Rocket Sizing (propulsion/rocket/rocket-sizing)

Use when the task is launch-vehicle propulsion sizing with the rocket equation: delta-v, mass ratio, propellant mass, and multistage delta-v summation.

Domain quick reference

• The ideal rocket equation gives delta-v = g0 * Isp * ln(m0 / mf), with g0 = 9.80665 m/s^2.
• Units: specific impulse in seconds, masses in kg, delta-v in m/s.
• The mass ratio is m0 / mf; the propellant mass is m0 - mf.
• A multistage vehicle sums the delta-v of its stages, each computed with its own stage masses and specific impulse.
• ECSS space-systems standards frame the launch-vehicle engineering context.

Workflow

1. Collect stage specific impulse and the initial and final masses.
2. Compute stage delta-v with rocket_equation_delta_v.
3. Derive the mass ratio with mass_ratio_from_delta_v.
4. Compute the propellant mass with propellant_mass.
5. Sum the stage delta-v with total_stage_delta_v.

Pitfalls

• Confusing mass ratio (m0 / mf) with propellant fraction ((m0 - mf) / m0).
• Summing delta-v without recomputing the rocket equation per stage with that stage's own masses.
• Using a zero final mass (or mf >= m0), which breaks the logarithm.

Behavior contract (gate 3)

The delta-v, mass ratio, propellant, and staging logic is exercised by the gate 3 contract test: scripts/test_rocket_sizing.py against scripts/rocket_sizing_logic.py (stdlib unittest, offline). Run: python3 scripts/test_rocket_sizing.py

Compliance

• Standards referenced, not reproduced: ECSS is a free ESA download (ecss.nl/standards); the rocket equation is common propulsion methodology, summary-only per standards-map.yaml.
• compliance: STANDARDS-REF, gated: false.