Cytherocentric orbit

The Cythero prefix is derived from Kythira or "Cythera." In Greek mythology, Cythera was an island associated with the goddess Aphrodite, who is the equivalent of the Roman goddess Venus. Therefore, naming an orbit around Venus "cytherocentric" is a way of referencing the planet's association with this goddess.

Venera 9 is the first satelite to achieve Venus orbit in 20 October 1975. Akatsuki is the latest probe to achieve Venus orbit in 2015. [1]

Eight probes have achieved Venus orbit till date,

• 4 Soviet Union probes, Venera 9, Venera 10, Venera 15, Venera 16
• Two NASA probe, Magellan, Pioneer Venus 1
• One JAXA probe, Akatsuki
• One ESA probe, Venus Express.

In order to enter Venus orbit, a satelite has to perform an engine burn in order to reduce the speed. Otherwise, the probe will be going too fast to be captured into an orbit and will be a Venus flyby. A noteworthy case is that of Japanese probe Akatsuki, which failed to enter orbit around Venus on 6 December 2010 [2] JAXA stated on 8 December that the probe's orbital insertion maneuver had failed,[3] 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 on 7 December 2015 by firing its attitude control thrusters for 20 minutes.

Magellan was the first interplanetary probe to use aerobraking to reduce the apocytherion. [4] By passing through the dense atmosphere, a probe can reduce its speed, shaving of velocity to attain the necessary delta-v suitable for scientific study. As Venus has a thick atmosphere, aerobraking can be used. This means that we can send a probe with relatively less fuel.

A satellite with revolutionary period same as the rotational period will always appear fixed at a position in the sky relative to an observer on the planet. Such an orbit on Earth is a Geostationary orbit. [5]

Orbital speed (how fast a satellite is moving through space) can be calculated as follows:

${\displaystyle R_{syn}={\sqrt[{3}]{G(m_{2})T^{2} \over 4\pi ^{2}}}}$[6]

G = Gravitational constant

m₂ = Mass of the celestial body

T = rotational period of the body

By this formula one can find the geostationary-analogous, stationary orbit of an object in relation to a given body, in this case, Venus. Such an orbit would be 713,200km away from the surface of Venus. This is because Venus has the slowest rotation rate of any planet. Slower the rotation, farther away a satelite have to be in order to be stationary. Due to this, Venus has the farthest distance of stationary orbit of any planet, that is, 117 times the radius of the planet. Hill sphere of a celestial body describes the region in which the gravity of that body is dominant. The Hill Sphere radius of Venus is just a bit more than 1 million kilometers. The satelite will be stable, but far away from the planet.

Till now, no such probe has been launched.

• Orbit of Venus
• Areocentric orbit