Sphere of influence (astrodynamics)

Sphere of influence (astrodynamics)

A sphere of influence (SOI) in astrodynamics and astronomy is the spherical region around a celestial body where the primary gravitational influence on an orbiting object is that body. This is usually used to describe the areas in our solar system where planets dominate the orbits of surrounding objects (such as moons), despite the presence of the much more massive (but distant) Sun. In a more general sense, the patched conic approximation is only valid within the SOI.

The general equation describing the radius of the sphere r_{SOI} of a planet:: r_{SOI} = a_p(frac{m_p}{m_s})^{2/5}where: a_p is the semimajor axis of the planet's orbit relative to the largest body in the system, usually the Sun: m_p and m_s are the masses of the planet and Sun, respectively.

In the patched conic approximation, once an object leaves the planet's SOI, the primary/only gravitational influence is the Sun (until the object enters another body's SOI). Since the definition of rSOI relies on the presence of the Sun and a planet, the term is only applicable in a three body or greater system.

Table of planetary SOI radii


*cite book
first=Roger R.
coauthors= Donald D. Mueller, Jerry E. White
title= Fundamentals of Astrodynamics
publisher=Dover Publications
location=New York
id=ISBN 0-486-60061-0

*cite book
first=Jerry J.
coauthors= Astore, William J., Giffen, Robert B., Larson, Wiley J.
editor=Kirkpatrick, Douglas H.
title= Understanding Space: An Introduction to Astronautics
publisher=McGraw Hill
id=ISBN 0-07-294364-5
pages= 228,738

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Sphere of Influence — Als Sphere of Influence (kurz SOI; engl. für Einflusssphäre) bezeichnet man eine u.a. in der Astrodynamik und Raumfahrt gebräuchliche Größe, die angibt, in welchem Bereich die Gravitation eines Planeten Auswirkungen auf andere Himmelskörper hat… …   Deutsch Wikipedia

  • Sphere (disambiguation) — A sphere is an object shaped like the surface of a ball, but can be used to refer to a ball shaped object, as well as a sphere like or annular region or shell. Additionally, it has several metaphorical uses.In mathematics: * Sphere, the set of… …   Wikipedia

  • SOI — might be an acronym or abbreviation for:Technology: * Silicon on Insulator * Signal operating instructions * Service Oriented Infrastructure * Start of injectionScience: * Southern Oscillation Index * Sphere of influence (astrodynamics), a term… …   Wikipedia

  • Trans Lunar Injection — Typical lunar transfer trajectories approximate Hohmann transfers, although low energy transfers have also been used in some cases, as with the Hiten probe. [cite web |url=http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1990 007A… …   Wikipedia

  • Spaceflight — For the magazine published by the British Interplanetary Society, see Spaceflight (magazine). For the 1985 PBS documentary series narrated by Martin Sheen, see Spaceflight (TV series). For the Sam Lazar album, see Space Flight (album). Part of a… …   Wikipedia

  • celestial mechanics — the branch of astronomy that deals with the application of the laws of dynamics and Newton s law of gravitation to the motions of heavenly bodies. [1815 25] * * * Branch of astronomy that deals with the mathematical theory of the motions of… …   Universalium

  • Current sea level rise — This article is about the current and future rise in sea level associated with global warming. For sea level changes in Earth s history, see Sea level#Changes through geologic time. Sea level measurements from 23 long tide gauge records in… …   Wikipedia

  • Sun-synchronous orbit — Diagram showing the orientation of a Sun synchronous orbit (green) in four points of the year. A non sun synchronous orbit (magenta) is also shown for reference A Sun synchronous orbit (sometimes called a heliosynchronous orbit) is a geocentric… …   Wikipedia

  • Astrophysics — is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as… …   Wikipedia

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.