Chemical Propulsion

An overhaul to the stock propellant system, replacing generic LiquidFuel, Oxidizer, MonoPropellant and SolidFuel with a handful of real chemicals.

Features

Core design

This mod is distinct from RealFuels in that it deals with only a small set of primary liquid propellants, for a more straightforward and curated propellant system more in line with e.g. Nertea's Cryogenic Engines. In fact, Nertea's mods are a particular target of this overhaul, which can be thought of as a Nertea-like soft alternative to RealFuels.

Each propellant has a part upgrade which provides switch subtypes on relevant parts when unlocked in the tech tree. Most propellants only appear in game if a using-mod is present, while the following six are used in a pure stock configuration:

• LqdOxygen
• Kerosene
• HTP (High-test peroxide)
• Hydrazine
• LqdHydrogen
• NTO (Dinitrogen tetroxide)

Engine changes

Bipropellant engines are categorised into particular fuel-oxidizer combinations with fixed mixture ratios. Any fuel can be paired with any oxidizer, though not all combinations are necessarily configured or available depending on which supported mods you use. The bipropellants used in stock are:

• Keroxide:
  • 1 Kerosene / 3 HTP
• Hypergolic:
  • 7 Hydrazine / 9 NTO
• Kerolox:
  • 3 Kerosene / 5 LqdOxygen
• Hydrolox:
  • 3 LqdHydrogen / 1 LqdOxygen

Monopropellant engines and tanks have a choice of two propellants: HTP which is cheap and available at the beginning of career mode, and Hydrazine which is unlocked later and more expensive but yields a significantly higher specific impulse.

Solid rockets have a similar progression from PBAN to the slightly more performant HTPB.

Liquid fuel jet engines use Kerosene, with the rocket mode of multimodal engines running on Kerosene and LqdOxygen.

Some mod engines have bespoke propellant configurations which are not typical monopropellants or bipropellants. For example, Near Future Launch Vehicles' KR-701 'Cougar' and KR-74 'Lynx' are bimodal hydrolox engines with an additional kerosene-augmented mode, based on their real-world analogues the RD-701 and RD-704:

• 1 Kerosene / 4 LqdHydrogen / 3 LqdOxygen (equivalent to 1 part kerolox + 2 parts hydrolox)

CryoTanks changes

This mod replaces all CryoTanks fuel switch types to Chemical Technologies tank types. One particular feature of this is the removal of CryoTanks' native 1.5x hydrogen packing density buff, which not-insignificantly affects the use of LqdHydrogen in the game. This is not just an arbitrary change purely motivated by realism. The ~14% higher density of LqdOxygen over Oxidizer and adjusted methalox mixture ratio (higher oxidizer mass fraction) make cryogenic bipropellants much more attractive, removing the need for any sneaky volume buffs in chemical rockets. Hydrolox suffers a little bit, but I've found this actually balances better against their high Isp. Nuclear engines naturally suffer the most, but again, these engines are very high Isp and it should really be expected that you'd need to haul massive tanks everywhere. I've always wanted my CryoTanks to be bigger, personally.

Extras

Some patches for additional propellant options are provided in the Extras folder.

Keroxide

Adds HTP as an oxidizer option to all kerolox engines, which is more expensive and yields slightly lower Isp than LqdOxygen, but has two main advantages:

• An ignition mechanism is not required as the hot gases produced by the catalytic decomposition of HTP ignite on contact with Kerosene
• HTP is much denser than LqdOxygen and has a higher oxidizer-fuel mixture ratio with Kerosene, so the volumetric impulse is actually slightly higher than that of kerolox

Hypergolics

Adds an alternative pair of cheaper, lower-performance fuel and oxidizer to all hypergolic engines:

• Aniline - Low-tech alternative to Hydrazine
• IWFNA (Nitric acid) - Low-tech alternative to NTO

Exotics

Adds four exotic propellants which are unlocked late in the tech tree and can replace certain conventional propellants for increased thrust and Isp:

• Pentaborane - Can be used in place of Hydrazine as a hypergolic fuel or Kerosene as a jet fuel
• Diborane - Can be used in place of LqdMethane as a cryogenic fuel
• N2F4 - Can be used in place of NTO as a hypergolic cryogenic oxidizer
• LqdFluorine - Can be used in place of LqdOxygen as a cryogenic oxidizer

