# Rockets and human power: Engineering methods

Kerosene, hydrogen, methane or solid: picking a propellant

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

What this tab covers The engineering methods that can do this conversion, compared on efficiency, scale, economics, limitations and reliability.

Chemical rockets differ by propellant pair; human power is the low-energy extreme of transport.

#### Comparison

| Method | Efficiency | Scale | Economics | Limitations | Reliability |
|---|---|---|---|---|---|
| **Kerosene and liquid oxygen (kerolox), e.g. Merlin 1D**^[3](https://en.wikipedia.org/wiki/Falcon_9)^[7](https://space.com/space-exploration/private-spaceflight/spacex-shatters-its-rocket-launch-record-yet-again-167-orbital-flights-in-2025) | Isp 283 s sea level, 312 s vacuum | 854 kN per engine; nine on a Falcon 9 first stage | cheap, storable fuel; enables booster reuse | lower Isp; soot can foul reusable engines | no Falcon 9 mission failures in 165 launches in 2025 |
| **Hydrogen and liquid oxygen (hydrolox), e.g. RS-25**^[2](https://l3harris.com/sites/default/files/2024-07/l3harris-ar-rs-25-spec-sheet.pdf) | Isp 452.3 s vacuum | 512,300 lb (about 2.3 MN) vacuum thrust; 7,774 lb dry mass | expensive engines and cryogenic handling | hydrogen is very bulky (large tanks) and very cold | flight-proven on the Space Shuttle and SLS |
| **Methane and liquid oxygen (methalox), e.g. Raptor, BE-4**^[11](https://www.blueorigin.com/news/new-glenn-launches-nasa-escapade-lands-fully-reusable-booster)^[7](https://space.com/space-exploration/private-spaceflight/spacex-shatters-its-rocket-launch-record-yet-again-167-orbital-flights-in-2025) | Isp between kerolox and hydrolox (no verifiable official figures published for Raptor or BE-4) | New Glenn (seven BE-4 engines) flew its second mission in November 2025; Starship (Raptor) made five suborbital test flights in 2025 | designed for full or partial reuse | young technology | limited flight history |
| **Solid rocket motors** | lower Isp than liquid engines | strap-on boosters, small launchers and missiles | simple and storable | no throttling or restart | high, few moving parts |
| **Bicycle and human power**^[5](https://www.sciencedaily.com/releases/1999/08/990819180058.htm)^[6](https://johk.pl/wp-content/uploads/2023/03/10078-67-2019-v67-2019-10.pdf) | rider about 18-22%; chain up to 98.6% | tens to hundreds of watts | lowest energy per km of any vehicle | low power, weather, distance | simple; chain wear and dirt are the main losses |

Hydrogen gives the best specific impulse but needs huge tanks; kerosene gives compact, cheap stages; methane sits between and suits reuse; solids give simple, high thrust. For launch cost, reuse matters more than engine efficiency. Per kilometre, a cyclist uses about one-thirteenth of the energy per km of a jet passenger (calculated), and a rocket uses vastly more than either because it must reach 7.6 km/s.

#### How each method works
**Kerosene and liquid oxygen (kerolox), e.g. Merlin 1D**

Refined kerosene (RP-1) and liquid oxygen are pumped into a combustion chamber; dense fuel keeps tanks small.
**Hydrogen and liquid oxygen (hydrolox), e.g. RS-25**

Liquid hydrogen and oxygen burn at high chamber pressure; very light exhaust gives the highest chemical Isp.
**Methane and liquid oxygen (methalox), e.g. Raptor, BE-4**

Liquid methane is cleaner-burning than kerosene and denser than hydrogen, suited to reuse and to making propellant on Mars.
**Solid rocket motors**

Fuel and oxidiser are pre-mixed in a rubbery solid cast into the casing; once lit it cannot be turned off.
**Bicycle and human power**

Leg muscles turn food energy into pedal force; a chain and sprockets transmit it to the wheel.

#### Sources

1. [RS-25 engine specification sheet](https://l3harris.com/sites/default/files/2024-07/l3harris-ar-rs-25-spec-sheet.pdf) L3Harris (Aerojet Rocketdyne), 2024
2. [Falcon 9](https://en.wikipedia.org/wiki/Falcon_9) Wikipedia (compiling SpaceX data; figures as reported), 2026
3. [Bicycle efficiency study (Spicer et al., Johns Hopkins University news release)](https://www.sciencedaily.com/releases/1999/08/990819180058.htm) ScienceDaily, 1999
4. [Gross efficiency and the relationship with maximum oxygen uptake in young elite cyclists during the competitive season (Artetxe-Gezuraga et al.), Journal of Human Kinetics 67, 123-131](https://johk.pl/wp-content/uploads/2023/03/10078-67-2019-v67-2019-10.pdf) Journal of Human Kinetics, 2019
5. [SpaceX shatters its rocket launch record yet again: 165 orbital flights in 2025](https://space.com/space-exploration/private-spaceflight/spacex-shatters-its-rocket-launch-record-yet-again-167-orbital-flights-in-2025) Space.com, 2025
6. [New Glenn launches NASA ESCAPADE, lands fully reusable booster](https://www.blueorigin.com/news/new-glenn-launches-nasa-escapade-lands-fully-reusable-booster) Blue Origin, 2025

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_rockets/index.md)
- [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)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_rockets/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_rockets/links/index.md)