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From: tomyee3@gmail.com (ProkaryoticCaspaseHomolog)
Newsgroups: sci.physics.relativity
Subject: Re: Weakness in the results of the three tests of GR shown in rhe lasr
 century,.
Date: Sun, 3 Nov 2024 00:11:17 +0000
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On Tue, 29 Oct 2024 17:15:20 +0000, J. J. Lodder wrote:

> JPL tracks and computes 'everything' in the solar system,
> from probes to planets, to an accuracy of about 10^-10.

That, of course, depends on *which* solar system objects one is
talking about, *what time period* one is talking about, and *what
specific parameters* one is discussing. For instance, Earth-planet
ranging measurements established the position of Mercury to within a
handful of meters while MESSENGER was in orbit, and they continue to
establish highly accurate distances to Mars because of the Mars
Reconnaissance Orbiter, Mars Express, and the various active Mars
landers. What these measurements mean in terms of how accurate the
various orbital elements are of the different planets would be the
subject of a _different_ detailed discussion.

I want to focus on LLR ranging measurements. The Moon's orbit is known
to within several centimeters because of the placement on the Moon
decades ago of five currently operational retroreflectors by the US
and the USSR. A sixth tiny retroreflector placed on the Moon by ISRO
in 2023 is used as a positional marker to help lunar orbiters
(currently NASA's Lunar Reconnaissance Orbiter) in their missions, and
is not useful for LLR measurements.

The five operational retroreflectors placed on the Moon during the
space race period are _old technology_, have degraded over time, and
their placements on the Moon are sub-optimal for ranging purposes. To
achieve sub-millimeter ranging to enable improved insights into the
Moon's dynamics, internal structure, Earth-Moon system evolution etc.
and for improved tests of GR, newer technology retroreflectors and
transponders need to be deployed.

1) The old retroreflectors used multiple corner cube prisms arranged
   on large sheets which flex from differential heating effects,
   lowering measurement accuracy. Large single-cube retroreflectors
   made from temperature-resistant silica or sapphire would provide
   higher reflectivity and stability over time.
2) Active transponders operating in two colors of light would allow
   for much stronger return signals and would allow precise
   calculation of signal delays from atmospheric refraction.
3) More widely distributed arrays placed with an eye towards improved
   lunar science rather than to meet the requirements of manned space
   missions would greatly improve LLR measurements.

If LLR measurements can be improved to the sub-millimeter or micron
level, they will approach the levels of measurement accuracy where
alternative theories of gravitation would expect GR to fail.