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AHeroReborn

why do relay satellites go in a geosynchronous orbit?

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If you put them in the same delta formation, but in a lower orbit, they would rotate in unison, ensuring you still have a connection without wasting fuel to get to geosync.

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1 hour ago, AHeroReborn said:

If you put them in the same delta formation, but in a lower orbit, they would rotate in unison, ensuring you still have a connection without wasting fuel to get to geosync.

The higher the altitude of relay satellites in the ring around Kerbin, the fewer of them you need.  At geostationary altitude, you only need 3.  Lower down, you might need 4, 5, or even 6.  So it's generally cheaper to build fewer satellites because it only takes about 650m/s to reach geostationary altitude anyway.

HOWEVER, the ONLY reason to but a ring of relays around Kerbin is if you disable the extra ground stations.  Without the extra ground stations, your distant ships have to link back to KSC itself.  Because KSC will be facing away from the distant ship about 50% of the time, you then need to recreate the extra ground stations in space with the ring of relays.  Then the distant ship links to a relay on the back side of Kerbin, which links to 1 or more other relays in the ring, until one of these can link to KSC.  With the extra ground stations turned on, the distant ship links to one of these stations directly on the far side of Kerbin, and all the ground stations have landline connections to KSC.  IOW, both the extra ground stations and the ring of relays do the same thing---they let your distant ship link to KSC regardless of which way KSC is facing.  You need one or the other, but you don't need both.

In general, I recommend leaving the extra ground stations turned on.  The problem with any sort of relay ring is that stock KSC doesn't give you enough data about your orbit to put something in a stable geostationary orbit, or any other finely synchronized orbit at another altitude.  And even if you use a mod that gives you that data, the orbit won't stay where you want it due to floating point errors and a general lack of fine control over maneuvering.  So over time, your satellites will drift until eventually your neat formation of relays gets out of whack and you get gaps in the coverage.  So I find it a lot less of a bother to skip the whole thing.

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In real life? You can use simple, cheap satellite dishes pointed at one static spot in the sky, no need to add tracking mechanisms that find the current location of the satellite.

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I never bother with geosynchronous orbits for my commsat hub or any other comm sat. I just don't see the point. As you point out, as long as their periods are the same, it still works just fine. My standard setup is 800-900 km for all comm satellites around Kerbin, 4 hub sats at 840 km, Mun and Minus get 2 at say 835 km, Moho/Eve 2 at 830 etc etc untl I replace all with 4 sats with full comm capabilities for all planets + 1 direct link to the active ship + 3 for a link to a Sun hub late in the game for link to planets in the Suns comm shadow from Kerbin. None of these sats ever go geosynchronous.

 

(Reason for these altitude bands is I don't have to think about where I can place other ships and sats with no risk of collisions. I use the same idea for pretty much the entire altitude band down to 70km, each 1000m or so meter is assigned a non-debatable purpose. Tourists/parts tests/one orbit trips etc get 71km, rescues are typically between 75 and 95km). Departure is 100km, return to LKO 101km etc etc).

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If you have ground stations turned on (the default), you can save even more by not launching relay satellites at all.

The two main reasons for launching keostationary satellites is for consistency (they've always in the same place over Kerbin) and to copy what humans do. Both are valid rp reasons but neither are particularly important to succeed at the game.

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 Off course relay satellites don't necessarily go on geosynchronous orbit.

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45 minutes ago, Geschosskopf said:

The higher the altitude of relay satellites in the ring around Kerbin, the fewer of them you need.  At geostationary altitude, you only need 3.  Lower down, you might need 4, 5, or even 6.  So it's generally cheaper to build fewer satellites because it only takes about 650m/s to reach geostationary altitude anyway.

You only need 3 from anything over 600km.

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1 hour ago, Spricigo said:

You only need 3 from anything over 600km.


But the margin of error disappears rapidly, both for the initial placement/spacing and the drift over time.  And if you're doing this at all, it's because you need it, so you want to build the system with a fair amount of overlap between the satellites.

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9 minutes ago, Geschosskopf said:


But the margin of error disappears rapidly, both for the initial placement/spacing and the drift over time.  And if you're doing this at all, it's because you need it, so you want to build the system with a fair amount of overlap between the satellites.

Another advantage that is not particular to the geostationary orbit. At higher altitudes its even less an issue.

 

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I play without extra ground stations and I do lots of automated stuff.  I find it useful in early career to put a coms sat in geo above the KSC before I send out probes.

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12 hours ago, Spricigo said:

Another advantage that is not particular to the geostationary orbit. At higher altitudes its even less an issue.

