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 Observatory2 Japan Aerospace Exploration Agency3 National Institute of Information and 　　　 Communications Technology 4 Iwate University

• 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

KAGUYA (SELENE) → SELENE-2

• Scientific instruments– Science of the moon

• Geophysical/geodetic instruments• Geological instruments

– Science from the moon• Astronomical instruments

• Engineering instruments• Environmental instruments

Mission instruments for SELENE-2

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

Observation method SELENE-# Purpose

VLBId-VLBI : Differential VLBI 2 (Kikuchi)

Gravity Fieldsi-VLBI : Inverse VLBI 2/3 (Kikuchi)

LLR Lunar Laser Ranging 2 (Noda) Librations

ILOMIn situ Lunar Orientation Measurement

3 (Hanada) Librations

Selenodetic Candidate instruments

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 ?

MOON

Molten core ? Solid inner core ??

Lunar Laser Ranging (LLR)

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.

Lunar Laser Ranging

Laser Ranging from the Earth to the Moon started by Apollo in 1969 and continue to the present

• Ephemerides and/or Reference systems

• Gravitational physics (General Relativity)

• Geodynamics

• Lunar science and Selenophysics

Objectives of future LLR

• Deployment ： Where on the Moon ?

• Type ： “ Array” or “Single”, “Prism or Hollow”

• Size ： Reflection Efficiency more than A11 or A15

• Structure ： Hard to be affected by gravitational and thermal effects

• Optical Performance ： Ray tracing simulation

• Dihedral Angle Offset ： What is the optimal value ?

• Adaptive Optics ： Option

Issues on LLR

新規 ?

● Area : Data Contribution (~77%)

Tycho （ 43.4S,11.1W ）

Schickard(44.3S, 55.3W)

For Physical Librations: Southern Hemisphere far from A15 site about 2000km or more

2,000km

Deployment ： Where on the Moon ?

• 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

Type : Array or Single, Prism or Hollow ?

D=20 cm (L = 14.14 cm), t = 1cm, “Cu”

Deformation: less than 1 μmby Earth’s Gravity Field

Taniguchi, 2010

LLDD

Structure : Deformation by Earth’s Gravity

L=14.14 cm (D=20cm), < 60 nm L= 7.07 cm (D=10cm), < 3 nm

NEC, 2010

(mm)

LL DD

Structure : Thermal Deformation of CCR

(mm)

.02888 mm

.02888 mm

0.0000

100.00

50.000

ccrtxm141_hex_1a 200mm ccr witBeam Intensity at Image Surface

Relative Field ( 0.000, 0.000 ) POSITION 1Wavelength 532.00 nm.Defocus: 0.000000 mm

15:46:13

23-Jul-10DEFOCUSING 0.00000

ccrtxm141_hex_1a 200

mm ccr with 1a defor

DIAMETER OF CIRCLE (MM)

DIFFRACTION ENCIRCLED ENERGY

0.0E+00 6.9E-03 1.4E-02 2.1E-02 2.8E-02 3.4E-02 4.1E-02 4.8E-02 5.5E-02 6.2E-02 6.9E-02 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

(0.000,0.000) DEGREES

Efficiency (Streal Ratio) : 95.8 %

Kashima, 2010L=14.14 cm (D=20cm), < 60nm

Optical Performance (Ray Tracing Analysis)

VLBI (Same-beam VLBI and Inverse VLBI)

Quasar

Noise

Noise

VLBI (Very Long Baseline Interferometer) ？

Orbiter

Survival module

VLBI : Improvement of Lunar Gravity field

Same-beam (Differential) VLBI Method◇ Doubly Differenced One-way Range Sensitivity : <20 cm

Inverse VLBI Method◇ Differenced One-way Range◇ 2-way range between orbiter and S-module Sensitivity : <10-20 cm

These new observations are expected to improve the lunar gravity field.

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.

Inverse VLBI

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

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

Conditions of the Simulations

In-situ Lunar Orientation Measurement　　　　　　　　　　　　　　　　　　　　　（ＩＬＯＭ）

Telescope

Motion of a star in the view

Principle of ILOM Observations

Other objectives than lunar rotationPilot of lunar telescope （ Engineering ）　Establishment of a lunar coordinate system

Star trajectory and Effects of LibrationsDecomposition of the trajectory

Trajectory of a star observed at the Lunar pole (June 2006– Sep.2007)

Polar motion and Librations extracted from the trajectory

After Heki

Tube

Objective

Motor

Frame

Tiltmeter

Mercury Pool

Tripod

0.1m

0.5m

After Iwate Univ.

Development of BBM(Cooperation with Iwate univ.)

Specifications

Aperture 0.1m

Focal Length 1m

Type PZT

Detector CCD

Pixel Size 5μm×5μm (1″×1″)

Number of pixels 4,096×4,096

View 1°× 1°

Exposure Time 40s

Star Magnitude M < 12

Wave length 550nm – 750 nm

Accuracy 1/1,000 of pixel size (1mas)

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 ?

• 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.

Summary

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

http://www.jst.go.jp/pr/info/info96/zu1.html

Fabrication of CCR