Reactors
Reactors are devices that are designed to use up some fuel in order to create heat. In this sense, a reactor could be anything from a bonfire to an antimatter reactor. The power output of a reactor is ultimately determined by the energy density of the fuel; in space travel it is important to maximize energy density in order to keep weight to a minimum.
In KSP Interstellar, reactors produce Thermal Power, which is consumed by either electrical generators to produce MegaJoules, or thermal rockets and turbojets to produce thrust. Generators and thermal rockets MUST be attached directly to a reactor in order to function.
This pack includes three types of reactors in various sizes:
- Nuclear reactors, powered by either uranium tetraflouride or thorium tetraflouride. They provide long term amounts of low power.
- Fusion reactors, powered by deuterium and tritium, requires MJ to start and operate the reaction laser. They provide a medium amount of power but with a shorter lifetime.
- Antimatter reactors, powered by (you guessed it) antimatter. They provide insane amounts of power but eat antimatter at an alarming rate.
Reactor effectiveness is determined by two properties: Power -- which is simply the amount of thermal power they produce -- and core temperature, which determines the efficiency that [generators](Electrical Generators) operate and the specific impulse of attached [thermal rockets](Thermal Rocket Nozzle and Thermal Turbojet). In general, antimatter reactors produce the more power than fusion reactors of the same size. Likewise, fusion reactors produce more power than fission reactors. Fusion reactors have higher core temperatures than fission reactors. The core temperature of antimatter reactors depend on the size of the reactor.
When upgraded, a reactor's power and core temperature both increase by a significant amount, along with fuel consumption to match.
Fission reactors are the first type of reactor you can unlock. They have the lowest temperature and thermal power of all the reactors, but they balance out with their long-lasting stores of UF4 or ThF4. Fission reactors can last a very long time without refueling. The actinide waste can also be reprocessed using a refinery or a science lab to vastly increase their lifespan, and the reactors can be refueled to extend it indefinitely. The fission reaction requires a minimum power level to sustain itself, and so these reactors cannot go below 30% power production unless they are shut off.
The smaller reactors last longer than the larger ones. However, the larger reactors have a better power to mass ratio, and so it is usually beneficial to use one larger reactor rather than several smaller reactors.
Fission reactors have two fuel modes: Uranium and Thorium. Thorium reactors produce more power than Uranium reactors and have a slightly higher core temperature (which is good!). However, Thorium reactors' power output declines as actinides build up, and so they need to be reprocessed regularly in order to maintain peak efficiency. The fuel a reactor uses can be set in the VAB, and can also be changed on-the-fly using a kerbal on EVA. In order to swap fuels, you need to have enough of the new fuel to fill up your reactor and enough empty space for the old fuel to be stored into. The reactor must also be shut down and cooled completely.
Reactors can be shut down via an EVA. They will also automatically shut down if waste heat on your vessel exceeds 95%. Shut down reactors enter a cooling state, where they will produce 10% of the maximum thermal power, which gradually decays down to 0% over several days. Once they are cooled completely, they can be refueled, have their fuel type swapped, or restarted using the context menu with an EVA kerbal.
Prior to being upgraded, fission reactors are difficult to use in thermal rockets. The unupgraded 62.5cm and 1.25m reactors are inferior to the stock LV-N when used as thermal rockets. They are best used to provide large amounts of electricity or to power thermal turbojets. The 2.5m reactor is usually somewhat inferior to the LV-N when using Uranium, but can match it in effectiveness when using Thorium. The 3.75m reactor is superior to the LV-N (albeit only when flying very heavy craft) using either fuel. Once you upgrade the reactors, they are all superior to the LV-N (With exception, perhaps, to the tiny 62.5cm reactor)
Fusion reactors are the second reactor type unlocked, and they serve as the mid-range reactor. They provide more power to mass than nuclear reactors and have comparable core temperatures to the upgraded fission reactors (which are unlocked at the same time as fusion reactors).
A fusion reaction is more complex than a fission reaction to maintain. Thus, fusion reactors require a constant supply of electricity in order to operate. The amount of power they require is much less than they produce with a generator, and therefore it is wise to always have an electrical generator attached to at least one fusion reactor so that they can sustain themselves. Unlike fission reactors, fusion reactors do not need a kerbal to shutdown or restart them. All they require to restart is a sufficient supply of electricity to run the internal laser for a fraction of a second in order to jump-start the reaction. On the other hand, like fission reactors, they must operate at a minimum of 30% power production.
