The rocket is mostly fuel
On a typical launch to low orbit, on the order of nine tenths of the mass on the pad is propellant. The payload is a few percent.
Tsiolkovsky’s relation says the change in speed is the exhaust speed times the logarithm of the mass ratio. Low orbit, once gravity and drag are included, wants on the order of 9 kilometres a second. Chemical exhaust speeds are a few kilometres a second. The logarithm then demands that you start several times heavier than you finish. Staging throws away empty tanks so the next stage does not accelerate dead metal. Even then, a kerosene rocket on the pad is mostly its own propellant.
Hydrogen exhausts faster and so needs a milder mass ratio, at the price of a bulkier, colder tank. Solids are simpler and less efficient. The shape of the result barely moves. What reaches orbit is the tip of a mass that was, minutes earlier, almost all fuel and oxidiser.
Caveats
- Nine tenths is a description of chemical orbital launchers, not a constant. The fraction moves with the propellant, the number of stages, and whether the rocket is reusable.
- The equation is ideal. Real flights add losses, which makes the propellant fraction larger, not smaller.
Sources
- 1Sutton G. P., Biblarz O.. Rocket Propulsion Elements. Wiley, 2017.