Knowledge Zone · Card 3 of 13
Staging
The rocket equation asks for a ratio of full to empty mass, and an empty tank is the worst possible cargo: it weighs, it costs Δv to accelerate, and it will never do anything again. Staging is the decision to stop carrying it. Drop the tank the moment it runs dry and every remaining engine is pushing a lighter ship for the rest of the climb.
It matters most where the ship already is. When the Scout separates it is at 84 km and 2 495 m/s, and it throws away 2.7 tonnes of empty first stage out of the 17.2 still moving — 16% of the ship, gone in one step, at the exact moment that mass had stopped being useful. Its little upper stage is then worth 10.4 km/s of the Scout's 14.2 all by itself, because it never has to lift the tank below it.
Do it more often and you get more of it, at the price of more engines and more plumbing. The Titan carries three stages where the Scout carries two, and the picker's stats strip shows what that buys: 16.0 km/s against 14.2.