BUILD CHALLENGE

Can you design a rocket that works?

One mission. One budget. Your choices. Then you launch it and find out — and nothing here is a quiz. Your design is judged by the same arithmetic every real launch vehicle is judged by: can it lift itself, and can it afford the speed? Get it wrong and the rocket equation will tell you exactly how wrong.

MISSION

Deliver a 200 kg satellite

A customer needs a 200 kg Earth-observation satellite in a 200 km orbit. Design a rocket that can do it — and stay under budget. Overbuild and you go broke; underbuild and you don't reach orbit.

1 · Engine

Which engine goes on the first stage?

2 · How many engines?

More thrust — but more mass and more money.

3 · First-stage propellant

Fuel is speed. Fuel is also mass, and tank.

4 · Second-stage propellant

The stage that actually does the orbiting.

5 · Recovery hardware

Legs and fins so the booster can fly again — dead weight on the way up.

BUDGET

$3.3Mof $30.0M

Rocket mass: 5.8 t
Engines: 3 × Rutherford
Payload: 200 kg
Target: 200 km orbit

Thrust-to-weight and the Δv budget are revealed when you fly.

The two questions every rocket must answer

1. Can it lift itself?

Thrust-to-weight at liftoff is thrust divided by weight. Below 1.0 your engines push up with less force than gravity pulls down and the rocket does not move — it just sits on the pad burning propellant. This isn't a rule someone invented; it's subtraction. It's also why a rocket that's too heavy for its engines fails before it has a chance to fail at anything else.

2. Can it afford the speed?

Orbit isn't about height — it's about going sideways so fast you keep missing the ground. At 200km that's about 7.8 km/s, plus roughly 1.4–2 km/s more lost fighting gravity and air on the way up. The rocket equation says the speed you can buy depends on the ratioof your full mass to your empty mass — which is why adding fuel only helps if you don't add just as much tank to hold it.

A note on honesty

The engine figures here are real (Rutherford and Merlin 1D thrust and specific impulse are published). The prices are simplified for play — real launch pricing is bundled and commercially secret, so these are plausible relative costs, not quotes. The physics is not simplified: the Δv budget is the same calculation used to decide whether a launch vehicle is worth building.