A near-equatorial orbit is an

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

that lies close to the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

ial plane of the

primary body A primary bodyalso called a central body, host body, gravitational primary, or simply primaryis the main physical body of a gravitationally bound, multi-object system. This object constitutes most of that system's mass and will generally be loca ...

orbited. Such an orbit has an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

near 0°. On Earth, such orbits lie near the

celestial equator The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. By extension, it is also a plane of reference in the equatorial coordinate system. Due to Earth's axial tilt, the celestial ...

, the

great circle In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point. Discussion Any arc of a great circle is a geodesic of the sphere, so that great circles in spher ...

of the imaginary

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

that is

coplanar In geometry, a set of points in space are coplanar if there exists a geometric plane that contains them all. For example, three points are always coplanar, and if the points are distinct and non-collinear, the plane they determine is unique. How ...

with the equator of Earth. A

geostationary orbit A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular orbit, circular geosynchronous or ...

is a particular type of equatorial orbit, one which is

geosynchronous A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...

. A satellite in a geostationary orbit appears stationary, always at the same point in the sky, to observers on the surface of the Earth. Equatorial orbits can be advantageous for several reasons. For launches of human technology to space, sites near the Equator, such as the

Guiana Space Centre The Guiana Space Centre (; CSG), also called Europe's Spaceport, is a spaceport to the northwest of Kourou in French Guiana, an Overseas departments and regions of France, overseas region of France in South America. Kourou is located approxim ...

Kourou Kourou (; ) is a commune in French Guiana, an overseas region and department of France in South America. Kourou is famous for being the location of the Guiana Space Centre, the main spaceport of France and the European Space Agency (ESA). It ...

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

, or Alcantara Launch Centre in Brazil, can be good locations for

spaceport A spaceport or cosmodrome is a site for launching or receiving spacecraft, by analogy to a seaport for ships or an airport for aircraft. The word ''spaceport''—and even more so ''cosmodrome''—has traditionally referred to sites capable of ...

s as they provide some additional

orbital speed In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter (the combined center of mass) or ...

to the

launch vehicle A launch vehicle is typically a rocket-powered vehicle designed to carry a payload (a crewed spacecraft or satellites) from Earth's surface or lower atmosphere to outer space. The most common form is the ballistic missile-shaped multistage ...

by imparting the

rotational speed Rotational frequency, also known as rotational speed or rate of rotation (symbols ''ν'', lowercase Greek nu, and also ''n''), is the frequency of rotation of an object around an axis. Its SI unit is the reciprocal seconds (s−1); other com ...

of the Earth, 460 m/s, to the spacecraft at launch. The added

velocity Velocity is a measurement of speed in a certain direction of motion. It is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of physical objects. Velocity is a vector (geometry), vector Physical q ...

reduces the fuel needed to launch spacecraft to orbit. Since Earth rotates eastward, only launches eastward take advantage of this boost of speed. Westward launches, in fact, are especially difficult from the Equator because of the need to counteract the extra rotational speed. Equatorial orbits offer other advantages, such as to communication: a spaceship in an equatorial orbit passes directly over an equatorial spaceport on every rotation, in contrast to the varying

ground track A satellite ground track or satellite ground trace is the path on the surface of a planet directly below a satellite's trajectory. It is also known as a suborbital track or subsatellite track, and is the vertical projection of the satellite's ...

of an inclined orbit. Furthermore, launches directly into equatorial orbit eliminate the need for costly adjustments to a spacecraft's launch trajectory. The maneuver to reach the 5° inclination of the Moon's orbit from the 28° N latitude of

Cape Canaveral Cape Canaveral () is a cape (geography), cape in Brevard County, Florida, in the United States, near the center of the state's Atlantic Ocean, Atlantic coast. Officially Cape Kennedy from 1963 to 1973, it lies east of Merritt Island, separated ...

was originally estimated to reduce the payload capacity of the Apollo Program's

Saturn V The Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, had multistage rocket, three stages, and was powered by liquid-propel ...

rocket by as much as 80%.

Non-inclined orbit

A non-inclined orbit is an

with a

plane of reference In celestial mechanics, the orbital plane of reference (or orbital reference plane) is the plane used to define orbital elements (positions). The two main orbital elements that are measured with respect to the plane of reference are the inclin ...

. The

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

is 0° for prograde orbits, and π (180°) for retrograde ones. If the plane of reference is a massive

spheroid A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface (mathematics), surface obtained by Surface of revolution, rotating an ellipse about one of its principal axes; in other words, an ellipsoid with t ...

body's

equatorial plane The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. By extension, it is also a plane of reference in the equatorial coordinate system. Due to Earth's axial tilt, the celestial e ...

, these orbits are called equatorial, and the non-inclined orbit is merely a special case of the near-equatorial orbit. However, a non-inclined orbit need not be referenced only to an equatorial reference plane. If the plane of reference is the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

plane, they are called an ecliptic orbit. As non-inclined orbits lack nodes, the

ascending node An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined. A non-inclined orbit, which is contained in the reference plane, has no nodes. Planes of reference Common planes of referenc ...

is undefined, as well as its related classical

orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same o ...

, the longitude of the ascending node and the

argument of periapsis The argument of periapsis (also called argument of perifocus or argument of pericenter), symbolized as ''ω (omega)'', is one of the orbital elements of an orbiting body. Parametrically, ''ω'' is the angle from the body's ascending node to it ...

. In these cases, alternative orbital elements or different definitions must be used to ensure an orbit is fully described. A

is a

example of an equatorial orbit, non-inclined orbit that is coplanar with the equator of

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

References

{{orbits Astrodynamics Orbits

Non-inclined orbit

See also

References