Health Factors

Health factors is what changes a kerbal's health. They can be of two types: ordinary and marginal.

Ordinary Health Factors

• Assigned (kerbal is on a mission): -0.5 HP/day
• Overpopulation (scaled in proportion to crew/capacity ratio): -6 HP/day for a full vessel
• Loneliness (only 1 kerbal on the vessel, badass kerbals immune): -1 HP/day
• Microgravity (orbital/suborbital flight or under 0.1 g conditions, e.g. Minmus): -0.5 HP/day
• EVA: -50 HP/day (don't abandon your kerbals outside for long!)
• Connected (having a working CommNet to home): +0.5 HP/day
• Home (at Kerbin at altitude of under 25 km): +1 HP/day
• KSC (kerbal is recuperating in KSC, i.e. available): +5 HP/day

Health Multipliers

Certain parts can reduce or increase the effect of a health factor allowing for much longer and healthier flights, in exchange for a good amount of EC. A part can give this bonus to a limited number of kerbals. If it affects more than its crew cap, its effect is diminished.

Marginal Health Factors

The Cupola provides "marginal health change" bonuses. If a kerbal receives, say, a 3% marginal health change bonus, he/she will recover 3% of their lacking health (i.e. of the difference between their current HP and the maximum HP) every day. This change works in parallel with the normal health factors above.

Example: A 5-star kerbal (maximum HP = 150) currently has 50 Health Points and is in a vessel that gives him a 5% marginal change bonus. The vessel is full and he has a crewmate. It means that he recovers (150 - 50) x 5% = 5 HP per day and loses (1 + 7 - 1) = 5 HP per day. It means that the marginal change balances out the "normal" change and his health will stay around 50 HP (33%) until the situation changes.

As you see, this mechanics may allow some kerbals to stay relatively healthy for an unlimited time. It may look cheaty, but the point is that: (1) there should be a way to design long-term missions without spamming crew space, (2) it requires a lot of heavy, relatively high-tech parts and therefore is still difficult, (3) the balanced health level is usually far from 100% and may fall lower if circumstances change (e.g., new crew arrives and fills the station), (4) these bonuses require a lot of EC.

Parts with Health Effects

• Hitchhiker: -50% to Overpopulation for up to 4 kerbals, 1 EC/kerbal
• Mk1 Crew Cabin: -50% to Overpopulation for up to 2 kerbals, 1 EC/kerbal
• Mk2 Crew Cabin: -50% to Overpopulation for up to 4 kerbals, 1 EC/kerbal
• Mk3 Passenger Module: -50% to Overpopulation for up to 16 kerbals, 0.75 EC/kerbal
• PPD-12 Cupola Module: +1% marginal change, -50% to Overpopulation for 1 kerbal, 4 EC total