# CommNet

CommNet is a relay and control communication system implemented first in KSP 1.2 pre-release. With CommNet enabled (as a difficulty setting), antennae have limited range from which control and transmission of science data is possible. Vessels without a Pilot require a link to a control source for full control (valid control sources are a vessel with an operational Probe Control Point, or more commonly the Deep Space Network on Kerbin). Locations may be linked either through a direct connection or indirectly via one or more relays.

The following table lists the maximum range for vessels with a single antenna signaling the Deep Space Network:

Antenna Type Tracking Station Level (Rating)
1 (2G) 2 (50G) 3 (250G)
5k
Command pods (Built-in)
3.16Mm (25% way to Mun)
15.81Mm (Mun)
35.36Mm (75% way to Minmus)
500k
Communotron 16 / 16-S
BG: Control Station
31.62Mm (67% way to Minmus)
158.11Mm (Kerbin SOI)
353.55Mm (Kerbin SOI)
5M
HG-5 High Gain
100Mm (Minmus)
500Mm (Interplanetary around Kerbin)
1.12Gm (Interplanetary around Kerbin)
2G
DTS-M1 / RA-2
2Gm (Interplanetary around Kerbin)
10Gm (Moho, Eve & Duna when close)
22.36Gm (Moho always, Eve, Duna & Dres (barely) if close)
10G
BG: HG-48
4.47Gm
22.4Gm
50.0Gm
15G
HG-55 / RA-15
5.48Gm (Eve when close)
27.39Gm (Always Moho & Eve, Duna & Dres if close)
61.24Gm (Dres, Jool & Eeloo if close, other planets always)
100G
Communotron 88-88 / RA-100
14.14Gm (Moho, Eve & Duna when close)
70.71Gm (Jool & Eeloo if close, other planets always)
158.11Gm (all bodies always)

## Range calculation

Individual vessels do not have a fixed maximum range: whether a connection is possible between two vessels that are a given distance apart depends on the transmission strength of the vessels at both ends of the connection. Each antenna has a "power rating", measured as a unitless number, which contributes to the overall power rating of the vessel it is attached to. A connection can be established between two vessels when the geometric mean of their power ratings is greater than their separation as measured in meters. This is calculated as follows:

${\displaystyle Range={\sqrt {Vessel_{1}\times Vessel_{2}}}}$
Where:
• ${\displaystyle Range}$ is the maximum distance in meters at which two vessels can connect with each other.
• ${\displaystyle Vessel_{1}}$ and ${\displaystyle Vessel_{2}}$ are the power ratings for the vessels that are attempting to connect to each other.

Power ratings for antennae range from 5k for the integrated antenna available in every Command module, to 100G for the largest dishes. Kerbin's Deep Space Network can be treated as a vessel with a rating of 2G/50G/250G (depending on the level of the Tracking Station) for the purposes of calculating range.

If (by difficulty setting) there is only one tracking station, a ship must depend on a CommNet relay manally placed around Kerbin, here are the general ranges between antennae.

5k 500k 5M 2G 15G 100G
5k 5km 50km 158km 3.1Mm 8.6Mm 22.3Mm
500k 50km 500km 1.58Mm 31.6Mm 86.6Mm 223Mm
5M 158km 1.58Mm 5Mm 100Mm 273Mm 707Mm
2G 3.1Mm 31.6Mm 100Mm 2Gm 5.4Gm 14.1Gm
15G 8.6Mm 86.6Mm 273Mm 5.4Gm 15Gm 38.7Gm
100G 22.3Mm 223Mm 707Mm 14.1Gm 38.7Gm 100Gm

### Combining antennae

When a craft has multiple, combinable antennae, the antenna's power ratings stack in a way that provides diminishing returns using the following formula:

${\displaystyle {\text{Vessel Power}}={\text{Strongest Antenna Power}}\times \left({\tfrac {\text{Sum of Antenna Powers}}{\text{Strongest Antenna Power}}}\right)^{\text{Average Combinability Exponent}}}$

The vessel's Average Combinability Exponent is the average of the combinability exponent values of all antennas on the vessel, where each antenna is weighted proportionally to its respective power rating. Note that all antennae and relays have a combinability exponent value of 0.75 except for the Communotron 16 and the Communotron 16S, with values of 1.0 and 0.0 respectively. This means that the Average Combinability Exponent will always be 0.75 for a vessel containing neither of these antennae. For vessels with a Communotron 16 or 16S, the Average Combinability Exponent is calculated:

${\displaystyle {\text{Average Combinability Exponent}}={\frac {P_{1}C_{1}+P_{2}C_{2}+\cdots +P_{n}C_{n}}{P_{1}+P_{2}+\cdots +P_{n}}}}$
Where:
• ${\displaystyle \{P_{1},P_{2},\dots ,P_{n}\}}$ are the power ratings of each antenna.
• ${\displaystyle \{C_{1},C_{2},\dots ,C_{n}\}}$ are the combinability values of each respective antenna.

For example, a vessel with a Communotron 88-88 (100G power, 0.75 combinability) and also a Communotron 16 (500k power, 1.00 combinability) would have the following as its Average Combinability Exponent:

${\displaystyle {\frac {(100\times 10^{9})\times 0.75+(500\times 10^{3})\times 1.00}{(100\times 10^{9})+(500\times 10^{3})}}=0.75000125}$

Antennae combinability exponent values can be found under "antennaCombinableExponent" in the part configuration files. If the value is missing, the default value of 0.75 is used.

