How do I install the Propellant Selection skill?

Run npx skillmds@latest add ashfordeou/propellant-selection in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Propellant Selection safe to use?

This skill has not completed SkillMD's automated safety review yet. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Propellant Selection?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Propellant Selection free to use?

Yes. Installing skills from SkillMD is free. This skill is licensed under Apache-2.

Who published Propellant Selection?

ashfordeOU (@ashfordeou) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Propellant Selection by ashfordeou — Agent Skill

Name: Propellant Selection
Author: ashfordeOU

Propellant Selection

Use when you must select and screen rocket propellants for a mission: classify propellant families (cryogenic, storable, hypergolic, solid, hybrid), compare specific impulse and density impulse, compute the mixture bulk density and the O/F ratio optimum, derive the required propellant mass fraction from a delta-v budget with the rocket equation, and judge storability and handling for the mission. Produces the propellant family classification, the density-impulse ranking, the O/F verdict, the mass fraction, and the suitability verdict, in SI units (s, kg/m^3, m/s). Trigger: propellant selection, specific impulse, density impulse, mixture ratio, O/F ratio, hypergolic, cryogenic, storable, solid propellant, storability.

ashfordeOU 1688e42 3 files · 18.8 KB Updated Sep 17, 2026

File contents

Propellant Selection (propulsion/rocket/propellant-selection)

Use when the task is rocket propellant selection for a mission: propellant families, specific impulse, density impulse, mixture ratio and bulk density, O/F ratio optimum, storability and handling, and the propellant mass fraction from the delta-v budget.

Domain quick reference

Propellant families: cryogenic (LOX, LH2, LCH4), storable (RP-1, H2O2), hypergolic (MMH/UDMH with NTO or IRFNA, ignites on contact), solid (HTPB/APCP composite grain), and hybrids.
Specific impulse Isp (s) measures propellant performance; density impulse = Isp * bulk density (kg s/m^3) measures it per unit tank volume, the figure that drives tank and vehicle size.
The mixture bulk density at an O/F mass ratio r, fuel density rho_f, and oxidizer density rho_o is rho = (1 + r) / (1/rho_f + r/rho_o).
The propellant mass fraction needed for a delta-v at Isp is 1 - exp(-delta_v / (g0 * Isp)), with g0 = 9.80665 m/s^2. It is the inverted rocket equation, kept lightweight here: staging and stage masses live in the rocket-sizing skill.
The O/F ratio optimum sits near the maximum Isp; running away from it trades performance for bulk density and burn time.
Storability decides the mission: cryogens boil off, hypergolics and storables hold indefinitely, solids cannot throttle or restart.
ECSS space-systems standards frame the launch-vehicle propulsion context.

Workflow

Name the candidate propellants and classify each with propellant_family.
Rank candidates on specific impulse and density impulse with density_impulse.
Compute the mixture bulk density with bulk_density at the chosen O/F ratio.
Check the O/F ratio against the optimum with o_f_optimum_verdict.
Derive the required propellant mass fraction with required_mass_fraction from the delta-v budget.
Screen storability and handling for the mission with propellant_verdict.

Pitfalls

Ranking on Isp alone while ignoring density impulse: a dense low-Isp pair can beat a light high-Isp pair on tank volume.
Treating hypergolic as separate from storable: hypergolics are storables that ignite on contact, not a third liquid state.
Computing bulk density as an arithmetic mean of the two densities instead of the mass-weighted harmonic mean.
Confusing the mixture ratio (O/F) with the rocket equation mass ratio (m0/mf).
Expecting solid motors to throttle, shut down, or restart.
Ignoring boil-off and loading time for cryogens on long-duration or quick-response missions.

Behavior contract (gate 3)

The family classification, density impulse, bulk density, O/F verdict, mass fraction, and mission verdict logic is exercised by the gate 3 contract test: scripts/test_propellant_selection.py against scripts/propellant_selection_logic.py (stdlib unittest, offline). Run: python3 skills/propulsion/rocket/propellant-selection/scripts/test_propellant_selection.py

Compliance

Standards referenced, not reproduced: ECSS is a free ESA download (ecss.nl/standards); propellant performance and selection methodology is standard propulsion practice, summary-only per standards-map.yaml.
compliance: STANDARDS-REF, gated: false.

