Basic regularities of the Sun's gravity effect on the satellites motion on almost circular low-Earth orbits

1Pirozhenko, AV, 1Maslova, AI, Pirozhenko, OO
1Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, Dnipro, Ukraine
Space Sci. & Technol. 2026, 32 ;(1):03-12
https://doi.org/10.15407/knit2026.01.003
Publication Language: English
Abstract: 
The effect of the Sun’s gravity on satellite motion in nearly circular low-Earth orbits (with eccentricity around 10-3 and altitudes up to 1000 km) is examined. These types of orbits are commonly used for satellites that conduct remote sensing of Earth.  Although the Sun's gravitational effect on satellite motion is minor compared to the non-centrality of the Earth’s gravitational field, modern requirements for remote sensing missions make such studies relevant.
To date, many studies have focused on how the gravity of a third body (the Moon and the Sun) influences the motion of artificial satellites of the Earth. Different approaches have been used to address the problem,  yielding profound and meaningful results. At the same time, in these studies, the primary focus is on the orbits of satellites with significant eccentricity, and rather cumbersome approaches and formulas make it difficult to extend the results to the case of nearly circular low-Earth orbits. Therefore, it is of interest to use simpler approaches and to obtain simpler formulas and estimates of changes in the parameters of nearly circular low-Earth orbits.
In the article, assuming that the Earth moves relative to the Sun along an unperturbed Keplerian orbit, the main regularities of changes in the parameters of almost circular orbits are determined, and analytical estimates describing changes in the orbital parameters of the satellite under the influence of the Sun’s gravitational attraction are constructed. It is shown that short-periodic oscillations with the period of orbital motion of the satellite due to the influence of the Sun’s gravitational attraction are negligibly small for the orbits under consideration. The long-periodic and secular motion of the orbital plane orientation is described by simple equations whose properties have been investigated in detail. These equations coincide with the equations of evolution of the kinetic momentum of a rotating symmetric solid body under the action of the gravitational momentum and, in particular, with the equations of evolution of the dumbbell motion. For the orbits under consideration, the resonance effects leading to a change in the shape of the orbit (eccentricity growth) are negligibly small, and their study is of no practical importance.
Keywords: basic regularities of satellite motion, gravity of the Sun, long-period and secular motion, nearly circular low-Earth orbit
Heading: 
Spacecrafts and Payloads
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