Nuclear

Adds four high-thrust, low-Isp propellant options to nuclear thermal rockets (multipliers vs. LqdHydrogen):

• Water - +92% thrust, -58% Isp
• LqdCO2 - +142% thrust, -69% Isp
• LqdCO - +158% thrust, -72% Isp
• LqdNitrogen - +158% thrust, -72% Isp

Configuration

Parts can easily be patched to replace their propellants with supported resources by setting one or more chemTechPropellant, chemTechFuel or chemTechOxidizer fields on the part or relevant module, the values of which are a resource name:

• chemTechFuel: A fuel which should be paired with an oxidizer or used in an air-breathing engine.
  • Ethanol
  • Kerosene
  • Aniline
  • LqdAmmonia
  • Hydrazine
  • LqdMethane
  • LqdHydrogen
  • Pentaborane
  • Diborane
• chemTechOxidizer: An oxidizer which should be paired with a fuel. Supported resource names:
  • LqdOxygen
  • IWFNA
  • HTP
  • NTO
  • LqdFluorine
  • N2F4
• chemTechPropellant: A single propellant which should not be combined with any specified fuel or oxidizer. All above resources are supported, plus the following:
  • Water
  • LqdCO2
  • LqdCO
  • LqdNitrogen

For example, the following patch will automatically remove any stock propellants stored on the part and replace them with a bipropellant tank with a switch for the two fuels:

@PART[partName]:BEFORE[zz_ChemicalPropulsion]
{
	chemTechFuel = Ethanol
	chemTechFuel = Hydrazine
	chemTechOxidizer = LqdOxygen
}

This patch converts a multimode engine with a pure LiquidFuel mode and a LiquidFuel-Oxidizer mode to use LqdHydrogen and LqdOxygen:

@PART[partName]:BEFORE[zz_ChemicalPropulsion]
{
	@MODULE[ModuleEngines*]:HAS[@PROPELLANT[LiquidFuel],!PROPELLANT[Oxidizer]]
	{
		chemTechPropellant = LqdHydrogen
	}

	@MODULE[ModuleEngines*]:HAS[@PROPELLANT[LiquidFuel],@PROPELLANT[Oxidizer]]
	{
		chemTechFuel = LqdHydrogen
		chemTechOxidizer = LqdOxygen
	}
}

Patch ordering

Patches are organised into six stages as shown below. If you're looking to add a compatibility patch for a mod, you'll probably only need BEFORE[zz_ChemicalPropulsion], perhaps AFTER[zz_ChemicalPropulsion], and only AFTER[zzz_ChemicalPropulsion] if you really want to get messy.

BEFORE[zz_ChemicalPropulsion]

• Main chemTech tag assignment, e.g.:
  • chemTechFuel = Ethanol on a PART (tank resource)
  • chemTechTankType = cryogenic on a PART (tank type, expanded in FOR below)
  • chemTechOxidizer = LqdOxygen on a ModuleEngines (engine propellant)

FOR[zz_ChemicalPropulsion]

• Chemical Propulsion automatically assigns tags, e.g.:
  • If a part has chemTechTankType = cryogenic, then the standard cryogenic propellants are added, e.g. chemTechPropellant = LqdHydrogen. Extras and other mods may expand this further, e.g. Chemical Propulsion Exotics would add chemTechPropellant = LqdFluorine and chemTechPropellant = N2F4
  • If an engine has PROPELLANT[SolidFuel] and no chemTech tags, chemTechPropellant = PBAN and chemTechPropellant = HTPB are added
  • If an engine is configured with chemTechFuel = Kerosene and chemTechOxidizer = LqdOxygen, then chemTechIgnitor = TEATEB is added
  • If chemTechOxidizer = LqdOxygen is present anywhere, Chemical Propulsion Exotics will add chemTechOxidizer = LqdFluorine in the same place
• Chemical Propulsion automatically computes tank volume, mass and cost, stored in variables like chemTechTankVolumePropellant, chemTechTankMassFuel, chemTechTankCostFuelOxidizer, etc.

