new scenario question and help

[HiPotOk1978]

I have included an image in this thread to help describe what I am trying to say. If my premise for this question is based on the fact (true or false but I am pretty sure I am right ) that you can NOT place a satellite into a Lunar synchronous orbit so here it goes

I am trying to find a way to place a satellite into an orbit around the moon so that it can act as a communications relay for a small mining operation on the far side of the moon. This is for an upcoming scenario I will be doing. I do realize (I think anyways) that in a 24 hour period, the satellite will not be available and there will be a dead time when it is flying around to reposition itself for the next comm window. I am wondering what might be the best way to do this. The base in question will be located very near the equator, 3.5N if I remember correctly. What would be the best orbit for such a device, flying around the equator or perhapse a polar orbit or something in between. I am looking to keep it in a position that will keep it in a position where the limited amount of fuel will be needed to correct orbit

 

[Hielor]

Don't think it's possible with just one satellite. Two could do the trick easily enough, and neither of them would need to use much fuel at all.

 

[TSPenguin]

Couldn't you put the sat in a polar orbit and have a small antenna tower in the base?
Since there is no air, the tower could be really lightweight.

Depending on the location, you might not even need a tower and you would have no outages at all!

 

[HiPotOk1978]

Couldn't you put the sat in a polar orbit and have a small antenna tower in the base?
Since there is no air, the tower could be really lightweight.

Depending on the location, you might not even need a tower and you would have no outages at all!

The satellite can't just hang over one of the poles nor can it be in a orbit around the Earth like the moon is, it would be useful for awhile, but after some time, it would drift out of a usable position and be space trash some poor Orbiter newbie would crash into

 

[TSPenguin]

If you put it into a polar orbit around the moon with a plane 90° to your base (if that makes sense... I'm tired), your base would always see the satelite and you might be able to use a solar sail every month to keep it in position.
I am really unsure (again... too tired to visualize) but shouldn't such an orbit be stable enough to use a solar sail every month?

 

[tblaxland]

You want to relay comms from the base to Earth? How about a halo orbit:
http://en.wikipedia.org/wiki/Halo_orbit


-----Posted Added-----

If you put it into a polar orbit around the moon with a plane 90° to your base (if that makes sense... I'm tired), your base would always see the satelite and you might be able to use a solar sail every month to keep it in position.
I am really unsure (again... too tired to visualize) but shouldn't such an orbit be stable enough to use a solar sail every month?

The trouble with a polar orbit is that the orbit won't precess fast enough to keep up with the rotation of the moon (and hence the base).

 

[TSPenguin]

The trouble with a polar orbit is that the orbit won't precess fast enough to keep up with the rotation of the moon (and hence the base).

Just to verify, I am talking about an orbit that when you see earth and moon in line looks like a circle.
I will think through this again tomorrow and probably see my error.
Just in case I don't, would you do me the favor of explaining your point?

 

[to be]

Just to verify, I am talking about an orbit that when you see earth and moon in line looks like a circle.
I will think through this again tomorrow and probably see my error.
Just in case I don't, would you do me the favor of explaining your point?

Basically you are proposing an 'earth-synchronous' orbit like a sun synchronous orbit on earth. But the question is would the lunar orbit precess enough that the movement of the moon around the earth doesn't misalign the whole thing. (so that 90deg later in the orbit your ring would be in line with the earth and moon).

What about the L2 point?

Edit: Yes, L2 will work, it seems NASA has studied this for you already: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680015886_1968015886.pdf

 

[TSPenguin]

It would be interesting to see if one could compensate for that with a solar sail. Not a static one of course, but this would enable us to have sats run indefenitely on solar power and thrust without the need for RCS.

 

[tblaxland]

Edit: Yes, L2 will work, it seems NASA has studied this for you already: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680015886_1968015886.pdf

In that document, the relay satellite is not at the L2 point but orbiting around it. That is the same as the halo orbit I was referring to earlier.

It would be interesting to see if one could compensate for that with a solar sail. Not a static one of course, but this would enable us to have sats run indefenitely on solar power and thrust without the need for RCS.

There have been studies into Earth "pole-sitter" satellites that use solar sails to maintain their position above either the north or south pole. So your idea may be feasible.

 

[TSPenguin]

And I don't even would want it to sit there, I'd just want it to keep a stable orbit

 

[HiPotOk1978]

Wow... some great info here from all u guys,:speakcool:

I got some reading and experimenting and I will hopefully have a new scn out in a month or so... Thx for the great resources all and wish me luck

 

[tblaxland]

And I don't even would want it to sit there, I'd just want it to keep a stable orbit

I understand that. I doubt that a lunar pole-sitter would be possible since too much power would be required by the solar sail to keep it in position because the angular accelaration required to keep its position relative to the Moon would be too great. I have a "gut feeling" that if it is possible to keep an Earth pole-sitter in place, it would be possible to use a solar sail to precess a polar lunar orbit sufficiently to keep up with the Moon's rotation. Calcs would be required to prove it however.

Another thought: if the commsat was in a polar lunar orbit with its orbital plane containing the Earth-Moon line, and the orbit was large enough (perhaps even approaching the L1 point) would the gradient of the gravitational potential be sufficient to precess the orbit? If you look at a plot of gravitational potential for a typical two body system, the gravitational potential falls towards the L1 and L2 points and the same would be case above and below the Moon's orbital plane. Perhaps one for Tony's Gravity Simulator.

 

[to be]

In that document, the relay satellite is not at the L2 point but orbiting around it. That is the same as the halo orbit I was referring to earlier.


There have been studies into Earth "pole-sitter" satellites that use solar sails to maintain their position above either the north or south pole. So your idea may be feasible.

A halo orbit was actually what I was thinking, I just didn't realize what 'halo orbit' meant. :lol: Another thing to remember I suppose.

 

[tblaxland]

Another thought: if the commsat was in a polar lunar orbit with its orbital plane containing the Earth-Moon line, and the orbit was large enough (perhaps even approaching the L1 point) would the gradient of the gravitational potential be sufficient to precess the orbit? If you look at a plot of gravitational potential for a typical two body system, the gravitational potential falls towards the L1 and L2 points and the same would be case above and below the Moon's orbital plane. Perhaps one for Tony's Gravity Simulator.

I tried this idea out in Gravity Simulator. Any orbit that was big enough to precess ended up being too big and too close to the Lagrange points to be stable and the sat ended up getting ejected out of the system.