CommNet is a relay and control communication system implemented first in KSP 1.2 pre-release. Probes now have limited attitude and thrust control if they are not linked back to Kerbin or a control point via a relay antenna.  Antennae have limited range from which control and transmission of science data is possible.
|Tracking Station Level||5k (Probes / Manned)||500k (Communotron 16)||5M (HG-5 High Gain)||2G (DTS-M1 / RA-2)||15G (HG-55 / RA-15)||100G (Communotron 88-88 / RA-100)|
|1 (2G)||3.16Mm (25% way to Mun)||31.62Mm (67% way to Minmus)||100Mm (Minmus)||2Gm (Interplanetary around Kerbin)||5.48Gm (Eve when close)||14.14Gm (Moho, Eve & Duna when close)|
|2 (50G)||15.81Mm (Mun)||158.11Mm (Kerbin SOI)||500Mm (Interplanetary around Kerbin)||10Gm (Moho, Eve & Duna when close)||27.39Gm (Always Moho & Eve, Duna & Dres if close)||70.71Gm (Jool & Eeloo if close, other planets always)|
|3 (250G)||35.36Mm (75% way to Minmus)||353.55Mm (Kerbin SOI)||1.12Gm (Interplanetary around Kerbin)||22.36Gm (Moho always, Eve, Duna & Dres (barely) if close)||61.24Gm (Dres, Jool & Eeloo if close, other planets always)||158.11Gm (all bodies always)|
Please Note: The above table presumes only 1 antenna/relay is used on a vessel signalling back to Kerbin's DSN.
Each antenna has a "power rating" measured in meters. It ranges from 5k (5000m) for integrated default antennas available in every spacecraft, to 100G (100 billion meters) for the largest dishes. A connection can be established between two stations (craft to ground, or craft to relay) when the square root of the product of the strength ratings is greater than the distance between the two objects. When a craft has multiple, combinable antennas, the antenna's power ratings stack in a way that provides a diminished return using the following formula:
- Vessel Antenna Power = Strongest Antenna Power * (Sum of Antenna's Powers/Strongest Antenna Power)^(Average of Combinability Exponents for All Antennas)
The range can then be calculated as stated above by taking the square root of the product of the two Antenna Strength ratings
- Range = SQRT ( Antenna Strength 1 * Antenna Strength 2 )
Please Note: All Antennas and Relays have a Combinability Exponent value of 0.75 except for the Communotron 16 having a value of 1 and the Communotron 16S having a value of 0. These values can be found in the part config files.
To obtain your signal strength for a link at any given distance between the two points it is mostly the relative distance between the two points. The true calculation requires plotting the relative distance on a Bezier curve with they keys '0 0 0 0' and '1 1 0 0' to obtain the true Signal Strength. This can be calculated as follows:
- 1 - ( Distance away from 'Link Point' / Max Range of Antenna Link ) = 0 < x < 1 (as a fractional percentage)
- Substitute the result above into the Bezier Curve equation (Cubic derivation) of y = -2x³ + 3x² = (3-2x)x²
This will give you the Signal Strength between the link at your specified distance.
Calculating the Signal Strength between a Level 3 DSN Tracking Center and a probe around Jool at a distance of 73.4Gm from Kerbin with two Communotron 88-88 antennas.
- Max Power of Lvl 3 DSN connection: 250,000,000,000
- Max Power of Probe: 100,000,000,000 * (200,000,000,000 / 100,000,000,000)^0.75 = 168,179,283,051
- Max Range of Connection: SQRT( 2.5E11 * 1.68E11 ) = 205,048,337,625m
- Relative distance between Link Points: 1 - ( 73.4 / 205 ) = 0.642
- Signal Strength: y = (3-2x)x² = (3-2(0.642))*(0.642)² = 0.707 = 71%
Therefore the Signal Strength for this connection would be 71%.
Each upgrade of the tracking center improves the strength of Kerbin's terrestrial-based Deep Space Network (DSN). Based on the provided figures, the Level 1 tracking station has an antenna strength of 2G, Level 2 is 50G, and Level 3 is 250G.
The same document from the KSP developers states that science returned via a relay satellite will have a bonus applied (some fraction of the difference between the recovery and transmission science potential). The exact amount of the bonus depends upon signal strength. The amount of available Science Points you can transmit back to the KSC depends on your Signal Strength and the total potential value of the experiment.
Any experiments transmitted will be multiplied by the percentage of your connection, therefore an EVA Report high over the Mun (24 Science) at a Signal Strength of 68% would allow you to transmit a total of 16 Science points back to the KSC.
Range Modifier = The value of this slider is a multiplier value that is applied to the power levels of all Antenna and Relay parts.
DSN Modifier = The value of this slider is a multiplier value that is applied to the power level of the DSN Network.
Tutorials, Calculators and Examples
A Google Sheets document that can help calculate Signal Strength and Ranges for you can be found here: CommNet Signal Strength Calculator & Antenna Selector
Example orbits for setting up a planetary network can be found at: Tutorial:Ideal Orbits for Communication Satellites