MoonLIGHT: A USA–Italy lunar laser ranging retroreflector array for the 21st century

doi:10.1016/j.pss.2012.09.006

Planetary and Space Science

Volume 74, Issue 1, December 2012, Pages 276-282

https://doi.org/10.1016/j.pss.2012.09.006 Get rights and content

Abstract

Since the 1970s Lunar Laser Ranging (LLR) to the Apollo Cube Corner Retroreflector (CCR) arrays (developed by the University of Maryland, UMD) have supplied significant tests of General Relativity: possible changes in the gravitational constant, gravitational self-energy, weak equivalence principle, geodetic precession, inverse-square force-law. LLR has also provided significant information on the composition and origin of the Moon. This is the only Apollo experiment still in operation. In the 1970s Apollo LLR arrays contributed a negligible fraction of the ranging error budget. Since the ranging capabilities of ground stations improved by more than two orders of magnitude, now, because of the lunar librations, Apollo CCR arrays dominate the error budget. With the project MoonLIGHT (Moon Laser Instrumentation for General relativity High-accuracy Tests), in 2006 INFN-LNF joined UMD in the development and test of a new-generation LLR payload made by a single, large CCR (100 mm diameter) unaffected by librations. In particular, INFN-LNF built and is operating a new experimental apparatus (Satellite/lunar laser ranging Characterization Facility, SCF) and created a new industry-standard test procedure (SCF-Test) to characterize and model the detailed thermal behavior and the optical performance of CCRs in laboratory-simulated space conditions, for industrial and scientific applications. Our key experimental innovation is the concurrent measurement and modeling of the optical Far Field Diffraction Pattern (FFDP) and the temperature distribution of retroreflector payloads under thermal conditions produced with a solar simulator. The apparatus includes infrared cameras for non-invasive thermometry, thermal control and real-time payload movement to simulate satellite orientation on orbit with respect to solar illumination and laser interrogation beams. These capabilities provide: unique pre-launch performance validation of the space segment of LLR/SLR (Satellite Laser Ranging); retroreflector design optimization to maximize ranging efficiency and signal-to-noise conditions in daylight. Results of the SCF-Test of our CCR payload will be presented. Negotiations are underway to propose our payload and SCF-Test services for precision gravity and lunar science measurements with next robotic lunar landing missions. We will describe the addition of the CCR optical Wavefront Fizeau Interferogram (WFI) concurrently to FFDP/temperature measurements in the framework of an ASI-INFN project, ETRUSCO-2. The main goals of the latter are: development of a standard GNSS (Global Navigation Satellite System) laser Retroreflector Array; a second SCF; SCF-Test of Galileo, GPS and other ‘as-built’ GNSS retroreflector payloads. Results on analysis of Apollo LLR data and search of new gravitational physics with LLR, Mercury Radar Ranging will be presented.

Highlights

► We have created a unique facility and a new industry-standard laboratory test. ► We have obtained a measurement of geodetic precession consistent with GR. ► The intensity of the FFDP decreases during no orthogonal lighting of the CCR.

Section snippets

Satellite/lunar laser ranging characterization facility

Starting from 2004 INFN invested resources and manpower to build and start the operation Fig. 1 of the Satellite/Lunar Laser Ranging (SLR/LLR) Characterization Facility (SCF), Fig. 2 in Frascati, near Rome, dedicated to the space calibration of the thermal properties and the laser ranging response of laser retro-reflector arrays (LRAs) in accurate laboratory-simulated space conditions (the SCF-Test).

The size of the steel cryostat is approximately 2 m length by 0.9 m diameter. The inner copper

The MoonLIGHT/LLRRA21 experiment

Lunar Laser Ranging (LLR) has for decades provided the very best tests of a wide variety of gravitational phenomena, probing the validity of Einstein's theory of General Relativity (Williams et al., 1996a, Williams et al., 1996b, Williams et al., 2006). The lunar orbit is obviously influenced by the gravitational fields of the Earth and Sun, but is also sensitive to the presence of many other solar system bodies.

In Table 1, we report the improvement in gravitational measurements possible

SCF-Test of the MoonLIGHT CCR

The SCF-Test Dell'Agnello et al. (2011) is a new test procedure to characterize and model the detailed thermal behavior and the optical performance of laser retroreflectors in space for industrial and scientific application. We performed an SCF-Test on the MoonLIGHT CCR to evaluate the thermal and optical performance in space environment.

The housing was controlled in temperature with resistive tape heaters.

For thermal measurements we use both an infrared (IR) camera and temperature probes,

Analysis of lunar laser ranging data

In order to analyze LLR data we used the PEP (Planetary Ephemeris Program) software, developed by the CfA, by I. Shapiro et al. starting from 1970s.

PEP was designed not only to generate ephemerides of the planets and Moon, but also to compare model with observations (Reasenberg et al., 1979, Chandler et al., 1996, Battat et al., 2007). One of the early uses of this software was the first measurement of the geodetic precession of the Moon (Shapiro et al., 1988).

PEP asserts that the solar system

Determination of the geodetic precession

With PEP software we are not able to directly measure the geodetic precession (de Sitter effect in Fig. 9), but we can measure the relative deviation from the GR value (deviation from zero) that is expressed by K_GP parameter.

We have used all the data available to us from Apollo CCR arrays: Apollo 11, Apollo 14 and Apollo 15. Results are reported in two tables, one until 2003, acquired with data by the old ILRS stations (Table 2) and one with data from 2007 to 2009 acquired by the new APOLLO

Conclusion

We have created a unique facility and a new industry-standard laboratory test to validate the thermal and optical behavior of CCR in space. The experimental apparatus and the test procedures are described in great detail in Dell'Agnello et al. (2011) and ETRUSCO (2011).

The MoonLIGHT experiment is the result of collaboration between two teams: LLRRA21 and the INFN-LNF. With MoonLIGHT we are exploring improvements in both instrumentation and the modeling of CCR.

For the SCF-Test, we can conclude

Acknowledgments

The work on the second generation LLR payload has been supported in Italy by INFN through the MoonLIGHT experiment and by ASI though the Phase A Study for the MAGIA lunar Orbiter (Exp Astron, 2011). In the USA it has been supported by NASA through two programs: Lunar Sortie Science Opportunities (LSSO) and the Lunar University Network for Astrophysics Research (LUNAR) consortium (http://lunar.colorado.edu), headquartered at the University of Colorado.

We thank Ryan Heller (DOE/INFN Summer

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