Propulsion in the Re-imagined Series
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In the Re-imagined Series, all ships have some manner of sublight flight ability. Sublight propulsion is convenient for intra-solar system travel (such as to or from the planets that comprise the Twelve Colonies), but cannot be used for travel outside of a solar system as the time to arrive at a destination may exceed the fuel supply of the ship or the lifetime of the crew that fly the ship.
As many of the ships of the Fleet are capable of landing on and taking off from planets, (such as New Caprica) it is clear that sublight engines work in an atmosphere as well as in space. Galactica is never seen doing this, and its large mass might prohibit planetary landings altogether, but it employs sublight engines for normal spaceflight. Few of the ships appear to have extremely large propellant tanks as would be required for rocketry as it is presently understood, in spite of having aft-mounted thrusters. This may be explained by the very high energy density of tylium fuel. Smaller vessels are known to employ rocketry-based RCS thrusters for maneuvering and small course adjustments.
Vipers are equipped with a thrust reversal system to counteract or arrest their forward momentum (The Hand of God). No such mechanism exists on capital ships, but such vessels might turn by 180° to decelerate.
Cylons baseships do not have any visible exhaust nozzles or other external structural mechanisms that suggest propulsion ability. It is possible that force fields of the artificial gravity generators are the source of the sublight propulsion.
Both Colonial (Hero) and Cylon missiles used in combat appear to be rockets, leaving a trail of gas behind them.
The law of conservation of momentum requires that any propulsion system which adds momentum to a spacecraft or missile in one direction must equal the amount of momentum that is imparted in the opposite direction to something else, as in the example of the controlled combustion of rocket fuel creating thrust in the opposite direction of a ship's or missile's movement. Pegasus, for example, possesses two very large thrusters on the bow of the ship to counteract the force of the main engines (Razor). However, many other vessels don't appear to have such thrusters.
Relativistic Sublight travel
The Thirteenth Tribe did not have jump drive technology, so FTL travel was unavailable to the Final Five on their voyage from Earth to the Twelve Colonies. They instead used a sublight drive able to reach relativistic speeds (a substantial fraction of the speed of light.) The journey took about 2,000 years according to a planetary reference frame, but a more modest (unspecified) number of years in their ship's reference frame.
FTL is an abbreviation for Faster-Than-Light. The term refers to a means of interstellar propulsion utilized by the Cylons and the Colonials. A common shorthand term for FTL travel is "jumping", as this space-folding drive involves making instantaneous "jumps" across vast distances in space.
The FTL drive makes interstellar travel possible for both the Colonials and Cylons. No longer confined to their own home solar system, the Cylons managed to avoid Colonial interference for 40 years after the Cylon War and establish their own home-world. However, not all ships — from small to large — are outfitted with these drives (Miniseries).
It is likely that FTL drives are not commonplace on many civilian ships because of the costs involved in using and maintaining the drive and the amount of fuel available. For some civilian ships that travel comparatively short distances between some destinations, such as the ill-fated Botanical Cruiser, FTL may simply be impractical or unnecessary.
The technology behind FTL systems is such that, providing the relevant data is known (how that data is acquired, for instance how ships can determine what obstacles are present at their destination, despite never having traveled there before, is not known) ships can jump with a high degree of accuracy, allowing ships to rendezvous in space and even "park" in a synchronous orbit directly above a given point on a planet's surface (Miniseries). Proper FTL use even enables vessels to arrive in crowded areas, such as the middle of an asteroid field or other ships, without the risk of collision and damage (The Hand of God).
Little specific information on the technology of an FTL drive has been given in the Miniseries or regular series. We know only that Galactica has two FTL drives, and that other smaller or civilian ships have a single drive. Ships also do not need to be in motion for the FTL drive to work, or at least smaller craft do not need to be, as Raptors during the Battle of the Colony jump directly from Galactica's starboard flight pod without engaging in forward momentum.
FTL drives on Galactica are said to be "spun up" in preparation for a jump, contain components such as the "spinner" ("The Captain's Hand") and "spin-sync generator" ("Faith") and display a rotational and possibly electromagnetic operation. Until the final-season episode, "Blood on the Scales", the expression was theorised by many fans to be either a turn of phrase, or an anachronism dating back to another form of propulsion, much like the use of the term "air" in reference to fighter operations in the vacuum of space ("Commander Air Group", "Combat Air Patrol", inter alia) and the real-world use of "sail" and "set sail" in reference to self-propelled vessels.
An operational FTL drive was first seen in "Blood on the Scales", specifically one of Galactica's two. Indeed, an assortment of long, thick shafts spin as part of the FTL drive mechanism. The FTL engine room includes a control terminal for diagnostic and auxilliary control. In order to prevent Felix Gaeta and his mutineers from jumping Galactica to an unknown location, former Senior Chief Petty Officer Galen Tyrol attempted to log into the engine room terminal which refused him access, recognising his duty status as "inactive". He was nevertheless able to manually disable the drive by removing a the synchronisation coil. Gaeta made no attempt to use the other FTL drive, indicating either that the other drive was inoperative, the two drives are not entirely independent, that neither drive alone is sufficient to jump the ship, or that Gaeta simply decided that the mutiny and Coup d'état were doomed and futher attempts were pointless.
