Is this a good idea for a comm network? (Theorycrafting)

[Spheniscine]

The basic idea is that the ideal goal is to have a constellation consisting of 6 relay satellites for every body.

3 are equatorial, in the same orbit, and 120 degrees apart from each other, forming an equilateral triangle. Its altitude must be greater than the body radius so that they all can communicate with each other and the surface.

3 are polar, in same orbit, 120 degrees apart too, altitude > body radius too. The 3 equatorial ones can be set up first, saving the polar ones only if you need to operate over the polar regions in low orbit or on the surface.

For the Sun, you have two powerful relays forming an equilateral triangle with Kerbin. (Too bad those aren't Lagrange points though...) Polar relays are probably not necessary nor worth the delta-v, as if you're close enough to the Sun to be blocked that way, you'll be vaporized anyhow.

I think these are the minimum required both to cover the entire surfaces of bodies and provide rerouting for any inconvenient syzygies / eclipses?

Edited December 8, 2016 by Spheniscine

[WanderingKid]

I believe you're better off, for the solar relays, to have them on Kerbin's orbit just behind/in front of Kerbin for relay duty.  This allows you to relay 'into' the system should Mun or Minmus be blocking at the time, and avoids orbital decay if you do it with precision.

[Snark]

Seems like extreme overkill to me... the problem here being, just what is meant by "good idea", since different people have different priorities.

For example, I've seen quite a few people post about setting up comm networks where it's clear that their first priority is to absolutely guarantee 100% rock-solid coverage to 100% of a body's surface and SoI, 100% of the time. From your post, I gather that you're in that camp.

There's nothing wrong with that... but for my own gameplay, I've never understood the motivation. I tend to prioritize for bang-for-the-buck, and the fact is, going for guaranteed 100% coverage at all times is simply not cost-effective for me (for virtually any definition of "cost", whether you're talking about funds, in-game calendar time, my play time, or anything else).  It's enormously simpler and easier to build a 98% coverage system than a guaranteed 100%.

For example, three satellites in a high circular orbit will give very close to 100% coverage of a planet's surface, and 100% coverage of its surrounding space.  Half the effort of your proposed constellation of six, while being really close to equal in effect. Heck, even TWO satellites can give over 95% surface coverage, if they're placed right.

You don't need the solar relays, because you already have them around the planets. The solar system is a very empty place, and it's extremely rare for the sun to occlude any given planet's LOS to Kerbin (especially given that the planets' orbits aren't perfectly coplanar). I seriously don't care if there's a chance of having a brief signal interruption once every few in-game centuries. And if you have a relay network around three or more planets, the chance of solar occlusion is effectively zero.

... But that's just me. You may very well have a different set of priorities and goals; all I'm saying is, advice is easier to offer if you can be more specific about exactly what those priorities are.

If you really do want guaranteed 100% coverage of a planet's surface at all times, incidentally, you can do it with just four.

 

[GoSlash27]

Spheniscine,

 The problem with DSN setups is that with the current balance of parts, they don't provide enough benefit to justify the time and expense to set them up.

For example, Consider the case of a level 2 tracking station. With a 15G antenna, you have Moho, Eve, and partial coverage of Duna. Setting up a 15G DSN gives you full time uninterruptible coverage of these same bodies. Is it really worth the (roughly) $50,000 and 6 years required to set this up when you could simply upgrade your tracking station instead? I mean it's not 100% uninterruptible, but it's a lot easier and quicker.

Best,
-Slashy

 

[Allocthonous]

Your system sounds about right for full coverage. One thing you might consider is that only the polar orbit relays around planets and the solar relays would need to be cable of interplanetary transmission. The circular orbit satellites could be relatively under-powered with no problems.

[Kryxal]

I really liked the network I read about not too long ago ... two polar sats on the planet with apses on the poles and a highly eccentric orbit for relay to other sats, then 2-3 sats around each moon with a 120 degree offset.  Add 3 sats to the planet on the equator if you want to land there safely without a mothership relaying.  Only the polar sats need a true long-range antenna.

[Spheniscine]

10 hours ago, Snark said:

For example, three satellites in a high circular orbit will give very close to 100% coverage of a planet's surface, and 100% coverage of its surrounding space.  Half the effort of your proposed constellation of six, while being really close to equal in effect. Heck, even TWO satellites can give over 95% surface coverage, if they're placed right.

Unless you're smack dab right on the poles? There's a bit of a difference between having coverage of everywhere most of the time, and outright missing some spots entirely.

edit: Well I guess if they're inclined, the blind spots will "track" along the ground as the planet rotates.

Quote

You don't need the solar relays, because you already have them around the planets. The solar system is a very empty place, and it's extremely rare for the sun to occlude any given planet's LOS to Kerbin (especially given that the planets' orbits aren't perfectly coplanar). I seriously don't care if there's a chance of having a brief signal interruption once every few in-game centuries. And if you have a relay network around three or more planets, the chance of solar occlusion is effectively zero.

