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WPLTN-2012 Technical Workshop

Research and Experiment of Lunar Laser ranging
Yaoheng Xiong, Zhulian Li, Yuqiang Li, Honglin Fu, Xiangming Zheng, Dongsheng Zhai, Yuncheng Zhang Yunnan Observatory Chinese Academy of Sciences
St. Petersburg , Sep24-28 2012


LLR researchs & experiments in Kunming
Overview
Key problems of LLR Very long distance ranging, sub-single photon detection,...... How to increase the echo photons from moon retro-reflectors ? New technical method research for LLR : Adaptive Optics (AO) technique applied to LLR Technical problems, some solutions : Adding OTL110P and A033-ET Event Timer Establishing the local pointing model for 1.2m telescope Realizing correlation tracking system to compensate the distortion of wavefront tilt of the extended source on real-time Developing aberrational compensation system Developing the control system for LLR Perspectives St. Petersburg , Sep24-28 2012


Key problems of LLR Lunar Laser Ranging is:
A expected goal in the LR field A significant job for scientific research of the Moon and the Earth An challenging experiment which relates to many fields such as optics, mechanism and electronics, e tc . Simultaneously, a tough job because of few returned photon

How to overcome this key problem?
St. Petersburg , Sep24-28 2012


New technical method research for LLR
A new technical method of increasing returned photon numbers: the real-time compensation low order atmospheric turbulence effects in LLR combining with the Adaptive Optics technique. The realization method is to use a small area near the retro-reflector array on the moon surface as an extended source to detect and calculate the atmospheric tip-tilt, and then carry on the real-time tip-tilt compensation for the laser beam on the LLR.


Adding OTL110P and A033-ET Event Timer
OTL110P(developed by group) A033-ET (Riga)

Parameters: dead time1µs resolution4ps precision typical 40ps dead time50ns resolution1ps precision <5ps
St. Petersburg , Sep24-28 2012

......


Establishing the local pointing model
Global Pointing Model
errors can be moved using a mathematics model & through star observation & CCD image processing, But the processing need long time, and the pointing accuracy is not higher for LLR.

local Pointing Model

dA sin Z = a0 + a1 в Z + a2 в A sin Z + a3 в Z 2 + a в Z в A sin Z
4

+a5 в (A sin Z )2 + a6 в Z 3 + a7 в (A sin Z )3

dZ = b0 + b1 в Z + ...... + b7 в (A sin Z )3
A and Z is the azimuth and zenith of star; a1, a2......a7 and b1, b2......b7 are the model's fitting coefficients.

Stars selected for model:
To choose a number of stars around a observed target as local calibrator of Directions in the pointing mode. i.e. to select several points as the center at lunar orbit, and choose the star whose distance is less than 10deg from the center, like the following picture. St. Petersburg , Sep24-28 2012


Establishing the local pointing model
Stars selected for model near the lunar orbit stars moon

Zenith (deg)

Azimuth (deg)

M

Asinz=

6.16pixel=(6.16*0.22) =1.35

Mz=3.51pixel=(3.51*0.22) =0.77
St. Petersburg , Sep24-28 2012


Realizing correlation tracking system

Computer PCI-E bus

PCI image collector card

PCI D/A card amplifying circuit

CCD camera

Tip-tilt mirror

This system introduced tilt-correction adaptive optical system to the LLR, it realized high-speed image acquisition based on PCI-Express bus, and adopted the absolute difference algorithm, etc. St. Petersburg , Sep24-28 2012


Aberration compensating system

aberration compensating device

Due to the earth rotation, movement of the moon is about 14.5/s relative to the earth, the aberration on laser emission path can be calculated by the prediction of lunar orbit, the laser echo is detected by single photon avalanche diode (SPAD) , as a detector, the SPAD surface diameter was only 0.1 ~ 0.2 mm, and the FOV is small, so, in order to increase the number of echo, the aberration compensating system is developed. St. Petersburg , Sep24-28 2012


Developing the control system

Rotation Shutter

designing rotation mirror to generate synchronous pulse generating C-SPAD gate for LLR developing control program, including lunar orbit generation, ranging control, returned photons recognition and data post-process functions. ......
St. Petersburg , Sep24-28 2012


The Perspectives of Kunming LLR
In order to successfully get returned photons and high precision distance data, the laser need have high or enough pulse energy and relative narrow width for LLR system,. Now Kunming station's SLR had upgraded to kHz laser ranging, so we hope to utilize the current laser to do the experiment of LLR. Energy: 3mJ@1KHz Width: 10~20ps Wavelength: 532nm Frequency: 1~10KHz Now energy of the laser is only 0.7mj/p! so we need a new laser to continue to our experiment of LLR.
St. Petersburg , Sep24-28 2012


LLR Experiments in Kunming Station

Thank you