Starship Navigation
Navigating a starship across vast interstellar distances requires an enormous amount of data and precise sensors which can pinpoint the vessel's position. Federation starships navigate around the Milky Way Galaxy by combining a massive database of information with sophisticated onboard sensors that can pinpoint the vessel's position accurately. Typically a Starfleet vessel can calculate its position relative to the galactic center, or another defined reference point, such as a specific planet, to within 10 kilometers; even at high warp speeds, the ship can determine its location to within 100 kilometers. In close maneuvering of the kind required when docking, a starship can maneuver within distances as accurate as 2.75 centimeters.
When calculating a course, Starfleet vessels plot a flight plan that avoids dangerous objects along the flight path, such as stars or other solid bodies. During travel, computers constantly update their flight plans, making course corrections as new information becomes available.
Setting Course
To the casual observer, starship navigation appears a simple task. Navigational operations are controlled from the conn; a commanding officer can give a destination or heading in one of five ways.
Destination Planet or Star System
The easiest method is to give a destination. As soon as this is input into the conn, the ship's computers consult the navigational database and automatically plot the ship's trajectory. Destinations can be planets, systems, or even orbital facilities. Any celestial object within the navigational database is acceptable as a destination, although the system will inform Conn in the event that a destination exceeds the operating range of the spacecraft. A sector identification number or sector common name is also a valid destination. In the absence of a specific destination within a sector, the flight path will default to the geometric center of the specified sector.
Spacecraft Intercept
This requires Conn to specify a target spacecraft on which a tactical sensor lock has been established. This also requires Conn to specify either a relative closing speed or an intercept time so that a speed can be determined. An absolute warp velocity can also be specified. Navigational software will determine an optimal flight path based on specified speed and tactical projection of the target vehicle's flight path. Several variations of this mode are available for use during combat situations.
Relative Bearing
A flight vector can be specified as an azimuth/elevation relative to the current orientation of the spacecraft. In such cases, navigational orders are often given as a relative bearing. This consists of two figures which relate to two perpendicular planes around the vessel; the first plane is horizontal, the second is vertical. Each plane is divided into 360 degrees, with 0 degrees deemed to be straight ahead. Thus a vessel given a heading of 000 mark 0 would not change its course. On the horizontal plane, values increase to the starboard; in the vertical plane, they increase in the direction above the ship. Therefore a heading of 150 mark 0 means that the ship will turn 150 degrees to starboard, and a heading of 150 mark 20 means that the ship will turn 150 degrees to starboard and then angle the vessel's nose up by 20 degrees.
Absolute Heading
Navigational orders can also be given as an absolute heading. The flight vector is specified as two figures, an azimuth and elevation relative to the center of the galaxy. A heading of 000 mark 0 is directly toward the galactic center. This system is very similar to that used in navigation on a planet's surface where headings are taken from the northern pole.
Galactic Coordinates
Navigational instructions can be given by specifying a destination's galactic coordinates; however, this method of navigation is rarely used, as it requires personnel to either calculate or look up the relevant coordinate information.
Stellar Cartography
The instructions given may be simple, but calculating a course across interstellar distances is an extremely demanding task. One has to know the position of the vessel, the speeds involved, and the position of the destination, but it is impossible to maintain an entirely accurate map of the Galaxy: all objects within the Galaxy are moving in their own direction, and many methods of observation involve a noticeable time lag. Despite these difficulties, the Federation has charted a significant proportion of the Galaxy and uses information gathered from subspace relays, Federation vessels, probes, and sensor platforms to ensure that its map, which is known as the galactic condition database, is as up to date as possible.
Starfleet's Stellar Cartography division has plotted the position of stars well beyond the reaches of manned exploration. Facilities such as the Argus Array, located on the edge of Federation space, gather data on the position and activity of systems which are light years away from explored space. This data is constantly updated and the information transmitted back to Federation outposts. Starfleet regularly sends probes and deep space exploration vessels into 'new' regions of space. These vessels record detailed information, which is then transmitted back to other ships and Starfleet installations by subspace radio.
Even in known space, Stellar Cartography departments on Starfleet vessels constantly observe changes in the position and movement of stellar phenomena. When a ship is at a Starbase or outpost, detailed logs are downloaded and transmitted to Starfleet, and integrated into the galactic condition database which is, in turn, distributed to all Federation vessels. Where accurate real-time information is not available, computers predict conditions with reasonable accuracy.
The information which the vessels regularly receive from the galactic condition database is combined with data gathered by the ship's own sensors on the position of stellar phenomena such as nebulae, pulsars and subspace phenomena to calculate the vessel's location, and the relative position of its destination.
Positional Data
Starfleet vessels are equipped with various external sensors which ensure that reliable positional data can be gathered even in difficult conditions such as magnetic storms or solar flares.
During travel, it is essential for a ship's computers to be able to calculate velocity accurately in order to plot the vessel's position and velocity. An extensive network of Federation Timebase Beacons allows ships to access absolute time values which are used to calculate speed. When the vessel is out of contact with the beacons, onboard timebase processors maintain records, but these are subject to some temporal distortion phenomena, and as soon as possible, the ship will synchronize them with a timebase beacon. Time distortion is particularly extreme at high impulse speeds, but the ship's guidance and navigation subprocessors can largely compensate for this.
The most accurate method of determining the position of a spacecraft with Federation Space is to use the subspace beacon system. This system consists of the central beacon, the beacons defining the sector boundaries, and the galactic north and south beacons. Each beacon continually transmits, on a specific frequency, its call sign followed by a code indicating the exact time the transmission was made. Since the speed of propagation of a signal through subspace is proportional to the power of the transmitter, and the power is known, the speed of the signal can be determined. By computing the time difference between when the signal was transmitted and the present time on the ship, the delay, and in turn, the distance from the transmitter, can be calculated. The first step in determining the position of the ship is to calculate the distance between the ship and all seven beacons. The two closest sector boundary beacons mark the edges of the sector wherein the ship is located. Which region of the sector the ship is in depends upon whether the north or south beacon is closer. If the north beacon is closer, the ship is in the northern region. Likewise, if the south beacon is closer, the ship is in the southern region. On rare occasions, when the distance to these two beacons is the same, the ship is on the midpoint of the sector's XY plane.
Another method of determining the position of the ship can be used, if it is not possible for the spacecraft to receive subspace signals. This method uses the various pulsars located in Federation space. Each pulsar, which is actually a rapidly rotating neutron star, has a unique pulse frequency which slowly decreases over time as the rotation of the star slows down. By determining the frequency of the signal received from the pulsar it is possible to identify it. Since the frequency change is linear over time, the present frequency of the pulsar can be calculated. The difference between the two frequencies tells when the signal left the pulsar and in turn the distance from the ship to the pulsar, since the signal travels at the speed of light. This distance defines the radius of a sphere with the pulsar at the center and the spacecraft located somewhere on the surface. If three widely separated pulsars are selected and the distances to them are determined, a series of intersecting spheres is produced.beacon is less than 90 parsecs the ship is inside the central sphere. This does not change the method of determining the position of the ship; it just means that the ship will not be in one of the quadrants.