# Rockets and human power

The two extremes of transport energy: chemical rockets and muscle-powered bicycles.

Source page: https://www.materialinsights.org/energy/e_rockets/

Conversion and use · Transport systems · No. 116

- Conversion and use
 Conversion and use · Transport systems · Foundation · Energy

A Falcon 9 burns about 28 kg of propellant per kilogram it puts in orbit; a cyclist needs 21 kcal per km.

Chart: Illustration: Rockets and human power

##### Where it comes from

Chart: Map of where it comes from

A rocket carries both its fuel and its oxidiser, burns them and throws the hot gas backwards through a nozzle. Propellant makes up about 89% of a Falcon 9 at lift-off.

##### Three things to know

1. The hydrogen-burning RS-25 already reaches about 87% of the chemical ceiling on specific impulse, so reuse, not better engines, cut launch costs.
2. One Falcon 9 booster had flown 36 times by August 2026, spreading the cost of the first stage.
3. Per kilometre, a cyclist uses about one-thirteenth of the energy of a jet passenger.

##### The journey

1. 1 **Propellant**Fuel plus oxidiser carried on board
2. 2 **Turbopumps**Force propellants into the combustion chamber
3. 3 **Combustion**Burns at about 206 bar in RS-25
4. 4 **Nozzle**Expands hot gas into a very fast jet
5. 5 **Orbit**Payload reaches about 7.6 km per second
 Covered in [Muscles, wood, water and wind: energy before fossil fuelsEnergy](https://www.materialinsights.org/learn/energy/energy-before-fossil-fuels/)

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## Other sections

- [Overview](https://www.materialinsights.org/energy/e_rockets/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_rockets/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_rockets/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_rockets/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_rockets/economics/index.md)
- [Engineering methods](https://www.materialinsights.org/energy/e_rockets/methods/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_rockets/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_rockets/links/index.md)