How spaceflight works

Spaceflight has its own rules that makes it unique. They can be obscure at times.

This is kind of guide to try and make things a little clearer. Hopefully not too pedantic nor too loaded with mistakes (I'm first a dreamer, not an rocket scientist, but there are true rocket scientists among the space jockeys).

Feel free to ask any question.

1 - How to travel into the solar system.

You need to escape Earth gravity. The basic rule is that every celestial body lies at the bottom of a well – a gravity well it dugs into spacetime curvature.

The heavier the body, the steeper the gravity well, the harder the escape.

Rule number 1. Once you escaped Earth gravity, you fall into the Sun gravity well. Which means, you end in orbit around the Sun.

Then if you manage to escape the Sun, you end into our Galaxy gravity well, orbiting around its center like stars do. That's what Voyagers, Pioneers and New Horizon did.

Travelling in space consists of accelerating to get out of a gravity well, then fire a rocket engine to slam the brakes and fall into another gravity well with hopefully, a smooth landing on the surface.

More on this later.
Last edited:


2 – How to get into orbit around Earth

Our beloved Earth is a big, heavy, rocky planet. So its pull of gravity is strong, and the gravity well is deep. First rule of thumb: to maintain a stable orbit, you need to reach, and sustain, a minimal speed. If you fall below that speed, you hit the planet sooner rather than later. Because the Earth is so big, that «speed» is enormous. It is 9 km/s, or burst. That's Mach 25, or 28 000 km per hour.

There is no workaround this.

It is no longer called «speed» but delta-V. Space travel is essentially a matter of delta-V expressed in km/s.

For the sake of comparison

  • the fastest jet aircraft – SR-71 – reached 1 km/s.

  • the fastest rocket plane – X-15A2 – reached 2 km/s.

  • Earth orbit is 9 km/s
The knee-jerk reflex is to think 1 km/s to 9 km/s is 9 times more. Which would already be... enormous. Alas, the rocket equation is neither linear nor decimal. There is a logarithm stuck into it. Which makes things even worse.

Hence leaping from 1 km/s or 2 km/s to 9 km/s represents an enormous gap in energy.

But that's far from over.