FTL jump drives can be used within an atmosphere. This Colonial tactic is used often to evade Cylon detection. While Raptors primarily perform these kind of jumps, Admiral William Adama performs a daring intra-atmosphere jump at approximately 100,000 feet altitude with Galactica during the Battle of New Caprica to evade immediate Cylon detection. The battlestar jumps back to space a few thousand feet above the planet's surface after its Viper deployment. When Galactica jumps, the clouds surrounding it and the re-entry fires consuming its hull are "sucked" into the vacuum created by the sudden loss of volume. A clap of thunder is heard afterward, likely caused by air rushing into the aforementioned vacuum (Exodus, Part II). A similar phenomenon occurs when Pegasus jumps from the attack on the Scorpion Fleet Shipyards; the resulting displacement not only draws in the burning gases from the nearby berthing superstructure, but also defuses two nuclear warheads bound for Pegasus itself (Razor).
An area of spatial distortion of some sort is also produced when a ship jumps. This effect has been observed twice thus far. Once, when the tylium refinery ship Hitei Kan is approached by a pair of Vipers and a Raptor in an effort to quell a mutiny aboard the ship. The Hitei Kan unexpectedly jumps and the Vipers and Raptor are repelled away by some force as soon as the ship dematerializes (A Disquiet Follows My Soul). The second time this is seen is when a Raptor stolen by Sharon "Boomer" Valerii executes a jump mere meters away from Galactica’s hull. When the Raptor disappears into the jump the section of the hull it was adjacent to is instantaneously indented. Just prior to that, Col. Saul Tigh expresses his fears of even greater damage should Valerii jump the Raptor while inside Galactica’s flight pod (Someone to Watch Over Me). During the Battle of the Colony, several Raptors actually do jump within Galactica’s sealed off starboard flight pod causing significant damage to the landing bay within the pod and most likely contributed to the catastrophic failure of her hull after the battle (Daybreak, Part II). It is not clear how this distortion field, which seems to produce effects like a shock wave, also coincides with the known effect of a jump acting as a sort of vacuum, which instead of producing an outwards wave should pull the surrounding space into it. The two effects might occur consecutively, the vacuum effect left in the ship's wake, then the expelled shock wave, as hangar equipment in the flight pod is seen being pulled towards the vacuum before being expelled outwards.
Later, the Fleet's FTL drives are upgraded by the Rebel Cylons so they can now travel as far and as fast as a Cylon ship. Not all ships are apparently upgraded as for some reason, the Raptor Boomer steals lacks the upgraded drive.
Limitations of Colonial FTL
Colonial FTL performance can be improved, demonstrated when a Raptor is successfully refitted by a team apparently led by Lieutenant Felix Gaeta with the navigational computer from a captured Heavy Raider (presumably the one used by Kara Thrace to return from Caprica in "Home, Part I") and, with the cooperation of a Number Eight, is used to navigate a squadron of Raptors back to Caprica on a rescue mission to retrieve a group of resistance fighters (Lay Down Your Burdens, Part I). A massive distance that would have taken Galactica 241 jumps one way (~482 jumps total), the Raptor squadron does in only 20 (10 to Caprica, 10 back).
Colonial FTL computers can be affected by highly-charged sub-atomic particles, corrupting their calculations and possibly causing a jump beyond the Red Line, as in the case of Raptor 718 (The Face of the Enemy, Episode 2).
The FTL drive apparently puts significant strain on a ship's structure. Galactica has substantial cracks in her hull adjacent to the FTL drive which Tyrol disabled. (Blood on the Scales) While discussing structural repairs with Adm. Adama, Tyrol asks him not to jump the ship for a while, whilst his crews upgrade the structure. (No Exit)
Cylon Advantages in FTL
Cylon FTL drives are—using the most conservative estimation—three times more effiicent than their Colonial counterparts (A Disquiet Follows My Soul). Despite being well-versed in maintaining Galactica's two FTL drives and being a Final Five Cylon, former Senior Chief Petty Officer Galen Tyrol is baffled by Cylon FTL technology and defers to "Sixes, Sharons and maybe even some Leobens" to upgrade Colonial ships' drives. The Fleet later gets the upgrade and the difference can be clearly seen in the jump capabilities: a Raptor stolen by Boomer which for an unknown reason doesn't have the upgraded drive, takes over a dozen jumps to reach The Colony, but Galactica and even an upgraded Raptor are able to make the distance that took that Raptor over a dozen jumps, they make in one.
The Cylons may also be capable of faster-than-light communication.