## Signal strength

The length of a communication link relative to its maximum range is represented by signal strength. Signal strength for a single-hop link starts at 100% at a distance of zero and decreases as distance increases, down to a signal strength of 0% at the maximum range of the link. The relationship is non-linear: the true value requires plotting the relative distance on a Bezier curve with the keys '0 0 0 0' and '1 1 0 0'. This can be calculated as follows:

• Calculate the relative distance between the vessels (the result should be between 0.0 and 1.0): ${\displaystyle 1-{\frac {\text{Distance From Link Point}}{\text{Maximum Range}}}}$
• Substitute the result above into the Bezier curve equation (cubic derivation): ${\displaystyle -2x^{3}+3x^{2}}$ or ${\displaystyle (3-2x)x^{2}}$

The result is the signal strength of the link at the specified distance. Note that the above applies to a single-hop link: if the signal is being bounced through one or more relays, the signal strength is the product of the signal strengths of each link making up the path to the control point.

### Example

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: ${\displaystyle 250\,000\,000\,000}$
• Max Power of Probe: ${\displaystyle 100\,000\,000\,000\times \left({\frac {200\,000\,000\,000}{100\,000\,000\,000}}\right)^{0.75}=168\,179\,283\,051}$
• Max Range of Connection: ${\displaystyle {\sqrt {(2.5\times 10^{11})\times (1.68\times 10^{11})}}=205\,048\,337\,625{\text{m}}}$
• Relative distance between Link Points: ${\displaystyle 1-{\frac {73.4}{205}}=0.642}$
• Signal Strength: ${\displaystyle (3-2\times 0.642)\times 0.642^{2}=0.707=71\%}$

Therefore the signal strength for this connection would be 71%.

### Science Transmission

If CommNet is enabled in the difficulty settings, then transmitting science through a connection with high signal strength will give a bonus the transmission efficiency of up to 40% (to a maximum of 100% value). This bonus decreases non-linearly with signal strength. For example, a Gravity Scan from low Jool orbit would give 90*0.4=35 Science if transmitted with CommNet disabled or over a marginal connection, but if transmitted through a connection with an overall strength of 100% would give 90*0.4*1.4=50.4 Science.

## Connections through relays

You can use ships with relay antennae to boost a weak signal or to transmit a signal when obstructed by a celestial body. You only need a ship with a probe core, a relay antenna, electricity and ways to generate it. You don't need to focus on your relay ship to relay a signal, it will be relayed automatically.

When considering the antenna power of your vessel, direct antennae and relay antennae combine to give you a 'Power' to calculate signal strength back to the KSC, however, if a different vessel is connecting through you to communicate with the KSC the direct Antennae are disregarded in any calculations made.

### Example

• A vessel with a Communotron 88-88 direct antenna and a RA-100 relay antenna orbiting around Eeloo at a distance of 105Gm from the KSC, with a Level 3 DSN, will connect back to the KSC with a signal strength of 48% as both antennae combine to give an increased antenna 'Power' for its own direct connection.
• A vessel rendezvoused with the above craft with a measly Communotron 16 will have to communicate back to the KSC through the relay as its antenna is not strong enough to communicate with the KSC directly. As this small, probe craft will only consider the RA-100 Relay Antenna on the relay craft when calculating its connection back to the KSC, the power rating of the relay vessel drops and therefore the signal strength will drop to 26% (please note the calculations for these numbers have been obfuscated from the example for easy understanding of the concept).

Relaying data does not consume electrical power, in contrast to transmitting science directly from a vessel containing science.

The game always favors a direct connection to Kerbin even if a more powerful relay is nearby.

## Effects of signal loss

Depending on your difficulty settings, several effects occur when the CommNet signal is lost, either from the KSC or a probe control point. This could be due to either electricty loss, out of CommNet range, or an antenna destruction. There is also a setting where you can force the signal to blackout when entering a body's atmosphere too fast.

• Manned without a pilot: You will lose the ability to create maneuver nodes, or delete existing ones
• Probe, require control unchecked: Your probe will lose three capabilities : rotation control (roll, yaw, pitch), precise thrust control (only 0 or maximum), and the ability to create or remove maneuver nodes. If your probe is capable of locking a maneuver axis through SAS, it is advised to create a maneuver node before transmission blackout (passing behind a body) to allow the ship to perform the maneuver.
• Probe, require control checked: You will completely lose control of your probe. Either wait for it to go back to a CommNet range, or send a ship with a probe control point capability to do general maneuvers (deploy solar panels, precise control,...).

SAS isn't transmitted by the KSC or a probe control point. If you cannot SAS, either look if your probe is controllable (batteries, CommNet range) or has a pilot onboard. The level of SAS depends on the ship itself (probe SAS levels or pilot level).

## Difficulty Settings meanings

Setting When OFF When ON
Activate CommNet All ships have full control and can plot maneuver nodes wherever they are. If they have an antenna they can transmit science from anywhere. Ships behave differently depending on they CommNet status, see below
Required signal for control When out of range, probe-only ships go into partial control (same as hibernation) where they can only lock to available SAS axis and throttle at 0 or 100% When out of range, probe-only ships will completely lose control
Plasma blackout Atmospheric re-entry has no effect on CommNet Atmospheric re-entry lowers the signal strength, you can hover the network icon in the telemetry bar to see how many
Range Modifier The value of this slider is a multiplier value that is applied to the power levels of all antennae
DSN Modifier The value of this slider is a multiplier value that is applied to the power level of the DSN Network
Allow additionnal ground stations There is only one ground station: the KSC Kerbin is covered with a lot of tracking stations that have the same level than the KSC

## 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

One method of setting up a full-system network can be found at Tutorial:Setting up a CommNet system.