Submitted by Scott (A'Kula) Schimmels
BSME - USAFA, 1984
MS-Aero/Structures - AFIT, 1988
PhD-Aero/Structures - AFIT, 1995
5/5/99

Note: Images are courtesy of Star Wars® Essential Guide to Vehicles and Vessels and Star Wars official web site.

Sublight drives, also known as 'realspace drives', are the basic propulsion system found aboard every starship, from the lowly space tug, to the X-Wing or TIE Fighter, and even the majestic huge Mon Calamari cruisers or the imposing the Kuat Imperial Star Destroyers. Even Lord Vader's dreaded Super Star Destroyer, the Executor, required sublight drives (a massive bank of them) to maneuver in the various systems such as Hoth and Endor. The sublight drive is used either to propel the spacecraft within a star system, or to bring it far enough from any planet so it can successfully and safely jump to hyperspace. During the landing cycle, a starship's sublight drive is aided by its repulsorlift drive (all coordinated by navicomps and flight computers), allowing the ship to maneuver with heightened precision within the planet's atmosphere.

Unlike hyperdrives, sublight drives cannot bring a spacecraft to exceed the speed of light, hence their name. Thus, spacecraft equipped only with a sublight drive, such as a space tug or the more commonly known Imperial TIE Fighter, are not designed to operate at great distances from their home base. Such craft are carried to their deep space destinations by a capital ship, such as a corvette, frigate, cruiser or star destroyer.

The most common fighter in the galaxy is the fighter developed and constructed by the Seinar Fleet Systems. Many sources have confirmed this fighter was named for its propulsion system using a typical military acronym - TIE stands for "Twin Ion Engine". Ion engines exist in this galaxy and are now flying on NASA’s Deep Space 1 spacecraft. The Deep Space 1's ion engines work by accelerating charged atoms (ions) of a Xenon propellant with electrical grids charged to high voltage. As the ions leave the engine, they impart thrust. Power on Deep Space 1 comes from its solar panels, but theoretically any means of generating electricity would drive its ion engine. This engine produces almost 10 times more thrust per kilogram of propellant than chemical rockets (such as Atlas, Delta and Space Shuttle boosters) can. As a result, even though ion engines in this galaxy generate only a few grams of force, they could operate for years nonstop, allowing a spacecraft to reach extremely high velocities.

TIEs, in that galaxy far, far away, are powered by two SFS P-S4 fission engines generating ion streams at near light speed. These ion streams are channeled through magnetic containment fields, similar to those being developed in England, at the Joint European Tokamak (JET) facility, and out relatively small nozzles. As in Deep Space 1, the exiting ion streams impart thrust to the TIEs, similar to kinematics of chemical rockets. The electromagnetic fields (minaturized versions of the Tokamak facility) accelerate and stream the ions to accentuate the thrust being generated, giving the TIE its incredible speed. Two SFS P-w401 ion manuvering jets, fed by the fission engines, give the TIE its amazing agility. Since most of the TIEs internal space is used for the pilot, flight controls, lasers, and fission engines, there is no room for any shield generators (such as the Novaldex generators on Incom's T-65 X-Wing). Thus, the TIEs survivability comes solely from its speed and manuverability, and the skill of its pilot.

The nuclear reactors on the Sienar TIEs are unusually powerful for the size of the fighter, as demonstrated by the TIEs firepower and incredible manuverability during countless battles including Turkana, Yavin, Hoth, and Endor. Since the fission reactor is so great for the mass of the TIE, the excess or waste heat from the nuclear fission process becomes a significant issue for this particular star fighter. In addition, the design of the Seinar ion engines adds to the problem, because their outlet nozzles are narrow, minimizing the amount of waste heat being vented. Thus, this excess thermal energy is only able to exit through an effective opening less than 0.01 m² per engine (measure the TIE from the Star Wars Essential Guide to Vehicles and Vessels and measure the exit nozzle to determine this ratio).

