homemade rocket thought experiment

[kunkmiester]

Read a blog post on a libertarian fantasy--basically large groups of libertarians secretly building large numbers of homemade rockets and making a surprise mass immigration to space. This was set a few decades into the future so they had all the current crop of 3d printers and such in the open domain as well as rocket designs.

It got me thinking about how feasible it is, especially today. I looked first at materials--I assume you couldn't use exotics like the Al-Li due to manufacturing it. Ignoring patents though, you could get this: http://www.sheffield.ac.uk/news/nr/3d-p ... m-1.332731

Which would be awesome, especially with the SLS machines. Aside from that you'd have basic aluminum and steel structural shapes. This has serious weight consequences, and on top of that you have to deal with less optimal connecting methods, like regular welding and rivets and the like. We're not worried about gov certification for this though, just getting it reliable.

So, we get the "free space project." The goal is to build an expendable booster capable of putting a five or six person module in orbit. This module is intended to be put together with others to form a larger habitat. The boosters need enough extra flight to put the used stages into the ocean, and to be able to hit the proper orbit from higher altitudes like Wyoming or even farther. Not sure where exactly the "proper" orbit is, it does need to be out of easy range of current asat weapons though.

You can probably make an engine with similar ISP to the merlin, I'd be looking at kerosene, methane, and propane for fuels, you'd also need to design an oxygen plant. Considering the conditions of construction, you'd also need designs that work with a lot more contamination and looser tolerances than most space systems. Spaces has been working a lot on this--they have cheaper computer setups and improved the ease of manufacture for components in various ways. I'd see a "free space rocket "looking an awful lot like a falcon heavy in fact.

Crazy idea, but I thought it'd be fun to think about. The big thing I think is getting it good enough, and not just for government but the crazy people who would be trying this.

[hanelyp]

Some thoughts:

- Kerosene / LOX is a good fuel combo for performance and handling.
- Welded steel sheet makes decent tanks.
- Explosive forming for tank domes doesn't look too complicated once the particulars are worked out, but doing it without attracting attention would be next to impossible.
- Aluminum 3D printed engines. Yes, aluminum. Possible with aggressive regenerative cooling, made possible by the high thermal conductivity of the metal.
- The free software OpenFoam CFD package appears capable of simulating rocket engines, but documentation for setting up a simulation is hard to come by.
- Upper stages, along with residual propellant, will represent a resource to be used.

If upper stages are a standard design, a tetrahedral lattice of tanks and hubs for the colony is a tempting design. But this implies the tanks have a suitable outer wall for a long duration station.

Under the premise of an underground effort, or simply assuming no dependable support from the ground afterwards, once the colonists make orbit they'll need means to harvest material and fabricate everything they'll need to survive, including eventual replacements for whatever tools they bring with them.

An unannounced launch seems likely to attract the most unwelcome of attention, being easily mistaken at first for a nuclear attack.

[Tom Ligon]

The Artemis organization wanted to do this for lunar colonization. The were looking at such bare bones equipment as a lunar surface to LLO 1-person launch vehicle that looked like a lawn recliner with rocket engines under it.

The old L5 Society, of which I was a member, would have appreciated this sort of scheme. They still exist in local chapters, but the national organization was swallowed into the National Space Society, which lobbies for space programs but does not have the same spirit of personal adventure as the Elf-Hivers.

A few old L5ers do participate in small industries trying for space on their own. Aleta Jackson comes to mind instantly.

John Carmack set up his own amateur company to compete in the Lunar Lander Challenge. They built their own rocket engines from scratch.

[kunkmiester]

There are places out here you could do the forming without bothering anyone with noise. You can also get prefabbed domes for a pretty penny if you desire. Even better though to figure out a flat ended tank or cone shaped ends.

The thought would be simply to set up a wiki on tor to carry the designs. Test and refine, and post.

I actually had a good thought for the basic design. I remember reading about a super modular design a while back, you built.t your rocket out of literally dozens of small engine modules strapped together. Very scalable, and the smaller rockets would be easier to repurpose to the lower thrust requirements needed in space when you get there. Big problem in this case is needing to be able to put the used staging down somewhere safe, which adds to the size to get the range needed. Still, if the module can literally be built in a garage and assembled into the rocket elsewhere, that's good for this project.

[hanelyp]

Whether you like it or not the tank of a rocket is a pressure vessel. Sharp angles on a pressure vessel, such as a plain conical end would need, are stress concentrators. A flat plate end would be worse.

On the subject of tank design, fuel weight would present more pressure on one end than the other, implying that minimum weight tanks should have thicker metal gauge or smaller diameter at the bottom. But we'd probably accept a less optimal tank in the name of simplicity.

A cluster of common design propulsion modules reminds me of http://en.wikipedia.org/wiki/OTRAG_%28rocket%29. If we're going to be launching people and repurposing upper stages to build a space colony than implies a minimum diameter for a common module.

[kunkmiester]

The otrag was it, couldn't remember the name. We'd be using a larger module with better performance I think but the concept would be the same.

[Tom Ligon]

"Whether you like it or not the tank of a rocket is a pressure vessel. Sharp angles on a pressure vessel, such as a plain conical end would need, are stress concentrators. A flat plate end would be worse."

Why do things the hard way? Bubbles are easy to form. In space, just blow the tanks. It's not as if they will have to deal with air resistance.

A couple of my fellow SF authors and I just had an article accepted. When it comes out I'll have more to say here on materials that can be found in space and which offer easy fabrication.

[kunkmiester]

Curves are harder to make on earth. While domes may be preferable, they are more complicated. The wiki article says the otrag tanks weren't pressurized to more than a few hundred psi. That's pretty easy, multiple industries do it all the time. Domes are still preferable, but not needed I think. You do have make sure you have very good welds, but you have to do that anyway.