Worksheet · Ages 9–11 · 30 min
Why is a rocket almost all fuel?
Real Falcon 9 numbers: 549,000 kg on the pad, 22,800 kg delivered to orbit. Children work out how little of a rocket is cargo — then test it in the Rocket Lab.
A Falcon 9 weighs 549,000 kg standing on the launch pad, full of fuel. It can carry 22,800 kg all the way to orbit. Let us see how much of the rocket is actually cargo.
- Work out 22,800 ÷ 549,000.
- Multiply by 100 to turn it into a percentage.
- Round it to the nearest whole number.
- Now draw 100 small squares. Colour in that many.
1. What percentage of the rocket is the thing it is actually delivering?
2. What do you think the other 96% mostly is?
3. A Merlin engine pushes with 845 kN at sea level. There are nine. What is the total?
4. Why does a rocket throw away its bottom half halfway up?
Now go to the Rocket Lab on the website and try to reach orbit. Add engines, add fuel, add a stage — and watch how quickly adding more fuel stops helping.
You have one more kilogram you are allowed to add to the rocket. Fuel, or cargo? Say why.
For the grown-up
- The answer is 4.15%, so 4% after rounding. Colouring 4 squares out of 100 lands the point far harder than the number does.
- The deeper idea is the rocket equation: extra fuel also has to be lifted, so each extra kilogram helps less than the one before. Children do not need the equation — the Rocket Lab lets them feel it by failing.
- The 22,800 kg figure is for an expended booster. If the booster flies home and lands, it is 18,500 kg, because landing needs fuel that has to be carried the whole way up.
Every number on this sheet comes from: Falcon 9 Block 5 — specifications · Merlin rocket engine family