Improving the Solar Wind Density Model Used in Processing of Spacecraft Ranging Observations

TL;DR

This paper evaluates and improves the model of solar wind density used to correct spacecraft ranging data, enhancing the accuracy of planetary orbit determination by incorporating in situ measurements and numerical models.

Contribution

It introduces alternative solar wind density models based on in situ data and numerical simulations to improve spacecraft ranging corrections.

Findings

Alternative models reduce residual delays in spacecraft data.

In situ data and ENLIL model provide more accurate solar wind density estimates.

Improved models enhance planetary orbit determination precision.

Abstract

Solar plasma as a cause of radio signal delay has been playing an important role in solar and planetary science. Early experiments studying the distribution of electrons near the Sun from spacecraft ranging measurements were designed so that the radio signal was passing close to the Sun. At present, processing of spacecraft tracking observations serves a different goal: precise (at meter level) determination of orbits of planets, most importantly Mars. Solar plasma adds a time-varying delay to those observations, which is, in this case, unwanted and must be subtracted prior to putting the data into planetary solution. Present planetary ephemeris calculate the delay assuming symmetric stationary power-law model of solar plasma. The present work, based on a custom variant of the EPM lunar-planetary ephemeris, raises the question of accuracy and correctness of that assumption and examines alternative models based on in situ data provided by OMNI and on the ENLIL numerical model of solar wind.