  Current and future optical technologies will aid exploration of the Moon and
Mars while advancing fundamental physics research in the solar system.
Technologies and possible improvements in the laser-enabled tests of various
physical phenomena are considered along with a space architecture that could be
the cornerstone for robotic and human exploration of the solar system. In
particular, accurate ranging to the Moon and Mars would not only lead to
construction of a new space communication infrastructure enabling an improved
navigational accuracy, but will also provide a significant improvement in
several tests of gravitational theory: the equivalence principle, geodetic
precession, PPN parameters $\beta$ and $\gamma$, and possible variation of the
gravitational constant $G$. Other tests would become possible with an optical
architecture that would allow proceeding from meter to centimeter to millimeter
range accuracies on interplanetary distances. This paper discusses the current
state and the future improvements in the tests of relativistic gravity with
Lunar Laser Ranging (LLR). We also consider precision gravitational tests with
the future laser ranging to Mars and discuss optical design of the proposed
Laser Astrometric Test of Relativity (LATOR) mission. We emphasize that already
existing capabilities can offer significant improvements not only in the tests
of fundamental physics, but may also establish the infrastructure for space
exploration in the near future. Looking to future exploration, what
characteristics are desired for the next generation of ranging devices, what is
the optimal architecture that would benefit both space exploration and
fundamental physics, and what fundamental questions can be investigated? We try
to answer these questions.
