Difference between revisions of "CommNet"

Revision as of 21:04, 14 November 2022

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). Locations may be linked either through a direct connection or indirectly via one or more relays.

Deep Space Network

The Deep Space Network (DSN) is the array of CommNet groundstations on Kerbin, including the Tracking Station at the Kerbal Space Center and (depending on your difficulty settings) various antennae scattered over the planet's surface.

The following table lists the maximum range for vessels with a single antenna signaling the Deep Space Network (note these change with Range Modifier in CommNet difficulty options):

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:

${\displaystyle Range={\sqrt {Vessel_{1}\times Vessel_{2}}}}$

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.

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:

${\displaystyle {\text{Average Combinability Exponent}}={\frac {P_{1}C_{1}+P_{2}C_{2}+\cdots +P_{n}C_{n}}{P_{1}+P_{2}+\cdots +P_{n}}}}$

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.

Relay Networks

Establishing a network of satellites around each planet can permit continuous communication back to KSC even for craft on the far side of the body. A minimum of three relay satellites per body is necessary to ensure continuous coverage. The satellites must be deployed in an equilateral triangle formation along a circular orbit or else there may be black-out periods. The minimum altitude for each satellite is the parent planet's radius, plus the altitude of the tallest peak on the surface. The easiest way to establish such a network is to plot an elliptical orbit for the conveyor, where the apoapsis is the desired altitude for the satellites' circularized orbit and the periapsis is such that the total period is 2/3 the relay period. Thus, each time the conveyor reaches apoapsis it can deploy a relay satellite. Example: To deploy three satellites around Kerbin, an elliptical orbit with altitudes of (2 868 751m , 1 225 553m) has a period of 4 hours, which is exactly 2/3 of 6 hours, which is the period of a circular orbit with an altitude of 2 868 751m.

The chief benefit to establishing these relay networks around the planets is one's missions no longer need to each carry a high-power antenna; in many situations the craft only needs a Communotron 16, or even the intrinsic 5K, and can rely on the relay when entering the target's SOI. All moons can reach their parent planet with nothing more than a HG-5 High Gain Antenna, provided there is a relay network in orbit around the parent planet, so one only needs to worry about calculating connectivity between the planet and KSC. Example: An HG-5 orbiting Pol is strong enough to connect to an RA-15 orbiting Jool, which means a craft operating within Pol's SOI could rely on the intrinsic 5K antenna to maintain a link with KSC via the DSN, rather than being encumbered with a more powerful antenna.

The following table lists minimum antenna power and configurations for each of the planets.

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

• Based on circumstantial evidence, the default DSN disabled groundstation antenna rating is approximately 36k, but CommNet prefers extra hops to the DSN on Kerbin, if a signal path is available.

The CommNet ranges of DSN disabled groundstations are:

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

An interactive tool for visualizing signal strength depending on planetary positions can be found here: KSP Visual Calculator

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.