The French Lunar-Laser Ranging Station

An Update-------

Presented by G.Vigouroux

Lageos 6000km

Glonass 19000km

Etalons à 19000km

GPS 20000km

Targets ranged withthe Grasse LLR system

LUNA 17 et 21

Apollo 11

LRE 250 to 36198 km

380 000 km

Grasse LLR system

SCIENTIFIC OBJECTIVES

For the Moon

• Geophysics

• Selenophysics

• Celestial mechanics

• Rotation of the Earth and Moon

• Precession and nutation

• Terrestrial and celestial reference frames

• Test of gravitation theories

For the distant satellites

• Orbitography

• Geodynamics

• Positioning

• Comparison of tracking techniques

• Terrestrial reference frames

13th Workshop

Washington, Oct.2002

Raw data productionon the Moon

13th Workshop

Washington, Oct.2002

13th Workshop

Washington, Oct.2002

It is possible by using an additional amplifier and double-frequency. This would permit toimprove the number of returns from the Moon without increasing the noise.

It is possible to increase

the energy of our laser

Mirror

Pockell cell

κ/4PolarizingPrism

Y.A.G. Rod of

Spatial filter

Electro opticalmodulator

Fabry-Perrot

Oscillator

Slicer Faraday isolator

κ/4Ampli. A’3 Harmonic

Generator D’

κ/2κ/4

Ampli. A3 Harmonic

Generator D

Ampli. A1Ampli. A2κ/2

Only one pulse400mJ

400mJ

200mJ

200mJ

400mJ

200mJ

200mJ

I.R. Polarizing Plate Green polarizing plate

Spatial

Filter

Green polarizing plate

Dichroic mirror

Dichroic mirror

13th Workshop

Washington, Oct.2002 Technical improvements for highaltitude satellites

• We use another laser with a semi-train and a 20 ps pulse width. It permits to

increase the precision on high-altitude satellites.

•For the satellites, we have implemented, on the return path, a wedge plate to

correct the angle, between the emission and reception axis, due to the velocity

aberration. The first tests will begin soon. It should permit to decrease the noise and

reduce the scattering of the transit time between the center and the edge of the

detection diode.

• We have just started, for the high-altitude satellites, the automation of the

observations.

• A major maintenance on the steering of the dome has been carried out in 2002 to

replace the worn-out main rail.

13th Workshop

Washington, Oct.2002 A quality assessment

• Objective: Evaluate the performances of the Grasse LLR system and try tounderstand their variations. It seems possible from nights where the number ofnormal points is superior to 6 , on Apollo XV.

•Method : We use the same method showed in 12th WS Matera. We add a thirddegree polynomial fit on residues and compute the Normal Points rms. Weanalysed 101 nights between Oct.1998 and Dec.2000.

•Results : The internal consistency per night is excellent, varying between 1 to 15mm, with no obvious correlation with the lunar libration, the number of normalpoints over each night, the pressure, the signal/noise ratio or the number of returns.

0

5

10

15

20

0 0.1 0.2 0.3ns

mm

Scattering of panel

0

5

10

15

20

5 15 25Number of NP

mm

0

5

10

15

20

860 865 870 875 880 885

mm

Pressure (mb)

13th Workshop

Washington, Oct.2002 A quality assessment (ctd)

ratio signal / noise

0

5

10

15

20

1.5 5 8.5

m m

mean nomber of returns

0

5

10

15

20

0 50 100 150 200 250

m m

• If the signal/noise ratio is > 6, the RMS. of the Normal Points is less than 15 mm.If the mean number of returns by serials in the night is larger than 100, the RMSgoes down below 10 mm.

• The sources of these variations are not properly indentified : noise, insufficientnumber of echoes, etc... and variation of the atmospheric properties ?

13th Workshop

Washington, Oct.2002 CONCLUSION

Internal consistency per night

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

No

mb

er o

f n

igh

ts

• For 20% of nights, the internal consistency is lower than 5 mm and for 50% falls between 5 and 10 mm.

•Interestingly the internalconsistency on GPS 35 and 36(with similar signature : panel of reflectors ) varies between 0.4 mm and 4mm, butwith a laser 20ps. It seems that it is a link with the windspeed.

• We hope in a near future, thanks to the doubling of the laser energy, to increase thenumber of returns and the signal / noise ratio, therefore the precision.