The parts tree follows how the rocket is put together. Stages sit at the top. Nose cones, body tubes and transitions build the airframe, while motors, recovery gear and internal hardware attach to the parts that hold them. The tree also controls placement and mass totals.
Rocket structure#
At the top level a rocket is a stack of stages. A single-stage sport rocket has one; a two-stage build has a booster and a sustainer, fired in order. Inside each stage, airframe parts — nose cone, body tubes, transitions — stack nose-to-tail automatically, so inserting a tube mid-airframe shifts everything below it without any manual repositioning.
Everything else nests where it physically lives: a motor inside a body tube or motor mount, a parachute under the nose cone, centering rings inside the tube that holds the mount.
Part families#
The parts toolbar groups the full catalog by role:
- Airframe
Nose cones (seven profile shapes, hollow or filled), body tubes and transitions — the aerodynamic outline of the rocket.
- Structural
Inside tubes (motor mounts, couplers), centering rings and bulkhead couplers — the internal skeleton that holds everything in place.
- Propulsion
Motors from the catalog or your own custom designs. Selection, ejection delays and radial clusters are covered in Using Motors.
- Recovery
Parachutes and streamers with full deployment configuration — covered in Recovery & Staging.
- Payload
Cylindrical or rectangular mass components — altimeters, cameras, ballast — with a direct weight entry.
- Surface
Fin sets with freeform profiles, rail buttons and launch lugs.
The parts panel#
The left panel is the design's table of contents, and each row carries live information:
- A type icon identifies the part family at a glance (motors are tinted orange, recovery gear green, payloads blue) and doubles as the row's drag handle.
- The name. Double-click it to rename a part, here or in the details panel header; names are kept unique automatically.
- The mass, right-aligned. The Σ toggle in the panel header switches every row between the part's own mass and its subtree roll-up, and the header always shows the vehicle total.
- A small dot before the mass marks a part whose mass is overridden with an entered value. It's the only override marker in the tree; CG and drag overrides show up in the details panel instead. See overrides.
Adding and arranging parts#
Adding a part takes two steps: pick it from the toolbar, and ZenRockets proposes a placement — new parts infer their diameter from their neighbors and land on the right parent with a sensible anchor. Confirm to keep it, adjust the placement first, or cancel.
Rearranging is drag and drop: drop a row above, below or inside another part. Valid targets highlight as you drag, and an invalid drop turns the preview red and is refused. The tree enforces what physically makes sense: stages accept airframe and hardware, tubes accept internal structure, recovery devices attach where they'd be packed. Clustered parts — a three-motor cluster, a ring of centering hardware — stay a single tree entry with a radial pattern, so editing one edits all instances at once.
Isolating a stage#
Multi-stage designs get a stage dropdown next to the view controls above the canvas. Full Rocket shows everything; Stage 1 Only, Stage 2 & Above and so on hide the stages below the one named. Hidden stages fade out and ignore clicks, and the CG, CP and mass readouts cover just the visible stack, so you can check a sustainer's stability on its own.
Selection and editing#
Click a part in the tree or directly on the 3D model — selection is the same either way, and the canvas outlines what's active. ⌘/Ctrl + click builds a multi-selection; clicking empty canvas clears it.
Every part opens with the same details-panel header — the type icon, the name (double-click to rename) and a color picker for the 3D model — followed by the Placement block: parent reference, anchor and offset, explained in Sizing & Positioning. Below that come the type-specific options: dimensions, material, fin profile, deployment, ejection delay, and so on.
Most parts can also carry measured values in place of computed ones — mass and center of gravity on every part, drag coefficient on external ones. Preparing to Simulate covers how overrides work.
Changes to a numeric field take effect when you press Enter or click outside it. The design then recalculates automatically, and the change can be undone from the edit history.