SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/aero-liquid-rocket-restart

What can many liquid-fuel rocket engines do that solid motors cannot?

Shut off, and some kinds can even restart in flight.

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  1. Fly without any oxidizer
  2. Burn without making any exhaust
  3. Shut off, and some can restart in flight ✔

Why: Liquid engines pump fuel and oxidizer into a combustion chamber. Stop the flow and the engine stops. Some can be relit later, which helps a spacecraft change orbits.

Huh, didn't know that: The first liquid-propellant rocket flew in 1926 using liquid oxygen and gasoline.

The dad joke
Liquid rockets are polite. They know when to stop talking.
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References

Answer: Shut off, and some can restart in flight. Liquid engines pump fuel and oxidizer into a combustion chamber. Stop the flow and the engine stops. Some can be relit later, which helps a spacecraft change orbits.

  1. NASA Science, Basics of Space Flight, Chapter 3 science.nasa.gov/learn/basics-of-space-flight/chapter3-2
    Liquid rockets, once started, can be shut off. Some kinds can later be restarted in flight.
    Checked 2026-10-10.

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