Laser Retroreflectors:From Lunar Laser Ranging to Planet-exploration Key Payload
Laser retroreflectors are a crucial legacy of the Apollo program.Sites on the surface of the Earth have successfully provided lunar laser ranging(LLR)service to 5 corner cube retroreflectors(CCRs)on the surface of the Moon for half a century,generating more than 26,000 normal points.Upgraded systems have led to millimeter-level range accuracy.With appropriate modeling and data analysis,laser ranging is able to determine parameters associated with geophysics,geodesy,interior structure and reference frame of the target planet system.The same planet system is also a good test body for fundamental physics since laser ranging has become a powerful tool for gravitational and relativistic physics,capable of testing equivalence principle and Lorentz violation in the solar system,as well as solving for the post-Newtonian parameters and the temporal variation of the gravitational constant.New types of CCRs,coupled by satellite-based laser transmitters,have been frequently seen in recent deep space exploration plans for Mars and asteroids,aiming to duplicate the success of LLR to other planet systems.This paper makes a brief review and analysis about the role and potential of laser retroreflectors in planet exploration.Following a short historical overview,several undergoing and ongoing planet exploration plans involving CCRs are introduced.The major scientific goals and requisite techniques are abstracted next according to past engineering experience of laser ranging projects.Considering the continuing revolution of next-generation CCRs and laser transmitters,future prospects on all fronts are described and advice is made for the use of CCRs in new deep space programs,especially in the next phase of Chang'e program and manned lunar exploration.
Laser retroreflectorsLunar laser rangingGravitational and relativistic physicsGeophysicsPlanetary exploration
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