Fusion reactors are unique in that in a portion of their power output is in the form of charged particles rather than thermal power. Charged particles are similar to thermal power, but they can only be used to generate electricity. The conversion rate of charged particles to electricity is much more efficient than thermal power at a theoretical maximum efficiency of 85%. In order to utilize charged particles, the attached generator must be a Direct Conversion generator, which can be set in the VAB.
The ratio of thermal power to charged particles a fusion reactor produces is dependent on the fuel it uses. By default, they come with a supply of deuterium and tritium. D/T produces 80% thermal power and 20% charged particles. It is therefore a good combination to use as a thermal rocket, as the 80% thermal power can be used to power the rocket while the 20% charged particles are used generate the power needed to sustain the reaction. If you have a supply of helium-3, you can also run the reactor in D/He-3 mode or pure He-3 mode. D/He-3 mode offers 21% thermal power and 79% charged particles, which makes it much more efficient than D/T when making electricity. A thermal rocket would not provide much thrust while D/He-3 mode, but a second generator may be attached instead to collect the thermal power, giving you more total electricity. Pure He-3 mode produces 100% charged particles and so provides the most efficient way to generate electricity with fusion. However, thermal rockets cannot be used with a He-3 reactor at all.
All three fuel modes have the same core temperature and total power output. Fuel and power consumption, however, is different. D/He-3 fusion consumes the least amount of fuel mass per unit of power generated and requires 1.5x the power of D/T to sustain the reaction. Pure He-3 is the most mass inefficient and requires 2x the power of D/T to sustain the reaction. The fuel mode of a reactor can be swapped at any time, provided you have the fuel for it.
Antimatter reactors are the last to be unlocked, and provide some of the best end-game performance. They operate counter-intuitively compared to fission and fusion reactors. The smaller reactors have lower core temperatures and therefore less efficiency, but they have a higher TWR over the larger reactors. They are also more flexible than either fission or fusion reactors, and thus have no minimum power output.
Their core temperatures are inferior to upgraded fusion reactors, which you will gain access to when you unlock antimatter. However, they provide so much more power for their mass that they are still very effective in any situation that requires a high level of thrust. If you require more fuel efficiency, they also can be used to power the high-efficiency plasma engine, which provide very respectable amounts of thrust at these power levels. Once upgraded, they outclass every other reactor in both core temperature and power production and therefore offer superior performance in every way.
All of the antimatter reactors are powerful enough to launch payloads to orbit using only thermal rockets, and thus can be used in high-efficiency SSTO rockets and spaceplanes, provided you have a way to fuel them with antimatter on the ground.
Powering these beasts requires antimatter. Antimatter is difficult to collect, and is the only resource that cannot be procured from the VAB. It must be created in a science lab or collected by an orbital collector farm. A thousand or so units of antimatter should be sufficient for most short-term missions. Unlike fission or fusion reactors, antimatter reactors will only consume antimatter when necessary, so you can get by with very little if you only perform a small amount of burns. It is recommended to provide a secondary power source such as a fission or fusion reactor in order to power the antimatter containment devices. Otherwise, you are likely to burn up your entire antimatter supply powering the containment devices during the long transfers.
All outputs assume liquid fuel. Visit the Thermal Rocket Nozzle and Thermal Turbojet page for a complete breakdown of different fuels
Fission reactor stats are for Uranium
- Mass: 0.3375 t (0.225 t dry)
- Resources: 0.0225 m^3 UF4 (0.1125 t)
- Core Temperature: 1674 K / 11,590 K
- Power Output: 1.5 MW / 4.5 MW
- Consumption: 7.82e-6 m^3 per day / 2.35e-5 m^3 per day
- Lifetime at 30%: 26 years 100 days / 8 years 277 days
- Lifetime at full power: 7 years 322 days / 2 years 229 days
- Mass: 2.5 t (1.5 t dry)
- Resources: 0.2 m^3 UF4 (1 t)
- Core Temperature: 1674 K / 11,590 K
- Power Output: 40 MW / 120 MW
- Consumption: 8.31e-5 m^3 per day / 2.49e-4 m^3 per day
- Lifetime at 30%: 21 years 357 days / 7 years 119 days
- Lifetime at full power: 6 years 217 days / 2 years 72 days
- Mass: 14 t (8 t dry)
- Resources: 1.2 m^3 UF4 (6 t)
- Core Temperature: 1674 K / 11,590 K
- Power Output: 500 MW / 1500 MW
- Consumption: 1.04e-3 m^3 per day / 3.12e-3 m^3 per day
- Lifetime at 30%: 10 years 196 days / 3 years 187 days
- Lifetime at full power: 3 years 59 days / 1 years 20 days
- Mass: 43 t (28 t dry)
- Resources: 3 m^3 UF4 (15 t)
- Core Temperature: 1674 K / 11,590 K
- Power Output: 3 GW / 9 GW
- Consumption: 6.24e-3 m^3 per day / 0.0187 m^3 per day
- Lifetime at 30%: 4 years 143 days / 1 year 169 days
- Lifetime at full power: 1 year 116 days / 160 days
- Mass: 0.2063 t (0.2 t dry)
- Resources: 3.125 kg Deuterium (0.0031 t), 3.125 kg Tritium (0.0031 t)
- Core Temperature: 10,394 K / 57,742 K
- Power Output: 22 MW / 66 MW
- Consumption: 5.51e-3 kg per day / 0.0165 kg per day
- Lifetime at 30%: 10 years 131 days / 3 years 165 days
- Lifetime at full power: 3 years 39 days / 1 year 13 days
- Mass: 1.55 t (1.5 t dry)
- Resources: 25 kg Deuterium (0.025 t), 25 kg Tritium (0.025 t)
- Core Temperature: 10,394 K / 57,742 K
- Power Output: 175 MW / 575 MW
- Consumption: 0.0438 kg per day / 0.131 kg per day
- Lifetime at 30%: 10 years 155 days / 3 years 173 days
- Lifetime at full power: 3 years 46 days / 1 year 16 days
- Mass: 2 t
- Core Temperature: 6698 K / 140,278 K
- Power Output: 5 GW / 15 GW
- Consumption: 0.1385 mg per second / 0.4155 mg per second
- Runtime on 1000 mg of Antimatter: 2 hours 20 seconds / 40 minutes 7 seconds
- Mass: 16 t
- Core Temperature: 15,012 K / 409,977 K
- Power Output: 40 GW / 120 GW
- Consumption: 1.108 mg per second / 3.324 mg per second
- Runtime on 1000 mg of Antimatter: 15 minutes 3 seconds / 5 minutes 1 second
- Mass: 54 t
- Core Temperature: 22,922 K / 646,146 K
- Power Output: 135 GW / 405 GW
- Consumption: 3.7395 mg per second / 11.2185 mg per second
- Runtime on 1000 mg of Antimatter: 4 minutes 27 seconds / 1 minute 29 seconds
- Available to: Fusion Reactor, Antimatter Reactor
- EVA Only: No
Fusion and Antimatter Reactors can be started and shutdown at will. Fusion reactors do require the available power to run their laser or they will immediately shutdown.
- Available to: Fission Reactor, Fusion Reactor.
- EVA Only: No
Nuclear reactors can also be used to breed Tritium, an important isotope of Hydrogen used in nuclear fusion. Enabling tritium breeding requires a source of Lithium on the ship, this Lithium will slowly be turned into Tritium.
- Available to: Fission Reactor
- EVA Only: Yes
Nuclear reactors require an EVA to turn off and restart. Once the reactor has been shutdown, it will continue to produce a small amount of power for the next three days, this is from the radioactive decay of fission products inside the reactor. The amount of power available will decay with a 9 hour half-life. It is not safe to do anything further with the reactor until the decay heating period has ended.
- Available to: Fission Reactor
- EVA Only: Yes
This option is only available when the Fission Reactor is shutdown and the decay heating period has ended (see the Manual Restart/Shutdown section).
It is possible to refuel the reactor whenever the reactor is less than 100% full of Actinides, though more fuel can be contained if the reactor is relatively free of Actinides. Refueling transfers the fuel from an available container of the appropriate resource type in to the nuclear reactor.
- Available to: Fission Reactor
- EVA Only: Yes
This option is only available when the Fission Reactor is shutdown and the decay heating period has ended (see the Manual Restart/Shutdown section) and the Reactor is (essentially) free of Actinides.
This option changes the reactor from using UF4 Fuel to ThF4 fuel, or vice-versa. In order to do this, you need not only a supply of the new fuel type but you also need some spare tank capacity of the old fuel type to put the old reactor fuel in.