PHYSICS · Multi-part · Fermi University Physics · Relativity & Gravitation · The equivalence principle and gravity as geometry · The equivalence principle and gravity as geometry
The Geometry of Gravity, Ch The equivalence principle under test
Problem
Early lunar laser ranging in the 1970s, using the retroreflectors left by the Apollo missions, could resolve range changes of about 0.20 m, compared with the millimetre precision reached by present-day stations. The forced polarisation amplitude of the lunar orbit is 13.1ηN m.
((a)) Estimate the smallest ηN that 1970s ranging could, in principle, have detected.
((b)) By what rough factor has the achievable sensitivity to ηN improved between 1970s ranging (0.20 m) and present-day ranging (about 1 mm), if the amplitude formula alone set the limit?