CommNet range?

[DarkPraetor]

Hi. I need help understanding interplanetary CommNet. I have 3 relays around Kerbin at 120° from each other (RA-15, lvl 3 tracking station).

Now I did the same at Eve (also RA-15). However they don't communicate with Kerbin's relays, so I only have signal (and control) while the KSC is in line of sight (79% signal strength).

Does this mean that the only way to have constant signal from other planets would be replacing everything with RA-100 antennas?

[Streetwind]

Commnet range is simply SQRT( antenna power of the first partner * antenna power of the second partner ). If you have two craft with identical antennas trying to communicate, this simplifies into SQRT(antenna power)², which in turn simplifies into antenna power itself.

The antenna power of an RA-15 is 15,000,000,000, so the maximum range two RA-15's can communicate with one another is 15 gigameters, AKA 15 million kilometers.

The semimajor axis of Eve is roughly 9.8 Gm. The semimajor axis of Kerbin is roughly 13.6 Gm.
Closest approach: SMA_Kerbin - SMA_Eve = 13.6 - 9.8 = 3.8 Gm
Largest separation: SMA_Kerbin + SMA_Eve = 13.6 + 9.8 = 23.4 Gm

Therefore, your relay system using RA-15's can link back home from Eve some of the time, but not all of the time. Eve is simply too far away from Kerbin in your save right now, but it will eventually return to being close enough again.

If you want to have a connection with Eve at all times, you have various options. The first and most obvious is to rely more on the DSN. It seems like you have extra ground stations disabled. If you did not, you would already have a stable link to Eve at all times. This is because the DSN, being a ground-based installation without limits in power and dish size, is absurdly powerful. The level 3 DSN has 250G antenna power. A RA-15 can talk to it from more than 61 gigameters away. This setup mirrors real life, where satellite based communication networks are pretty much nonexistant because the sheer power of ground-based antennas render them completely pointless.

Of course, you may have the extra ground stations disabled for a reason, and actually want to play with commsat networks. In that case, you have no choice but to increase the antenna power of your satellites. Thankfully, due to the way the math works, it's enough for you to upgrade one side of the equation only. Upgrading both sides helps even more, but for the closer planets like Eve, it's probably not necessary.

Upgrading your Kerbin constellation to RA-100's will boost your Eve-Kerbin link to SQRT( 15G * 100G ) = ~38.73 gigameters. With Eve's maximum distance to Kerbin at just 23.4 Gm, you can see that you don't need to replace the RA-15's at Eve. You still get a permanent link. Upgrading the Eve constellation as well would improve the signal quality, but nothing more.

If you don't have the RA-100 yet, you can also improve your satellites' antenna power by stacking multiple antennas. The equation for vessel antenna power is:
Vessel Antenna Power = Strongest Antenna Power * ( Sum of Antenna's Powers / Strongest Antenna Power ) ^ ( Average Weighted Combinability Exponent for Vessel )
...which looks super complicated, but in practical application ends up being far simpler than you think. As long as you only stack the same kind of antenna, it simplifies into (number_of_antennas^0.7) * antenna power.

Assuming you replace your Kerbin constellation with commsats that have three RA-15's each, that would give them an antenna power of 15G * (3^0.7) = ~32.4. Plugging this into the commlink range equation, you get SQRT 15G * 32.4G ) = ~22.0 gigameters. Meaning you can talk to Eve for 95% of the time, only dropping your link at the point of furthest separation. If your Kerbin commsats carried four RA-15's each, you'd have 100% link uptime.

Stacking RA-100's like this will eventually be your only way to maintain permanent links to really far out places like Jool and Eeloo without relying on the DSN.

[JedTech]

9 minutes ago, Streetwind said:

Commnet range is simply...

So basically you have to be able to read the Matrix in live time in order to know if your going to be able to communicate with your probe at Eve.

[Streetwind]

7 minutes ago, JedTech said:

So basically you have to be able to read the Matrix in live time in order to know if your going to be able to communicate with your probe at Eve.

No, you need to know how the square root button on your operating system's calculator app looks.  Literally nobody does this in their head. Unless you have the simple case of two identical antennas, which I dearly hope you are able to do in your head (hint: the entire equation removes itself).

[Spricigo]

2 hours ago, Streetwind said:

No, you need to know how the square root button on your operating system's calculator app looks.  Literally nobody does this in their head. Unless you have the simple case of two identical antennas, which I dearly hope you are able to do in your head (hint: the entire equation removes itself).

Have to disagree...I do it in my head.

But I only neeed to do it once, at design time. And I only need to know if [max link range] > [max distance].

[Streetwind]

...Very well, @Spricigo. Henceforth, your forum title shall be Literally Nobody.

 

(Now if only I actually had moderator powers to sneakily edit it in...)

[Spricigo]

9 hours ago, Streetwind said:

...Very well, @Spricigo. Henceforth, your forum title shall be Literally Nobody.

 

(Now if only I actually had moderator powers to sneakily edit it in...)

NO worry..Done

Edited February 21, 2018 by Spricigo
Oh" And a fitting profile picture too

[klesh]

2 hours ago, Spricigo said:

Oh" And a fitting profile picture too

 

You are my evil twin.