3.5 meter NMSU Telescope | observatory, research, ILRS station (International Laser Ranging Service), satellite navigation / satnav system

 observatory, research, telescope, ILRS station (International Laser Ranging Service), satellite navigation / satnav system

3.5 meter New Mexico State University telescope.
The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) is a new initiative in lunar laser ranging (LLR), that utilizes thise 3.5 meter telescope at Apache Point Observatory. The large aperture of the telescope in combination with the good atmospheric "seeing" at the site has enabled us to explore the regime of recording multiple returned laser photons per pulse (in contrast to the 0.01 photon-per-pulse average experienced by previous LLR facilities.)
APOLLO measures the round-trip travel time of laser pulses bounced off the lunar corner-reflectors to a precision of a few picoseconds, corresponding to about plus or minus one millimeter of precision in range to the moon. Using this information, we will be able to gauge the relative acceleration of the earth and moon toward the sun in order to ascertain the free-fall properties of earth's gravitational self-energy.
If the earth's gravitational self-energy does not precisely obey the Equivalence Principle, the orbits of the earth and moon around the sun would be slightly displaced from one another (think of Kepler's third law), which would show up as a signal in our lunar range data.
Various string-motivated theories, quintessence, and other alternatives to General Relativity almost all predict a violation of the Equivalence Principle at some subtle level. Given the recent hints that there may be some new and mysterious modification to the laws of large-scale gravitational attraction (as indicated by supernovae and cosmic background an-isotropies), it is important that we examine every aspect of the basic nature of gravity.
vide:
www.physics.ucsd.edu/~tmurphy/apollo/basics.html