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LALT is one of the instruments on board KAGUYA main orbiter for laser ranging from the satellite to the surface of the Moon in the nadir direction. LALT is able to obtain the range data globally along satellite's trajectory on the polar orbit. These range data of LALT will enable us for the first time in the world to construct a global, accurate and precise topographic map of the Moon.
| Weight | 20kg |
|---|---|
| Dimensions | 306 x 450 x 408 (LALT-TR) 301 x 241 x 88 (LALT-E) 1064nm |
| Laser wavelength | 1064nm |
| Range | 50km~150km |
| Laser output Energy | 100mJ |
| Pulse repetition rate | 1Hz |
| Ranging accuracy | 5m |
LALT transmits laser pulses to the Moon from the main orbiter and measures precisely round trip times of returned signals from the Moon.
Distances between the orbiter and lunar surface are obtained as follows,
(distances) = (light speed) x (round trip times of laser signals) / 2.
The round trip time of 0.666 milliseconds corresponds to the range of 100 km.
Mission objectives of LALT are as follows;
- Much more accurate and global measurement of lunar figure than U.S. Clementine mission Fundamental selenodetic parameters. (radius, COM-COF offset, low degree topography)
- Making a global and precise topographic map of the moon including both polar regions.
- Lunar internal structure by the analysis of gravity / topography data of the moon (New accurate Lunar gravity data including far-side will be obtained from RSAT/ VRAD mission in KAGUYA.).
Footprints by LALT around Copernicus crater
(diameter is about 90km) after one year mission period.
･in the figure is the point of measurement. Intervals of points are about 1.6 km in the North-South direction, and 2 km in the East-West direction, respectively. More than 30 million points will be obtained in one year.
Hiroshi Araki
RISE (Research In Selenodesy) Project,
National Astronomical Observatory of Japan
