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Changelog#

This project follows Semantic Versioning.

Unreleased#

4.0.0 - 2026-10-13#

A rebuild. The physics was checked line by line against its sources, the desktop application was redrawn from scratch, and the library can now be installed without any GUI packages. Projects from 3.x open unchanged, but results differ: see Moving to 4.0.

Breaking changes#

  • pip install ensim installs the library only. The desktop application needs pip install "ensim[gui]".
  • Propellants are named by their storage state (LH2, LOX, LCH4, RP-1, NTO, HTP, …) and enter the chamber with CEA's liquid enthalpies. 3.x names still load from project files.
  • StageEngine.thrust_sl and thrust_vac are now thrust_sl_per_engine and thrust_vac_per_engine. 3.x multiplied an already clustered thrust by the engine count.
  • simulate_flight_6dof takes exit_area=0.0 by default (was 0.01 m²), which removed most of the thrust of small rockets at sea level.
  • run_monte_carlo no longer prints or plots; plot_dispersion and print_dispersion_summary are gone. Landing statistics count only flights that reached the ground (n_landed).
  • ensim.utils.units was rewritten around Quantity; UnitCategory, UnitConverter and get_unit_symbol were removed.
  • The command line has subcommands: ensim engine, ensim run, ensim check, ensim gui.
  • Project files are written as format 4.0.
  • The legacy equilibrium solver, get_atmosphere_table and the 3.x GUI modules were removed.

Physics#

  • Engine performance uses a frozen isentrope with temperature-dependent heat capacity, as CEA does. Against NASA CEA 3.3.2 for five liquid propellant pairs: chamber temperature within 0.01 %, vacuum Isp within 0.05 %.
  • Standard state is 1 bar, matching the NASA Glenn data.
  • Staging thrust was overstated by the engine count (9 and 5 times for the reference vehicles).
  • The US Standard Atmosphere now converts geometric to geopotential altitude. 3.x skipped the conversion and underestimated pressure by 1 % at 20 km, 5 % at 50 km and 16 % at 80 km. Above 86 km the atmosphere continues smoothly.
  • The 6-DOF derivative is evaluated from the full state at every Runge-Kutta stage, so thrust, drag, mass and inertia change within a step. The adaptive integrator keeps its step controller between steps and reports steps forced at the minimum size.
  • Apogee and impact are interpolated within the step; landing points no longer depend on the output interval.
  • Dual deploy with drogue and main, and a canopy fill time.
  • Liftoff waits until thrust exceeds weight along the rail, and the run says so when it never does. Steps on the rail are a tenth of the normal step.
  • The stability margin at liftoff used the dry centre of gravity.
  • Monte Carlo ignored the user's drag coefficient and parachute.
  • Pitzer departure enthalpy was wrong by a factor of 1/Tr.
  • Haack nose cones had no centre-of-pressure coefficient.
  • Cooling: wall temperature converges to 0.01 K, Bartz uses Eucken's Prandtl number and Bartz's viscosity estimate by default, N2H4 and MMH coolant data, and invalid inputs raise instead of returning numbers.

Desktop application#

  • New interface: a test-stand console with one accent colour, IBM Plex type and its own icon set, in dark and light versions.
  • Four sections (Engine, Vehicle, Flight, Analysis) instead of three levels of tabs. Every long calculation runs in the background and can be cancelled with Esc.
  • The window is usable in about half a second; heavy parts load when first shown.
  • SI and Imperial units throughout.
  • Chamber contour from L*, contraction ratio and an 80 % bell, exported as CSV or STL.
  • A Markdown report and a JSON export of the whole workspace; every plot saves as PNG, SVG or CSV.
  • The first start opens an example project.

Library and tools#

  • analyze_engine returns vacuum, sea-level and operating-point performance in one call; performance_at evaluates any back pressure.
  • sweep_engine for parametric studies.
  • ensim engine and ensim run work without Qt and write JSON.
  • Example projects ship inside the package.
  • Documentation rebuilt as a site with theory, validation and API reference.

3.0.1 - 2026-08-20#

Distribution#

  • Added self-contained desktop downloads for Windows x64, Linux x86-64, and macOS on both Apple Silicon and Intel.
  • Added release-time smoke tests and SHA-256 checksum files for every desktop bundle.

3.0.0 - 2026-08-13#

Scientific models#

  • Reworked packaged thermochemistry and NASA-format parsing with explicit conservation and CEA 3.3.2 reference comparisons.
  • Corrected frozen ideal-nozzle operating-point reporting and removed hidden geometry changes and empirical separation penalties.
  • Made thrust, mass flow, c* efficiency and specific impulse mutually consistent and removed the single-threshold flow-separation verdict.
  • Removed the heuristic shifting-equilibrium API; equilibrium nozzle flow remains out of scope until energy, entropy, chemistry and element conservation are solved together at each station.
  • Corrected Bartz inputs, added Gnielinski coolant convection, counterflow energy balance, pressure loss and explicit correlation-domain validation.
  • Replaced heuristic cooling-channel auto-sizing with explicit geometry, mass flow and coolant inlet-state inputs.
  • Replaced geometry-only combustion-stability verdicts with acoustic modes and user-supplied growth/damping classification.
  • Added WGS-84 geodesy, ECEF/ECI transforms, J2 gravity and NASA NESC case 1/2 reference subsets.
  • Removed the undocumented synthetic transonic drag curve; trajectory drag now uses an explicit user-supplied axial coefficient and RK stages use depleted mass.
  • Replaced proxy optimization objectives with reproducible reduced-order physics.
  • Added positive-support uncertainty sampling, explicit seeds, failure accounting and correctly labelled confidence ellipses.

Application and package#

  • Migrated the installed namespace to ensim and packaged data/assets with the wheel.
  • Rebuilt the advanced panel around MOC design and engine uncertainty analysis.
  • Fixed propellant identifier mapping and mass-to-mole conversion in the GUI.
  • Removed nonfunctional replay, unit-toggle and duplicate optimization controls.
  • Replaced unsourced hardware replicas and static propellant-performance previews with three reproducible, neutral engine input cases.
  • Added safe headless 3-D fallback and GUI workflow/smoke tests.
  • Rewrote scientific documentation around reproducible evidence and limitations.

2.0.0 - 2026-01-02#

  • Added the initial multi-stage, cooling, optimization, materials, mission, propellant-preset and desktop analysis modules.
  • Published the ensim package and trusted-publishing workflow.

1.0.0 - 2026-01-02#

  • Initial open-source release with thermochemistry, ideal nozzle performance, PyQt6 interface, plotting and project export.