Fire lance and atomic clock: what they have in common

1. Step 1. Fire lance — uses — Gunpowder. A gunpowder charge.
2. Step 2. Gunpowder — is used in — Rocket. The first rockets were powered by gunpowder.
3. Step 3. Rocket — evolved into — Liquid-propellant rocket engine. Goddard switched to liquid fuel.
4. Step 4. Liquid-propellant rocket engine — is part of — Reusable rocket. Liquid-propellant engines.
5. Step 5. Reusable rocket — has part — GPS (satellite navigation). Navigation during landing.
6. Step 6. GPS (satellite navigation) — uses — Atomic clock. The satellites carry atomic clocks; the position is calculated from signal arrival times.

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