Astrometric VLBI Observation of Spacecraft with Phase Delay

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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

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NOZOMIs Earth Swing-by

• NOZOMI was launched in July 1998.
• Due to some troubles, new orbit plan with Earth
  swing-by was proposed.
• RRR observations were difficult in a period.

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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)
Kashima (CRL)

Kagoshima(ISAS) (uplink)
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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

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VLBI delay model for finite distance radio source
VLBI for finite distance radio source
Normal VLBI
(Fukuhisma 1993 AA)
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Relativistic VLBI delay model for finite
distance radio source
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 (tg, tp)(O) with
software correlator.
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Group Delay(Post-fit Residual)
Delay Residual
Rate residual
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Estimated Coordinates(Group Delay)
6/4(RRR)
6/4(VLBI)
June 4
Orbit motion
May 27
Origin is Orbit on May 27, which was Determined
by ISAS with RRR
Origin is Orbit on June 4.
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Observable Phase Delay Group delay
2p n ambiguity
tgGroup Delay
Dtp 1/RF 1 pico second
Phase
Phase Delay
Dtg 1/BW 1 nano second
(Spacecraft)
Band width
0
Frequency
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Phase delay
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Phase Delay Post fit residual
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Estimated CoordinatesComparison with RRR
measurement
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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.

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Thank you for attention.
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Space
Orbit of NOZOMI
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Group Delay(Range signal)
Closure
Observation 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 (ISASNASDAJAXA)
• NOZOMI(Japanese Mars Explorer)
• Needs to support orbit determination with VLBI.
• Mission as our own Project

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Spacecraft Navigation
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ObservationIP-VLBI Sampler board
K5 VLBI System

• Sampling rate40k-16MHz
• Quantization bit 1-8bit
• 4ch/board
• 10MHz,1PPS inputs

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Phase Delay Analysis
4 June 2003
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Estimated CoordinatesComparison with RRR
measurement