Transcript VLBI Observation for Spacecraft Navigation (NOZOMI) – Data

Astrometric VLBI Observation of
Spacecraft with Phase Delay
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
VLBI
R&RR
+
R01
R02
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.
May 22, 24, 27
Jan. Feb. Mar. Apr. May Jun.
June 4
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Japanese and Canadian VLBI
Stations participated in
NOZOMI VLBI observations.
ISAS,CRL,NAOJ, GSI,Gifu
Univ, Yamaguchi Univ.
Hokkaido Univ.
SGL, NRCan supported.
Algonquin
SGL & NRCan
Tomakomai
(Hokkaido Univ.)
Mizusawa
(NAO)
Usuda
(ISAS)
Gifu
(Gifu Univ.)
Tsukuba
(GSI)
Yamaguchi
(Yamaguchi Univ.)
Koganei
(CRL)
Kagoshima(ISAS)
(uplink)
Kashima
(CRL)
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
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VLBI delay model for finite
distance radio source
Normal VLBI
B  X-Y
BS

c
BK

c
S
RY0
RX0
B
X
VLBI for finite distance
radio source
Y
R 0X  R 0Y
K
R0 X  R0Y
K
X
(Fukuhisma 1993 A&A)
B
Y
Relativistic VLBI delay model
for finite distance radio source
CONSENSUS MODEL (M.Eubanks 1991)








2
K0 b 
Ve  2Ve  w 2  Ve  b 
K 0  Ve

t g 
1  (1  γ)U 

2
2
1 
c
2c
2
c
c





τ 2  τ1 

K 0  (Ve  w 2 )
1
c




Finite Distance VLBI MODEL (Sekido & Fukushima 2003)

 
 
 

 

2




Ve  2Ve  w 2
Ve  b
V2 K  Ve  2w 2
K b
1  R 02 
t g 

1  (1  γ)U 

2
2

c 
c
2c
2c
c


τ 2  τ1 



V 
1  R 02  2 

c 




Finite-Infinite : Delay Difference
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
y  O  C

y 
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x
 x
Group Delay(Post-fit
Residual)
Delay Residual
Rate residual
Estimated Coordinates
(Group Delay)
6/4(VLBI
)
6/4(R&RR)
June 4
May 27
Origin is Orbit on June 4.
Origin is Orbit on May 27, which was
Determined by ISAS with R&RR
Observable:
Phase Delay & Group delay
Phase
2p n ambiguity
g:Group Delay
p ~ 1/RF
~1 pico second
g ~ 1/BW
Band width
0
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Frequency
~1 nano second
(Spacecraft)
Closure of Phase delay
Phase delay
(Kashima-Usuda-Tsukuba)
A
C
B
Kashima-Usuda-Tsukuba
Phase Delay Post fit residual
Estimated Coordinates
Comparison with R&RR measurement
Summary
• VLBI observations for spacecraft were
performed 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
differential VLBI technique.
Thank you for attention.
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Space
Orbit of
NOZOMI
Jan. Feb. Mar. Apr. May Jun.
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Group Delay
(Range signal)
Closure
Observation
mode
= 2MHz, 2bit
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
VLBI
R&RR
+
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R01
R02
Observation：IP-VLBI Sampler board
K5 VLBI System
•
•
•
•
Sampling rate:40k-16MHz
Quantization bit: 1-8bit
4ch/board
10MHz,1PPS inputs
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Phase Delay
Analysis
4 June 2003
Predicted Orbit
Determined
Orbit
Estimated
Coordinates
Comparison with R&RR
measurement
Predicted
Orbit
Determined
Orbit