Are there any geostationary orbits around the Moon?

In summary, there are no satellites currently in geostationary orbit around the Moon as it is not possible to have a true geostationary orbit around the Moon due to its smaller size and the limitations of stable orbits within its sphere of influence. However, the concept of a synchronous orbit can be expanded to include any orbit where the same side of the body is always facing the orbiting object, and in this sense, the Earth could be considered a synchronous satellite of the Moon due to its tidal locking. There are currently no satellites in Earth-Moon Lagrange points, but the idea of an Earth-Moon L1 space station has been considered and may be a possibility in the future.
  • #1
mersecske
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Are there any satellite around the Moon on geostationary orbit?
 
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mersecske said:
Are there any satellite around the Moon on geostationary orbit?
The Earth is in a sense in a synchronous satellite of the Moon. We only see one face of the Moon, after all.

That's probably not what you are asking about, though. First let's look at lunar orbits that are direct analogs of geostationary orbits. Such orbits cannot not exist. A true geostationary (geo means Earth) orbit, has an orbital radius given by [tex]r^3 = GM_{\oplus}/{\Omega_{\oplus}}^2[/tex] where [tex]M_{\oplus}[/tex] is the mass of the Earth and [tex]\Omega_{\oplus}[/tex] is the Earth's rotational angular velocity. With some abuse of terminology, we can extend this meaning to any object, [tex]r^3 = GM/\Omega^2[/tex].

For the Moon this comes out to an orbital radius of 95,000 km. That is well beyond the Moon's sphere of influence (66,000 km) or its Hill sphere (61,000 km). Stable orbits only exist within 1/2 to 1/3 of the Hill sphere radius, so the highest stable orbit around the Moon is somewhere in the 20,000 to 30,000 km range. So a direct analog of an Earth synchronous orbit is not possible for the Moon.

So, let's broaden the meaning of a synchronous orbit to mean any orbit about some body such that the same side of that body is all that is seen. Because the Moon is tidally locked to the Earth, the Earth is in a sense a synchronous satellite of the Moon. That might seem a bit snide, but its not. This expanded definition means that a satellite in one of the Earth-Moon Lagrange points can be viewed as being in a synchronous orbit about the Moon.

There are none yet. However, the concept of an Earth-Moon L1 space station is quite appealing. The idea keeps coming up as a possibility in NASA and elsewhere.
 

1. What is a satellite around the Moon?

A satellite around the Moon is a man-made object that orbits the Moon. It is used for various purposes such as research, communication, and navigation.

2. How many satellites are currently orbiting the Moon?

As of 2021, there are currently five active satellites orbiting the Moon. These include NASA's Lunar Reconnaissance Orbiter, China's Chang'e 2 and 5-T1, and India's Chandrayaan-1 and Chandrayaan-2.

3. How do satellites around the Moon stay in orbit?

Satellites around the Moon stay in orbit through the use of thrusters and gravity. Thrusters are used to adjust the satellite's speed and direction, while the Moon's gravity helps to keep the satellite in a stable orbit.

4. What is the purpose of having satellites around the Moon?

The main purpose of having satellites around the Moon is for scientific research and exploration. These satellites can gather data and images of the Moon's surface, as well as study its atmosphere and gravitational field. They can also serve as communication relays for future missions to the Moon.

5. How are satellites around the Moon launched?

Satellites around the Moon are typically launched using a rocket. The rocket provides the initial thrust and speed needed to reach the Moon's orbit. Once in orbit, the satellite's thrusters are used to fine-tune its trajectory and maintain its orbit.

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