But then you run into 2 other issues:

#1:  Mun.  You can't go too far above geostationary altitude without Mun hosing you up during high-speed time warp (such as used during interplanetary trips).  High warp levels effectively increase bodies' SOIs significantly, which means that your satellites can get eaten by Mun or ejected from the Kerbin system.  Thus, the upper limit on how high you can put the relays is about 2x Mun's SOI diameter below Mun's orbital altitude.  You can, of course, put the relay out beyond Mun, but then Mun will periodically block the link.  Not often, and not for very long, but the whole point of building a relay ring around Kerbin is to NOT have the signal blocked.

#2:  Uncrewed Launches:  The main reason for parking a geostationary relay directly above KSC is to ensure you always (within the lifespan of orbits) have a link to ships that won't circularize until about 120^ around Kerbin from KSC.  If you do this, then you've got launches covered with just 1 relay and can delay putting up the others until you have the need and/or money to do so.  Because you've got 1 at geostationary orbit already, the others need to be there as well, to give the proper spacing and to remain in formation.

So really, taking all the practical gameplay and game quirk factors into account, a geostationary ring of 3 relays, with 1 directly over KSC, is the best solution IF you have disabled the extra ground stations.  It's not the only solution, but it's the best compromise, which is why it's been the usual method of RT-users for many years.  And that's the real answer to the OP's question.  It's just convenient.

Still, the best solution is to leave the extra ground stations enabled, so you can link to Kerbin as a whole instead of just KSC.

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I'll just add, by having the sats in a lower orbit, you can get away with shorter range antennas for local network which consume less power. Combined with a shorter time on the planet's night side, it means you need fewer/smaller  ->  cheaper and lighter battery packs, making the overall launch cheaper which is always nice in career mode.

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With ground stations turned on there's no need for relay satellites inside the orbit of Mun.  However, I like to put a ring of relay satellites out near Kerbin's SOI to provide communications to the far side of the moons.

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59 minutes ago, Geschosskopf said:

#1:  Mun.  You can't go too far above geostationary altitude without Mun hosing you up during high-speed time warp (such as used during interplanetary trips).  High warp levels effectively increase bodies' SOIs significantly, which means that your satellites can get eaten by Mun or ejected from the Kerbin system.  Thus, the upper limit on how high you can put the relays is about 2x Mun's SOI diameter below Mun's orbital altitude.  You can, of course, put the relay out beyond Mun, but then Mun will periodically block the link.  Not often, and not for very long, but the whole point of building a relay ring around Kerbin is to NOT have the signal blocked.

Did you realise that twice the Mun's SoI diameter is 9.7Mm? With that ludicrous 'safety margin' you can't even have your satellites in geostationary orbit.

This is not an issue, there is plenty of space between Kerbin and Mun, and the later will not catch your satellite halfway between the two celestial bodies.

 

1 hour ago, Geschosskopf said:

#2:  Uncrewed Launches:  The main reason for parking a geostationary relay directly above KSC is to ensure you always (within the lifespan of orbits) have a link to ships that won't circularize until about 120^ around Kerbin from KSC If you do this, then you've got launches covered with just 1 relay and can delay putting up the others until you have the need and/or money to do so.  Because you've got 1 at geostationary orbit already, the others need to be there as well, to give the proper spacing and to remain in formation.

Point is: I don't have any motivation to delay the placement of the 2nd and 3rd satellites. A single launch make things a lot simpler, faster, and, even on hard settings, the cost is not that much anyway.

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2 hours ago, LN400 said:

I'll just add, by having the sats in a lower orbit, you can get away with shorter range antennas for local network which consume less power. Combined with a shorter time on the planet's night side, it means you need fewer/smaller  ->  cheaper and lighter battery packs, making the overall launch cheaper which is always nice in career mode.

To a point, going higher means less need for batteries, but only to a point.  There's an optimal altitude for it, above which the reduction in orbital velocity causes you to spend more time in the planet's umbra, even if the arc is shorter due to being straighter.

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19 hours ago, Spricigo said:

Did you realise that twice the Mun's SoI diameter is 9.7Mm? With that ludicrous 'safety margin' you can't even have your satellites in geostationary orbit.

Yeah, I meant radius. [Snip]

Edited by Deddly

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Some personal remarks have been removed from this thread. There's no need to make enemies out of each other over comms satellites in a space game. 

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Relays can be expensive. For example, this one consists of 16 RA-100 dishes, giving a rated power of 800G (the level 3 DTS is only 250G). So I only sent one into geosynchronous orbit opposite to KSC. Its shadow is covered by a ground station near KSC.

screenshot22.png

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I usually put 4 basic relays at the edge of Kerbin SOI as soon as I can (single launch and resonant orbit stunts so it takes a bit of in-game time before all 4 is in position).

They've saved me several time when vessels otherwise would have ended up in radio shadow around Mün or Minmus.

