Lightspeed is the term for a Colonial battlestar accelerating to the speed of light or faster. Galactica is one of the few ships in the rag-tag Fleet that have lightspeed ability, so normally the battlestar moves no faster than the slowest ship in the Fleet during its exodus from the destroyed Twelve Colonies (TOS: "Lost Planet of the Gods, Part I").
It is rarely mentioned, but beyond the following references, FTL is implied several times in the original Battlestar Galactica. Even just the mention of leaving star systems (possibly mentioned inaccurately as 'galaxies') and showing up in other star systems within short periods of time, lead one to suspect that some form of superluminal propulsion is employed.
- Commander Cain brings Pegasus to lightspeed in order to outflank Baltar's attack force, though Cain earlier commented that such a maneuver would result in using half of Pegasus's fuel (TOS: "The Living Legend, Part I").
- Commander Adama orders Colonel Tigh to take Galactica to lightspeed, despite Tigh's objections that suggest that it had been some time since the battlestar was ordered to accelerate that fast (TOS: "Experiment in Terra").
- Baltar and Lucifer have a conversation in which Lucifer states that the Cylons could easily catch up to the slowly moving rag-tag Fleet if they used lightspeed (TOS: "Lost Planet of the Gods, Part I").
- Starbuck's Viper "Recon 1" could be inferred to be able attain this lightspeed as well, as it has to drop to sub-light when it detects a freighter and fighter (TOS: "The Long Patrol").
Other than these oblique references, there is nothing that would substantiate how the ships achieve this form of propulsion other than by just accelerating until they reach their top speed.
Propulsion systems of spaceships in the Original Series exhibit a number of characteristics, including --
- Slow relative movement near planets or other spacecraft, in interplanetary space. The approximate distance between Colonial Vipers and Cylon Raiders in space battles can be estimated since the sizes of both are known. The range is typically a few tens of meters (<100 feet) and the relative velocities only ~100 meters/second (240 mph) or comparable to WW II fighter aircraft. Colonial Battlestars and Cylon Basestars also move slowly during space battles.
- Extremely rapid acceleration in deep space, or otherwise the Battlestars could never achieve near-lightspeed within a matter of minutes or hours in the episodes "The Living Legend, Part I" and "Experiment in Terra". This requires some sort of acceleration damping forcefield or else the crew would be crushed out of existence. A ship constantly accelerating at one Earth gravity (9.81 meters per second) would need more than a year to achieve light speed, clearly ruling out missions to other star system in next week's episode even when relativistic time dilation is factored in.