Communications relays- basic setup

[FlyingPete]

This is my first playthrough of the game for a while really; the first since communications were involved. I'm at the point of beginning explorations of the Mun, and obviously on the Farside communications with Kerbin are blocked. So I need some relay satellites.

Positioning- I was thinking of two satellites in polar orbits 90 degrees apart, at an altitude where at least one satellite has a clear line of sight to the far side and to Kerbin or the other satellite. There should be very few times where a base/lander is out of contact with Kerbin with this setup. Any more efficient setups?

Communications- any advantage to one type of antenna over another? I presume not for short-range operations in the Kerbin system. For operations around other planets, I guess it's worth equipping the relay satellites with something long-range, and since space stations etc are only communicating with a relay they only need the smaller antenna.

I'm guessing that the satellites don't need to be anything more than a basic probe core, batteries, solar panels and an antenna.

[JK_Kerbineer]

@FlyingPete The satellite constellation I use is a satellite in a highly eccentrical equatorial, another in an eccentric 45-degree orbit, and a eccentric polar orbit.

[Oiff]

It can be good to place sat’s with scanners in a polar orbit and use these as relays.

Two birds with one stone

[Plusck]

I can't say it's a real issue, maybe I'm imagining it, but I worry a bit about CPU overhead with too many relays in range all the time. So my approach has been to limit numbers and power to what is actually needed.

A single 2G relay can talk to a command module's internal antenna from any height of Mun orbit. A pair of HG-5s can similarly talk to any single Cummunotron 16. [edit: virtually... I just checked the spreadsheet and it says the very edge of the Mun's SOI might not work...]

I also only put 2 relays up. Polar orbits are fine, but the chances of there being no coverage at a critical time are quite high - especially if they are too close.

Instead, I'd recommend having two relays on the same plane (which might be polar, or at 30° or even equatorial if you don't plan to go right to the poles), but on opposing highly eccentric orbits. So on one side Pe would be around 15km and Ap on the other side would be about 1,500 km, and the other relay would mirror that.

That way, each relay spends virtually all of the time out near its Ap. If you only use two relays there will be spots that aren't covered at times but they will be easily predictable and that only really concerns the far side of the Mun twice per Munar orbit around Kerbin.

It's impossible to get the poles covered all the time without doubling the number of relays and getting them perfectly synchronised. Two relays on opposite elliptic sides of a 30-45° plane will keep both poles covered the majority of the time.
 

Edited November 9, 2017 by Plusck

[bewing]

Generally, there's not a lot of point in spending a lot of time on the Farside. Often, you only want to hit the biomes there one time, in a batch. If you want a base on the Mun, it's generally better just to land the base so it has LOS to Kerbin.

So for a Farside relay sat, it only has to be in position for a short time. You only need one, and you can put it pretty high -- so it can see nearly all of the Farside + Kerbin. If you put it at a medium altitude and polar, then you can get complete coverage just by waiting for it to fly over your location, no matter where you go.

 

[Geschosskopf]

On 11/9/2017 at 7:11 AM, FlyingPete said:

This is my first playthrough of the game for a while really; the first since communications were involved. I'm at the point of beginning explorations of the Mun, and obviously on the Farside communications with Kerbin are blocked. So I need some relay satellites.

Not necessarily.  It depends on what you're doing on the on the far side, for how long, and any role-playing house rules you impose on yourself.  If you don't need communications to control a probe, then you really only need communications to transmit science.  But science will keep so if the ship will return to orbit, it can transmit the science later once it's got an LOS back to Kerbin again.  So really, unless you're building a permanent base on the far side,, there's really no need to invest much if any thing in a network for the far side of Mun.

 

On 11/9/2017 at 7:11 AM, FlyingPete said:

Positioning- I was thinking of two satellites in polar orbits 90 degrees apart, at an altitude where at least one satellite has a clear line of sight to the far side and to Kerbin or the other satellite. There should be very few times where a base/lander is out of contact with Kerbin with this setup. Any more efficient setups?

What I like to do is put 2 relays in highly eccentric polar orbits at Kerbin, Pes about 150km and Aps just inside the edge of Kerbin's SOI.  One relay goes up, the other down, and they're 180^ out of phase with each other so when 1 is at Pe, the other is at Ap.  These relays will spend the bulk of their time in the Ap half of their orbits, millions of km above or below Kerbin.  From this position, they can see the polar and temperate latitudes of the far side all by themselves, so you only need a relay at Mun to cover the equatorial latitudes of the far side.  This Munar relay just needs to be in a reasonably high equatorial orbit, so that whichever one of the Kerbin polar relays is closest to its Ap can see it.  That's why you have 2 polar relays and they're out of phase with each other.  But you only need the Munar equatorial relay if you've really got a need to communicate from the far side equatorial latitudes.

