DEVELOPMENT OF SELENODETIC INSTRUMENTS FOR JAPANESE LUNAR EXPLORER SELENE-2

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DEVELOPMENT OF SELENODETIC INSTRUMENTS FOR
JAPANESE LUNAR EXPLORER SELENE-2
H. Hanada1, H. Noda1, F. Kikuchi1, S. Sasaki1, T.
Iwata2, H. Kunimori3, K. Funazaki4, H. Araki1, K.
Matsumoto1, S. Tazawa1, S. Tsuruta1
1 National Astronomical Observatory 2 Japan
Aerospace Exploration Agency 3 National Institute
of Information and Communications Technology
4 Iwate University
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KAGUYA (SELENE) ? SELENE-2

• Successful KAGUYA
• Study of lunar landing mission(s) in JAPAN.
• SELENE-2 lunar lander
• SELENE Series 2, 3, X
• Launch by H-IIA in 2016 ?
• Lander of 1000kg including
• scientific instruments of 300kg

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Mission instruments for SELENE-2

• Scientific instruments
• Science of the moon
• Geophysical/geodetic instruments
• Geological instruments
• Science from the moon
• Astronomical instruments
• Engineering instruments
• Environmental instruments

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Proposal for SELENE-2
SELENE-2 instruments for Lunar intererior
study ?Gravity observations by VLBI
(Same-beam and Inverse VLBI) ?Rotation
observations by Lunar Laser Ranging
(new reflectors and a new ground
network) They are under review for onboard
instruments Another rotation observations by
ILOM (In-situ Lunar Orientation Measurement) is
proposed for SELENE-3
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Selenodetic Candidate instruments
Observation method Observation method SELENE- Purpose
VLBI d-VLBI Differential VLBI 2 (Kikuchi) Gravity Fields
VLBI i-VLBI Inverse VLBI 2/3 (Kikuchi) Gravity Fields
LLR Lunar Laser Ranging 2 (Noda) Librations
ILOM In situ Lunar Orientation Measurement 3 (Hanada) Librations

• Questions to be addressed
• Is there a core in the Moon ?
• Is the core metallic ?
• Is the metallic core liquid ?
• Is there an inner core center of the liquid core ?

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Molten core ? Solid inner core ??
MOON
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Lunar Laser Ranging (LLR)
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Lunar Laser Ranging
Laser Ranging from the Earth to the Moon started
by Apollo in 1969 and continue to the present
4 reflectors are ranged Apollo 11, 14 15
sites Lunakhod 2 Rover
LLR attained the accuracy of less than 3cm with
observations for longer than 25 years.
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Objectives of future LLR

• Ephemerides and/or Reference systems
• Gravitational physics (General Relativity)
• Geodynamics
• Lunar science and Selenophysics

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Issues on LLR

• DeploymentWhere on the Moon ?
• Type Array or Single, Prism or Hollow
• SizeReflection Efficiency more than A11 or A15
• Structure Hard to be affected by gravitational
  and thermal effects
• Optical PerformanceRay tracing simulation
• Dihedral Angle OffsetWhat is the optimal value ?
• Adaptive OpticsOption

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Deployment Where on the Moon ?
? Area Data Contribution (77)
???
2,000km
For Physical Librations Southern Hemisphere far
from A15 site about 2000km or more
Schickard (44.3S, 55.3W)
Tycho(43.4S,11.1W)
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Type Array or Single, Prism or Hollow ?

