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What is NASA CEA, and how is rocket performance calculated?

Short answer

NASA CEA (Chemical Equilibrium with Applications) is NASA’s reference program for the chemistry and ideal performance of rocket engines, developed at NASA Glenn since the 1950s and documented by Gordon and McBride in 1994. Given propellants, mixture ratio, chamber pressure and nozzle area ratio, it computes the combustion products, chamber temperature, exhaust velocity and specific impulse. Since the end of 2025 a modernised version is open source with a Python interface.

The calculation in three steps

  1. Combustion. The propellants react to chemical equilibrium at constant pressure and constant enthalpy. This gives the chamber temperature and the gas composition.
  2. Expansion. The gas expands through the nozzle at constant entropy. In “shifting equilibrium” the composition keeps adjusting as it cools; in “frozen” flow it stays fixed.
  3. Performance. From the enthalpy drop follows the exhaust velocity, and from it the characteristic velocity c*, the thrust coefficient and the specific impulse.

What it does not include

CEA gives ideal performance: no friction, no heat loss, no incomplete mixing. Real engines reach a few to ten percent less. It also says nothing about geometry or cooling; those need separate tools.

Getting it

The open-source release is on GitHub and installs with pip install cea. It runs on a laptop and in Google Colab.

Sources

  1. Computer program for calculation of complex chemical equilibrium compositions and applications, Part I: AnalysisSanford Gordon, Bonnie J. McBride · 1994 · NASA RP-1311
  2. CEA: Chemical Equilibrium with Applications (open-source release)NASA Glenn Research Center · 2025 · github.com/nasa/cea

In practice: from our engineer’s log

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Last updated 2026-10-21