NOTE:  As you start exploring other planets, put a similar pair of relays at each one (except Moho).  Then you'll be able to talk to Jool and Eeloo in multiple hops instead of trying to do it all in 1 go, and you'll be able to talk around the sun when it gets between the ship and Kerbin.

As to the Munar relay, it doesn't even have to be permanent.  You could do the mission Apollo style and use the CM/SM in orbit as the relay for the LM on the far side.  

 

On 11/9/2017 at 7:11 AM, FlyingPete said:

Communications- any advantage to one type of antenna over another? I presume not for short-range operations in the Kerbin system. For operations around other planets, I guess it's worth equipping the relay satellites with something long-range, and since space stations etc are only communicating with a relay they only need the smaller antenna.

Permanent relays (especially those in polar orbits of the main planets) should always be the biggest ones you have available.  Bigger antennae have longer ranges and don't lose as many science points (or may actually increase them) compared to smaller antennae.  

 

On 11/9/2017 at 7:11 AM, FlyingPete said:

I'm guessing that the satellites don't need to be anything more than a basic probe core, batteries, solar panels and an antenna.

It helps if they have propulsion, too.  But because they're so small and light, you can put a few thousand m/s in them with tiny tanks and engines, so this isn't a problem.

I'm not entirely sure if battery size matters actually matters for relays.  It certainly matters for the ship actually transmitting the science, but whether any non-focused relays along the path back to Kerbin actually use EC or not relaying the signal is a mystery.  Best thing would be to assume that they do, so always put several thousand EC worth of battery on your relays.  And be aware that solar panels are pretty weak from Dres out (a Gigantor at Jool produces about 0.8 EC/sec), so if the relay does consume EC when relaying science, it will take a while to recharge the battery after each transmission.

[Spricigo]

3 hours ago, Geschosskopf said:

Permanent relays (especially those in polar orbits of the main planets) should always be the biggest ones you have available.  Bigger antennae have longer ranges and don't lose as many science points (or may actually increase them) compared to smaller antennae. 

No, it don't need to always be the biggest antenna. The player may prefer to bring the science back to Kerbin instead of transmitting.  Just to vessel  control signal strength is irrelevant as long it maintain the link, in that case a strong relay may be necessary to close the gap between where you are and kerbin, but to bounce the that signal around the celestial body even the smallest relay antenna will suffice.

 

 

 

 

 

[Geschosskopf]

2 hours ago, Spricigo said:

No, it don't need to always be the biggest antenna. The player may prefer to bring the science back to Kerbin instead of transmitting.  Just to vessel  control signal strength is irrelevant as long it maintain the link, in that case a strong relay may be necessary to close the gap between where you are and kerbin, but to bounce the that signal around the celestial body even the smallest relay antenna will suffice.

If the OP didn't need relays, he wouldn't have asked how to do them.  So the point about bringing science home is irrelevant.

Permanent relays, the pair in eccentric polar orbits, should always be the biggest ones you've got for the simple reason that planets move around the sun.  During any interplanetary trip, the sun will be between the ship and Kerbin at some point.  If you do multiple interplanetary missions at once, going to different places, then this happens frequently.  When this happens, you must talk around the sun--you can't talk over or under it.  This requires bank shots around the solar system to 1 or more other planets.  And depending on how many relays you've already established and where those planets are at the moment, any one of those relays might have to talk more than halfway across the solar system.

As an example, you have a ship at Duna that is currently blocked by the sun.  But you've already put some relays at Dres, so the signal goes Duna - Dres - Kerbin around the sun.  However, if Dres is on the far side of the sun from Kerbin (but visible, not blocked), then link between Kerbin and Dres must travel the full diameter of Kerbin's orbit plus most of the distance between Kerbin's orbit and Dres' orbit.  This link will work a lot better if you've got your big antennae at Dres.

[Spricigo]

10 hours ago, Geschosskopf said:

If the OP didn't need relays, he wouldn't have asked how to do them.  So the point about bringing science home is irrelevant.

It may or may not be relevant, the OP didn't stated how he pretend to use the relays. And even if he pretend to transmit it don't make your statement true for all the other player out there that will not transmit.

11 hours ago, Geschosskopf said:

During any interplanetary trip, the sun will be between the ship and Kerbin at some point.... When this happens, you must talk around the sun--you can't talk over or under it.

Or I can just make sure  commnet will not be necessary at that moment. Or I can send a pilot with RGU for the planets where  I think that can be an issue. There are several options available.