Fission Engine

Do not confuse with the fanmade Expanded Fission Engine or Fissile Fuel Cell Engine. An older technology still encountered occasionally, particularly in the Periphery, fission engines use nuclear fission by splitting heavy atoms for energy. Most often, the goal is thermal energy used to drive either a gas or steam turbine to generate electrical power which is then harnessed for various ends.

History
The use of nuclear fission for propulsive power was an early goal of nuclear research, one attained by the predecessors of the Western Alliance in under two decades from the end of World War II. At first limited primarily to large maritime applications (particularly submarines) and initially used by military vessels for reasons of cost, the idea of using fission engines for smaller-scale work was an enduring one that blossomed as technology advanced. Despite the drawbacks (primarily safety and the sheer weight of the engines themselves), fission engines are not an uncommon choice for powering IndustrialMechs and support vehicles. Military use is much rarer, particularly on smaller units like BattleMechs or combat vehicles, and was pioneered by the Taurian Concordat in 2882.

Benefits and Drawbacks
Fission engines have certain distinct advantages compared to Internal Combustion and Fuel Cell engines. They are very fuel efficient, providing ground vehicles with a functionally unlimited range defined more by a time measured in months to years, and the efficiency is such that the rules do not track fission engine fuel use for such units. Fission engines are a high power energy source, meaning that units using them do not need power amplifiers for certain energy-intensive applications and are even able to use heavy Gauss rifles. Finally, fission engines require a somewhat simpler, less advanced industrial base to build and maintain than even the simplest fusion engines do, although the details of this point are obscured by the broad classification by Technology Rating; they are both classed as D.

Fission engines are not without their drawbacks. A caveat to their fuel efficiency is seen in aerospace operations, where the fission reactor's own fuel duration is unaffected, providing a considerable endurance of power, but propellant use is much less efficient. Fission engines use radioactive fuels by definition, making a damaged engine a danger to the unit's operator(s) and requiring heavy radiation shielding for normal safe operation that makes them one of the heaviest engine types, even compared to internal combustion engines. The size of fission engines frequently makes them more costly than an equivalent but safer and lighter fusion engine. Safety concerns also make them a controlled item.

Manufacturing
Many entries on this list represent best guesses based on support vehicle entries, which do not always note manufacturing location or engine brands and models. Customarily, the name and, if known, world of the vehicle's manufacturing company is used in these cases and marked with a question mark. Fission engines are manufactured on the following planets:

Fanmade extras
Fission Engines are universally and objectively awful compared with Fusion engines. They are 33% more expensive, have the same Tech requirements; they are also always heavier, and have half the amount of heatsinks, which doesn't even make up for their increased weight. They also require additional shielding on vehicles with makes them heavier still, even heavier than ICE. All in all, they are nearly completely useless as written, and there would be no reason to take one given that Fusion prices are lower for being better in literally all regards, with the same tech rating.

There is a chance to use Fission in a 'mech that barely requires heating as a very narrow (on the weight and cost scale) alternative to Fusion, Fuel Cell, or Light engines; however, all things considered, you are most probably better off with one of those. In vehicles, you are *always* better off with one of those, and there is no circumstance at all to justify Fission.

These rules and extra equipment aim to offset that imbalance somewhat, thus giving something in return to its drawbacks to fission tech.

Fan variants

 * The Expanded Fission Engine is meant to provide Fission engines with more usability, since they are otherwise strictly inferior to Fusion ones, while also being more expensive and having the same tech rating. This version occupies more slots, equivalent to an XXL engine, and weights 1/3 of the base one, while not being nearly as expensive as a Fusion XXL.
 * Fissile Fuel Cell Engines (FFCE) are Fuel Cell Engines that use fissile nuclear fuels such as Plutonium to power up a vehicle or 'mech. The fission provides power without a reactor.

Fission tech downgrade
''Fission Engines are normally classed as D-level on the tech scale, which puts them in the same classification than Fusion. However, Fission Engines were already used in vehicles from the middle 20th century, when Fusion wouldn't be viable, let alone miniaturized, for a long time. Fission Engines would be more available to primitives, rogue actors, Periphery, and Deep Periphery states.''  As such, with this optional rule, Fission Engines should be considered C-level tech.

Fission C-bill discount
''Fission Engines would be easier to construct than Fusion ones due to the lower concentration of forces involved in splitting atoms rather than joining them. They would also not require lostech facilities during the darkest times of the Sucession Wars, when Fusion engines were explicitely scarce. As a result, many Fission engines would be built, making them cheaper due to greater supply. Even when Fusion engines are reintroduced to a greater extent, their superiority would drive down the price of pre-existing Fission engines.''  When playing with this optional rule, C-bill cost of Fission engines is halved, so they cost 2/3rds of a Fusion one rather than 4/3rds. This discount doesn't apply to Expanded Fission Engines, which would still cost 5/3 of the regular C-bill cost of a basic Fusion engine.

