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A System is an astrographic term for a star and its family of secondary stars, planets, planetoids, asteroids, moons, and artificial satellites. It is also known as a Star System, Stellar System or a World-System.

Description (Specifications)[edit]

The term system denotes a major world and its associated star, plus any other stars, planets, satellites, asteroids, and other bodies in a significant gravitational relationship with the source star. It also includes all bands of system including the close inner system and the far outer system of Oort clouds and orbiting comets or other astrographic objects.

Stellar system objects[edit]

A number of different types of objects can be found within a single system.

Primary Star
The largest (in terms of mass) star in the system is always designated as the primary.
Secondary Star(s)
The system may include one or more additional stars in orbit around (or co-orbital with) the primary star. These include stellar objects like Brown Dwarfs, White Dwarf stars, Neutron Stars, and Black Holes.
Gas Giants
These are the largest of the planets, consisting of a hydrogen atmosphere without any surface.
A planet is a single body with enough gravity to form a sphere. They may or may not have an atmosphere, hydrosphere, or be inhabited.
A single body orbiting a planet or gas giant. Some moons may be the size of planets, and may be co-orbital with their parent planet.
A single small body, too small to have the gravity to form a sphere. In some cases the is a group of Planetoids gathered into a single orbit, which is termed a Planetoid Belt or Asteroid Belt


Orbit Number Distance (AU) Light-distance
0 0.2 100 light-seconds
1 0.4 200 light-seconds
2 0.7 5.5 light-minutes
3 1.0 8 light-minutes
4 1.6 13 light-minutes
5 2.8 30 light-minutes
6 5.2 43 light-minutes
7 10 83 light-minutes
8 20 3 light-hours
9 40 5 light-hours
10 77 10 light-hours
11 154 21 light-hours
12 308 41 light-hours
13 615 3 light-days
14 1,230 7 light-days
15 2,500 14 light-days
16 4,900 4 light-weeks
17 9,800 8 light-weeks
18 19,500 16 light-weeks
19 39,500 32 light-weeks
20 78,800 1 light-year

Worlds, and other objects, generally move in a elliptical path around the primary star, in the same direction, and in the same plane (called the orbital plane or or plane of the elliptic). The direction of the orbital path and plane of the orbits are a consequence of the formation of the system.

The mapping convention assumes a fixed set of circular orbits common to every system. Orbits are numbered from 0 to 20 with the distances along a geometric progression. The distances are measured from the gravitational center of the primary star.

In reality orbits are elliptical, rarely fall exactly onto the common set of orbits, and the individual object's orbital plane may not match the other objects in the system. In systems with two or more stars, the center of the system may not be in the primary star at all but at the gravitational center of the system somewhere in space between the multiple stars.

Orbital Zones[edit]

Every star has a defined set of zones covering one or more orbits.

The surface of the star itself. While most stars are much smaller that even orbit 0, some giant stars cover multiple orbits. The largest stars can extend out to orbit 5.
Inner limit
The inner limit for planetary formation. Within the inner limit the temperature will vaporize rock preventing the formation of planets. In some cases planets will move into the inner limit orbits but are quickly vaporized.
Habitable Zone
The range where the temperature would allow liquid water to exist on the surface of a world. Not all worlds in the Habitable Zone are habitable, but it is the best place to look.
Outer limit
The outer limit is the largest orbit where a planet would be created when the system was formed. Beyond the outer limit there are usually only comets and small worlds.
The boundary at which the radiation from the primary is balanced against the interstellar medium. This is generally defined as the edge of the system, beyond which is interstellar space.

The orbits between the Inner Limit and the Habitable Zone is the Inner System. Orbits between the Habitable Zone and the Outer limit are the Outer System. Orbits beyond the outer limit are the Remote System. Orbits beyond the Heliopause are simply noted as Beyond, and objects in the Beyond are not considered part of the system.

Orbital positions of interest[edit]

In addition to the orbital distances based on astronomical observations there are orbital distances defined by technology and sophont use that are of interest.

Safe Distance
The minimum safe distance to approach the star by standard space craft. The limit is defined by the temperature of the star. Unless the ship is specifically designed to handle the heat and radiation, approaching closer to the star can present significant danger to the craft and occupants.
100D limit
The 100 diameter limit for the Jump Drive. For most main sequence stars, the 100D limit is close to the Habitable zone of the star. For some cool giant stars the habitable zone can be weeks of travel from 100D limit, making trade a challenge.
1000D Maneuver Drive limit
The standard gravity based maneuver drive does not function very well beyond the 1000D limit of any star. For travel to worlds beyond this limit require careful navigation, an alternative drive system, or both.

Polystellar Systems[edit]

Polystellar star system are system with two or more stars.

Star Systems
Type # Stars Rough % Remarks
Monostellar Star System 1 60 Most common star system. Not a polystellar system.
Binary Star System 2 30 Common star system.
Trinary Star System 3 4 to 5 Uncommon star system.
Quaternary Star System 4 2 to 3 Infrequent star system.
Quinary Star System 5 1 to 2 Rare.
Sextenary Star System 6 N<1 Very rare.

Image Repository[edit]

  1. An IISS Scout Manual diagram of planetary orbits within a Star System.
    Orbit-Star-System-Tom-Mouat 20-May-2019a.jpg

History & Background (Dossier)[edit]

The IISS or its counterparts typically only have fairly comprehensive star charts for inner systems (Inner zone, HZ and outer zone). Outer systems (remote and far) typically remain very roughly charted or nearly uncharted.

See also[edit]

Star systems[edit]

§ == ( Please refer to the following AAB Library Data for more information: ) == §

Fringian Variant System Description

References & Contributors (Sources)[edit]

This list of sources was used by the Traveller Wiki Editorial Team and individual contributors to compose this article. Copyrighted material is used under license from Far Future Enterprises or by permission of the author. The page history lists all of the contributions.