Craft not connecting to relay satellite?

[MFToast]

Hello, I'm working on putting an unmanned satellite in orbit of the Mun, but when it goes around the "dark" side, it loses all connection, and isn't connecting to the relay satellites I have orbiting Kerbin. What am I doing wrong here? The relay satellites have a connection to Kerbin, but aren't relaying the signal to my station in orbit of the Mun. My tracking station is at Level 2.

 

Here are a few screenshots to show what's going on:

Screenshot 1

Screenshot 2

Screenshot 3

 

 

Edited January 16, 2019 by MFToast

[Geonovast]

Without seeing the relay satellites themselves, it's hard to say for sure.  But to guess, I'd say that your relay sats are simply too weak.  They can talk to Kerbin because the antennas on Kerbin are really powerful.

You might notice your two relays are not speaking to each other.  That implies their antennas are pretty weak.

Cue @Snark to come in with 3 paragraphs of headache-inducing math to touch more on this.

Also could be that you don't actually have relay antennas on your relay satellites.

[MFToast]

The relay satellites each have a Communotron 16 and an HG-5 relay dish. The craft orbiting the Mun has a Communotron 16-S.

Looking at CommNet in the KSP wiki it looks like it should work? Maybe I'm reading it wrong? Please clarify if you can!

Edited January 16, 2019 by MFToast

[4x4cheesecake]

1 hour ago, Geonovast said:

Cue @Snark to come in with 3 paragraphs of headache-inducing math to touch more on this. 

Is a short explanation from me also ok?^^

@MFToast Your third screenshot already tells the whole story The relay sats are somewhere around the edge of the SOI of Kerbin, at least even further out as the orbit of Minmus.
Let's take a look at the Antenna Range Diagramm:

We'll look at the first column which is basically the same for vessel-to-vessel connections. As you can see, to cover the distance from Kerbin to the Mun, you will need at least a 500k antenna (your Communotron 16-S is a 500k antenna). But I already mentioned it: Your relay sats are somewhere at the edge of Kerbins SOI, so you will need at least a 5M antenna to establish a connection.

Got this wrong...after seeing the calculation of @bewing , I remembered that the DNS Level 1 station is actually a 2G antenna,so that's not compareable...

Also, keep in mind that both vessel need a reach each other, so even if your relay sats are able to connect to the Mun probe, the CommNet will not work until the Mun probe can also connect to the relays and in this case, the relays are out of range.

I would suggest to build a small craft with a 5M 2G antenna and dock it to the probe to extent the range

Edited January 16, 2019 by 4x4cheesecake
Got some numbers wrong :o

[bewing]

First, direct antennas and relay antennas do not combine with each other. The Comm 16 is a direct antenna, and the HG-5 is a relay, and is more powerful than the Comm 16. So the Comm 16 is not accomplishing anything on that craft.

Second, Geonovast was correct about calculating signal range. One HG-5 has a signal strength of 5M, and the craft at the Mun has a signal strength of 1M. The communication range is calculated correctly according to reality -- the formula is sqrt(strength1 * strength2). So sqrt( 5M * 1M) = 2.2Mm.

The distance to the Mun is 11.4Mm, so your antennas could only reach about a fifth of the way to the Mun.

 

[Snark]

3 hours ago, bewing said:

One HG-5 has a signal strength of 5M, and the craft at the Mun has a signal strength of 1M.

Actually, it's even worse than that:

4 hours ago, MFToast said:

The relay satellites each have a Communotron 16 and an HG-5 relay dish. The craft orbiting the Mun has a Communotron 16-S.

The craft at the Mun has a Communotron 16-S, which has a power of 500k, I believe (not 1M).

The relay satellite has an HG-5, with a power of 5M.  (The Communotron-16S on the relay satellite is irrelevant, as bewing explains above. It's not a relay antenna, it doesn't combine with relay antenna power.)

So the max range from your Mun craft to your relay satellite is going to be sqrt(500k * 5M) = 1.58Mm, i.e. not quite 1600 km.

In other words, your relay satellites can't reach your Mun craft because there's not enough range.

So, how can you fix this?  A few things.

