The Gear Ratio: the Rocket Equation for Decision-Makers
Why does every kilogram on the Moon need about five kilograms in Earth orbit, and what can reduce that ratio?
Chapter summary
Going from low Earth orbit to the lunar surface needs a velocity change of about 5.9 km/s: about 3.1 km/s to leave Earth orbit, about 0.8–0.9 km/s to brake into lunar orbit and about 1.9–2.0 km/s to descend and land.
Key takeaways
- 1
The rocket equation turns that into a mass ratio: with methane and oxygen engines, a vehicle must start with about 5.3 times the mass it lands.
- 2
Hydrogen engines cut the ratio to about 3.8, refuelling in lunar orbit splits it into smaller steps, and propellant made on the Moon removes the return leg entirely.
- 3
Every lunar business plan rests on how it handles this ratio.
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The Delivery Cost Stack: Launch, Transfer, Landing, Operations
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