Simulate mode uses the geometry, masses, motor curves and deployment settings from your design. Set the launch conditions, then run the simulation.
Flight conditions#
- Launch site
A curated set of real launch sites around the world — or any custom latitude, longitude and elevation. Site elevation and latitude feed the atmosphere and the physics.
- Rail
Rail length, inclination and compass heading.
- Wind
Built-in layered wind profiles, from light and variable to a fast jet aloft — or resolve a live forecast for the launch site and date from ECMWF, GFS, ICON or ICON-EU.
- Surface finish
Normal, smooth, polished or perfect — the airframe finish feeds the drag model.
How a run works#
Run Simulation stays disabled while validation has errors. If you're using a live forecast, ZenRockets loads the atmosphere for the selected site and date before the simulation starts. In a multi-stage flight, each stage is simulated in sequence from the conditions at the previous separation. When the run finishes, the workspace opens the results with the summary, charts, trajectory and events. Most simulations complete within a few seconds.
A complete simulation includes:
- Time-series for position, velocity, acceleration, attitude and angular rates, angle of attack, path angle, thrust, drag, lift and stability margin.
- Events — liftoff, rail departure, burnout, max-Q, separations and ignitions, deployments, apogee and landing, each with its key numbers.
- Summary metrics, the resolved atmosphere, and any flight alerts the run raised — a deployment at dangerous speed, a charge firing under thrust, a hard landing.
Model assumptions and limits#
The flight model uses rigid-body 6-DOF motion, including attitude dynamics, the motor's thrust curve, aerodynamics from the rocket geometry and a layered wind profile.
Recovery events follow the deployment settings on the rocket. In a multi-stage flight, each stage starts from the conditions at the previous separation.
The model does not include turbulence or wind gusts, fin flutter, flexible structures, or detailed parachute inflation beyond the configured lag.
The maximum simulated flight duration is ten minutes. The simulation stops if the flight reaches that limit. Each run also has a compute limit. If the solver cannot finish within that limit, the run stops and reports an error.
Advanced solver settings#
Start with the default solver settings. Use Advanced Solver Settings to adjust tolerances, limit the solver's time steps or try another solver when a run does not finish.
- Solver
LSODA is the default and works well for most flights. It switches automatically between non-stiff and stiff methods. RK45 is an alternative for smooth, non-stiff flights and can be worth trying if LSODA is unusually slow or fails to finish. DOP853 is intended for smooth flights where you want tighter numerical accuracy.
- Tolerances
Tighter tolerances reduce the allowed numerical error but take longer to solve. Looser tolerances run faster with a greater risk of numerical drift. The defaults are intended for hobby-scale flights.
- Time step limits
The maximum step limits how far the solver can advance at once, which can help around short events. LSODA also uses a minimum step to stop the solver from spending too long on a case it cannot resolve.
- Stop at Apogee
End the run at the highest point. When you're iterating on altitude — fin sizing, motor selection, mass trades — skipping the descent makes each run faster.
If a simulation stops with a solver-convergence error, review the design inputs and the error message before changing the solver settings. Trying RK45 may help when LSODA does not finish. Loosening the tolerances allows more numerical error, so treat any resulting change with care.
Viewing results#
Results open in four tabs: 3D View for trajectory playback, Charts for the summary numbers and time-series, Events for the milestone timeline, and Environment for the atmosphere the flight flew through. Understanding Flight Results walks through each one.
Updating stale results#
Results stay attached to the design that produced them. Edit the rocket or the flight conditions after a run and the results are flagged out of date, in the results view and on the editor tab, until you re-run.