• Prism array of small aperture (Apollo, Luna)
• Large range error due to optical libration
• Single prism with large aperture
• High accuracy of ranging
• Extremely high quality prism is necessary
• ? less than 10cm size CCP
• Single hollow with large aperture
• Lighter weight
• High accuracy
• Change of dihedral angle due to
• thermal distortion will be a problem

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Structure Deformation by Earths Gravity
D20 cm (L 14.14 cm), t 1cm,
Cu Deformation less than 1 µm by Earths
Gravity Field
Taniguchi, 2010
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Structure Thermal Deformation of CCR
(mm)
(mm)
L 7.07 cm (D10cm), lt 3 nm
L14.14 cm (D20cm), lt 60 nm
NEC, 2010
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Optical Performance (Ray Tracing Analysis)
Efficiency (Streal Ratio) 95.8
Kashima, 2010
L14.14 cm (D20cm), lt 60nm
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VLBI (Same-beam VLBI and Inverse VLBI)
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VLBI (Very Long Baseline Interferometer)?
Quasar
Noise
Noise
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VLBI Improvement of Lunar Gravity field
Orbiter
Same-beam (Differential) VLBI Method ?Doubly
Differenced One-way Range Sensitivity lt20 cm
Survival module
Inverse VLBI Method ?Differenced One-way
Range ?2-way range between orbiter and S-module
Sensitivity lt10-20 cm
These new observations are expected to improve
the lunar gravity field.
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Inverse VLBI

• Radio signals transmitted from orbiter and lander
  are received at a ground antenna. These signals
  are synchronized via a reference signal from
  orbiter.
• Received signals are cross correlated and a
  difference of the propagation time is measured.
• Expected accuracy is several tens to several ps.
  These time difference corresponds to the distance
  of a few cm to a few mm.

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Same-beam VLBI method Improvement of lunar
gravity model
Simulation result
2nd degree coefficients are improved by factor 3
or more. ?Moment of inertia Topography,
Moho, GRAIL/LRO/Kaguya data ? Constrain core
density and radius
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Conditions of the Simulations
Orbit parameters Perilune height
100km, Apolune height 800km,
Orbit inclination 70 Landing position
(0?0) Tracking station Usuda(64m) and
VERA(20m) Data weight 2-way Doppler 1
mm/s, VLBI 1 mm Arc length of orbiter 14
days. Observation Period 3 months
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In-situ Lunar Orientation Measurement
(ILOM)
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Principle of ILOM Observations
Telescope
Motion of a star in the view
Other objectives than lunar rotation Pilot of
lunar telescope (Engineering) Establishment of a
lunar coordinate system
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Star trajectory and Effects of Librations
After Heki
Decomposition of the trajectory
Trajectory of a star observed at the Lunar pole
(June 2006 Sep.2007)
Polar motion and Librations extracted from the
trajectory
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0.1m
Development of BBM (Cooperation with Iwate univ.)
Objective
Motor
0.5m
Frame
Tube
Mercury Pool
Tiltmeter
Tripod
After Iwate Univ.
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Specifications
Aperture 0.1m
Focal Length 1m
Type PZT
Detector CCD
Pixel Size 5µm5µm (1?1?)
Number of pixels 4,0964,096
View 1 1
Exposure Time 40s
Star Magnitude M lt 12
Wave length 550nm 750 nm
Accuracy 1/1,000 of pixel size (1mas)
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Issues on ILOM Technical issues
Improvement of the accuracy of centroid
experiments Correction of effects of
temperature change upon star position
Keeping power during the night Keeping warm
during the night Keeping inside thermally
stable Important condition of the lunar surface
? How is the lunar dust ? How dark
is the lunar surface at night ? How stable
is the lunar surface ? How quiet is the
lunar surface ?
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Summary

• Technical developments and scientific evaluations
  for LLR, VLBI and ILOM are going on.
• LLR and VLBI instruments are under review for
  SELENE-2 onboard instruments.
• ILOM is prepared for SELENE-3.
• We will investigate the lunar deep interior by
  further improving accuracy of observations of the
  lunar rotation and the gravity fields with new
  technologies.

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Fabrication of CCR

• ELID and Electroforming with Omori Lab., RIKEN
  Inst.
• ELID (Electrolytic Inprocess Dressing)
• For making the Master of CCR
• Surface Roughness 10 nm
• Electroforming Electrolysis
• Fabrication of One-unit CCR from
  Cu
• Now trying to make a surface with Cu

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