---name: propellant-selectiondescription: Use when you must select and screen rocket propellants for a mission: classify propellant families (cryogenic, storable, hypergolic, solid, hybrid), compare specific impulse and density impulse, compute the mixture bulk density and the O/F ratio optimum, derive the required propellant mass fraction from a delta-v budget with the rocket equation, and judge storability and handling for the mission. Produces the propellant family classification, the density-impulse ranking, the O/F verdict, the mass fraction, and the suitability verdict, in SI units (s, kg/m^3, m/s). Trigger: propellant selection, specific impulse, density impulse, mixture ratio, O/F ratio, hypergolic, cryogenic, storable, solid propellant, storability.license: Apache-2.0---# Propellant Selection (propulsion/rocket/propellant-selection)Use when the task is rocket propellant selection for a mission:propellant families, specific impulse, density impulse, mixture ratioand bulk density, O/F ratio optimum, storability and handling, and thepropellant mass fraction from the delta-v budget.## Domain quick reference- Propellant families: cryogenic (LOX, LH2, LCH4), storable (RP-1, H2O2), hypergolic (MMH/UDMH with NTO or IRFNA, ignites on contact), solid (HTPB/APCP composite grain), and hybrids.- Specific impulse Isp (s) measures propellant performance; density impulse = Isp * bulk density (kg s/m^3) measures it per unit tank volume, the figure that drives tank and vehicle size.- The mixture bulk density at an O/F mass ratio r, fuel density rho_f, and oxidizer density rho_o is rho = (1 + r) / (1/rho_f + r/rho_o).- The propellant mass fraction needed for a delta-v at Isp is 1 - exp(-delta_v / (g0 * Isp)), with g0 = 9.80665 m/s^2. It is the inverted rocket equation, kept lightweight here: staging and stage masses live in the rocket-sizing skill.- The O/F ratio optimum sits near the maximum Isp; running away from it trades performance for bulk density and burn time.- Storability decides the mission: cryogens boil off, hypergolics and storables hold indefinitely, solids cannot throttle or restart.- ECSS space-systems standards frame the launch-vehicle propulsion context.## Workflow1. Name the candidate propellants and classify each with propellant_family.2. Rank candidates on specific impulse and density impulse with density_impulse.3. Compute the mixture bulk density with bulk_density at the chosen O/F ratio.4. Check the O/F ratio against the optimum with o_f_optimum_verdict.5. Derive the required propellant mass fraction with required_mass_fraction from the delta-v budget.6. Screen storability and handling for the mission with propellant_verdict.## Pitfalls- Ranking on Isp alone while ignoring density impulse: a dense low-Isp pair can beat a light high-Isp pair on tank volume.- Treating hypergolic as separate from storable: hypergolics are storables that ignite on contact, not a third liquid state.- Computing bulk density as an arithmetic mean of the two densities instead of the mass-weighted harmonic mean.- Confusing the mixture ratio (O/F) with the rocket equation mass ratio (m0/mf).- Expecting solid motors to throttle, shut down, or restart.- Ignoring boil-off and loading time for cryogens on long-duration or quick-response missions.## Behavior contract (gate 3)The family classification, density impulse, bulk density, O/F verdict,mass fraction, and mission verdict logic is exercised by the gate 3contract test: scripts/test_propellant_selection.py againstscripts/propellant_selection_logic.py (stdlib unittest, offline). Run:python3 skills/propulsion/rocket/propellant-selection/scripts/test_propellant_selection.py## Compliance- Standards referenced, not reproduced: ECSS is a free ESA download (ecss.nl/standards); propellant performance and selection methodology is standard propulsion practice, summary-only per standards-map.yaml.- compliance: STANDARDS-REF, gated: false.

Frequently asked questions