CommNet range question

[ThirdHorseman]

Long time player back with a new Career save in 1.12 and I'm still trying to wrap my head around using the CommNet.

So I think I understand range calculations and all that, I just want to make sure I'm reading all this correctly.   I have my Tracking Station upgraded to level 2 and I have the additional ground stations turned off.  I have three relay sats in a 777k equatorial orbit around Kerbin, each with two HG-5 relay antenna.  I want to setup some ground science on the far side of the Mun, so I am planning on putting three of the same relay sats (dual HG-5) in orbit around the Mun.  But from my calculations that will not be sufficient to connect with KSC since the HG-5 only has a 5M power (~10M with the two, not sure about the combinable factor).  So even assuming a full 10M power the relay sats around the Mun will not be able to connect to the relay sats around Kerbin, correct?

Or does the fact that the relay sats around Kerbin connect to the Tracking Station increase the power?  I believe the range calculation is just between the two sats that are talking, not including everything in the relay?

Thanks for any help!

[Streetwind]

Vessel antenna power = strongest antenna * ( sum of antennas / strongest antenna ) ^ Combinability

Combinability is always 0.75, except for the starter antennas.
So: 5,000,000 * ( 10,000,000 / 5,000,000 ) ^ 0.75 = 5,000,000 * ( 2 ) ^ 0.75 = 5,000,000 * 1.6818 = 8,409,000

Maximum Range = SQRT(Vessel_1 power * Vessel_2 power)

When the two vessels are identical, you're just taking the square root of a square, so the result is always the vessel's own power: 8,409,000

The Mun's orbit is perfectly circular with a semimajor axis of 12,000,000 meters. Therefore, you are correct: these satellites will not be able to establish a connection. Even three HG-5 per satellite would fall just ever so slightly short. Four would work, but with terrible signal quality.

Honestly, Mun/Minmus exploration without a DSN connection somewhere in the mix requires jumping through hoops until you unlock the 160-point node that contains the DTS-M1 and RA-2 antennas. It might be worth to just accept that your Mun rely satellites will only link back to Kerbin while the KSC is above the horizon from their view. This should not be a great problem for the science ground station, as it is perfectly capable of waiting for a valid comms link before transmitting its latest batch of science. And you'll still have a link for an entire half of each day anyway.

 

30 minutes ago, ThirdHorseman said:

I believe the range calculation is just between the two sats that are talking, not including everything in the relay?

Correct, no third party ever influences the connection between any two given antennas, except perhaps for a celestial body eclipsing one of them.

 

Edited September 7, 2021 by Streetwind

[Blaarkies]

Someone made a visual tool for figuring out CommNet satellite constellations, maybe this helps

https://ksp-visual-calculator.blaarkies.com/

[jimmymcgoochie]

As a rule, assume the HG-5 will be useless as a relay beyond LKO and you’ll be fine. The RA-2 is several hundred times more powerful for not much increase in cost and weight- which when you consider the cost of multiple HG-5s is actually a significant discount for both- and is well worth the effort of unlocking before building a Mun relay network. You’ll need to time your probe missions so they arrive at the Mun when the KSC is facing it to have control for landings until then though.

[ThirdHorseman]

Thanks all, I was pretty sure I understood the system but I was curious since most tutorials just talk about connecting back to the DSN....not from relay-to-relay.

[Blaarkies]

23 hours ago, jimmymcgoochie said:

As a rule, assume the HG-5 will be useless as a relay beyond LKO and you’ll be fine. The RA-2 is several hundred times more powerful for not much increase in cost and weight- which when you consider the cost of multiple HG-5s is actually a significant discount for both- and is well worth the effort of unlocking before building a Mun relay network. You’ll need to time your probe missions so they arrive at the Mun when the KSC is facing it to have control for landings until then though.

The HG-5 works perfectly well out to Minmus even at Hard difficulty with a Tracking Station level 1. It really made the Caveman Challenge so much easier by just sticking to the HG-5.

It has a strong direct connection at that distance (in orbit around Minmus), and can relay to other HG-5s beyond Minmus' sphere of influence. It is by no means a permanent "long term" solution to having a CommNet in Kerbin's SOI, since it can't relay much farther than either of the moons' SOIs (say from Minmus to Mun, if the other spacecraft is in Kerbin's commnet shadow).

Edited September 9, 2021 by Blaarkies