Subject: Re: Testing A Supplemental Earth Orientation Model
From: Daniel Adamo <[email-masked]>
To: "ATIG (L-Z)" <[email-masked]>
Date: Mon, 11 Sep 2023 10:07:24 -0700

ATIG Members-

My colleagues at JPL Solar System Dynamics have persuaded me the results I reported to you on August 10-11 suffer position errors on the order of 10 km in a trans-lunar trajectory context because Earth axial rotation modeling had been driven by UTC.  Consequently, my original results can incur up to 0.9 s of asynchronous east/west displacement with respect to Earth’s true orientation as reckoned by the UT1 time scale.

The attached “r1” revision to my report reflects testing of a more accurate UT1-savvy orientation model whose timing is typically better than 0.01 s from year 1950 through 2023.  This will introduce position errors no more than several hundred meters when processing geocentric NASA Apollo trajectory elements for trajectory reconstruction purposes.  The r1 revision completely supersedes its predecessor.  Redlines to the original report thereby producing the r1 revision will be supplied to anyone requesting them.

-Dan

From: Daniel Adamo <[email-masked]>
Date: Thursday, August 10, 2023 at 21:58
Subject: Testing A Supplemental Earth Orientation Model

ATIG Members-

The subject model computes rotation, nutation, and precession (RNP) dynamics transforming coordinates between an Earth-fixed system such as latitude/longitude/altitude and an inertial system such as the Earth mean equator and equinox of epoch J2000.0.  The Swift-based trajectory design/modeling system I’ve been developing since 2017 uses data files from JPL to provide precision Earth orientation transformations, but these highly accurate files do not support times before year 1972.  In accurately reconstructing Apollo Program trajectories, it is therefore necessary to perform precision RNP computations in Swift code.  The attached paper provides testing data demonstrating these computations are sufficiently accurate for Apollo trajectory reconstruction.  Your comments on this material are invited.

-Dan