1. ROLE

3. GETTING STARTED

When you trigger this skill, I'll work with whatever you give me — but the more context, the better the output.

Minimum I need (pick one):

• "Design a rocket to put 5 tonnes in LEO"
• "Compare Raptor vs BE-4 for a reusable first stage"
• "What's the delta-v budget for a lunar lander?"

Helpful if you have it:

• Payload mass and destination orbit
• Reusability requirements (expendable, booster-back, full reuse)
• Preferred propellant or engine family
• Launch site (latitude matters for delta-v)
• Budget class or cost constraints
• Reliability requirements (human-rated vs cargo)

What I'll ask if you don't specify:

• "What's the destination? LEO, GTO, lunar, Mars?" — I won't assume
• "Expendable or reusable?" — changes the architecture fundamentally
• "Payload mass range?" — if not given, I'll provide parametric brackets (1t, 5t, 15t, 30t)

4. CONNECTORS

Shared Tools (in shared/tools/)

Shared Data (in shared/ — pack-level)

Cross-skill Connectors

5. TAXONOMY

5.1 Propulsion Systems Classification

5.2 Reference Engines Database

5.3 Delta-v Budget Reference

5.4 Engine Cycle Classification

6. PROCESS

Step 1: Mission Definition

• Destination: LEO, GTO, GEO, lunar, interplanetary
• Payload mass: kg to destination orbit
• Reusability: expendable, booster return, full reuse
• Reliability class: human-rated (LOC < 1:500), commercial, experimental

IF destination is not specified → ASK. IF payload mass is not specified → provide parametric analysis for 1t, 5t, 15t, 30t.

Step 2: Delta-v Budget

Total delta-v = Orbital delta-v + Gravity losses + Drag losses + Steering losses + Margin

IF reusable → add landing delta-v: boostback 0.8 + entry 0.5 + landing 0.4 = ~2.0 km/s penalty.

Step 3: Staging Architecture

Step 4: Engine Selection

Decision matrix: Isp (25%) + TWR (20%) + Reliability (20%) + Cost (15%) + Restartability (10%) + TRL (10%).

Step 5: Performance Verification

1. Mass ratio per stage via Tsiolkovsky
2. Structural feasibility check
3. TWR at stage ignition > 0.7 (vac) or > 1.2 (SL)
4. Payload fraction: > 2% LEO expendable, > 1% reusable

Step 6: Trade Study

If xlsx skill available → parametric spreadsheet. If pptx skill available → mission review deck.

7. OUTPUT TEMPLATE

# [Mission Name] — Propulsion Architecture

## Mission Parameters
| Parameter | Value |
|-----------|-------|
| Destination | [orbit/body] |
| Payload | [X] kg to [orbit] |
| Reusability | [expendable/partial/full] |

## Delta-v Budget
| Maneuver | Delta-v (m/s) | Cumulative |
|----------|--------------|-----------|
| [maneuver] | [value] | [total] |
| **TOTAL** | **[value]** | |

## Vehicle Architecture
### Stage 1: [Name]
- Engine: [X] × [Engine]
- Propellant: [type], [mass] kg
- Delta-v: [X] m/s

## Engine Trade Study
| Criterion | [Engine A] | [Engine B] | [Engine C] |
|-----------|-----------|-----------|-----------|
| Isp (25%) | [score] | [score] | [score] |
| **TOTAL** | **[X]** | **[X]** | **[X]** |

## Recommendation
[Selected architecture, rationale, next steps]

8. CLASSIFICATION

9. VARIATIONS

• A: Small Sat (<500 kg) — Cost over performance, pressure-fed, 2-3 stages, <$15M
• B: Reusable Booster — Landing dv 1.5-2.5 km/s, engine-out N+1, throttle <40%
• C: Upper Stage — Max Isp, restart 3+, cryo management
• D: Human-Rated — LOC <1:500, abort TWR >10:1, engine-out always
• E: Interplanetary — Gravity assist, ISRU, aerocapture trades

10. ERRORS & PITFALLS

• E1: Ignoring gravity losses (7.8 km/s orbital ≠ 9.4 km/s total to LEO)
• E2: Using vacuum Isp for sea-level (SL is 10-15% lower)
• E3: Unrealistic mass fractions (new designs: 0.08-0.10, not 0.03)
• E4: Isp-only engine comparison (density matters for first stages)
• E5: LH2 volume blindspot (71 kg/m³ = 5x tank volume vs kerolox)
• E6: "Reusable = cheaper always" (needs >10 flights/year to break even)
• E7: No engine-out design (9-engine cluster: 4.4% chance of 1 failure/flight)
• E8: Mixing metric/imperial (Mars Climate Orbiter: $327M lost)

11. TIPS

• T1: Start from payload + destination → work backwards through Tsiolkovsky
• T2: Evaluate density-Isp product for first stages, not Isp alone
• T3: Use proven engines as anchors for new engine estimates
• T4: Margin: 15-25% conceptual, 10-15% preliminary, 5-10% detailed
• T5: Odd engine counts (1,3,5,7,9) for axial symmetry
• T6: Sanity: payload fraction 2-4% LEO expendable, 1-2% reusable
• T7: Calibrate against Falcon 9 (549t, 22.8t LEO, 4.2%), Saturn V (2970t, 140t, 4.7%)
• T8: Cost: $1,500-5,000/kg reusable, $10,000-30,000/kg expendable

12. RELATED SKILLS