Seinar's solution was to add radiator panels to the sides of the ship, in the form of the distincive hexagonally shaped wings or vanes we've all come to know and hate so well (at least, for those who fly for the Rebellion). The reactor's waste heat was pumped into these wings and then radiated into space. From any thermal handbook, one can determine an effective radiator requires several things: surface area, thermal conductivity, and emissivity. Thermal conductivity is a material's ability to transmit thermal energy from a high energy source (in this case the TIE's reactor core) to a low temperature source (space) without absorbing it and is given in typical units of Watts per meter per degree Celsius (W/m*C^o. I will discuss potential materials used in starfighter construction in my next article, so I will not discuss this particular property in detail now. Emissivity is a material's ability to emit thermal energy and is governed by the Stefan-Boltzman Law (E_b = σT⁴) and is usually measured in Watts per square meter (W/m²). Obviously the greater the surface area, the more thermal energy that can be conducted and then emitted off the radiation panels. However, if the wings are too large, they would interfere with the pilots' ability to effectively see in a furball (close-in dogfight). A perfect example of this is the MiG 25 Foxbat. It was a Mach 3 aircraft, and was designed by the Soviets as an interceptor to defeat the XB-70 Valkeyrie supersonic bomber. As such, the pilot's sole mission was to close on the target and fire his missile. No thought was given to using the MiG 25 for anything but this limited interceptor role. When the U.S. cancelled the Valkeyrie program, the Foxbat was relegated to an air superiority role and suffered as a result. The pilot had extremely limited visibility (due to the design of the Foxbat's cockpit) and would have been easy prey the F-15 Eagle or even the F-16 Falcon in an air-air engagement. Understanding the need for the pilot's visual requirements, Seinar made a compromise between the need to emit thermal energy, and giving the TIE pilot enough visibility for close-in combat.

One technique Seinar employed to aid in the thermal management issue was incorporating an effective "black body" surface. Darker surfaces make more effective radiators. Refer back to the Stefan-Boltzman equation and notice the term E_b which is a constant for a perfect black body. Thus, the closer the surface resembles a "black body", the better thermal energy emitter it becomes. This is why all fighters in the Seinar TIE family exhibit the predominant charcoal-black vanes. Also, as in many conventional thermal systems, to enhance the surface area of a thermal radiator, fins and ridges are added to the construction. Close inspection of a TIE's quadanium panel reveals that Seinar has included this feature in their design, adding to the efficiency of the TIE's passive thermal radiation system. As noted in several sources, radiators held at only a few hundred degrees (much less than the several thousand degrees in the interior of a nuclear reactor) enhances the thermal conductivity of the TIE's vanes, and ultimately it's ability to emit the waste heat into space.

There has been much discussion as to the location of the TIE's reactor systems. Since the quadanium panels are limited in volume, this leaves only the cockpit ball to house the reactor core. There are two primary locations to be considered. The first is the ring structure in the rear of the cockpit ball (the most likely location) which conforms to a layout similar to the Tokamak facility in the UK. The other possible location is below the pilots seat, in the bottom of the ball. In either case, the compact design of the TIEs engines reduces its vulnerability to enemy fire. The thruster nozzles, located on the rear of the TIE cockpit ball, are less than a foot apart, and most of its drive mechanisms are contained within the strucure of the cockpit ball. As such, TIEs rarely suffer engine hits and damage, unlike Rebel starfighters, whose sublight engines are oversized and exposed (most notably the Y-Wing). Apart from the wings, the TIE Fighter design is very compact and reduces vulnerability. Most of the flight controls and systems management is packed within a cockpit ball and the pylons supporting the hexagonal vanes. Were it not for the thermal managament requirement, the TIE could be nearly spherical.