It's the sun though, which is more than just a small point in the sky; that's gotta account for a significant portion of each planet's orbit? Though I see your point of networks on other planets being able to reroute if they're powerful enough.

Edited December 8, 2016 by Spheniscine

[Snark]

59 minutes ago, Spheniscine said:

Unless you're smack dab right on the poles? There's a bit of a difference between having coverage of everywhere most of the time, and outright missing some spots entirely.

edit: Well I guess if they're inclined, the blind spots will "track" along the ground as the planet rotates.

Exactly.  It's a question of what you want.  For example, are you actually going to be using the poles?  Dunno about you, but I practically never land anything there-- it's the least convenient spot on the planet.  So, if you know you're not going to be using 'em, you can just give them scanty coverage, and you get 100% coverage everywhere else.

Or if you do use the poles, you can put your three satellites in an inclined orbit, and then the two "blind spots" can track along the ground at whatever latitude you pick.  So, if there's any latitude band on the planet that you use less, just put the blind spots there.  And even at the "problem latitude", you'd still have coverage most of the time; there would just be a brief outage each time the planet rotates.

Also, depending on the topology of the planet... three satellites in equatorial orbit may actually provide 100% coverage, including the poles-- if they're at a reasonably high elevation.  Radio occlusion in KSP is based on the planet's radius, and ignores terrain; if the poles are at 3 km altitude, for example, it's the same as if your polar base were flying 3 km above the oceans.  Which may give it radio LOS to high-altitude equatorial satellites, even if they're slightly below its visible horizon.

59 minutes ago, Spheniscine said:

It's the sun though, which is more than just a small point in the sky; that's gotta account for a significant portion of each planet's orbit? Though I see your point of networks on other planets being able to reroute if they're powerful enough.

Nope.  At least, not unless you're orbiting super close to it.  It actually is just a pretty small point in the sky.

Kerbin orbits at an altitude of 13.6G meters from the sun.  The sun is 261.6M meters in radius.  That means that the Sun's diameter subtends an angle of 2.2 degrees as seen from Kerbin.   That's over four times bigger than Sol as seen from Earth... but it still occludes only 0.6% of the plane of the ecliptic.  One part in 163.  So, if you ignore the Sun, you've got 99.4% coverage, even for stuff that's precisely aligned on the ecliptic.  I don't know if you care about that 0.6%, but I sure don't.  I could play KSP 40 hours a week, and run into that situation for less than 15 minutes of that.

And the blockage is actually even a lot less than that.  The planets aren't (quite) coplanar.  In descending order, the inclination of the planets' orbits are:  Moho (7 degrees), Eeloo (6.15 degrees), Dres (5 degrees), Eve (2.1 degrees), Jool (1.304 degrees), Duna (0.06 degrees).

In other words, every planet except Duna has an orbital inclination that's greater than the visual radius of the sun as seen from Kerbin.  So, even during that vanishingly tiny 0.6% of the time that a given planet is exactly 180 degrees on the opposite side of the sun from Kerbin, there's a pretty good chance that it'll still have LOS to Kerbin, passing over the sun's north or south pole.  (Well, okay, in the case of Moho and Eve, they'll be in the 180-degrees-opposite position somewhat more than 0.6% of the time, but the principle still holds.  Eve's orbital inclination is double the sun's visual radius.  Moho's is more than six times.)

And... if you've got communications relays around two or more planets (besides Kerbin), then that means even in the very tiny, extremely rare, probably one-in-a-thousand cases where one of those planets happens to be occluded from Kerbin by the sun... it's pretty much guaranteed to be able to see the other planet, which can see Kerbin.  The chance that all three of them get precisely lined up so that the sun blocks communications would happen at most once every few thousand years... and may actually be physically impossible, given that the inclined planets have different longitudes of the ascending node.  (For example:  You have relays at Kerbin, Dres, and Moho.  It is geometrically impossible to ever have a situation where one of those planets is cut off from both of the others, because they're both hiding behind the sun at the same time.)

So, no.  You really, really don't need to worry about the sun blocking communications, at least not unless you have a ship that dives down really close to it or something.

 

[Sublight]

What is the point to doing this?  Just for fun, or is there a benefit?

[Snark]

1 minute ago, Sublight said:

What is the point to doing this?  Just for fun, or is there a benefit?

Certainly would be interested to hear the OP's perspective on this... but it's worth noting that the point of, well, pretty much anything in KSP is "just for fun".  Or, perhaps, "because it's a challenge", which is just another variant of "for fun". 

[CSE]

Two suggestions:

1 hour ago, Snark said:

Or if you do use the poles, you can put your three satellites in an inclined orbit, and then the two "blind spots" can track along the ground at whatever latitude you pick.  So, if there's any latitude band on the planet that you use less, just put the blind spots there.

