Satellite in earth orbit in opposition to the moon?

[Odahs]

Hi, as the titles says I'm interested in creating a satellite in low earth orbit which is at all times on the opposite side of the earth to the moon.

Is it physically possible and which mathematical theories would I be looking into to calculate how to do it?

I have a background in aerospace but no experience of orbital calculations at all. Any help or guidance much appreciated.

 

[Urwumpe]

Hi, as the titles says I'm interested in creating a satellite in low earth orbit which is at all times on the opposite side of the earth to the moon.

Is it physically possible and which mathematical theories would I be looking into to calculate how to do it?

I have a background in aerospace but no experience of orbital calculations at all. Any help or guidance much appreciated.

No, not at all. Thats impossible.

Remember: Orbit period depends on semimajor axis. If you want to orbit Earth in the same time as the moon, you have to be in an orbit with the same Sma.

Which in your case would result in your satellite being at the instable L3 lagrange point, which does not allow long-term missions without constant maneuvering.

 

[Odahs]

Many thanks,

I'll look into it further so I can understand why it is not possible, I thought it wouldn't be from gut feeling.

The source of the information is science fiction, a satellite positioned always in opposition to the moon. The source states that the satellite is the same distance from the earth as the moon. This immediately sounded unlikely as something with a small mass surely couldn't be in orbit that far out? The source is contradictory in any case as all the pictures of the satellite show it clearly in low earth orbit with the earth visible. That it can't be both low orbit and always in opposition to the moon seems logical to me.

 

[Shifty]

Which in your case would result in your satellite being at the instable L3 lagrange point, which does not allow long-term missions without constant maneuvering.

It should be possible to set up a [ame="http://en.wikipedia.org/wiki/Halo_orbit"]Halo orbit[/ame] around EML3 that is stable.

The source of the information is science fiction, a satellite positioned always in opposition to the moon. The source states that the satellite is the same distance from the earth as the moon.

This should actually be possible. A satellite at the moon's altitude would have the same orbital period as the moon and, if initially placed in opposition to the moon, would be somewhat stable there under the influence of Earth's gravity.

 

[Urwumpe]

It should be possible to set up a Halo orbit around EML3 that is stable.

Not for all eternity... we are speaking of a few years without corrections even with a Halo orbit, because of the other seven planets.

 

[Odahs]

Interesting stuff, so if there were an overwhelming reason to achieve the desired goal (such as preventing pesky aliens steeling our body organs), it could be possible but would require regular adjustment.

This could be a positive outcome, as my subject doesn't as far as I know have its own thrusters, but it can dock with a spacecraft for maintenance.

The need to dock with it, and put it back where it should be occasionally, could make a good mission scenario.

 

[Quick_Nick]

Now someone needs to calculate how much maneuvering would be necessary. See if it requires solar sails, ion thrusters, or fully chemical rockets.

 

[Urwumpe]

Now someone needs to calculate how much maneuvering would be necessary. See if it requires solar sails, ion thrusters, or fully chemical rockets.

An ion thruster system should be enough, once you are only station keeping. Many small corrections can be better than waiting for the final big corrections.

But ion thrusters also have finite life-time.

 

[sorindafabico]

A solar sail would be interesting.

 

[Unstung]

Not for all eternity... we are speaking of a few years without corrections even with a Halo orbit, because of the other seven planets.

Many satellites have occupied halo orbits around Earth-Moon L2, and other Lagrangian points have been used. So halo orbits are a reasonable thing to use. But is Earth-Moon L3 any less stable than L2 due to the Moon's constant presence at opposition?

 

[Odahs]

Can anyone recommend a site where I can research the EML3 halo orbit further? This sounds like the one to look into, but being new to this my googling isn't getting me far.

Am I right it thinking that L3 is on the other side of the sun? If so what is the difference between L3 and EML3 (Having established that EML3 is the halo orbit in direct opposition to the moon, I've got that far on my own with the help already provided!)

 

[Urwumpe]

Can anyone recommend a site where I can research the EML3 halo orbit further? This sounds like the one to look into, but being new to this my googling isn't getting me far.

Am I right it thinking that L3 is on the other side of the sun? If so what is the difference between L3 and EML3 (Having established that EML3 is the halo orbit in direct opposition to the moon, I've got that far on my own with the help already provided!)

Every planet has a L3 around the sun and every moon has an L3 around this planet. Its pretty universal. But the stability of each point depends on the world outside as well.

EML3 = Earth-Moon L3; its no official term.

 

[Shifty]

Can anyone recommend a site where I can research the EML3 halo orbit further? This sounds like the one to look into, but being new to this my googling isn't getting me far.

Am I right it thinking that L3 is on the other side of the sun? If so what is the difference between L3 and EML3 (Having established that EML3 is the halo orbit in direct opposition to the moon, I've got that far on my own with the help already provided!)

EDIT: Ninja'd by Urwumpe

Most information about Halo or Lissajous orbits is from academic papers, and most of those focus on the more useful EML1 and EML2 points. L1, L2, L3, etc are generic names for the Lagrange points in any two-body system. (L1 is between the two bodies; L2 is on the far side of the smaller body; L3 is on the far side of the larger body; and L4/5 are offset from the axis that connects the two bodies.) EM denotes Earth-Moon, so EML3 is the Lagrange point that lies on the Earth-Moon axis that is in opposition to the moon. SEL2, for another instance, is the Sun-Earth Lagrange point that is on the dark side of the Earth. (The James Webb Space Telescope is supposed to orbit there eventually.) SJL4/5 are the locations of the Trojan asteroid formations at the Sun-Jupiter L4 and L5 points.

There's a decent explanation of L-points and Halo orbits here:
http://www.scilogs.eu/en/blog/go-for-launch/2009-05-28/how-to-orbit-a-lagrangian-point

 

[Odahs]

Really appreciating the help with this :thumbup: