Radiation - GarwelGarwel/KerbalHealth GitHub Wiki
Radiation Effects
Radiation in Kerbal Health accumulates and gradually but permanently reduces maximum Health Points that a kerbal can have. Radiation is measured in banana equivalent doses (bananas, for short) per day. By default, 1e7 (10,000,000) bananas reduce max HP by 10%. Therefore, 4e7 bananas will kill any kerbal, even if his/her health is full.
Sources of Radiation
There are two types of radiation in Kerbal Health: cosmic radiation and artificial radiation. The former affects all assigned kerbals, but its strength depends on the location of the vessel. Artificial radiation is produced by certain craft parts such as nuclear engines and reactors. Finally, some celestial bodies may be radioactive on their own (but this is extremely rare).
The main radiation formula is this:
Radiation = Exposure x (LocationCoefficient x CosmicRadiation + ArtificialRadiation)
Exposure is measured in percent and is 100% by default. Kerbals on EVA are more vulnerable to radiation and have 1000% exposure. Exposure can be lowered with Shielding (see below).
Cosmic Radiation
Cosmic Radiation consists of Solar Radiation and Galactic Rays. Galactic radiation is uniform everywhere while solar radiation follows the square root law:
SolarRadiation = NominalSolarRadiation x Sqrt(SunDistance),
where SunDistance is measured in Astronomic Units (distance from the Sun to the home planet). At 1 AU from the Sun, both solar is 2,500 bananas/day each and galactic radiation is 12,500 bananas/day.
Artificial Radiation
Artificial Radiation is created by certain parts. The stock game only contains one such part: NERV engine, which produces 500 bananas/day. RTGs are not radioactive, because they use Plutonium-238, which is much safer than Uranium. You can check a part's radioactivity by holding mouse over it in the Editor.
Location Modifiers
Location Coefficient determines the fraction of cosmic radiation that reaches your vessel: the lower, the better. It is always 1 (or 100%) in interplanetary space, but elsewhere it can be reduced by magnetosphere, atmosphere and occlusion.
Magnetospheres
Most planets and some moons have magnetospheres that stop some radiation. Kerbin's magnetosphere is considered standard and it works as follows:
- In space high (i.e. below 160 km in stock KSP): 40% of cosmic radiation reaches the vessel
- In space low (above 160 km): 20% of cosmic radiation reaches the vessel
Some celestial bodies have stronger magnetospheres and some have weaker or none (see below). Moons by default lack a magnetosphere of their own. However, magnetospheres' effects are additive (or rather, multiplicative): if you are in a SOI of a moon that has a magnetosphere, its Location Coefficient will be multiplied by that of its parent planet. See a table below for data on stock celestial bodies.
Atmospheres
Atmosphere is usually very effective in shielding the surface from radiation (high atmosphere less so than low atmosphere). Kerbin is again considered standard with the following effects:
- Stratosphere (flying high): 20% of radiation passes through
- Troposphere (flying low): 1% of radiation passes through
Note that these numbers are multiplied by the planet's magnetosphere effects. So in Kerbin's case, where in-space low coefficient is 20%, only 4% of cosmic radiation will reach the vessel in the upper atmosphere and merely 0.2% in the lower. Again, some planets and moons have thicker atmospheres than Kerbin and some have thinner.
Occlusion
A celestial body itself is the best radiation shield and prevents all radiation from passing through it. So the closer you are to it, the more radiation will be stopped by the planet or moon. On the surface (sea level), it will be 50%. Note that Kerbal Health doesn't take day or night time into account.
Radioactive Planets
Some celestial bodies may emit radiation. It means that the closer you get to the surface, the higher dose your kerbals receive. This radiation negates atmospheric and magnetosphere effects, but can still be reduced by ship's shielding. As of v1.3.1, only one celestial body in Outer Planets Mod uses this feature, but more might be added by planet pack authors.
