Transcript VLBI Observation for Spacecraft Navigation (NOZOMI) – Data

ASTROMETRY OBSERVATION OF
SPACECRAFT WITH VERY LONG
BASELINE 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)
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)
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
CONSENSUS 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
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
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
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)
Group Delay(Post-fit
Residual)
Rate residual
Delay Residual
Group Delay
(Domestic Baselines)
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
Closure of Phase delay
Phase delay
(Kashima-Usuda-Tsukuba)
Kashima-Usuda-Tsukuba
Phase Delay
Analysis
4 June 2003
Predicted Orbit
Determined
Orbit
Estimated
Coordinates
Predicted
Orbit
Determined
Orbit
Summary
• NOZOMI VLBI observations were
performed 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.
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.
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
+
The National Institute of Information and
Communications Technology
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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