An interesting side note of this discussion is the vanes themselves. After the initial TIE Fighter production, the TIE Bomber and TIE Interceptor were produced. These were followed by even more advanced designs such as Lord Vader's TIE, the TIE Phantom, Defender and Scimitar classes. Those with angled vane designs, such as the TIE Interceptor or Lord Vader's TIE, appeared to incorporate smaller radiator panels than the TIE Fighter. There are various interpretations of this change in design. The first is that Seinar may have improved the efficiency of the reactor core, thereby reducing the amount of waste heat requiring venting. A second possibility is the bent vane actually enhances the the emissivity of the radiator, thereby minimizing the surface area needed. Tied in with this is a third possibility, that of reducing the TIE's tactical profile, making it even harder to hit. Since most TIEs are intended for space combat, there are tactical constraints that drive the design. As in conventional fighters here on Earth, one consideration in a fighter's design is it combat profile (i.e. the surface area presented to the enemy to be hit). In space furball, the most deadly situation is when facing the enemy head-head or when he is on your six. This presents the enemy with the maximum amount of time to aim and fire either his lasers or missiles at you. Note: the next time you play X-Wing vs TIE Fighter (or any of the X-Wing series of combat sims), see which is easier to hit the TIE, when it's directly in front of you or when it's sliding from one side to another, requiring a deflection shot. Seinar included this consideration in their design of the TIE family which is why most vanes are very thin to present a minimal profile for head-head dogfighting. In fact, this design is very successful when facing an X-Wing as the quad lasers will simply pass between the vanes and cockpit ball when the X-Wing's pilot has the TIE centered in his HUD reticule. For the bent vaned designs, the surface area is even further minimized, making them very difficult to hit even on a deflection shot. Try taking out a TIE Fighter using a deflection shot, and then try a TIE Interceptor. Guess which one is easier to hit? The bent wings may not have been a direct tactical consideration when Seinar developed the TIE Interceptor, but the tactical benefit is clear when the TIE Interceptor is flown in combat. Since TIE Interceptors have a greater survival rate than TIE Fighters when flown in combat with the Rebels, this may be one reason why only seasoned Imperial TIE pilots fly them, and the rookies are given the TIE Fighter.

After the debacle at Turkana, Seinar was forced to improve their original TIE design to meet the threat of a new Rebel starfighter. The result is the TIE Interceptor, faster and more maneuvarable than a TIE Fighter, and sporting quad laser turrets. Seinar specifically designed the TIE Interceptor for dogfighting with the Incom T-65A X-Wing, using captured X-Wings for reverse engineering analyses. In fact, much of the technology incorporated into the Interceptor was originally slated for Vader's TIE Advanced X1 prototype. Seinar, in an attempt to lower costs and reduce material considerations, incorporated the standard TIE Fighter cockpit ball and vane supports into the TIE Interceptor. As such, the TIE Interceptor has the same vulnerability as the TIE Fighter, namely no shield generators and minimal armor. However, the TIE Interceptor has some improvements. The first being four laser cannons, that could be fired individually, dual-mode, or in quad-mode. Combining this firepower with advanced targetting computers gave the TIE pilot greater accuracy. The TIE Interceptor has improved ion drive engines and is nearly as fast as the Rebellion's A-Wing (110 MGLT). One improvement was Seinar's incorporation of a new ion stream projector allowing pilots to execute tight turns and rolls. Twin-port deflectors are manipulated individually for control and counter-balancing of the TIE's inertial movements, making the TIE interceptor superior for dogfighting against Rebel ships. If you recall my X-Wing® vs TIE Fighter® Strategy Guide article, I mention the TIE Interceptor as the "King of the Turning Battle", this is why. Interceptor pilots need their ship's maneuverability and speed to survive dogfighting the better armored and shielded Rebel fighters. Baron Soontir Fel, commander of the 181^st, was the most feared Imperial pilot when flying the TIE Interceptor. Only his brother-in-law, Commander Wedge Antilles, had a better record with two Death Stars to his credit.

Rebel fighters usually exhibit a blueish or greenish exhaust glow. This is usually attributed to the Incom Fusion or Koensayer Ion Jet engines used for their X-Wing and Y-Wing star fighters. These engines provide a greater energy reservoir than the standard fission ion engine on the Imperial TIE class of fighters. This energy reservoir is what provides the Rebels with their edge: shields, and more powerful laser blasts. The TIEs are faster, more manueverable, as their ion engines need only provide thrust and laser power. Whereas they do not have ion cannons nor shields, TIEs can deliver a greater volume of laser energy, based on their faster rate of fire. This rate of fire, combined with superior number of fighters, was thought to offset the Rebel advantage of armored hulls and the use of shields.

