Rotational Variation of the Earth and the MoonLuni-solar tidal torques exerted on the Earth with an inclined spin axis let the axis change its direction with various periods (forced nutation). The motion of surface fluids such as ocean and atmosphere excites the EarthUs free polar motion called the Chandler wobble. Amplitudes and phases of these variations provide valuable information on the EarthUs interior. Likewise, the Moon has rotation variations called physical (free and forced) libration, and their measurements are important to know the physical status of lunar core and lower mantle.
Rotational Variation of the Earth and the Moon
In-situ Lunar Orientation Measurement (ILOM)
In the lunar exploration project after the SELENE, soft landing onto the lunar surface is planned. We are proposing the in-situ lunar orientation measurement(ILOM) project, a polar lander is equipped with an optical telescope with diameter of 20 cm and focal length of 2 m. It is designed to enable accurate measurement of lunar rotational variation by analyzing the star trajectories associated with the lunar spin. This will greatly improve the accuracy of the measurement of the lunar physical libration and provide important information on the lunar interior. |
 Consept Image of ILOM |
PZT(Photographic Zenith Tube)
 PZT |
Mercury pool is set at the middle point of focal length for compensation of tilt. A beam splitter set on the objective sees both polar and equatorial stars. Target accuracy is 1-milli-arc-second. |
Thermal Simulation Model
 Thermal Simulation Model |
For observations on the Moon where the surface temperature ranges from about P190 to +120 degrees centigrade, the tube is made of CFRP (Carbon Fiber Reinforced Plastic) the thermal expansion coefficient of which is about 10-7. |
Mercury Surface
 Mercury Surface |
Distortion of a mercury surface is measured by Twyman-Green interferometer. We can reduce the distortion by changing the shape of the case. |
Mercury Pool
 Mercury Pool |
Mercury surface is used as a reference of a horizontal plane. Liquid mercury is sealed in a stainless steel case with an optical parallel and is kept warm at the bottom of the tube. |
Download ILOM Project Report (in Japanese) Gravity: VRAD, RSAT |
 Topography: LALT |
 Rotational Variation: ILOM |
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