Electrothermal Thrusters Framework. Resistojets & Arcjets (Multi-Fuel, Thermal & Degradation)

[Alumina]

Introduce a flexible, modder-friendly backend framework for electrothermal thrusters (Resistojets and Arcjets). Rather than flooding the stock game with dozens of engines and realistic fuels, KSA could provide the core mechanism‒handling electrical power scaling, thermal management, fuel-dependent performance, and propellant aggressiveness/wear. Stock KSA could feature just 1–2 simple thrusters, while modders get a fully scalable system out of the box without needing hard custom code assemblies.

Why Electrothermal Thrusters?
In realistic (and semi-realistic) spaceflight, electrothermal engines bridge the massive gap between chemical thrusters (high thrust, lower Isp ~200–450s) and electrostatic/electromagnetic ion drives (very low thrust, ultra-high Isp ~3000s+).

Resistojets (Isp ~300–500s) and Arcjets (Isp ~500–1000s) offer moderate thrust with high efficiency, making them ideal for station-keeping, attitude control, and precise orbital adjustments.

Key Framework Mechanics​

1. Power & Thermal Coupling
   • Thrust and Isp scale dynamically with electrical power input and heat generation. If power drops occur, efficiency degrades.
2. Native Multi-Fuel Capability
   • A single thruster module should natively support multiple working fluids (e.g., Hydrazine, Ammonia, Hydrogen, Argon, Water, CO₂).
   • Propellant selection alters total mass flow, thrust, and Isp.
3. Fuel Aggressiveness & Part Wear (Degradation)
   • Resistojets: Heating elements experience minimal to no wear with non-aggressive gases, but reactive fuels cause chemical oxidation/degradation over operating time.
   • Arcjets: High-temperature arc discharge causes physical/chemical erosion of the cathode and anode. Inert working fluids result in significantly lower erosion rates than aggressive ones.

Modder-First Architecture (Scalability)​

The biggest value of this proposal is giving modders a robust stock module (PartModule / config framework) so they don't have to build hard custom code libraries.

A modder should be able to define an electrothermal engine entirely via config files by specifying:

• Allowed propellant types + efficiency/thrust multipliers per propellant.
• Degradation / erosion rate coefficient per propellant.
• Power-to-heat curves and operating temperature limits.

Suggested Minimal Stock Implementation​

To keep developer workload light:

• 1 Stock Resistojet: satellite propulsion unit / station-keeping thruster (configured by default to a single monopropellant, but using the multi-fuel backend).
• 1 Stock Arcjet: Upper-stage / satellite propulsion unit.

Propellant Wear & Performance Matrix (Conceptual Model!)​

To give developers a concrete baseline, propellants trade off performance (Isp/thrust) against hardware wear. Degradation behaves differently based on engine physics:

• Resistojets: Degrade primarily via chemical oxidation/corrosion of the heating element (non-aggressive propellants cause ~0% wear).
• Arcjets: Degrade via electric arc sputtering/erosion plus chemical reaction (baseline erosion exists even with noble gases).
  
  
  

• Propellant	Fuel Type	Relative Wear	Primary Degradation Mechanism
  Neon	Noble Gas (Most Inert)	0.77x	Lowest mechanical sputtering; zero oxidation. Ideal for long-life arcjets. Low-Medium Thrust. High Isp.
  Argon	Heavy Noble Gas	0.84x	Minimal cathode erosion; dense storage, zero oxidation. Medium Thrust. Moderate Isp.
  Hydrogen	Non-Aggressive (Baseline)	1.00x	Baseline arc erosion; semi-zero wear in resistojets. Highest Isp. Low Thrust.
  Ammonia	Mildly Reactive	1.15x	Mild chemical reaction/nitriding under high-temperature arc discharge. Medium-High Thrust. High Isp.
  Carbon Dioxide	Weak Oxidizer	1.70x	Moderate oxidation of heating element (resistojet) and arc core. High Thrust. Moderate Isp.
  Water H₂O	Heavy Oxidizer	3.00x	Severe thermal oxidation and rapid electrode erosion. High maintenance tradeoff. Highest Thrust. Moderate Isp.

 

[Barsik]

i think that adding so many fuel types isn't very good for new players. for example we can use Hydrogen which already implemented in game and Argon which also will be a fuel for ion engines

 

[Alumina]

i think that adding so many fuel types isn't very good for new players. for example we can use Hydrogen which already implemented in game and Argon which also will be a fuel for ion engines

Great point!

I completely agree that stock KSA shouldn't overwhelm players with dozens of new fuels. Using already existing propellants like Hydrogen and Argon for stock engines is actually the ideal approach!

The propellant table in my post was purely a conceptual example to demonstrate what the mechanics could support, not a request for developers to populate the stock game with all those fuel types or pre-define their properties right now.

The primary goal of this suggestion is the backend framework. If developers build multi-fuel capability and degradation mechanic into the base code structure, it keeps the stock game clean and beginner-friendly, while giving modders the native tools to create custom thrusters without hard code.