Why Two Warp Nacelles Are Better Than Three

A Treatise on Warp Drive Dynamics

By:

Rear Admiral Adrian Newey

Technical Director - Starfleet Spaceship Design Advisory Commission

For most of its history, Starfleet vessels have been fitted with two warp nacelles, with single nacelles being much less common. Certain “heavy” vessels, mainly the dreadnoughts, have employed three nacelles, and we have even seen some four-nacelle designs over the past century. Why do Federation starship designers seem “stuck” on two nacelles? It all comes down to efficiency.

A common misconception amongst laymen is that the nacelles generate power. In fact, the nacelles use the power to generate the warp field that propels the ship. However, having additional nacelles does allow a larger M/AM reactor to be fitted, so the vessel does in fact produce more power.

A vessel with two nacelles produces 50% more power while consuming only 25% more reactants than a vessel with a single nacelle. Two nacelles also optimize vehicle control. By altering the timing differences of each nacelle, the warp field geometry can be varied on the X/Y-axis’s, thereby altering the ship’s heading. Single nacelle vessels require advanced field-control systems to perform these maneuvers, and only the smallest ships (such as scouts) use a single nacelle, since the cost of the control system is smaller than using two nacelles. Still, this is a rare case, and by the early 2300’s, most single-nacelle designs were retired.

After the Romulan and Klingon wars, Starfleet began development of the dreadnought class of starships to provide a high-speed weapons platform. To reduce costs and speed introduction, Starfleet decided to modify the Constitution class heavy cruiser rather than designing an entire new class of vessels. Additional phaser emplacements were added and, to increase speed, a third PB-31 warp nacelle was grafted to the top of the primary hull. And thus the Federation class dreadnought was born. Though the addition of the third nacelle required extensive modification to the impulse engines and required the moving of Main Engineering from that location to it’s present location in the secondary hull, it did raise the top speed of the vessel by two full warp factors. Total ship’s power increased 50%, but the consumption rate of reactants doubled. The ship’s handling characteristics were worsened, but this was deemed acceptable as the mission objectives were to keep the ship docked at Starbase until the start of hostilities. The dreadnought would then deploy to the trouble spot and engage the enemy forces in conjunction with smaller, more maneuverable vessels, acting as a “gun platform”. These vessels never saw their intended service, but their deterrent effect probably helped contribute to that.

With the introduction of new and improved starship designs by the Klingon and Romulan Empires, Starfleet decided to uprate the Federation class dreadnoughts to the technology and systems employed on the new Enterprise class of heavy cruisers. The dorsal section was lengthened to better integrate the LN-64 nacelle mounted there, without sacrificing impulse design or efficiency. The original mounting design of the side-mounted LN-64 nacelles was the same as that for the Enterprise class, but this was scrapped when the shaft design was found to interfere with the expanded hangar bay. A new design, with the shafts mounted flush to the top of the secondary hull and with a direct horizontal feed from one nacelle to the other. An added benefit of this arrangement appeared during design modeling, since it made the warp field more triangular, providing better X/Y/Z-axis control. Improvements in warp core design increased power to 150% of that of the Enterprise class, though reactant consumption also rose, now to 200%. A second class of dreadnoughts, the Ascension, was also created, using the Belknap class cruiser as its model. It had similar power and reactant adjustments.

Four nacelles did not enter Fleet service until the commissioning of the Constellation class exploratory cruiser. These vessels were designed to operate on the extreme edge of Federation space for mission periods exceeding ten years or more. As repair facilities would be few and far between, it was decided to use four LN-68 nacelles to reduce the stress on the warp system as a whole, to provide spare parts for repairs and, if necessary, act as a “backup” set of warp nacelles in the event of a severe systems failure in the warp propulsion system. This design, while inelegant, was functional and a number of ships were built. With all four nacelles in use, total power was 200% and reactant consumption was 300% compared to when she ran on two nacelles. Since the Constellation class was somewhat unique in its mission design objectives, the ridiculous waste in consumables of four-nacelle operation was considered acceptable, though it remained the only four-nacelle vessel built.

In the late 2300’s, the arise of more Threat elements against the Federation once again brought the call for vessels with more than two nacelles. And once again, a third nacelle was grafted to a cruiser, in this case the Galaxy class, resulting in the Olympus class dreadnought. The Starfleet Corps of Engineers, in a guerrilla war worthy of the Maquis, finally rammed through a new four-nacelle design, the U.S.S. Peacekeeper diplomatic cruiser, again based on the Galaxy class.

The ASDB is generally against vessels with more than two nacelles, siting the new LF-43 series which, when mounted on the Galaxy (II) class large exploratory cruiser, raised its top speed to within 10% of the Olympus, while using nearly half as much reactants. Therefore, it is unlikely we will see any more three or more nacelle designs in the near future.

Admiral Newey is a Technical Director at the Starfleet Spacecraft Design Advisory Commission and is an acknowledged expert in high-warp design dynamics.