Rocket guidance unit and tunnelling shield: what they have in common

1. Step 1. Rocket guidance unit — is part of — Multistage rocket. Gyroscopes and a computer hold the trajectory.
2. Step 2. Multistage rocket — is a kind of — Rocket. A multistage rocket is a rocket that drops its empty tanks on the way.
3. Step 3. Rocket — uses — Gunpowder. The first rockets were powered by gunpowder.
4. Step 4. Gunpowder — evolved into — Dynamite. A replacement for gunpowder in mining.
5. Step 5. Dynamite — works like — Tunnelling shield. Two ways of driving tunnels — mechanical and explosive.

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