Real O2 is a lightweight, highly compatible revamp of the O2 system in Starfield.
Oxygen is now a limited resource in zero-atmosphere environments, and must be managed carefully.

As always, the mod is a function of two central concepts: Minimalism and Realism.
This is one of the more difficult balancing acts in video games, so I will attempt to explain the philosophy here briefly.

Minimalism:
All effects are applied independently, and no vanilla records are touched except notifications.
Additionally, there are no external requirements for basic functionality.
As far as design philosophy, the systems are designed to feel like they were always there, as much as possible.

Realism:
This part is simple: You have a set amount of O2 in your pack.
If you run out, you will eventually suffocate and die.

The system revolves around two features: An O2 Reserve and an O2 Drain.
Both are covered in detail below.



Reserves

Your Pack now holds a set amount of O2, varying per category.
Categories are as follows:

• Survival - Holds just enough O2 to avoid instant death in vacuum.
• Balanced - Suitable for short on-foot traversal, or vehicular exploration.
• Standard - Suitable for combat encounters or light exploration.
• Exploration - Holds tremendous O2 for extended planetary expeditions.
  

If this step is skipped in installation, or if RTFP is absent, all packs will hold a Standard amount.
Categories are now applied individually according to model, instead of following Suit Up's categories.

Note: Removing or switching your pack while in vacuum will cost you a majority of your reserves. 

Restrictions

When you are drawing on Reserves, Fast Travel is no longer available in Simulation mode.
Switching to Streamlined mode or disabling the mod will revert Fast Travel characteristics to vanilla.

Constant Drain

When you are in a location without breathable air, you will use O2 at a set rate.
This rate is influenced by your Aerobic Fitness.

Other Drains

Exertion
Running and sprinting will cause varying amounts of O2 usage.

Conditions
Extreme weather or adrenaline from combat will cause varying amounts of additional O2 usage.

Boosting
By default, Boost Jumping when in zero-atmosphere uses O2 instead of 'boost fuel'.
This varies depending on the Boost Type where Power packs use the most and Skip packs use the least, as expected.
Taking Boost Pack Training reduces this amount. 

Punctures
In Simulation mode, taking gunfire or being bitten can cause a Puncture - instantly draining a certain amount of O2.
This is mostly combated by installing Hypercure Sealant or, if Suit Up is present, using an Assault suit.

Fitness System

Aerobics is a new meta-skill derived from vanilla skills like Boxing, Fitness, Gymnastics, Wellness, and Sniper Certification. The Spaced trait also enhances it.

It represents your ability to do more with less oxygen and in Simulation mode, it is visible under the Status display menu.

All drains will scale down to ~70% of their original as your Aerobics skill increases.

Asphyxiation and CO2

When you are drawing on your Reserves, CO2 will slowly build up over time. Improving your Anaerobic Fitness reduces CO2 buildup rate.
The rate of buildup becomes higher the lower your O2 meter falls.
At very low levels of O2, you will begin taking Health damage and any Regeneration is nullified.
The only way to recover from this is to either enter somewhere with environment, cast Personal Atmosphere, or use an Emergency Reserve.

If your CO2 has built up excessively, a Purge Valve may be needed to drain it before O2 can be restored effectively.

Vehicles

While in a vehicle, O2 will (very) slowly Regenerate.
If your O2 is Low when you enter the vehicle, a Kickstart will be triggered for safety.
Let me know if you have any balancing ideas or opinions on Vehicle handling.

Craftable Items

A few new consumables are available with the mod installed.

Heliox can be made at Pharmaceutical workbenches and will greatly reduce resting O2 usage for a while (e.g. while standing, sitting, or walking).

Emergency Reserves can be created at Industrial workbenches and will instantly replenish a large portion of your O2.

Finally, a Purge Valve can be created also at Industrial workbenches. This will allow you to safely drain built-up CO2 and can be re-used indefinitely.

There are also new Spacesuit Mods.

Experimental Scrubbers for Packs will allow slight O2 regeneration when sitting, standing, or walking. 
Hypercure Sealant for Suits simply reduces the amount of O2 lost when a Puncture is caused by incoming gunfire.

Note: Some vanilla suits have these features by default - for example, Starborn suits have O2 Regeneration.
This is visible in the Status Effects menu.

Kickstart

When you enter a breathable location, your O2 is quickly replenished to full and all behavior reverts to normal.
All systems will be paused until you next enter an environment without breathable air.



Compatible with anything except for mods that do the same exact thing.
Mods that alter regen, capacity, etc will generally stack their bonuses as expected.
Flat boni from other mods may or may not be impactful depending on mode.

Smarter Spacesuit Auto-hide is fully compatible. Most similar mods should also be fine.
Theoretically, if they hid the spacesuit in non-breathable environments, they would be visually inconsistent but still compatible.



Starfield updated to at least 1.14.70 is required.

Real Time Form Patcher is not a hard requirement, but the categorization system relies on it.

Suit Up is recommended - but no longer required for categorization system to function properly.



Simply install with your mod manager.

The mod will initialize the first time you exit your ship after installation.



Simply set both options to Disabled before uninstalling. It is recommended but not mandatory to be somewhere with breathable air (e.g. your ship).



There is a Gameplay Option controlling the mod’s state.

[SIMULATION] Mode considers all modifiers and effects, and care must be taken when entering zero-atmosphere environments.
[STREAMLINED] disables all auxiliary systems - like Fast Travel restrictions, and relaxes the general scaling of O2 drains.
[DISABLED] simply disables the mod.

The Boosting Uses O2 setting is self-explanatory: on or off.



Bethesda for Starfield and the Creation Kit.
TommInfinite for Real Time Form Patcher.
RenamonNonaka’s Ash & Adoring Fan for accompanying me in a convenient savegame for testing.


SPACEFARER is a modular, immersive Vanilla+ overhaul that aims to bring out the best of what Starfield already has to offer. Check it out below.

Combat
Deadly Effective - Overhauls numerous combat-related vanilla perks for playstyle diversity (and fun!)
Balanced Ballistics - Lightweight and immersive overhaul to weapon handling for Ballistic and Laser weaponry.
Suit Up [RTFP] - Smart and compatible system to make spacesuit selection more impactful.
Space Economy
Cost of Spacing - Simulates a reactive and complex space economy by introducing costs to space travel.
Spacefaring Economy [RTFP] - Overhauls prices and rewards with heavy scaling to avoid hyperinflation.
Captain’s Choice - Rebalances ship classes and modules for more thoughtful shipbuilding and combat.
Survival
Real Fuel - A lightweight and immersive solution to Fuel and Exploration.
Real O2 - Makes O2 a real consideration when exploring zero-atmosphere environments.
Peak Performance - A lightweight system to handle Hunger, Thirst, and Rest.
Immersion
Magic Boost Disabler - Disables the vanilla behavior of magically appearing Boost Packs.
First Person Messages [RTFP] - Converts game messages to first person.