astrometric vlbi observation of spacecraft with phase delay m.sekido, r.ichikawa,h.osaki,...
DESCRIPTION
The National Institute of Information and Communications Technology NOZOMI’s Earth Swing-by NOZOMI was launched in July Due to some troubles, new orbit plan with Earth swing-by was proposed. R&RR observations were difficult in a period. VLBI Observations Apr.MayMar.Jan.Feb. Jun. May 22, 24, 27 June 4TRANSCRIPT
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), andNOZOMI VLBI group(NICT,ISAS,NAOJ,GSI,Gifu U
niv. Yamaguchi Univ., Hokkaido Univ., Japan)The National Institute of Information and Communications Technology
The National Institute of Information and Communications Technology
Spacecraft Navigation with VLBI: Motivation
Requirments for increased accuracy of orbit control for future space missions: – For landing, orbiting, & saving energy
R&RR
R01R02
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.
VLBI 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
cSB
Y-XB
BB
XX YY
SS
cKB
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
ccccV
Uγc
tττ
eeeeg
202
220222
22
12
1
22
122
)1(1
VR
wVKVR
bVwVbK
c
cccV
Uγc
tττ
e
eeeeg
)(1
21
22
)1(1
20
022
22
0
12 wVK
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 AstometoryI. 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
Phas
e
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 residualPo
st F
it D
elay
Res
idua
l (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 differe
ntial 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
The National Institute of Information and Communications Technology
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
Post
Fit
Del
ay R
esid
ual (
sec)
DeterminedOrbit
Estimated Coordinates
Comparison with R&RR
measurement
DeterminedOrbitPredicted
Orbit