Sensors

There are three types of sensors in Aurora, Active Grav Sensors, passive Thermal Sensors and passive EM (electro-magnetic) sensors. Active Sensors are needed for target acquisition, but may give away your position. Passive sensors don't give you as much information as actives, but they could allow you to stay undetected.

Note that every military and commercial ship has intrinsic thermal and EM sensors of strength 1 (not listed as components).

Active Sensors

Active sensors consist of grav pulse sensors and allow a ship to detect other ships or missiles equal to or above it's stated resolution size within it's stated range. The tradeoff is that progressively stronger active sensors can themselves be detected by passive EM sensors, which can prove a serious tactical vulnerability.

Passive Sensors

See Beam Warships for an in depth explanation of this technology.

The basic calculation is :

 detection distance = sensitivity * signature strength * 1000km

You can view the passive sensors' detection radius of your ships and installations in the System Maps window by adjusting the Sensors tab values. If you think a 500-strength contact might be out there somewhere, move the slider to 500 and you'll at what distance your sensors would pick it up.

Thermal Sensors

Passive sensors that detect thermal signatures such as Engines, reactors and colony activity. An engine's heat signature is usually equal to its power, but can be reduced by Thermal Reduction tech making your engines harder to detect by this type of sensor. Traveling at less than full speed also reduces engine heat. You can set the speed in the Task Group window.

A few more or less typical thermal signatures, early-mid-game tech:

 Size 4 Missile                  8
 1,000-ton gunboat              88 (no thermal reduction, thus equal to engine power)
 38,000-ton freighter         1350 (they use a lot of big engines)   
 4,000-ton frigate             123 (would have 352 without thermal reduction tech)
 6,200-ton alien cruiser       640 (probably not thermally shielded)
 Mars colony, pop. 67m       7,600
 Earth, pop. 1.5 billion    22,500

A strength-28 (sensitivity 14, size 2) Thermal Sensor, small enough to fit on most ships, would detect them at:

 Size 4 Missile            224,000 km  
 1,000-ton gunboat            2.2m km  
 38,000-ton freighter        37.8m km   
 4,000-ton frigate            3.4m km
 6,200-ton alien cruiser     17.9m km
 Mars colony, pop. 67m      212.8m km
 Earth, pop. 1.5 billion    630.0m km

Not ideal, but at least a ship equipped isn't completely blind. And if you doubled the size, you'd double the range. If you equipped a ship with a thermal sensor 10 times that size (size 20, or 1,000 tons), it would spot the cruiser at 179m km, which is pretty sweet. Just remember that it wouldn't tell what the contact is, just how hot it is. And you can't fire at thermal contacts, unless you play around with missiles that have active sensors, but that's a different matter.

And the size-20 sensor would detect the Earth or Mars colonies from anywhere in the solar system.

EM Sensors

An EM Sensor is a passive sensor that detects EM signatures, similar to the thermal sensor picking up heat signatures. These can be used to detect a ship's shields (if active?), Active Sensors (if active) or the presence of colonies on a planet. Note that many ships will not emit any EM at all, unless they switch on their actives.

Also note that Earth, in the above example game, has an EM signature of 95,000. That means EM sensors are particularly useful for finding enemy colonies.

Other Sensors

Geological Survey Sensors - These generate Geo Survey points, which are used to determine environmental and mineral properties of a stellar body.

Gravitational Survey Sensors - These are used to detect jump points.