Sensors are the primary means by which a starship can sense the sector around it. Since updates from anywhere in the sector appear to be instantaneous, sensors must work by some form of FTL technology. Sensors come in three types: Short Range Sensors, Long Range Sensors, and Targetting Scanners.
Short Range Sensors
Short Range Sensors are the most commonly used sensors. They have a range of about 7500, and are used to generate the view shown on the Main screen. Any enemy ship which enters this range will be automatically scanned, displaying its type and shield strength. The Science officer will still have to scan the ship a second time to determine its shields frequencies and Intel report.
Objects on the Main screen will not appear until they get within this range. Nebulas will actually fade in gradually until they reach the 5000 mark, at which time they will be completely visible. Black Holes also appear rather suddenly, at slightly less than the standard range of 7500. Most ships are too tiny to see clearly at this range, but some generic objects in missions (like planets) can appear out of nowhere at a fraction of full size as you approach them.
Short Range Sensors is sometimes called "Visual Range", although of course the view the Main screen represents is not a visual representation of the Artemis's view. (The Artemis can even be visible on the screen, making it a third person view) Ships are not hidden from Short Range Sensors when they are in a Nebula, as they are with Long Range Sensors.
Long Range Sensors
Long Range Sensors are the most powerful sensors on the Artemis. They also come in two types; Passive Sensors, and the Active Sensors controlled by the Science officer. Passive Sensors detect all moving and unmoving objects in the sector, including asteroids, mines, and other stellar phenomena. Passive sensors are blocked by nebulae, and can be fooled by enemy ships with stealth technology. It is likely that friendly ships broadcast an identifier signal so the Artemis can identify them, and the friendly bases may provide maps of the permanent features (Black Holes, Nebulae) in the sector. (Which explains why they can be seen outside of the Artemis's sensor range)
Active Sensors are directly controlled by the Science officer, and can penetrate Nebula, locate Anomalies, and scan ships for their energy signature, identifying them and displaying their shield strength and frequency. The Science officer's scans are directly tied in to a database of all known enemy ships and their captains, providing valuable Intel on the ship gathered by TSN agents. Until an enemy ship is scanned by Active Sensors, it cannot be identified, so such ships will show up as generic grey markers on the LRS and Science console.
Although the Tactical screen has a shorter range than the Long Range Scan screen, it appears to use the same Passive Sensors for input, as it does not show enemy ships that are in Nebulae. It also has much longer range than the 7500 range for Main screen. The compass rose on the Tactical screen appears to be about the 16000 mark, while depending on resolution, the whole screen can be as much as 30,000 units, which can be more than the range of Long Range Sensors, depending on the setting.
The maximum range for Long Range Sensors depends on the setting on the server setup screen under the "Sensors" setting. This setting ranges from "Unlimited", which shows everything in the sector, to 8k, which is only marginally better than the range of Short Range Sensors. Note that friendly bases have Long Range Sensors as well, and Science can access both their Active and Passive sensors, extending the range of their scans. Base sensor range is normally the same as ship sensor range (and is effected by the same Sensors setting) but this can be changed in artemis.ini.
Targetting Scanners
Targetting Scanners are used by the Artemis's weapons systems to get a target lock on an enemy ship. The Targetting Scanners are part of Short Range Sensors, but have a range of only 5000. This range is indicated on the Weapons officer's display as a grey circle. At Zoom level 4, the grey circle exactly corresponds to the compass rose on this display. Ships will not appear outside of this circle, as they cannot be targeted beyond this range.
Targetting Scanners appear to overlap somewhat with Long Range Sensors, as they are able to identify enemy ships and determine their shield strength. Active Sensors are still required to determine an enemy ships' shield frequency, but in the absence of a Science Officer the Weapons Officer is still able to view a simplified representation of a nearby ship's shield strength and facing, and tell when an enemy or friendly ship's shields fail.
Although Helm does not have to target enemy ships, Helm makes use of this targeting system as well. The grey circle marks the 5000 range, and enemy ships cannot be seen outside of this range. Potential collision threats, such as asteroids and mines (including the Artemis's own mines) will only appear within this circle as well. Nebulas and other large objects can appear outside of this range. This may suggest that the precise location of physical objects, such as asteroids, can only be determined at a range of 5000, even though they can be detected at 7500 range.
(This discrepancy between targeting range and visual range may go back to the very first version of Artemis. In that version, they were the same range. In Artemis 1.4, the main screen view distance was changed to its current value, presumably because it was annoying to have objects appear "out of nowhere" on the screen)
Ultrawave Communications
The communications systems used by the Artemis, like its sensor systems, make use of faster than light technology. In fact, all five races in the game appear to make use of the same technology, referred to as "ultrawave". The Terrans developed this technology independently, in order to facilitate communications between its colonies, only to find that the Kraliens used the same ultrawave communications when they made first contact.
Ultrawave messages seem to be able to transmit audio as well as data, and are usually sent as a broadcast message on a common channel. That is, messages are identified by their sender and usually an intended recipient, but they can be heard by any ship or base station in the sector. Less commonly, signals may be sent over longer distances, directed at a particular target, and these messages typically cannot be intercepted unless the intercepting ship is along the path of the signal. Messages may be relayed from base station to base station until they get within the same sector as their intended target.
All of the messages sent within the standard Artemis game modes will be either player to enemy ship, player to player, player to base station, player to ally ship, enemy ship to player, base station to player, ally to player, or enemy to enemy. Scripted missions, however, open up limitless additional possibilities, including messages from TSN Command, which is well outside of the sector. The Intel that Science displays when scanning a ship may actually come from a TSN Command database, which is transmitted to the ship via ultrawave and stored in its own library.
TSN communications systems automatically convert speech to a text record for clarity and ease of retrieval. It also includes translation software for alien races that do not speak Terran or can't be bothered to learn it. The Comms officer normally interacts with the communications system through a computer interface, although a microphone/earpiece may also be used. Although video communications are not used onboard TSN starships at this time, personal communications often involve video images. Most base stations are capable of transmitting and displaying video ultrawave messages.
(The name "ultrawave" comes from the Artemis 1.7 game manual. It is not found in any other canon documents, but seems like a descriptive name for the technology. The nature of this technology is unspecified, but it most likely makes use of tachyons, particles that move faster than the speed of light. Other possibilities could be micro-wormholes or the use of quantum entanglement)