CommNet questions

[Bandus]

Greetings! I've finally worked on building my first CommNet, but I find myself a bit confused after reading https://wiki.kerbalspaceprogram.com/wiki/CommNet and doing some searching here on the forums. Here is my situation:

• Level 2 Tracking Center
• 4 Satellites orbiting Kerbin at an altitude of ~777km (Screenshot:https://i.imgur.com/Po3BR5g.png)
  • Each satellite has 4 antennas. Three RA-2s and one 16-S
  • Two RA-2s from each dish are pointed at sibling satellites. One RA-2 is available for tasking as needed. One 16-S is used for comms with Mission Control

My confusion is, the RA-2 has a stated range of 200Mm which, as I understand it means 200,000,000 meters. As a result, my expectation was that this commnet would be good for unmanned missions to Minmus or closer. However, on the CommNet wiki page (specifically the table on top) it states that with a level 2 tracking center and a RA-2 that the range is 10Gm or all the way to Moho (if it is close). I am unclear how it could possibly have that range with the RA-2 only have a max range of 200Mm.

Can someone help me understand what I'm missing? Thank you!

Edited March 8, 2018 by Bandus

[Superfluous J]

Antenna-to-antenna range is far less than antenna-to-tracking-station range. Though I didn't realize it was that much lower.

[Bandus]

2 minutes ago, 5thHorseman said:

Antenna-to-antenna range is far less than antenna-to-tracking-station range. Though I didn't realize it was that much lower.

I'm not sure I follow. Does that mean that 200Mm is the range (I realize it's not exactly 200Mm necessarily) if a RA-2 is pointed at another RA-2, but, if a RA-2 is pointed at a level 2 tracking station, then it's 10Gm?

[Superfluous J]

I didn't have time to more fully answer before, but I was able to load the game and I can now make things a little more clear.

4 hours ago, Bandus said:

• Each satellite has 4 antennas. Three RA-2s and one 16-S
• Two RA-2s from each dish are pointed at sibling satellites. One RA-2 is available for tasking as needed. One 16-S is used for comms with Mission Control

This is totally mostly unnecessary. You don't need to "point" antennas at anything. All you need on the ship is one relay antenna (or more if you want to stack them to make the signal go further) and it'll automatically point at anything, all the time. This means that to talk to Kerbin from the far side of Minmus, you can have a single relay antenna on a satellite on the far side of Minmus (but in view of Kerbin) and it'll happily relay the signal to Kerbin.

4 hours ago, Bandus said:

RA-2 has a stated range of 200Mm

The RA-2 does not have a "range" per-se. It has a "rating." that rating is 2.00G. That means that with a Level 1 tracking station, it can talk to Kerbin from 2Gm away. With a level 2 tracking station, that's 10Gm away. With a Level 3, that's 22.4Gm away. I didn't memorize these numbers, I got them from the stats of the part when right clicking it in the VAB:

This rating (2.00G) makes it a "Class 3" antenna, which I think matches the table in the wiki. But it surely matches the table in KSPedia, in the game. Click the book with the A on it in the lower right of the VAB and go to Comm Netowrk -> Commnet -> Range and you'll see:

Pretty much ignore anything other than this that you see, unless that thing is easier to use and also matches with this table

tl;dr I don't know where you got "it's a 200Mm rating" from, but that's basically and blatantly wrong.

Edited March 9, 2018 by 5thHorseman

[HebaruSan]

I believe the maximum functional range for a given pair of endpoints to talk to one another is:

sqrt(rating1 * rating2)

where the rating is the sum of each craft's relay antennae ratings, and M=1000000m and G=1000000000m. As @5thHorseman stated above, the RA-2 has a rating of 2G. The level 2 tracking station is 50G. So they can talk to each other up to:

sqrt(2000000000*50000000000)=10Gm

which is 75% of Kerbin's orbital radius, so you'll be in contact part of the time for most planets depending on their alignment. Note this is the same as on the table. If you upgrade the tracking station one more level it goes to 250G, which gives you:

sqrt(2000000000*250000000000)=22Gm

also as per the table. This is approximately Duna's orbital radius, but the distance between Duna and Kerbin ranges from (Radius of Duna - Radius of Kerbin)=7Gm, to (Radius of Duna + Radius of Kerbin)=33Gm. So a 22Gm connection would also give you partial connectivity, but more of the time.

The product/square root relationship has some nice properties. For example, suppose you need to double a craft's range (a good idea for Duna with R-2's). Suppose its current rating is R, so its current maximum distance from a level 2 tracking station is: D=sqrt(R*50G). To boost it to 2*D, you need:

2*sqrt(R*50G) = sqrt(4*R*50G)

which is the formula for a craft with rating 4*R. In other words, you can quadruple its current array of antennae to double the range.

[Bandus]

1 hour ago, 5thHorseman said:

l;dr I don't know where you got "it's a 200Mm rating" from, but that's basically and blatantly wrong.

I am running RemoteTech and I didn't realize that it changed the stats of the RA-2. You've absolutely answered my question though. Thank you!