Silent Running mode can be activated to reduce the visibility of a ship to others, allowing it to remain undetected and making it harder to be targeted.
The visibility of a ship depends on its heat signature - that is the amount of heat that it generates. A high heat signature means that the ship will be easier to see on the sensors of other ships and can be detected from further away.
All powered ship modules (including the reactor) generate heat. When a module's thermal limit is exceeded, heat is transferred to the ship’s cooling system which radiates the heat away from the ship via cooling vents. If more heat is being generated than radiated, the excess heat will build up in the modules, causing overheating. When heat levels exceed set thresholds, some modules may automatically turn off or begin to suffer damage. Excessive heat puts a strain on the ship’s atmosphere control, reducing the capability of life support modules. Further increase in heat directly impacts the pilot and crew’s ability to function and will eventually kill them.
Most ships have articulated heat vanes which can be raised, significantly increasing heat dissipation from the ship. However, such activity normally affects the flight model of the ship and always increases the ship’s thermal signature whilst active. Heat stored in a ship’s cooling system generates a thermal signature for the ship; a high signature makes it easier for other ships to locate it using heat-based sensors, and for heat-tracking weapons to lock on.
Engaging Silent Running
When silent running is engaged, shields immediately go offline (and won't recharge until silent running is disengaged), and the cooling vents of the ship shut, preventing any heat from escaping. The heat signature dramatically reduces, causing the ship to become more difficult to detect on nearby ships’ scanners. The less heat a ship generates and the farther away it is from another ship, the more effective this will be.
Heat generated by any active ship systems and modules starts to build up inside the ship, causing the ship’s temperature gauge to rise.
Using systems that generate heat (such as firing energy weapons) while in silent running will cause the ship to show up on other ships’ scanners.
The heat signature may be reduced even further while in silent running by switching off non-essential ship modules (even including life support). The total current heat output of active systems on the ship can be seen on the Modules section of the right-hand systems panel, and individual modules can be toggled on and off from this screen.
To go totally dark (i.e. completely undetectable), the ship must generate virtually no heat, to the point where it is so cold that ice forms on the cockpit canopy, with weapons stored in their bays and engines turned off.
Silent running never, by itself, hides a ship completely from the scanner. It will make the ship appear as a "ghost" or "vague" contact though, so other pilots will know something is there but they won't be able to lock on to it.
- Main article: Heatsink Launcher
Heatsink Launcher modules can be fitted to Utility Mounts. When activated (i.e. fired), a heat sink module flushes the cooling system’s heat into a heat sink, an expendable unit which is then ejected from the ship. This will cause a blip to be generated on the scanners of any nearby ships. Ejected heat sinks can also be used as a form of chaff against heat tracking missiles, causing them to lock on to the sink instead of your ship (n.b. This is not a behaviour of regular chaff, which only disrupts enemy gimballed and turret weaponry, so does not affect missiles that have already been launched).
(This info needs to be cleaned up and the info put into the above...)
From Sandro Sammarco (Lead Designer- Elite: Dangerous)
Just thought maybe I could help out with explaining "rigged for silent running".
Ship heat: As you power draw increases (from turning on modules that require power), your power plant generates heat inside the ship. This is represented by the heat bar to the left of your sensor disc.
The effects of heating up your ship are that eventually some systems might shut down and the ship will start taking damage - effectively cooking itself.
Separately from this, your ship has a signature, which describes how visible you are to other ship's sensors. As heat is radiated out, your signature increases. This radiation rate is not the same as your internal ship heat, though obviously there is a direct connection. The hotter your ship is, the more heat it's radiators put out, and the bigger its signature.
When you rig for silent running, you close off your ship's radiators. Your ship still generates heat and cooks, but to other vessels it appears cold. As part of silent running you also turn off shields as the context is that these effectively radiate heat directly.
So how does signature work? Well, the smaller your signature, the closer a ship has to be before its sensors will detect you as a fuzzy contact (where the sensor marker flickers and moves around) and then as a resolved contact.
You can gain a similar benefit that silent running gives you by manually turning off modules. Your power plant runs cooler so less heat is generated and radiated. However, unless you basically turn off everything (including life support) the effect will be less effective.
There are two caveats to silent running benefits:
A) when your ship gets very close to another vessel its sensors will be able to detect you even if you are rigged for silent running. This auto-resolve distance is normally around two to three hundred metres.
B) ships can be fitted with more powerful sensors that increase the distance that they can detect you, and that can push the auto-resolve distance out to around five hundred metres or more (good sensors are the silent runner's worst nightmare).
All this being said, silent running can be used during combat, but it's a very dangerous gambit. Missiles, turrets and gimbal-mounted weapons *do* use signature to determine when they can lock on, so going silent can often make them lose lock until you are very close. In fact, if you rig for silent running and you're not within auto resolve distance then an aggressor will not even be able to target you to check your shield/hull status.
Silent running is certainly most effective at range, of course, out beyond the auto-resolve distance.
It's also important to note that we specifically did not want a "cloak" stealth ability that was indefinite, which is why silent running has various limitations.