FTL jump ranges
The range that Galactica can jump at has never been specified on-screen. However, in a deleted line from the mini-series the jump from Ragnar to the Prolmar Sector is said to be "30 light-years", which is way beyond the red line (maximum safely calculable jump range). This is consistent with Colonel Tigh saying that Galactica could search every planet within 12 light-years for water before having to jump to another sector altogether (Water). On this Wiki, producer Bradley Thompson suggested that internally, the writers had been working on the idea the Fleet had been jumping about 5 light-years at a time, although that does not have to have been its maximum range. Finally, on composer Bear McCreary's blog, science advisor Kevin Grazier and producer Bradley Thompson suggested that the final six digits for the jump coordinates Kara interprets from the Music represent distance in SUs. 999,999 SUs - the maximum possible distance that can be inputted - would relate to 15.812 Colonial light-years. The distance inputted during the Battle of the Colony is 365,321 SU or 5.77 Colonial light-years, which is presumably the distance from the Colony to Earth (Daybreak, Part II). There may also be a factoring scale at work, and at close ranges Galactica appears to be able to jump much more accurately, as demonstrated by its jump from several million kilometers directly into New Caprica's atmosphere 100,000 feet above the surface (Exodus, Part II), or a jump of unknown range to within one kilometre of the Colony's surface (Daybreak, Part II).
Cylon FTL ranges are considerably larger. At the end of the series, the Fleet's larger ships have their jump ranges tripled by the installation of Cylon technology (A Disquiet Follows My Soul). However, during the rescue of Colonial resistance forces from Caprica three years earlier, a Raptor squadron outfitted with a Cylon FTL navigation computer traversed in 10 jumps (Lay Down Your Burdens, Part I) a distance that Galactica would have required a minimum of 230 jumps (conservatively) to cross (Pegasus), an improvement by a factor of 23. However, this rescue team was just using the navigation computer to improve their jump calculations. Another example is how many jumps it ended up taking to reach The Colony. When Boomer stole a for some reason un-upgraded Raptor, it took her over a dozen jumps to reach The Colony. But the recon Raptor that was dispatched and even Galactica herself were able to make that distance in one jump with their upgraded FTL drives. Lee Adama even specificly said that The Colony was in Galactica's FTL range which it wouldn't have been before with the un-upgraded drive given Boomer's journey there. With the upgraded drives, Tyrol said that the efficency of the Fleet's jump drive would be trippled and give them a much longer jump range which they believed was key to finding a new world for humanity to settle on. Cylon FTL's were so complicated that even Tyrol didn't understand them fully and said they were going to need rebel Cylons just to do the upgrades.
Background to FTL in the Re-imagined Series
In establishing the series the creators of the Re-imagined Series determined to keep everything within the show very "natural". This means steering away from the standard clichés of television science-fiction: no bumpy-head aliens, no remarkable technology such as matter/anti-matter conversion, etc. So how is the concept of faster-than-light travel possible within this precept?
The FTL drive technology used within the Re-imagined Series might be based on the use of Superstring Theory and M-Theory that essentially enable the "jump drive" systems to "fold" space, reducing the distance between any two points by creating a "corridor" through space that links them together (essentially forming a wormhole, or Einstein-Rosen Bridge). Such "corridors" are allowed by the general theory of relativity; what M-Theory does is provide a way to change the topology of space-time dynamically.
The use of such wormholes is based on the tenet that space is curved. Hence the term "wormhole", which arises from the analogy that space can be seen as an apple. A worm can travel from one side of the apple to the other in two ways:
Obviously, the second option is considerably shorter than the first.
A key point concerning the use of wormholes within the new Battlestar Galactica is that they do not break the fundamental limiting factor of our universe: the speed of light. Vessels in Battlestar Galactica do not accelerate to faster-than-light velocities. Rather, they use the wormhole to reduce the distance to their destination, thus giving the impression of faster-than-light travel.
However, the FTL jumps in the series do allow information to be sent faster than light can send it, which results in a violation of causality within the special theory of relativity. (ie. If event A comes before B from one viewpoint, there will be other equally valid viewpoints where event B takes place before A.) Causality is not violated by FTL in a universe that has a special fixed reference frame, however this contradicts current understanding.
This is the reason why FTL jumps are virtually instantaneous within episodes. It also means that the only direct form of propulsion available for vessels is generated by their sublight drive systems.
While the use of wormholes in this manner is not currently possible, work is progressing on superstring and M-Theory which may make the creation of wormholes possible in the future. The limiting factor is the ability to generate negative energy densities, which are allowed (though severely restricted) by quantum mechanics. As such, the use of such systems again meets one of the stated desires of the the producers of Battlestar Galactica: not to rely on the "traditional" trappings of science-fiction that require exotic science and technology. Theoretical physicist Kip Thorne has carried out extensive research into wormholes, and helped develop a scientifically-consistent means of wormhole travel used by Carl Sagan in his novel "Contact" which bears a remarkable similarity to the technology employed within Battlestar Galactica.