Measuring Radiation
Since version 1.3, there is a way to check radiation level in a certain location before sending in your kerbals. Some parts now include a magnetometer and/or a Geiger counter. The latter measures current cosmic radiation in bananas while the former only measures the percentage of radiation blocked by the magnetosphere(s), i.e. not taking into account atmospheric and occlusion factors. This feature is provided by relevant parts in DMagic Orbital Science and KSP-IE mods (as well as some other mods). If you don't have those, some advanced probe cores will have these modules included.
Solar Weather and Radiation Storms
In addition to the rather stable background radiation, your kerbals run a risk of being hit by a radiation storm (a.k.a. coronal mass ejection). These events are rare, happening on average less than once a year, but can be extremely powerful. You should take them into account when planning any long-term mission.
Radstorms
A radstorm always targets a specific planet (together with its moons) or ship in the interplanetary space. It travels from the Sun very fast (average speed being 500 m/s) losing magnitude with distance and is affected by all normal location modifiers (magnetosphere, atmosphere and occlusion). So your kerbals will barely notice it on the surface of Kerbin, but can be roasted if they are hit in the vicinity of Moho orbit.
You will be warned about an incoming radstorm, usually about a day before it happens (depending on its speed). There will also be an estimate of its strength, ranging from medium (average of 800 days of normal solar radiation, or 2M bananas at 1 AU from the Sun) to extreme (average of 16,000 days of normal solar radiation, or whopping 40M bananas). Some estimates may be incorrect, and you will know the actual level of radiation damage when the storm passes.
Solar Weather
The chance of a radiation storm depends on the phase of the solar cycle. Solar cycles are 11 years long, and they start at minimum solar activity. At its peak, the Sun will have a radstorm on average every 437 days against 6,667 days at its minimum (for every possible "target"). At the beginning of every year you will receive a message telling what part of the solar cycle you are in and the current chance of a radstorm.
Radiation Shelters
Whenever a radstorm hits a vessel, the crew is assumed to hide in the radiation shelter. You don't need to move them manually. A shelter in Kerbal Health is a part, or several parts, that (1) have enough sits for the entire crew and (2) have the lowest possible _local _exposure. Local exposure of a part is provided by shielding of that specific part and all its neighboring (directly attached) parts without crew capacity. If local exposure in all parts is higher than the exposure in the vessel, the latter is used instead. See section below for discussion of radiation shielding and exposure calculation.
Radiation Protection
The only way to reduce the amount of radiation your kerbals receive is by reducing their Exposure with Shielding. The bigger the vessel, the more Shielding you will need, but you will never achieve 0% exposure due to diminishing returns:
Exposure = 2 ^ (- Shielding x (CrewCapacity ^ (-2/3))
Example: A simple 1-man pod with a shielding rating of 1 will have an exposure of 50%. It means that 50% of radiation (both cosmic and artificial) will reach the kerbal inside. A shielding rating of 7 will bring this value to less than 1% (because 2^(-7)=0.0078125). But a 2-seat vessel will require a shielding rating of 11 to achieve the same exposure. These figures are shown in the Health Report window in the Editor.
There are three ways to increase Shielding. First, it is provided by a special resource called, well, Radiation Shielding. You can add this resource to most crewed parts and to some others too. 1 unit of Radiation Shielding weighs 0.1 t and provides, you guessed it, 1 level of Shielding. Just note that, by default, this resource is empty, so you'll have to add it to the parts in the Editor if you want radiation protection. It also cannot be transferred in-flight, so plan ahead.
If it's not enough, Shielding is also provided by certain craft parts: heat shields (ablator is not required), panels and very large cargo bays. You can further strengthen them by adding more Radiation Shielding.
Lastly, for the most creative, some other resources can also be used as radiation protection: Lead, Water, WasteWater as well as water-containing Supplies and Mulch (used by USI-LS). When used with right mods, it allows you to even produce your own makeshift shielding in-situ.