Deep Field

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Deep Field
29 September 2026 2518 stories tracked

Glossary · Launch & Flight

Cryogenic propellant

Fuel kept liquid only by being extremely cold, which starts a clock the moment you load it.

Liquid oxygen boils at minus 183°C and liquid hydrogen at minus 253°C, so a fuelled rocket is continuously boiling off and being topped up until the moment it launches. That is why a cryogenic vehicle cannot sit fuelled for long, why the tanks frost over on the pad, and why a hold late in the count can drain a launch window. The payoff is performance: hydrogen and oxygen give the highest specific impulse of any practical chemical combination, which is why upper stages use them even though the plumbing is miserable.

Related terms

Delta-v The currency of spaceflight: how much you can change your velocity, in metres per second. NET (no earlier than) A launch date that is a lower bound, not a promise. Max-Q The moment of peak aerodynamic pressure on an ascending rocket. Staging Throwing away the empty part of the rocket so you stop accelerating it.

Questions

What is Cryogenic propellant?

Fuel kept liquid only by being extremely cold, which starts a clock the moment you load it.

Why does it matter?

That is why a cryogenic vehicle cannot sit fuelled for long, why the tanks frost over on the pad, and why a hold late in the count can drain a launch window. The payoff is performance: hydrogen and oxygen give the highest specific impulse of any practical chemical combination, which is why upper stages use them even though the plumbing is miserable.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.