Fission Extra Shielding Optional Removal
''Fission Engines use extra shielding in vehicles, which means 50% more weight, making them much more weighty than even Internal Combustion and thus mostly untenable for an efficient machine. However, it is possible to not utilize this extra shielding and dedicate the weight to more components instead. Take into account that it still uses the standard shielding which is enough for 'mechs, so we are not talking of an exposed core.''  When playing with this optional rule, vehicles can be designed or refit with a "Minimal shielding Fusion Engine" which weights equal to its 'mech counterpart.

'''However, removing the extra shielding does have its drawbacks. If the engine receives a critical hit, a cascading radiation containment failure will immediately occur. This will instantly kill all the crew (with no chance to eject or escape, unless they are using anti-radiation suits), and destroy any and all the following components (due to radiation frying complex electronics):''' '''Crewmembers with Radiation Suits will have just enough measure of protection to escape the vehicle, but don't have the chance to survive should they be unconscious at the moment of the hit, or foolishly choose to stay on the unit. The unit cannot be piloted in the rest of that combat; any crew entering it, friend or foe, radiation suit or not, will be instantly killed by the still-leaking radiation.'''
 * Drone control systems
 * Targeting Computers
 * ECM and BAP (and their variants)
 * Communications Equipment
 * Neuro-Gunpacks and Robo-Guns (fanmade)

'''At the end of combat, the unit can be salvaged with no additional damage, given the regular assumption that the salvage crew can clean up the radiation and shut down the reactor. The destroyed components will need to be replaced or removed.'''

The removal of extra shielding can't be done on Expanded Fission Engines, as they already have a reduced amount - and would already be lighter than a removed-shielding standard Fission, even with their 50% weight increase.

Fission Criticality
 If playing with this optional rule, Fission Engines always use the Stackpoling rules, while Fusion engines don't.

Fission Deliberate Meltdown
 If this optional rule is active, you can use the full turn of a Fission-toting unit to try to deliberately melt down the reactor. This produces 1 heat in heat-tracking units for every full 50 of the Fission engine's rating (no rounding). Then, if your unit is above its heat limit, roll 2d6. If the result is equal or lower than your unit's pilot Piloting skill (yes, bad pilots have higher chance of blowing up; this is deliberate), the unit Stackpoles. Non-heat tracking units always roll the 2d6 but only Stackpole on a natural 2 or 3.

Destruction Waste Radiation
 If playing with this optional rule, after the unit is destroyed (including by stackpoling explosion), an area is contaminated with radiation for 100 years (so permanently, for normal gameplay purposes). This radiation deals 1d6-1 damage to infantry and Battle Armor for each turn they end inside it. To non-infantry units, it deals 1 damage per turn they end inside it to their center structure (body or center torso, for example), bypassing armor, unless that armor is Ablative Armor, in which case the armor is damaged.

The size of the area contaminated depends of the rating of the engine:
 * 10-100: Only contaminates the same hex.
 * 110-200: Contaminates same hex and 1 hex radius.
 * 210-400: Same hex and 2 hex radius.
 * 410+: Same hex and 3 hex radius.

Contamination of a ground hex can be cleared permanently by firing 1 ton of water through Sprayers. However, water hexes aren't immune to contamination. In the case of water hexes, the contamination clears automatically in 10 turns.

Fusion Engine Inexistence (ban)
''Fission Engines do have some advantages over Internal Combustion and Fuel Cell engines: They don't use explosive fuel tanks vulnerable to critical hits that destroy your unit, they have effectively unlimited operating range, and they don't require Power Amplifiers. However, that all goes through the window with the existance of Fusion engines which are just cheaper, lighter, cooler, more common, and better in just about every conceivable way. But... what if we were to say fusion engines just didn't ever exist? Hoho, delightfully devilish, laws of physics...

Well, this is our lucky day, because they don't, and in real life there is no perspective that they ever will, at least as depicted in BattleTech (the only known fusion power plants are stars, after all). Since all other sublight engines, and most weapon types, are based on proven physical principles - only Fusion Engines (which can even be man-portable at a size of 10) are complete fantasy. As such, we can (and arguably should) exclude them from the game completely! Then, we finally have some reasons to mount Fission engines (sometimes), to gain some extra heatsinks and become immune to fuel tank explosions - by paying the difference in regards ICE and Fuel Cell in tonnage and C-bills.

It is possible to even think the game is much better balanced this way, since Fusion engines and their variants obsolete not only fission (strictly), but also all other engine types, specially on higher ratings and given that C-bills are not often a tracked issue in the gaming tables - being lighter (specially LT, XL and XXL variants which are much lighter even than fuel cells), not exploding, not requiring power converters, and coming with a nifty 10 heatsinks (which can be doubly OP if upgraded to Double Heatsinks at nil ton or slot cost while internal. Of course, all of these unbalanced issues dissapear if Fusion Engines as a whole are no more.''  When playing with this optional rule, any and all units of any type mounting Fusion Engines are disallowed from the game, as well as the equipment itself.

''This can be fluffed in a myriad of ways, from the encounter being in the Deep Periphery with no fusion tech, to an Alternate Universe of a fission-powered BattleTech lore as a whole. (including appliable 'mech redesigns with non-fusion engine types, if you want to go that far)''