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Radiation
This chapter applies to Kerbal Health v1.0.0, which has not yet been released
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 25%. Therefore, 4e7 bananas will kill any kerbal, even if his/her health is full. As of v.1.0.0, there is no way to reduce accumulated dose, so watch it carefully!
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.
The main radiation formula is this:
Radiation = Exposure x (LocationCoefficient x CosmicRadiation + ArtificialRadiation)
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 SunDistance ^ (-2),
where SunDistance is measured in Astronomic Units (distance from the Sun to the home planet). At 1 AU from the Sun, both solar and galactic radiation are 5,000 bananas/day each.
Artificial Radiation is created by certain parts. The stock game only contains one such part: NERV engine, which produces 250 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.
The actual level of cosmic radiation that reaches the vessel depends on its altitude, presence of the atmosphere and whether it is on/near a planet or a moon. Here are the radiation levels in different locations, on a planet:
- Interplanetary space: 10,000 bananas/day (100%)
- In space high: 5,000 bananas/day (50%)
- In space low: 1,000 bananas/day (10%)
- High atmosphere: 200 bananas/day (2% = 20% stratosphere coefficient x 10% low space coefficient)
- Low atmosphere and on the ground (if atmosphere is present): 10 bananas/day (1% troposphere coefficient x 10% low space coefficient)
- On the ground of non-atmospheric planets: 1,000 bananas/day (10%, same as in space low)
Moons don't have a magnetosphere of their own, so they have different values:
- A non-atmospheric moon, regardless of situation: 5,000 bananas/day (50%, same as in space high for planets)
- Atmospheric moon, flying high: 1,000 bananas/day (10% = 20% stratosphere coefficient x 50% high space coefficient)
- Atmospheric moon, flying low and on the ground: 50 bananas/day (1% troposphere coefficient x 50% high space coefficient)
The only way to reduce the amount of radiation your kerbals receive is by reducing their Exposure with Shielding. Each level of Shielding reduces Exposure by half. Shielding is provided by certain craft parts: panels and heat shields, ablator is not required. Shielding of all the parts adds up; their location on the vessel is unimportant. Bigger vessels need more shielding:
Exposure = 2 ^ (- Shielding x (CrewCapacity ^ (-2/3))
Example: A simple 1-man pod with a 1.25m heat shield will have a shielding rating of 1 and 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 about 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.