First... make your relay satellite more powerful.  If you can unlock the RA-2 antenna, that has literally 400 times the power of the current HG-5 on it, which ought to solve an awful lot of problems.    However, if you don't have RA-2 unlocked and can't do so easily right now, you can at least boost the power of your relay satellite by spamming HG-5 antennas.  Most antennas (the HG-5 among them) stack, meaning that if you have multiple antennas on the craft, it boosts the power, though not linearly.  If you could, for example, loft a relay satellite that has six HG-5's on it, then that would have an antenna power of 19.2M, nearly four times its current power.  If you could put eight HG-5's on the relay, that would give a power of 23.8M.

Second... make your Mun craft more powerful, too.  At the very least, give it an HG-5; that's 10x the power of its current antenna.  If you could give it, say, a pair of HG-5 antennas, that would have a power of 8.4M.  If you could give it four HG-5's, that would have a power of 14.1M.  Eight would give 23.8M.

So, for example, if you could put eight HG-5's on your relay and also eight HG-5's on your Mun craft, then your max communications range would be 23,800 km, which would be a vast improvement over your current 1600 km.  The Mun orbits at an altitude of 12,000 km; looks as though your relay sats are orbiting at about double that.  So 23,800 km would  be enough to talk to them as long as they're currently on the same side of Kerbin as the Mun is.

Another thing you could do to improve your situation is just to improve the communications geometry.  If the goal is to talk to something in orbit around the Mun, then putting low-powered (i.e. just HG-5, no RA-2) relay satellites at an altitude double the Mun's puts you in a difficult situation, because the distances are pretty big.  Your weak link is the comms between Mun ship and relay, so if you can reduce that distance, it'll help you a lot.

For example, you may want to consider putting the relay sat in orbit around the Mun, rather than Kerbin-- i.e. a high polar Mun orbit.  That way, the relay can nearly always see Kerbin (because of its high polar orbit), and the relay will always be within a couple thousand km of your Mun ship, which means less of an "out of range" problem.

[MFToast]

Okay, thanks for everybody's input! I don't *completely* understand everything being said but it seems that basically everything needs more power. I definitely misread the CommNet wiki page at any rate!

So it seems that the HG-5 can RECEIVE a signal from Kerbin 500Mm away with a Level 2 Tracking Station, but it can't TRANSMIT that far? Am I getting that right?

https://wiki.kerbalspaceprogram.com/wiki/CommNet

[Snark]

39 minutes ago, MFToast said:

So it seems that the HG-5 can RECEIVE a signal from Kerbin 500Mm away with a Level 2 Tracking Station, but it can't TRANSMIT that far? Am I getting that right?

No.  Receiving and transmitting have the exact same range as each other.  The game makes no distinction between transmitting and receiving; range is range.  In the example you give, 500 Mm applies to both.

If you have two things in different locations that want to talk to each other (e.g. "two ships", or "a ship and KSC"), be aware that the maximum range depends on the antenna power at both ends.  Even if following the math is tricky, just remember that it depends on both.  So you can increase the range by increasing the power at either end of the connection.

The tracking station on Kerbin has an antenna power that's much more powerful than the early-to-mid-career antennas, especially if you've upgraded it to level 2.  That's easily enough to talk directly to any ship with any antenna (even a dinky one) that's inside Kerbin's SOI.  Talk to the Mun?  Talk to Minmus?  No problem.

However, that's not the problem you're having.  Neither of your ships has any trouble talking to Kerbin.  Your relay sat can talk to Kerbin just fine.  And your Mun ship can talk to Kerbin just fine, too, as long as the Mun's not getting in the way.

No, the problem you're having is talking between the Mun ship and your relay satellite.  So all that matters there is the antenna power on those two things.  Your Mun ship and your relay satellite are much too far apart from each other, given the current amount of power on them.

So, basically, there are only three things you can do to improve the situation:

1. Increase the antenna power on the relay satellite (so that it has a longer reach when talking to the Mun ship)
2. Increase the antenna power on the Mun ship (so that it has a longer reach when talking to the relay)
3. Move the relay satellite into high Mun orbit instead of high Kerbin orbit (so that it's a lot closer to the Mun ship and doesn't need so much power)

You can do any or all of the above things.  If you choose to do #3, then that would probably solve your problem right there even without giving more antenna power to either of the two ships involved.  On the other hand, if you leave the relay satellite in its current high-Kerbin-orbit situation, then I think you'd need to do both #1 and #2 to get enough antenna power to reach the needed distance.