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Newsgroups: sci.physics.relativity
Subject: Re: Weakness in the results of the three tests of GR shown in rhe lasr century,.
From: nospam@de-ster.demon.nl (J. J. Lodder)
Reply-To: jjlxa31@xs4all.nl (J. J. Lodder)
Date: Sun, 3 Nov 2024 23:30:01 +0100
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ProkaryoticCaspaseHomolog <tomyee3@gmail.com> wrote:

> 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.

It is a clockwork in which everything hangs together.
Having some distances at some time to some nanoseconds correct
means that you must have the whole system to comparable accuracies.
(or the computations will go off)

> I want to focus on LLR ranging measurements.

Eh, the Moon is at 300 000km, so 3 x10^13 cm.
So her distance is known to 10^-13 accuracy,
so three orders of magnitude beter than the planetary distances
that we were discussing.

Jan


> 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.