The Earth-Moon-Sun system has traditionally provided the best laboratory fortesting the strong equivalence principle. For a decade, the Apache PointObservatory Lunar Laser-ranging Operation (APOLLO) has been producing theworld's best lunar laser ranging data. At present, a single observing sessionof about an hour yields a distance measurement with uncertainty of about 2~mm,an order of magnitude advance over the best pre-APOLLO lunar laser rangingdata. However, these superb data have not yet yielded scientific resultscommensurate with their accuracy, number, and temporal distribution. There aretwo reasons for this. First, even in the relatively clean environment of theEarth-Moon system, a large number of effects modify the measured distanceimportantly and thus need to be included in the analysis model. The secondreason is more complicated. The traditional problem with the analysis ofsolar-system metric data is that the physical model must be truncated to avoidextra parameters that would increase the condition number of the estimator.Even in a typical APOLLO analysis that does not include parameters of gravityphysics, the condition number is very high: $8 \times 10^{10}$.
展开▼
