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Kerbolsynchronous orbit


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Greetings everyone!

I recently started to built larger communication infrastructures supporting massive explorations towards Duna and Eve.

Now I've seen a video by Scott Manley talking about sunsynchonous orbits and was wondering if those mechanics might help in optimizing communication networks.

So, is it possible to have 2 different satellites orbiting both Duna and Ike, Eve and Gilly so that the planetary satellites keep a sunsynchonous orbit with their respective moons as the "sun"?

Same goes for the moons. Espescially in case of Duna and Ike, who are tidally locked where I could have permanent outposts on their surface both facing each other.

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Well, 3 satellites at the edge of SOI and away from moons is enough for every communications.

56 minutes ago, Jester Darrak said:

Espescially in case of Duna and Ike, who are tidally locked where I could have permanent outposts on their surface both facing each other.

This sounds fun, how come I never considered this?

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I don't think it's possible to do a true sun synchronous orbit in KSP.  The real life orbit depends on the oblateness of the earth to cause precession.  But KSP does not simulate that - a given orbit will have a fixed longitude of ascending node.   By the same token,  I don't think it would be doable around other bodies.

https://wiki.kerbalspaceprogram.com/wiki/Synchronous_orbit

 

Edited by Aegolius13
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First, you'd need Principia installed. Sun-synchronous and analogous orbits work because of equatorial bulges... something not modeled by stock KSP.

Second, such orbits may not be possible even then. Ike would require precessing by one degree every three minutes, and Gilly would require precessing by a degree every 15.5 minutes. That would require a very, very strong equatorial bulge; Earth SSO orbits have to precess less than one degree per day.

Third, if the goal is to maintain near-constant communication with Kerbin, there are simpler methods of achieving that.

1 minute ago, Kryxal said:

If you're asking about Lagrange points L1 and L2, no, it's not possible.  L3 to L5 can be used but aren't actually helped by anything in particular.

I think he's talking about orbits that precess to maintain a constant orientation w.r.t. the parent body (Eve, Duna), much like how real-world sun-synchronous orbits precess to maintain a constant orientation w.r.t. the Sun.

Edited by Starman4308
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10 minutes ago, Duck McFuddle said:

You can't have a synchronous around Duna, because Ike is there already. You would eventually enter Ike's SOI, either messing up your orbit or hitting you. 

You could position satellites at the L4 and L5 points in Ike's orbit (I think; I am not actually fully certain that that is out of range of its SOI) - however, L4 and L5 points are not actually simulated so you would simply have to time a transfer well enough to get close to those points (or at least, to the places where they would be in a more realistic situation), and then match the orbital period to Ike's orbital period precisely enough that your satellite is not likely to drift and be captured by Ike at any point in the near future (I use MechJeb's displays to get such precision, and I do not think it is remotely practical in stock without a readout of orbital period that is precise to the range of ±5 milliseconds).

Edited by septemberWaves
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2 hours ago, septemberWaves said:

You could position satellites at the L4 and L5 points in Ike's orbit (I think; I am not actually fully certain that that is out of range of its SOI) - however, L4 and L5 points are not actually simulated so you would simply have to time a transfer well enough to get close to those points (or at least, to the places where they would be in a more realistic situation), and then match the orbital period to Ike's orbital period precisely enough that your satellite is not likely to drift and be captured by Ike at any point in the near future (I use MechJeb's displays to get such precision, and I do not think it is remotely practical in stock without a readout of orbital period that is precise to the range of ±5 milliseconds).

Well, I guess it's easier then to have satellites at 120° and 240° in Duna-stationary orbit with Ike being at the 0°/360° position. This will, together with a relay station on the ground at the near side of Ike, cover Duna as a whole, right?

My plan always was to have a quite big relay satellite on polar orbit around the main body with a smaller ore scanning probe around the respective moon, giving as much coverage as possible.

But sending two more tiny relay satslellites is not a matter of cost, just time. ;)

Btw: Only mod I use is MechJeb, so the periods shouldn't be that hard to achieve.

Edited by Jester Darrak
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On 1/26/2019 at 2:26 PM, Jester Darrak said:

Well, I guess it's easier then to have satellites at 120° and 240° in Duna-stationary orbit with Ike being at the 0°/360° position. This will, together with a relay station on the ground at the near side of Ike, cover Duna as a whole, right?

That will cover Duna but will require periodic checking because unless your orbits are absolutely exact, you will eventually lose the network to orbital drift and Ike's hungry maw.  You can't get that level of precision (and in fact, just loading the satellite will introduce rounding errors in the numbers used) so you might be better off either having a cluster of satellites closer to Duna (cool, but not realistic--in real life the gravitational interaction would make the orbit terribly unstable), or else a cluster farther out from Duna with an Ike station (or Ike network) to connect to the larger constellation and keep everything in communication.

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In KSP, there isn't necessarily a need to place satellites in keostationary orbit, or the equivalent around other planets, because the game doesn't require communications antennas to physically remain pointed at and track their targets.  KSP relay antenna mechanics are kind of like the low-Earth-orbit Iridium network in real-life.  As one satellite passes beyond the horizon, the signal is picked up by the next one right behind it.

In essence, you could place 3 or 4 relay satellites, equally-spaced apart, halfway between Ike and Duna and it will still function the same way as a keostationary network.  The difference being they won't be holding position over set points on the Duna surface.  However, since dish antennas operate identically to omnidirectional antennas in KSP, this detail is irrelevant (aside from user preference to emulate real-life).

As for maintaining orbits that have no signal occlusion occurances, I normally place a "master" comms satellite, that serves as a single dedicated communications bridge between other SOI's, on a high-inclination highly-elliptical "Molniya" orbit.  This ensures that comms blackouts are quite infrequent but predictable, and having a mirrored pair ensures none.  The "lower tier" network is optimized for continuous coverage of the planetary surface, while the "upper tier" comms bridge satellites are optimized for little to no signal occlusions.  This two tier approach IMO is the easiest and cheapest means to establish a continuous, planet-wide communications network.

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