AFTER[zz_ChemicalPropulsion]

• Reserved for post-processing steps, e.g. manipulating the auto-computed tank parameters.
• You can also assign propellant tags here, like BEFORE, in order to bypass the FOR step, e.g.:
  • You want an engine to run kerolox, but not require an ignitor and lack the fluorine option provided by Chemical Propulsion Exotics, so just assign chemTechFuel = Kerosene and chemTechOxidizer = LqdOxygen here

BEFORE[zzz_ChemicalPropulsion]

• The presence of finalised chemTech tags is used to create Ignition modules and switches as appropriate
  • Modules are given a second layer of tags which prepares them for the next stage but are not yet fully configured

FOR[zzz_ChemicalPropulsion]

• Stock resources/propellants and any Chemical Propulsion resources/propellants which are not tagged are removed
• Pre-existing propellant switches are removed
• Ignition modules and switches are fully fleshed-out with their required data
• Various other changes to parts, e.g.:
  • Converter recipes
  • Changing part titles which include stock propellant names
  • VABOrganizer subcategory assignment
  • Changes to engines which can't be done by Ignition alone

AFTER[zzz_ChemicalPropulsion]

• Reserved for any final post-processing

Dependencies

• ModuleManager (4.2.3)
• B9PartSwitch (2.21.0.3)
• Community Resource Pack (112.0.1)
• Chemical Core (1.4.4)
• Ignition (1.2.2.1)
• Space Dust Next (3.3.0) (only if using Space Dust)

Compatibility

Recommended

The following mods are recommended to make the most of core set of propellants.

• Alcoholic Aeronautics (1.0.0)
• Cryogenic Engines (2.0.8)
• Cryogenic Tanks (1.6.7)
• Kerbal Atomics (1.3.4)
• Labradoodle (1.0.1)
• Near Future Launch Vehicles (2.2.2)
• Near Future Spacecraft (1.4.6)
• Restock and Restock+ (1.5.1)
• Space Dust (0.5.5)
• Supplementary Electric Engines (1.3.2)
• VABOrganizer (1.1.0)

Suggested

I would also suggest at least a couple of these mods for more bipropellant rockets and useful tanks, or all of them if you like having hundreds of parts.

• BlueSteel (1.3)
• CRE (2.3)
• CryoEngines Extensions (1.0.4)
• Knes (1.9.9)
• Near Future Aeronautics (2.1.2)
• Near Future eXploration (1.1.3)
• OCRAP (1.0.1)
• Taerobee (1.4.3.0)
• Tantares (28.0.0)
• TantaresLV (16.2.0)
• TantaresSP (6.0.0)
• Universal Storage II Finalized (4.0.2.2)

Compatible

Some mods are explicitly patched to work with Chemical Propulsion, while others are patched implicitly or are simply unaffected and have been found compatible.

• Airplane Plus (26.5) (courtesy of Ari Lana @ratemisia)
• Configurable Containers (2.6.2.1)
• Far Future Technologies (1.4.2)
• Firespitter (7.17)
• Grounded - Modular Vehicles (5.0) (courtesy of Ari Lana @ratemisia)
• Internal RCS (1.3)
• Kerbal Reusability Expansion (2.9.3)
• Kerbalism (3.25)
• MissingHistory (1.9.3)
• Mk-33 (1.3.2)
• Mk2 Expansion (1.9.1.4)
• Mk3 Expansion (1.6.1.4)
• Modular Fuel Tanks (5.13.1)
• Moldavite Machines (1.4) (courtesy of @Aebestach)
• Near Future Construction (1.3.3)
• Probes Before Crew (3.0.0)
• Procedural Parts (2.8.0.0)
• Rocket Motor Menagerie (1.1.2)
• Shuttle Orbiter Construction Kit (1.1.8)
• Silly Photon Drives (1.1.1)
• Skyhawk Science System (1.1.2) (courtesy of @Arofire)
• SXT Continued (0.3.31.1)
• SMURFF (1.9.1)
• SystemHeat (0.8.2)
• Tundra Exploration (7.1.2)
• UnKerballed Start (1.3.2)
• Ursa (Crew pod and spaceship parts) (1.0)
• Many more, though might do unexpected things. Let me know what else to support!

License

Distributed under the GNU General Public License.