(Domestic Baselines)
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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Phase delayClosure of Phase delay(Kashima-Usuda-Tsukuba)
Kashima-Usuda-Tsukuba
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Phase Delay Analysis
4 June 2003
Predicted Orbit
Pos
t F
it D
elay
Res
idu
al (
sec)
DeterminedOrbit
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Estimated Coordinates
DeterminedOrbitPredicted
Orbit
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Summary• NOZOMI VLBI observations were perform
ed with domestic and intercontinental baselines.
• Formula for Finite VLBI delay model was derived.
• An analysis software is developed with that delay model based on CALC9.
• Astrometric SC coordinates were obtained with Group/Phase delay observables.
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Summary• Least square solution with Predicted orbit
did not give consistent solution with determined orbit.=>Probably due to nonlinearity of observable.
=>Iterative solution will solve this problem.
• Next step:SC Astrometry => Orbit estimation
Thank you for attention.
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SpaceOrbit of
NOZOMI
Apr. MayMar.Jan. Feb. Jun.
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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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