The Incom T-65 X-Wing has four fusion engines. Those flown in the Battle of Yavin IV during A New Hope, were fitted with Incom 4J4 engines and had an optimum speed of 100 MGLT. Soon after the debacle at Hoth, X-Wings were refitted with the Incom 4L4 series of engines, giving them an optimum speed of 105-110 MGLT during the Battle of Endor, and a faster laser recharge rate. However, due to mainenance difficulties, very few X-Wings were able to achieve this performance. The X-Wing, as do all Rebel starfighters, use oversized engines that are exposed. To compensate for this vulnerability, Rebel technicians and engineers install Novaldex shield generators to enhance their starfighter's survivability. Since the engines are direclty exposed to the cold of space, the venting of waste heat from the fusion or fission engines is moot. Thus, the need for thermal radiation is eliminated. Also, since the reactor is housed directly in the main engines, much of the internal space of a Rebel starfighter becomes available for a host of systems unavailable to the Sienar TIEs. The exception is the A-Wing, which must used smaller systems, thereby reducing its shield strength and ability for long range patrols. Combining the robust navicomp of the X-Wing with its astromech droid, a Rebel pilot can have at least 10 hyperjumps preset, giving the pilot an incredible ability for conducting long range patrols. By synchronizing the output of the four fusion engines (each offset from the centerline axis of the fighter) with the control stick of the X-Wing, the Rebel technicians were able to allow the X-Wing to roll and dive with surprising agility. This, combined with shields and superior flying skills, allowed many Rebel pilots such as Keyan Farlander and Wedge Antilles to wreak havok with TIE Fighter and TIE Interceptor squadrons. The X-Wing's manuverability, combined with shields and quad lasers, were the major reason why the Rebels gave the Imperial fleet at Turkana a resounding defeat. Reports indicate that of the six wings (72 fighters to a wing) of TIEs that met the Rebel's at Turkana, none survived intact. Less than three wings worth of TIEs (216 fighters) were considered combat capable after the Imperial fleet withdrew. The rest were either space debris or scrapped.

The Y-Wing's Koensayer Ion Jet engines were not as powerful as the Incom fusion engines and give the Y-Wing an optimum speed of 80 MGLT - only the TIE Bomber was slower. However, Koensayer was the prime builder of the Y-Wing, and was reluctant to redesign and re-engineer the venerable Y-Wing for the more powerful Incom engines. Some also attributed pride as a reason for not re-engineering the Y-Wing, since the Y-Wing was the Rebellion's first starfighter, and had served admirably for many years before the advent of Incom's X-Wing. Either way, the reduced thrust-to-mass ratio, and only having two engines (instead of the four on the X-Wing) severly hampered the Y-Wing's ability and effectiveness in dogfighting. As such, the Y-Wing's lack of ability to roll and dive (only having two engines, widely spaced from the center of gravity) relegated the Y-Wing to an light assault/bomber role. As with the X-Wing, the Y-Wing's navicomp was extensive, and combining an astromech droid, gave the Rebel pilot 7-8 preset hyperjumps. This alone was one reason why the BTL-AF Y-WIng (LP) or Longprobe was developed. With additional provisions and enhanced sensors, the Y-Wing was ideal for long-range patrol duty in the early years of the Rebellion. The Y-Wing is heavily armored, making it very durable and allowing the Y-Wing to survive an initial blast of laser fire while closing with its target. In the hands of a combat-hardened veteran, who constantly adjusted thrust and exhaust vane settings, the Y-Wing could deliver a deadly blow to convoys and depots that were not heavily defended. Indeed, as more X-Wings were produced following the Rebel's victory at Yavin IV, most Y-Wings were relegated to outer Rebel posts for patrol, convoy escort, and "hit-n-fade" runs on Imperial convoys and depots. Combined with X-Wing or A-Wing escorts, a squadron of Y-Wings could easily deliver enough proton torpedoes and ion cannon blasts to make even the most stubborn ISD commander withdraw.

