satellite in geosynchronous orbit around the Moon

[RaputerXpert]

Why don't we, or can we, place a satellite in geosynchronous, geostatic orbit around the Moon since the moon is always facing one side toward Earth? Nothing expensive, just a few cameras and a few instruments to make meteorological and climate related detections from booth the Moon and Earth. For power you would use solar panels since it would be drowning in sunlight w/o clouds for hours per day. Use a battery system and design a system in which any charge over 24 vdc(or whatever volt is needed) will not go to the battery system thus reduce chances of overheating, degrading the life of the battery or a small explosion which would likely be the end of the life of the satellite.

 

We should name it 'Omega 666'

[Guest]

Well for starters, 'Geo' means Earth.. the moon does that because of where it is caught in Earth's gravitational pull..

[tikker]

In addition to the above, a geostatic orbit (a special case of geosynchronous) means it's above the same position on Earth (more or less) and a geosynchronous orbit means it orbits at the same speed as the rotation of the Earth.

 

We have put satellites in orbit around the Earth for the exact purpose of studying climate and weather already. The main reason for putting something further away would be to test our ability to detect signs of life from exoplanets by treating the Earth as one and purposefully lowering our resolving power by putting the thing further away. We aren't ready for that yet though.

 

[Blue4130]

Also we have 4 satellites around the moon as is that monitor the moon and many satellites that monitor earth... 

[akio123008]

11 hours ago, RaputerXpert said:

Nothing expensive

This phrase doesn't go together with spacecraft very well...

[harryk]

A geosynchronous orbit is special because the satellite's orbital period matches the rotational period of Earth (~24 hrs), thus the satellite stays in the same space above Earth. In principle the Moon also has an equivalent orbit, a luna-synchronous orbit where the period is ~27 days. However in reality such an orbit is not stable because the Moon is near the Earth and any satellite in orbit around the Moon is also affected by Earth's gravity, it's a three-body system. But there are special geometries in the three body system called Lagrange points where there are stable orbits. At the Lagrange points the gravity of the Earth and Moon are balanced and a satellite placed there will stay there (actually they move around the Lagrange point in a Lissajous orbit).

So you could place an Earth-observing weather satellite at one of the Lagrange points and record weather data. But why would you? The Lagrange points are very far from Earth so the camera's and sensors would need to be very good. The satellite itself will almost always be illuminated by the Sun so power by solar panel is great, but for 14 days every lunar day the satellite will be looking at the dark side of the Earth which is not so good when looking for clouds and such. Besides, we have already have constant weather surveillance from geo orbit. The GOES satellites provide a live view of the entire Earth. There are dozens of weather satellites in orbit right now recording all manner of data. 

 

But there is great interest in the Earth-Moon Lagrange points, in particular for space exploration and communications. In 2011, NASA previously placed two of the THEMIS spacecraft at Lagrange points as part of an extended mission. This was the first time anyone has flown spacecraft at an Earth-Moon Lagrange point. In 2018, China placed its Queqiao satellite at the L2 point behind the Moon in order to relay communications to the Chang'e 4 lunar probe with landed on the far side of the Moon. 

 

Furthermore, there are more than just the Earth-Moon Lagrange points. There are also the Sun-Earth Lagrange points which host a number of spacecraft. 

[tikker]

1 hour ago, harryk said:

So you could place an Earth-observing weather satellite at one of the Lagrange points and record weather data. But why would you?

It might be useful for exoplanet science using the Earth as an exoplanet, but e.g. modeling exoplanet atmospheres is a rather active field already anyway so there wouldn't be much of a point to put something specifically for Earth observing there.

[orbitalbuzzsaw]

5 minutes ago, tikker said:

It might be useful for exoplanet science using the Earth as an exoplanet, but e.g. modeling exoplanet atmospheres is a rather active field already anyway so there wouldn't be much of a point to put something specifically for Earth observing there.

AFAIK there's not any specific measuring instruments for it so who knows

[Arika]

i don't think the moon spins fast enough for a satellite to be able to stay in a geosynchronous/geostatic orbit without just being constantly powered. therefore it would actually make more sense to just land it on the moon's surface if we just want it to stay in the one place

[RaputerXpert]

On 9/25/2021 at 6:47 AM, tikker said:

The main reason for putting something further away would be to test our ability to detect signs of life from exoplanets by treating the Earth as one and purposefully lowering our resolving power by putting the thing further away. We aren't ready for that yet though.

