Thread by @bramcohen

Now a few highly speculative thoughts on better ways of getting things into space (thread)

The most important thing to understand about getting things into space is the role of the atmosphere. It both slows things down with air resistance and provides propellant which can be conveniently grabbed onto and flung backwards

As it happens, Earth's atmosphere is designed exactly wrong for space launches. It's so thick at the surface that hitting escape velocity will melt anything before it gets out, and becomes thin so fast that you can't use it to get any significant height

There's a bit of an anthropic reason for this: Earth's atmosphere is thick enough to protect us from getting cooked by the sun, but thin enough that the sun's energy can hit the surface, allowing for our survival

It is a bit quirky though. If there was an Olympus Mons on earth we could simply drag a railgun to the top and launch space vehicles from there. But we can't.

Anyway, the other role of the atmosphere is that it has oxidizer conveniently present so you don't have to bring that with you. But that stops being useful once it gets thin, which isn't very high up.

Another important thing to understand is that getting off the Earth is only slightly about achieving height. It's mostly about achieving speed. Once you get going fast enough you can coast away, but escape velocity goes down very slowly with elevation.

Surprisingly both escape and orbital velocity are completely independent of which direction you're headed. Regardless of whether you're pointed straight up, horizontally, or straight down (if there was a hole drilled in the Earth for you) escape velocity is exactly the same

This fact can be used to make the atmosphere work in your favor, Whatever speed you happen to be going there's an optimal density of the atmosphere to not melt you but still provide useful propellant at that speed.

Since it doesn't matter which direction you're pointed, you can precisely control the density of the atmosphere simply by adjusting your altitude. Of course you need to bring your own oxidizer on board, but that can be done.

Thing brings me to my proposed three-stage vehicle for getting things into space cheap. The first stage is a conventional turbofan which gets the everything else as high in the atmosphere as possible before it suffocates from the air being too thin.

Counterintuitively the purpose of this first stage is not particularly to pick up speed or height. It does those things, but only in small amounts. Its purpose is to get to a high enough altitude that you can go fast without the atmosphere destroying you.

The second stage is a fanned jet which has its own on-board oxidizer, probably liquid oxygen and liquid methane. The fan blades will very long and almost straight.

Being designed to go from Mach 2 to Mach 20 it's going to need a very good torque curve. The wings will have conventional flaps for controls, but I have no idea what they should look like.

Oddly even though this concept is straightforward I don't even know what it's called. Usually crazy engineering concepts have maniacal fanbases for whom it's their fantasy project, even (or especially) completely nuts concepts, but \

I've never seen mention of such a vehicle anywhere. It probably doesn't help that there's no way to test it on the ground. Good luck making a wind tunnel which can make Mach 10 wind at 0.005 atmospheres.

That said, the concept seems straightforward enough and not completely insane from a mechanical engineering standpoint. All that's left is the third and final stage, which is a conventional rocket probably using liquid oxygen and liquid methane again.

That second stage having all the propellant it needs should in principle massively improve the amount of weight which actually makes it into space. On board propellant is dead weight, you accelerate it forward only to shoot it backwards.

Trying to be cute and reduce the number of stages seems like a very bad idea. The three stages are wildly divergent in terms of their functioning and engineering, and there's no need to drag along the machinery for earlier stages which propelling at later stages.

This is, of course, all highly speculative and I'm musing just for fun. Feedback from people who know what they're talking about and links to existing work much appreciated.