But mostly because I can and my mild OCD demands that I launch them :wink:

 

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On 06/11/2017 at 1:31 PM, Geschosskopf said:

#2:  Uncrewed Launches:  The main reason for parking a geostationary relay directly above KSC is to ensure you always (within the lifespan of orbits) have a link to ships that won't circularize until about 120^ around Kerbin from KSC.  If you do this, then you've got launches covered with just 1 relay and can delay putting up the others until you have the need and/or money to do so.  Because you've got 1 at geostationary orbit already, the others need to be there as well, to give the proper spacing and to remain in formation.

Well, no, they don't. Ignoring that you can put three relays up in one launch for not really all that much extra fuel ( resonant orbits are fun ), if you stick one geo relay above KSC you've effectively got a giant antenna to retransmit to lower-orbit relay networks ( like, say, ones in polar orbits ) which can relay on further. No need for more geo sats. Last RT run I put a gigantic - big enough to blanket the entire system - relay in Kerbin polar orbit at a distance somewhere between Mun & Minmus & just relied on low-orbit relays to get the signal to it.

For humans, knowing where a commsat is & knowing it's going to stay there makes actually using it considerably easier.

Edited by Van Disaster

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If you play(ed) career and you adhere to the bogus contract system you have at least 1 comm satellite in between Kerbin and Mun that can re-transmit to lower orbit relay networks like Van Disaster suggested.
By the time you need coverage for probes you already did several of such missions. Unless you skip the whole satellite launch contracts altogether, but I hereby assuming you do a few.

It was fun putting sats into geostationary or geosynchronous orbit the first time trying.

For me it went like this: Hey look, the ground moves with us, this is so cool for a day or so, past that point just boring to re-execute.

Like one is actually going to switch to his geostationary satellite just for the fun of it during your occasional weekly or monthly boredom crisis.
I also see no use for this on other planets. I also don't see the use of geostationary networks around other planets/moons.

I usually only need 1 with several dishes around let's say, Duna. If the sat proves to be in the wrong location upon arrival at the Pe, I just reload a week or so before the encounter and do a small burn to change time to Pe so that the Sat is in the correct place.
I usually put the relay sat in a highly elliptical orbit so I can change it's orbital time period aswell if the sat appears to be in the wrong spot when I need to execute important maneuvers on a probe. By the time career progresses I usually add the second and third sat. But not go on a full out coverage of a particular system to patch all the holes in a network. Unless you really want it to ofcourse, this is just me.

Edited by Helmetman

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On 11/5/2017 at 3:51 PM, HebaruSan said:

In real life? You can use simple, cheap satellite dishes pointed at one static spot in the sky, no need to add tracking mechanisms that find the current location of the satellite.

Exactly and in KSP

If you want to build a colony on Kerbin and want to relay Science have a fixed satillites right above your position to relay back to KSC Is good. 

Geostationary is when Your Orbital Period is matched to the Speed of Rotation of the orbiting Body of mass

Orbital Period is the time it takes to complete 1 orbit.

so in real life 24 hours is one rotation of the earth, so if a Ship reaches certain Altitude above earth it's Orbital Period is 24 h so then they are matched and orbits directly above that spot until the orbit is decayed, Retrograde burn or indefinitely with futuristic propulsion. 

Got it?

Edited by Cheif Operations Director

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On 05/11/2017 at 6:01 PM, Geschosskopf said:

And even if you use a mod that gives you that data, the orbit won't stay where you want it due to floating point errors and a general lack of fine control over maneuvering.  So over time, your satellites will drift until eventually your neat formation of relays gets out of whack and you get gaps in the coverage

This is very true. But there are ways to diminish the effects of orbit imprecision,  up to a point where the difference is so small,  it becomes almost irrelevant.

This is what I usually do:

First,  the problem with two objects not being in absolutelly identical orbital parameters is that one will be faster than the other. So the faster one will overtake the slower one, even if it takes a million years. The key is to... well,  make it so as it _does_ take a million years. The higher the orbit,  the slower is the orbital speed. So I always put my relay constellation as high as I can - certainly higher then Minmus. It minimizes the effects of speed differences between two different satellites,  because not only they will be much,  much slower,  but also the distance between them is much greater. So whatever differences in their respective orbits,  it may take decades or hundreds of game years for them to start disaligning in a relevant way.

The second thing is,  of course,  to try to have their orbits be as similar as possiblr. Fine tuning is the thing here. First you need some mods. Kerbal Engineer,  Basic Orbit.... mods that help you visualize orbit data more precisely. Then you also need your satellites to have fine RCS. By clicking on the rcs thrusters you can decrease the thrust power of the part. By doing that you can make cirurgicly precise inputs in your orbit,  making the different satellites fall into a much more similar pattern (albeit,  I agree,  "identical" seems to be impossible).

My "finely-tuned, higher-than-minmus" relay constellations always last a long time in an usefull patern.

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The answer to this problem is the same as every problem in KSP.

MOAR!

More satellites to be specific. You don't need perfect geosync and neat formations if you just have a metric crap ton of sats. This is coming from a guy who plays with ground stations turned off btw.

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