While the X-Wing was considered to be the Alliance's all around fighter, the A-Wing is the Rebel's premier interceptor and dogfighter. Based on Jan Dodonna's design, the first A-Wings were handcrafted singly on various systems sympathetic to the Rebellion. Most of these original A-Wings were powered by Novaldex J-77 "Event Horizon" engines, relying on centered thruster-control jets for maneuverability. The J-77's also incorporated thrust vectoring principles (like in the F-22 and Joint Strike Fighter) for enhanced performance. Later versions were powered by Hoersch-Kessel (H-K) ion drives (similar to the Sienar PS4 drives), which propels a ship by having its reactors generate a stream of charged particles. In either case, the A-Wing can reach a blistering speed of 120 MGLT. The HK ion drives avoid the thermal management issues of the SP4 drives mainly by incorporating large exhaust vanes in the A-Wing's rear. However, what the A-Wing has in speed, it lacks in shield and hull strength, and laser regeneration capacity. A-Wings were originally posted for base and convoy defense, but Rebel tacticians soon realized their potential for replacing Y-Wings on the "hit-n-fade" assaults on Imperial shipping. Given its cramped conditions within its wedge-shaped hull, the A-Wing's shields and hull strength are normally minimal. A smart Rebel pilot keeps his thrust near 100% and uses his adjustable stabilizer wings, and thrust vectoring in the A-Wing to accomplish incredible feats of maneuvering to avoid enemy fire. Even the lightest hit can cause critical systems failures. Two advantages the A-Wing does have is its wing-mounted pivoting blaster cannons and a relatively large concussion missile magazine (10). Combined with the latest and most advanced computer targetting and sensor suite, these advantages allow the A-Wing to perform its interceptor role beautifully. The combination of speed, variable blaster cannons, extensive missile capacity, and the latest in guidance and tracking, allows a squadron of A-Wings to devastate several squadrons of TIEs before they closed with the Rebel fleet. The "A-Wing Slash" was a devastating attack that used slower fighters (Y-Wings) to distract the enemy TIEs while the A-Wings closed in on the Imperial fighters and cut them to ribbons. Enhancements in the A-Wing's navicomp led to having 6 preset hyperjumps without the need of an astromech droid.

As fast and nimble as the A-Wing is, the Slayn and Korpil B-Wing is a lumbering giant. Each fighter is powered by a single immense Quadex Kyromaster engine with four individually adjusted thrust nozzles. The engine is fed by a single Vinop 02 K ionization reactor and four Slayn and Korpil JZ-5g7 power converters. There are four cooling plates (radiators) to dissipate exhaust heat. The B-Wing is almost as quick as the X-Wing (91 MGLT). The original fighters had an unusual cockpit gyro-stabilization system alloiwng the cockpit to remain stable while the rest of the ship rotated around it. This systems signficantly reduced stresses on the fighter's structure due to sudden shifts in inertia during combat. However, since the thrust nozzles are tightly packed near it's center of gravity, the B-Wing simply had no effective turning capability. These small thrust nozzles are only marginally effective in redirecting the ion stream, making the B-Wing nearly unsuitable for dogfighting. Combined with its odd laser and ion cannon layout, the B-Wing frustrates many a combat pilot when forced into a turning battle with Imperial TIEs. Couple this with a tiny navicomp that only allowed two hyperjump presets, and it becomes apparent why B-Wing pilots are few and far between. Those who do become qualified for the B-Wing tend to love the B-Wing's relative speed, immensely powerful shields and rugged hull strength. The Novaldex shield generators are some of the best and largest in the Rebel's inventory, giving the B-Wing an incredible ability to take punishment. Combining B-Wings with escorting A-Wings allowed the Rebels to field an incredible fighting force, as they learned in the waning moments of the Battle of Endor. When Admiral Ackbar commenced his "Ackbar Slash" maneuver (a variation of which is the previously mentioned "A-Wing Slash"), it's suddeness and ferocity broke the remaining Imperial ISD commanders' resolve and drove many of them into emergancy hyperjumps.

