Relativistic Travel

Last updated: July 21st 2026

RELATIVISTIC TRAVEL IN BtFF

In this house we don't do faster-than-light travel. Relativity is sacred in this universe - the challenge is not to circumvent it, but to live with its consequences.

The rating of relativistic speed of starships in this universe is given as integers of the Lorentz factor (γ) instead of decimal fractions of the speed of light - that is, how many times the subjetive ship time appears to compress due time dilation in comparison with restframe time.

For example, a relatively fast starship with a rating of γ ~ 6 experiences a subjective time that is 1/6th of the restframe - for a 10 light-year trip, thats about 1yr8m trip experienced by the crew. So keep that in mind whenever that gamma rating gets thrown around.

It is also commonplace to use stasis chambers for the slowing down of biological clocks for really long trips or at lower cruise ratings, pre-fall humans managed to make it work for an additional 40 years of subjective time while in their prime.

CUSTOMARY METHODS OF PROPULSION
Choice of propulsion is determined less by maximum cruise velocity than by economics. Fuel cost, available infrastructure, expected travel time, maintenance requirements, and intended cargo all influence the selection of a propulsion system. Consequently, no single architecture has displaced all others, and vessels of widely differing performance routinely share the Dominion's starlane network.

Practical cruise ratings throughout the Dominion rarely exceed γ≈10. Although higher Lorentz factors greatly reduce the time experienced aboard a vessel, they offer progressively smaller reductions in arrival time as measured by the outside universe. Since fuel consumption and engineering complexity increase far more rapidly than the logistical benefits gained, most commercial operators regard higher cruise factors as economically unjustifiable.

Pure Aneutronic Matter-Antimatter Rockets

Typical cruise factor: γ ≈ 2-10

The standard propulsion system throughout most of the Dominion. Matter and antimatter are reacted producing primarily charged pions whose momentum is directed magnetically to generate thrust. Their high thrust-to-weight ratio, operational flexibility and comparatively simple engineering have made them the preferred propulsion method for commercial, military and civilian spacecraft alike.

Although fuel-intensive, matter-antimatter rockets are capable of sustained acceleration and deceleration over interstellar distances, allowing routine travel between neighboring systems within acceptable subjective travel times.

Most Dominion freight, passenger traffic and naval operations rely upon some variation of this architecture.

Pion "Drip" Drivers

Typical cruise factor: γ ≈ 1-6

Among the oldest propulsion systems still in widespread service, Pion Drip Drivers accelerate vessels through the gradual release of small quantities of antimatter over extremely long burn periods. Their comparatively low thrust results in months or years of continuous acceleration, making them poorly suited for passenger transport but exceptionally economical for bulk cargo.

They remain common aboard autonomous freighters, industrial tugs, ore transports and long-duration logistical missions where travel time is of secondary importance. Their modest top speed means they can more safely and frequently venture across uncharted interstellar space for shortcuts and direct routes rather than using starlanes, with reduced risks of high relativistic impacts or abrasion.

Ion-Fusion Drivers

Typical cruise factor: γ ≈ 2-5

Ion propulsion remains popular among smaller spacecraft operating within developed regions of the Dominion. By continuously accelerating ionized reaction mass through powerful electromagnetic fields, these engines provide excellent efficiency at the cost of relatively low thrust.

Although incapable of the rapid departures characteristic of matter-antimatter vessels, Ion Drivers are regarded as remarkably reliable and inexpensive to maintain. Patrol craft, survey vessels, scientific expeditions and privately owned starships frequently employ them for regional traffic between nearby systems.

Light Sails

Typical cruise factor: γ ≈ 1-4

Rather than carrying significant quantities of reaction mass, light sail vessels derive propulsion from immense laser arrays positioned throughout developed star systems. These arrays illuminate highly reflective sails over distances of several astronomical units, accelerating vessels with no onboard fuel expenditure.

Because propulsion infrastructure must exist at both departure and arrival systems, light sails are almost exclusively employed along heavily trafficked commercial corridors and within mature planetary systems. Their exceptionally low operating costs have made them popular for passenger liners, luxury transport and scheduled commuter services despite their comparatively modest cruise velocities.

Many Core worlds maintain dedicated beamways linking orbital habitats, neighboring planets and nearby systems, functioning as an interstellar equivalent of public rail infrastructure.

Ramscoop Matter-Antimatter Drives

Typical cruise factor: γ ≫ 10

No confirmed Dominion civilization is presently known to possess operational Ramscoop Matter-Antimatter propulsion. The only documented examples have been observed aboard Elder Starships of the Great Expedition.

The immense forward structures characteristic of these vessels are widely interpreted as magnetic collection systems capable of harvesting the sparse interstellar medium while simultaneously serving as radiation shielding during extreme relativistic flight. If correct, such systems would permit effectively unlimited operational range without conventional refueling while sustaining cruise velocities approaching several hundred to over one thousand in Lorentz factor.

Whether harvested hydrogen is directly fused, converted into antimatter, or merely supplements onboard reserves remains unknown. Likewise, many observed performance characteristics continue to defy satisfactory theoretical explanation, leading some researchers to suspect the presence of additional propulsion systems operating alongside the ramscoop architecture.