Orbital Ascent

Prompt Claude Code Claude Opus 4.8 Let's create a new doodle for a rocket launch orbit simulator. The user selects their rocket, they launch, and they command their rocket's movement, staging, and rocket throttle in an attempt to reach orbit. They may overshoot (leave orbit) or undershoot (crash back down). There should be several different rocket configurations with a mix of liquid and solid motors. We will want to support basic orbital mechanics, and also simulate basic atmospheric effects like drag against the rocket.

Let's create a new doodle for a rocket launch orbit simulator. The user selects their rocket, they launch, and they command their rocket's movement, staging, and rocket throttle in an attempt to reach orbit. They may overshoot (leave orbit) or undershoot (crash back down). There should be several different rocket configurations with a mix of liquid and solid motors. We will want to support basic orbital mechanics, and also simulate basic atmospheric effects like drag against the rocket.

Pick a rocket, ride the countdown, and fly it to orbit. The whole game is the gravity turn: climb straight up out of the thick lower air, then gradually pitch east and trade vertical climb for the sideways speed that orbit is actually made of. Keep burning until your periapsis (the low point of your projected path, drawn live in front of you) rises clear of the atmosphere. Hold the burn too long and you'll fling yourself onto an escape trajectory; cut it too early and the planet reels you back in.

Controls (keyboard, or the on-screen buttons for touch):

A / D (or ← →): steer, pitching the nose left and right
W / S (↑ ↓), Z full, X cut: throttle (liquid engines only)
Space: stage, dropping the spent stage and lighting the next
T: cycle attitude hold between prograde (point along your velocity), retrograde (point backward, to slow down), and off
, and .: time warp, for the long coast up to apoapsis
P: pause

Four vehicles, two kinds of motor

The fleet is a deliberate spread of the liquid/solid trade-off:

Comet I: a forgiving all-liquid trainer. Both stages throttle freely and can be shut down and relit, with delta-v to spare.
Ember: a solid booster slings you off the pad at full thrust (no throttle, no shutdown, so commit), then a nimble liquid upper stage does the delicate circularization.
Titan Heavy: three liquid stages and brute delta-v. Easy to reach orbit, and just as easy to blow right past it into a hyperbolic escape if you don't ease off.
Firecracker: three solid motors and zero throttle. All you control is the steering and when to light each motor. The trick is to coast between stages and ignite the next one near apoapsis. Expert mode.

Liquid engines throttle from 0–100% and restart at will. Solid motors, once lit, burn flat-out until they're empty and can't be shut off, so with solids your only real levers are attitude and ignition timing.

What's actually being simulated

It's a real little orbital sandbox, not a scripted animation:

Inverse-square gravity around a planet (Kerbin-scale: 600 km radius, 9.81 m/s² at the surface), integrated with a symplectic step so orbits stay stable.
Live trajectory projection: every frame it forward-integrates your ballistic coast and draws the conic ahead of you: a closed ellipse once you're orbital, an arc to a marked impact point when you're not, an open curve when you've gone hyperbolic. Apoapsis and periapsis are computed from the orbital elements (energy, eccentricity vector) and tagged on the path.
An exponential atmosphere (density falling off with a 5.6 km scale height) and quadratic drag that opposes your velocity, so go too fast too low and you'll feel it bleed your speed and redden the nose with dynamic-pressure heating. The lesson real rockets teach: don't fight the thick air, climb above it first.
Staging and the rocket equation: thrust comes only from the active stage, mass drops as propellant burns and as you jettison empty stages, so your acceleration climbs through each burn exactly as it should.

The camera follows you in close for the ascent and smoothly pulls back to frame the whole planet and your orbit once you're up there. Reaching a stable orbit is genuinely the goal, and missing it in both directions (a fiery re-entry, or sailing off into the dark) is half the fun.