In Return of the Jedi, when the Rebel fleet arrived at Endor, and when the fleet of star destroyers moved into its attack position, both fleets did so with a net deceleration of several thousand g's. Starfighters are considerably faster. An Imperator-class star destroyer (ISD) is able to outrun the Millennium Falcon in linear sublight acceleration (as evidenced in Empire Strikes Back), and most starfighters are significantly faster than the Falcon. Therefore, most starfighters are capable of straight-line accelerations and decelerations on the order of at least thousands of g, no less than some tens of thousands of ft/s². So why aren't the pilots and crews of these ships squashed flat? Devices called inertial dampers are used to prevent these accelerations from destroying the pilot/crew and instruments. This technology is a commonplace use as part of artificial gravity generators and compensators. Computers, tied into the ships flight control and engine systems, apply a force through a compensator to the ship's interior, varying to counterbalance the inertial forces caused by external acceleration and maneuvers. Like any mechanicsl system, even inertial dampers have practical limitations. Sometimes a force is too violent or sudden for the compensator to adjust and counterbalance, leaving a potentially deadly residual force. As in fighter and transport aircraft on this planet, which has safety limits imposed by the number of g's the airframe can sustain, so to is there safety limits of inertial integrity for starfighters, which is a critical parameter in determining starfighter performance. Because starfighters are subject to more severe accelerations than commercial vessels like freighters and corvettes, they are fitted with a higher grade of inertial dampers. Nonetheless, many pilots turn down their dampers slightly, so that they experience a tiny fraction of the true acceleration. This aids a pilot's intuitive physical sense of his craft's motion. However, some pilots foolishly turn their dampers on full, elminating any sense of their fighter's motion and or performance, usually leading to deadly consequences (e.g., Jek Porkins during the battle at Yavin IV).

Most, if not all, star fighters, transports, and capital ships possess some form of repulsorlift generator for movement near a planet's surface. The most noteable exception to this group is the TIE fighter which is normally berthed and manuvered throughout the docking bay with tractor beams. Most of the TIE family of starfighters do not have landing gear (again there is no room in their compact design). The preferred method of launching and docking is hanging from a specialized rack of gantries, providing access for pilots and technicians. Review of various comics and novesl suggest the wings actually carry the weight of the unpowered TIE. On the otherhand, it simply may small repulsorlifts in some form of active mode holding the TIE in place while it's parked. Heavier Imperial transports rely entirely on landing pads because of their enormous weight (i.e. the Lambda shuttle and the Imperial landing craft) and their wings are raised to avoid impact with the landing surface. All Rebel fighters are equipped with repuslors, thereby allowing them to have greater versatility since they can launch on their own from either a ship's hanger bay, or the surface of a planet or moon.

As previously mentioned, most TIEs lack hyperdrives. The lack of a navicomp and hyperdrive motivator reduces the TIE's mass, adding to its sublight flight performance. The Imperials viewed this as not a serious tactical or strategic restriction since the Imperial forces can send enormous warships or surface garrisons virtually anywhere in the galaxy, there was no shortage of potential motherships or bases for short-range fighter missions. On the other hand, the Rebel Alliance installed navicomps and hyperdrive motivators on all their ships, tranports and fighters. This allowed them a tactical, and sometimes strategic, advantage of conducting hit-and-fade attacks in the early days of the Rebellion. Later on, Rogue squadron, and Wraith, used their hyperjump capability with great effectiveness in dealing with threats from Director Isard, Grand Admiral Thrawn, and Warlord Zjinn.

So it may be possible one day to strap on a star fighter and join the battle. All we'll need is a fission or fusion reactor capable of generating large quantities of ions (in the mega-joule range), computer-enhanced electromagnetic fields capable of controlling this ion stream, and computer-controlled inertial dampers to handle thousands of g's of force generated in starfighter combat. Sounds far fetched? Maybe not. Thrust vectoring exists on current fighter technology. NASA has been pursuing nuclear reactors for ion engines since the early 70's, and inertial dampers will be used on the spacestation Freedom being constructed as we speak. We are only limited by our imagination, creativity, and the will to pursue our dreams.

• 1. Scientific American, Article 2/99
  2. NASA JPL Web-Site
  3. NASA Web-Site
  4. Star Wars Essential Guide to Vehicles and Vessels
  5. TIE Fighter Collector's CD-Rom
  6. Heat Transfer textbook by J.R. Holman 7. Star Wars Essential Guide to Weapons and Technology
  8. X-Wing Collector's CD-Rom
  9. X-Wing vs TIE Fighter
  10. X-Wing Rogue Series Novels
  11. X-Wing Rogue Series Comics

  (Scott (A'Kula) Schimmels is a mild, meek-mannered engineer in real life. He has worked on several of the lastest AF projects to include: Global Hawk UAV, F-22 Raptor and the Joint Strike Fighter programs. He currently designs new advanced composite structures, when not playing the X-Wing® series of games {VBG})

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