That's what I was kinda hinting at. we could eliminate Earth's radio signals in our SETI list very very quickly and cut the time of discarding frequencies by a minimum of 50%-75% especially since the satellite would have one sole purpose. I thought it would be a great idea... Guess not

[RaputerXpert]

On 9/25/2021 at 12:07 PM, harryk said:

A geosynchronous orbit is special because the satellite's orbital period matches the rotational period of Earth (~24 hrs), thus the satellite stays in the same space above Earth. In principle the Moon also has an equivalent orbit, a luna-synchronous orbit where the period is ~27 days. However in reality such an orbit is not stable because the Moon is near the Earth and any satellite in orbit around the Moon is also affected by Earth's gravity, it's a three-body system. But there are special geometries in the three body system called Lagrange points where there are stable orbits. At the Lagrange points the gravity of the Earth and Moon are balanced and a satellite placed there will stay there (actually they move around the Lagrange point in a Lissajous orbit).

So you could place an Earth-observing weather satellite at one of the Lagrange points and record weather data. But why would you? The Lagrange points are very far from Earth so the camera's and sensors would need to be very good. The satellite itself will almost always be illuminated by the Sun so power by solar panel is great, but for 14 days every lunar day the satellite will be looking at the dark side of the Earth which is not so good when looking for clouds and such. Besides, we have already have constant weather surveillance from geo orbit. The GOES satellites provide a live view of the entire Earth. There are dozens of weather satellites in orbit right now recording all manner of data. 

 

But there is great interest in the Earth-Moon Lagrange points, in particular for space exploration and communications. In 2011, NASA previously placed two of the THEMIS spacecraft at Lagrange points as part of an extended mission. This was the first time anyone has flown spacecraft at an Earth-Moon Lagrange point. In 2018, China placed its Queqiao satellite at the L2 point behind the Moon in order to relay communications to the Chang'e 4 lunar probe with landed on the far side of the Moon. 

 

Furthermore, there are more than just the Earth-Moon Lagrange points. There are also the Sun-Earth Lagrange points which host a number of spacecraft. 

That REPLY was, at least to me, very educating since I had never heard of Lagrange points or the sheer number of satellites orbiting the moon.

I was more interesting in helping SETI, which my OP didn't make clear. SETI could use the satellite to vastly speed the process of discarding frequencies that originate from Earth and well known FREQ's that are from 100+ year old place in our galaxies and beyond. We could make SETI 50%-75% faster, thus giving it several fold more chances to find a unique intelligent signal. I thought it was a grand idea, but clearly I am no astrophysicist. But thank you for such a serious reply.

[mariushm]

And a bit off topic but if you want to see how many satellites and how much debris we have orbiting earth , you can check out http://stuffin.space/

You can click on individual objects to get more details and then go on Wikipedia or google to search for the name and get more details.

 

The Starlink sattellites are particularly cool to see there ... you find one and then click on "Find all objects from this launch" and it will show you a bunch of satts launched at same time, and their trajectories, see them evenly spaced across some region of the world making loops..

 

 

[tikker]

3 hours ago, RaputerXpert said:

That's what I was kinda hinting at. we could eliminate Earth's radio signals in our SETI list very very quickly and cut the time of discarding frequencies by a minimum of 50%-75% especially since the satellite would have one sole purpose. I thought it would be a great idea... Guess not

I was talking more from an optical and/or spectroscopy perspective. We know the Earth-made radio signals, because, well, we make them. Removal of unwanted interference has been a standard procedure for a while now. Radio waves also happily travel into space, so you wouldn't be rid of them anyway.

[harryk]

10 hours ago, RaputerXpert said:

That REPLY was, at least to me, very educating since I had never heard of Lagrange points or the sheer number of satellites orbiting the moon.

I was more interesting in helping SETI, which my OP didn't make clear. SETI could use the satellite to vastly speed the process of discarding frequencies that originate from Earth and well known FREQ's that are from 100+ year old place in our galaxies and beyond. We could make SETI 50%-75% faster, thus giving it several fold more chances to find a unique intelligent signal. I thought it was a grand idea, but clearly I am no astrophysicist. But thank you for such a serious reply.

There have been a handful of radio telescopes in space over the decades. Most notable is Russia's Spektr-R. While not at a Lagrange point, its orbit was quite large with apogee at ~330,000 km, almost the distance to the Moon. So it did go quite far from Earth to escape the noise from anthropogenic radio. 

 

Perhaps of more interest to SETI though is the long-talked idea of building a radio telescope on the far side of the Moon. Not only would this be far from Earth, but the Moon itself will block almost all the radio noise coming from Earth. It really is the best place to build a radio telescope, especially for large >100 m apertures.

 

Nature | Put telescopes on the far side of the Moon

NASA's Lunar Crater Radio Telescope

[GoldSrc]

The reason we only see one side, is because the moon is close enough that the near side has more mass due to its proximity to the Earth.

This mass causes the Earth to apply a torque to the moon that keeps it pointed towards us.

Every time the moon tries to rotate away, the bulge steers it back towards the Earth, it's not really the orbit what causes that.

 

Just like the moon creates a bulge on the Earth's oceans, the Earth also creates a bulge on the side of the moon closer to us.

Take a spoon or any other long object and try to hold only one side, the side with more mass will be pulled towards the Earth.

I may be wrong about some of that, but that's the basic principle.