H. Hanada1, S. Tsuruta1, H. Araki1, S. Kashima1, K. Asari1, S. Tazawa1, H. Noda1, K. Matsumoto1, S. Sasaki1, K. Funazaki2, A. Satoh2, H. Taniguchi2, H. Kato2, M. Kikuchi2, Y. Itou2, K. Chiba2, K. Inaba2, N. Gouda3, T. Yano3, Y. Yamada4, Y. Niwa3, H. Kunimori5, N. Petrova6, A. Gusev6, J. Ping7, T. Iwata8 S. Utsunomiya8, T. Kamiya8 & K. Heki9

Technical Development of a Small Digital Telescope for In-situ Lunar Orientation Measurements (ILOM)

1) National Astronomical Observatory, RISE2) Iwate University3) National Astronomical Observatory, JASMINE4) Kyoto University5) National Institute of Information and Communications Technology6) Kazan Federal University7) Beijing Astronomical Observatory, CAS8) Japan Aerospace Exploration Agency9) Hokkaido University

PZT used in the International Latitude Observatory of Mizusawa (ILOM)

Another observation independent of LLR is necessary

Photographic Zenith Tube (PZT)

Mercury Pool

Lens

CCD array

Tilts of the tube are nearly cancelled

Tube

(1/2

of t

he fo

cal l

engt

h)

(after Heki)

Photographic plate

Bread Board Model (BBM) : Improvement of an accuracy Environmental test of key elements. in cooperation with Iwate University

Experimental Model (EM) : Development of a PZT for observations of the Deflection of the Vertical (DOV) related to Earthquakes and volcanic eruptions (0.1 arc-seconds). in cooperation with Shanghai Astronomical Observatory

Proto-Flight Model (PFM) Development of a PZT for observations of Lunar rotation

on the Moon (1 milli-arc-second)

Strategy of Development of a New PZT

Earth Moon

Core (liquid ?)

Outer Core (liquid)Inner Core (solid)

How the lunar core is ? (liquid or not ?)

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

Tube

Objective

Motor

Frame

Tiltmeter

Mercury Pool

Tripod

0.1m

0.5m

After Iwate Univ.

Development of BBM(Cooperation with Iwate univ.)

Specification of the PZT

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

Equipment for Centroid Experiment

Artificial Star Images in Centroid Experiment

An Algorithm for Centroid Experiment

: Photon weighted means

: Real position

where

We estimate the parameter k as well as the real positions

Relative distance between two stars by linear correction of the photon-weighted mean. (Yano et al., 2004)

Centroid Experiment

The accuracy is about 1/300 pixel. (1 pixel : 20μm×20μm)

ObjectiveCover Glass

CCD windowCCD

Optical System of the PZT

Prism

Mercury surface

Cover glass for Mercury pool

Plane-parallel plate

Relation between Temperature Change and Shift of the Center of Star Image (Conventional Objectives)

Temperature (℃ ）

Shift

of S

tar I

mag

e (m

as)

Incident Angle

Temperature change of larger than 0.5 degrees is not allowed.

Degree

Temperature (℃ ）

Shift

of S

tar I

mag

e (m

as)

Relation between Temperature Change and Shift of the Center of Star Image (Objectives with a Diffractive Lens)

Degree

Incident Angle

Displacement due to thermal expansion etc.

Displacement due to lunar rotation

Initial Star position on CCD

Distinguish between the Real Displacement and the Artificial OnesFrom Patterns of Distribution

Concluding Remarks

We developed a BBM of PZT for observation of the deflection of the vertical and the lunar rotation.

Using BBM, we are doing performance tests of the driving mechanism and the optical system.

We succeeded in determination of star position with the accuracy of about 1/300 pixel, which corresponds to about 6 milli-arc-seconds for the PZT with 1m focal length and CCD of 20μm×20μm.

The attitude control system can make the tube vertical within an error of 0.006 degrees (or about 20 arc-seconds), which can be compensated by PZT to the positioning accuracy of 1 milli-arc-seconds.

By introducing a diffraction lens, we can loosen thermal condition by about ten times compared with the case not introducing it, and temperature change of about 5 degree centigrade is permissible to realize the precision of the 1 milli-arc-seconds.

As to the shifts of star images due to thermal distortion of the optical elements, they can be approximated with a simple model and can be corrected for with the accuracy higher than 1 milli-arc-seconds except for that with a horizontal gradient.

We adopt a shallow copper shale for mercury pool of the Experimental Model, and confirmed that the effect of vibration is on the level of 0.1 arc-seconds.