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)|
- 1 Range calculation
- 2 Signal strength
- 3 Connections through Relays
- 4 Effects of signal loss
- 5 DSN Strength
- 6 Science Transmission
- 7 Difficulty Settings
- 8 Tutorials, Calculators and Examples
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:
- is the maximum distance in meters at which two vessels can connect with each other.
- and 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.
When a craft has multiple, combinable antennas, the antenna's power ratings stack in a way that provides diminishing returns using the following formula:
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 antennas 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:
- are the power ratings of each antenna.
- 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:
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.
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):
- Substitute the result above into the Bezier curve equation (cubic derivation): or
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.
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:
- Max Power of Probe:
- Max Range of Connection:
- Relative distance between Link Points:
- Signal Strength:
Therefore the signal strength for this connection would be 71%.
Connections through Relays
When considering the antenna power of your vessel, Direct Antennas and Relay Antennas 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 Antennas are disregarded in any calculations made.
- 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 antennas 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).
Please keep the above in mind when creating relay vessels for you other craft to connect through in the depth of space.
Another issue to keep in mind when creating relay vessels is that relaying data does not consume electrical power, in contrast to transmitting science directly from a vessel containing science.
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.
SAS doesn't depend on the CommNet signal. It depends only on the ship's ability to use SAS (pilot or capable probe, kerbal XP or all probes have SAS settings).
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,...).
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.
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 tranmitted through a connection with an overall strength of 100% would give 90*0.4*1.4=50.4 Science.
Activate CommNet = If unchecked, all ships have full control, antennas still work but are just used to check range.
Required signal for control = Unchecked : probes have limited actions when out of range (full thrust only, SAS,...). Checked : probes will be uncontrollable until back in range.
Plasma blackout = If checked, a fast atmospheric re-entry might block the signal and put a probe in an uncontrollable state.
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.
Allow additional ground stations = Adds antennae on the surface of Kerbin, or else only the KSC has an antenna and you must build your own Kerbin relay sat system.
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.