4 ms·
Orbit is not about height, it is about speed. You have to get to almost 30km/s otherwise you aren't in orbit and you fall back into the atmosphere.
by rjmunro 3y ago
Orbit is not about height, it is about speed. You have to get to almost 30km/s otherwise you aren't in orbit and you fall back into the atmosphere.
- 3m 3y agoI think you are confusing the speed at which the earth orbits the sun (~29.8km/s) with the speed at which an object needs to travel to maintain earth orbit (~7.8km/s).
- rjmunro 3y agoWhoops, you are right. I think it's too late to edit my original post. The point still stands, though, you have to get to nearly 8km/s otherwise you aren't in orbit and you fall back into the atmosphere. You can't get to anywhere near that speed while still in the atmosphere - SR-71s only manage about 1km/s, and because kinetic energy is proportional to the square of the speed, at that point you are only 1/64th of the way there.
- seabass-labrax 3y agoTo get to an appropriate speed, you need to accelerate eventually. But it's easier to do that at a higher altitude, where you have thinner air to travel through: less drag, less severe transonic effects to mitigate and, on the way up, a wider variety of air-breathing engine types to choose from (including the Astro Mechanica one).
- pfdietz 3y agoThe wider variety of air-breathing engines points out a problem: the launcher necessarily goes through a wide variety of aerodynamic regimes where different engines work. Making a single engine that works over a wide range of speeds is difficult. And for what? Using more fuel in a larger first stage just so you can save on cheap oxidizer (LOX at $.10/lb)?