Physics

Launch a rocket

Orbit is not about going up. It is about going sideways fast enough to miss the ground — and the fuel bill for that is brutal in a very specific way.

4 steps 8 min read 3 tools chained Physics

The rocket equation is exponential, and that is the whole problem

Every extra unit of velocity costs exponentially more mass, because the fuel you add has to be carried by fuel. Set a two-stage vehicle and watch the mass ratio climb far faster than the Δv it buys.

Low Earth orbit needs≈9.4 km/s Δv
Of a rocket on the pad≈85–90% is propellant
Rule of thumbMost of a rocket is fuel it will burn on the way up. Payload is the small number left over after the exponential has taken its share.
Open Rocket Equation & Delta-v Budget with these numbers →

Throw away the empty tank

Staging exists because carrying an empty tank to orbit is pure waste. Switch the third stage on and the same propellant buys noticeably more Δv — that is the entire justification for the complexity.

Two stagesbaseline Δv
Three stagesmore Δv, same propellant
Rule of thumbStaging pays whenever the mass you can shed is a meaningful fraction of what is left to accelerate.
Open Rocket Equation & Delta-v Budget with these numbers →

Spend the Δv on an actual orbit

A Δv budget is only meaningful against a destination. A 400 km circular orbit — roughly where the space station sits — needs about 7.7 km/s of orbital speed, and the tool will show the period and the velocity that go with it.

Altitude400 km
Orbital speed≈7.7 km/s
Period≈93 min
Rule of thumbOrbital speed falls as you go higher, but the Δv to get there rises. Higher orbits are slower and more expensive at the same time.
Open Orbital Mechanics with these numbers →

Strip the physics back to a thrown ball

An orbit is a projectile that keeps missing. Take gravity down to the Moon's 1.62 m/s² in the projectile tool and the same throw goes six times further — the clearest way to feel what "fast enough sideways" means.

Earth g9.81 m/s²
Moon g1.62 m/s²
Best angle in vacuum45°
Rule of thumb45° maximises range only without air and on level ground. Add drag and the optimum drops into the 30–40° range.
Open Projectile Motion & Golf Ball Flight with these numbers →

From a mass ratio to an orbit

The exponential sets what you can carry, staging claws some of it back, and the orbit decides what you needed in the first place. Change the payload and walk the chain again — the whole vehicle resizes around it.

All chains → Next: Cut your energy bill Rulebook
Reference only. Stories chain real tools — the numbers shown are worked examples, so check them against your own figures before relying on them.