Once your three satellites are in their nice, evenly-spaced inclined orbit, make small plane changes to two of them. Now the three satellites permanent blind spots are at slightly different latitudes, reducing the chance of any location having no coverage at all.

Or, for a two-satellite network, try one in a high polar orbit and the other in a low, short-period polar orbit perpendicular to the first. This should ensure your out-of-coverage periods are short at any latitude. Many planetside operations don't need hours of in-communcation time to complete the necessary activities; minutes may be enough.

[Snark]

Lots of ways to slice this. Again, it just comes down to what one's goal is. For example, I'm pretty practical, and for most of what I do, 60-70% coverage of my area of interest is plenty.

So, let's say I'm pioneering my way to a planet, and I've just got ONE relay satellite for my surface operations to talk to. So, I just decide which hemisphere I'm primarily going to be operating in, north or south. Then I put my relay in an extremely elliptical orbit, with a very high Ap over that pole, and a fairly low Pe over the opposite pole. And voilà, I've got my good-enough coverage. The relay spends most of its time loitering for days on end, high over the pole where it has an excellent view of the entire hemisphere, as well as all 360 degrees of the ecliptic. There will be brief outages once every many days, as it whips past the opposite pole, but that's not a problem; I just pause surface operations until the short outage is past.

[Birdco_Space]

21 hours ago, GoSlash27 said:

Spheniscine,

 The problem with DSN setups is that with the current balance of parts, they don't provide enough benefit to justify the time and expense to set them up.

For example, Consider the case of a level 2 tracking station. With a 15G antenna, you have Moho, Eve, and partial coverage of Duna. Setting up a 15G DSN gives you full time uninterruptible coverage of these same bodies. Is it really worth the (roughly) $50,000 and 6 years required to set this up when you could simply upgrade your tracking station instead? I mean it's not 100% uninterruptible, but it's a lot easier and quicker.

Best,
-Slashy

 

What if you play extra hard mode on the comms net?  I like playing with KSC being the only ground station, and set for minimum probe control out of LOS.

 

My strategy starts with a few low power LKO comms relays to get the basic network in place around Kerbin to launch satellites.   Next a higher power relay in Keostationary with vision of KSC, then the highest power relays I can stack on a rocket (multiple antennas and all that), one each in highly elliptic N or S polar orbits (all the way out to SOI edge).  This gives me 2 Relays that can see almost anywhere in Kerbin's SOI nearly all the time, and, if I've packed enough antennas, see out to much of the rest of the Kerbol system. 

For the rest to Kerbins SOI, a single relay in a high equatorial orbit of Minmus can get me high percentage of coverage time in Minmus' blind spot, and a medium percentage of coverage time in the Mun's blind spot.  From there, investment in a Mun relay network depends on how important it is for what you have planned, as diminishing returns kick in (not as much extra coverage for each additional relay satellite)   

Interplanetary, I've found a high power relay at Eve is very useful, as it can drastically shrink the comms dead zones at other planets, making insertion burns less likely to occur somewhere I cannot control a probe (and Eve is easy to get to).  From there, a single relay with enough power to talk to one of the high power relays in a highly elliptic orbit around the other planets is usually enough to adequately cover the gaps, especially the more planets you get these established at.  Further development is dependent on what you have planned, as you get deeper into diminishing returns past this point 

 

Edited December 9, 2016 by Birdco_Space
corrected for accuracy

[wumpus]

For planetary orbits (including Kerbin), I'm pretty sure it is hard to beat highly eccentric orbits.  "In the same orbit" is pretty tough to achieve (I suppose that Kerbal Engineer can help a lot, but you might think such is "cheating" since you don't have to worry about the gravity of anything else in the SOI).  Eccentric orbits spend such a large span of time near AP to consider them basically stationary.  As long as you don't manage to have two satellites at PE at the same time you will have full coverage with 4 satellites.  You could put 5 up and make it closer to three consecutive birds in PE to lose coverage for all but a sliver.

This won't help solar orbit at all, but that takes a long time to get out of orbit, and I'm not sure that a solar array is well justified.

[FancyMouse]

Just throw in some fun numbers. Suppose you have some "95%" coverage on, let's say, a base. Looks like a high number, right? Assuming the base can only talk to relay, and let's say you have mining operation/science labs so that you want to go back pretty often. If you go back to this base 20 times at random, the probability that you'll have no connection at least once is a whooping ~64% (~1-1/e if you recognize the approximation).

That's why commnet is fully usage driven - in the above usage, if I can't do anything when I come back to my base, even just once, I'll become salty. So maintaining 100% coverage for frequently used base is a must to me. However - I can accept other places (like polar area if I don't have a polar base) which are completely uncovered.