A Cytherocentric orbit is an orbit around the

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

. Venus has no moon, but several man-made objects orbit the planet. The name is analogous to the term

geocentric orbit A geocentric orbit, Earth-centered orbit, or Earth orbit involves any object orbiting Earth, such as the Moon or artificial satellites. In 1997, NASA estimated there were approximately 2,465 artificial satellite payloads orbiting Earth and 6,21 ...

for an orbit around Earth and

heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun ...

for an orbit around the Sun. The

apsides An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

of an Cytherocentric orbit are pericytherion, the

pericenter An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

(analogous to

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

), and the apocenter is named apocytherion (analogous to

apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

Etymology

The ''Cythero'' prefix is derived from

Kythira Kythira ( ; ), also transliterated as Cythera, Kythera and Kithira, is an island in Greece lying opposite the south-eastern tip of the Peloponnese peninsula. It is traditionally listed as one of the seven main Ionian Islands, although it is dist ...

or "Cythera." In

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

mythology, Cythera was an island associated with the goddess

Aphrodite Aphrodite (, ) is an Greek mythology, ancient Greek goddess associated with love, lust, beauty, pleasure, passion, procreation, and as her syncretism, syncretised Roman counterpart , desire, Sexual intercourse, sex, fertility, prosperity, and ...

, who is the equivalent of the Roman goddess

. Therefore, naming an orbit around Venus "cytherocentric" is a way of referencing Venus' association with this goddess.

Satellites in Cytherocentric orbit

Venera 9 Venera 9 (), manufacturer's designation: 4V-1 No. 660, was a Soviet uncrewed space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 8, 1975, at 02:38:00 UTC and had a mass of . The orbiter was the first sp ...

was the first satellite to achieve Venus orbit in 20 October 1975.

Akatsuki may refer to: Places * Akatsuki Gakuenmae Station, is a passenger railway station located in the city of Yokkaichi People *, Japanese author in the I Novel genre *, Japanese manga artist *, Japanese light novel author and manga writer Ships * ...

was the latest probe to achieve Venus orbit in 2015. Eight probes have achieved Venus orbit: * 4

Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

probes,

Venera 10 Venera 10 ( meaning ''Venus 10''), or 4V-1 No. 661, was a Soviet uncrewed space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 14, 1975, 03:00:31 UTC and had a mass of 5033 kg (11096 lb). Orbiter W ...

Venera 15 Venera 15 ( meaning ''Venus 15'') was a spacecraft sent to Venus by the Soviet Union. This uncrewed orbiter was to map the surface of Venus using high resolution imaging systems. The spacecraft was identical to Venera 16 and based on modificat ...

, Venera 16 * Two

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

probe, ''Magellan'', Pioneer Venus 1 * One

JAXA The is the Japanese national air and space agency. Through the merger of three previously independent organizations, JAXA was formed on 1 October 2003. JAXA is responsible for research, technology development and launch of satellites into o ...

probe,

* One ESA probe, Venus Express. In order to enter Venus orbit, a satellite has to perform an engine burn to reduce the speed. Otherwise, the probe moves too fast to achieve orbit and will be a flyby. A noteworthy case is that of Japanese probe

, which failed to enter orbit around Venus on 6 December 2010. JAXA stated on 8 December that the probe's orbital insertion maneuver had failed, because of a defect in the orbital insertion burn. After the craft orbited the Sun for five years, engineers successfully placed it into an alternative Venusian

elliptic orbit In astrodynamics or celestial mechanics, an elliptical orbit or eccentric orbit is an orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. Some orbits have been referre ...

on 7 December 2015 by firing its

attitude control Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, ...

thrusters for 20 minutes. ''Magellan'' was the first interplanetary probe to use

aerobraking Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit (periapsis). The resulting drag slows the spacecraft. Aerobraking is ...

to reduce the apocytherion. By passing through the dense atmosphere, a probe can reduce its speed and attain the necessary

delta-v Delta-''v'' (also known as "change in velocity"), symbolized as and pronounced , as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as launching from or l ...

. Venus's thick atmosphere supports

. This reduces fuel needs.

Stationary and synchronous orbits

satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...

with revolutionary period that matches the planet's rotational period appears fixed at a position in the sky relative to an observer on the planet. Such an orbit on Earth is 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 ...

. The height of a stationary or synchronous orbit can be calculated as follows: :

R_ = \sqrt /math> where G is the

gravitational constant The gravitational constant is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's general relativity, theory of general relativity. It ...

, m₂ is the mass of the celestial body, and T is the sidereal rotational period of the body. By this formula one can find the

geostationary 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 geosynchronous orbit in altitud ...

-analogous cytherostationary orbit. Around Venus, such 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 ...

would be 1,536,600 km or about 253 Venus radii from the planet's surface. This is because Venus has the slowest rotation rate of any planet. The slower the rotation, the farther away a satellite must be in order to be stationary. The

hill sphere The Hill sphere is a common model for the calculation of a Sphere of influence (astrodynamics), gravitational sphere of influence. It is the most commonly used model to calculate the spatial extent of gravitational influence of an astronomical ...

of a celestial body describes the region in which the gravity of that body is dominant. The

radius of Venus is about 1 million kilometers; and as the cytherostationary orbital distance lies outside of it, no stable cytherostationary satellite can exist.

References

{{reflist Orbits Venus

Etymology

Satellites in Cytherocentric orbit

Stationary and synchronous orbits

See also

References