Logistics: How to move humanity onto a spaceship that is being built from planet Earth?

Question

Humanity builds a spaceship to leave Earth. For eight billion people or so, that vessel has to be gigantic. Using the metal from Earth's core for the construction and the biosphere to create a habitat, building the spaceship more or less uses up all of planet Earth.

But how do you get all the people onto a spaceship that hasn't been completed yet, while their planet is being deconstructed under their feet?

---

Notes.

You may use other celestial bodies in the solar system to solve the problem of logistics. You may use other celestial bodies as a resource for building materials, as long as the basic premise of using up (most of) Earth to build a spaceship is kept intact.

The passengers aren't stored but living on the spaceship. They need to take with them everything they need to sustain them indefinitely (as space travel takes a long time). For that, the spaceship needs its own biosphere, and taking the one that has served us well for the past couple of thousand years is probably the easiest strategy.

The whole process of moving humanity onto the spaceship should be completed in a few decades at most. Whatever technology you need is available. Again, this is not a question of technology, but of logistics. "Beaming up" people does not work, though. They have to travel, but you can make this quick and large scale (ocean liner sized rockets or space elevators).

Moving Earth itself doesn't seem an option to me. First, it takes too long to accelerate Earth into a useful direction and a meaningful speed (see How can I move a planet?). Second, the atmosphere would be stripped away once we moved out of the protection of the Sun and into denser parts of space. Third, we would have to move an orbiting source of light along to have a source of sunlight. It seems easier to have a light source on the inside of a vessel.

I'm not saying that Earth's biomes have to remain unchanged. I want to move humanity, and to do so we need food, air, etc., all of which are easiest to produce on something like Earth's biome. I mean, you could probably synthesize proteins etc., but why not simply grow wheat etc., which would also solve the oxygen problem? Also, some people need "nature" to remain psychologically sane. Not everyone is made to live inside a room and never be out in the open. So recreating something like the surface of Earth seems necessary to me. But we may not need to have the same kinds of plants and animals, not all of them, not the same kind of landscape, etc. The goal, again, is not to move Earth, but to move humanity. If you can do that by moving Earth, fine, but it is not a requirement of my question.

Answer 1

With the edited question... we're essentially looking at stripping the surface of the planet off and rebuilding it in a ship, which emulates the original situation as best we possibly can.

Option 1) Just move the whole planet out of danger. This is by far the simplest option.

Option 2) Create a rotating tube or ring, for artificial gravity; transplant the planet surface into that, piece by piece. Of course, this gives us all the problems that cartographers have had forever. Specifically, how do you map the spherical stuff onto the inside of a tube? You could have either end of the tube be cold (the "poles"), and the equator in the middle. But there'd need to be at least roughly the same length of land at the highest latitudes and the equator, in order for gravity and sea level to still work, which is a challenge.

One possible answer is not to take all of earth's surface, but only a proportion of it, leaving maybe half of the stuff at the equator.

That's not even close to the biggest engineering challenge

Say you lift everything one square KM of land at a time, and line the tube with it. To do that, you need to lift 1 square km of planetary surface, including any mountains, so we're talking at maybe a 1km cube in reality, and you need to lift that into orbit. And you need to do that without killing everything upon it in a massive "earthquake", nor exposing it to vacuum.

We don't have this technology. We don't really have even any idea what such tech would look like. It may even be impossible.

But let's say the ship was built in geostationary orbit, and has some kind of orbital elevator or skyhooks that can lift the planet's surface in cubes up to the ship in a hermetically sealed box. That's some crazy handwaving, and completely ignores how orbital mechanics would work on this elevator, and the stuff it lifted up, and how the box was put around a cubic km of earth in the first place without killing everything, but...

Most stuff on the planet would still die

That's just the way things are. Biomes are extraordinarily complex webs of interwoven interactions at every level. Tweak just one thing and a species dies, causing the death of all species which depended upon it, and so on in a cascade of effects. If a species relies on tides, seasonally flooded mangrove swamps, following magnetic fields for ten-thousand-mile migrations with the seasons...?

To get the weather systems and ocean currents and magnetic fields for migratory beasts to work even vaguely the same as the Earth would be a mindboggling challenge. To get tides you'd "only" need to have the ship rotate slightly off-center, so that's possible, but perhaps not long-term stable.

Overall... it's almost unimaginable. But if the sun was dying, we could do it, given a few tens of thousands of years. We could make it kinda work. We could craft a generation ship, and give it a biosphere that contained most of the biomes from Earth, and populate it from Earth, like an ark.

And from that ark... we could move to other planets, and craft more generation ships, and in these ones, we would have to seed them anew, rather than as a copy, and hope that the new environments would thrive and fill out.

And then the flotilla would split up and make its way to the nearest few stars. Would it terraform the planets there, or cannibalize them to make more ships? Probably the latter. By the time we reached the planets, nobody alive would remember what a planet was, nor want to be pinned in a gravity well.

Answer 2

Spaceship as massive as the Earth... without questioning specifics, I suggest it should be done in a similar way as whole site reconstruction is done today. If we have an airport, or a mall, or a factory that needs to be rebuilt from scratch, and yet to stay operational through the process, it is done section by section. One section is being closed, then demolished, then rebuilt. During the rebuilding, occupants of this section are squeezed into other sections that are still open. This process can be completed section by section until entire site is a brand new construction.

Similarly, we can build this giant spaceship and start moving people inside while it is still being constructed. Fortunately, you don't need even a noticeable fraction of Earth's mass to provide a temporary accommodation for all of the Earth population.

Answer 3

You do not. Move the biosphere I mean. The surface of our planet is a living, dynamic and interconnected thing. Without magic it is impossible to move it elsewhere without breaking it. Fortunately it is also unnecessary.

You can handle it the same way file systems handle moving large files between volumes. They just copy the data and then delete the original. If you use the GUI they usually even default to doing just a copy instead of a move by skipping the delete so you still have a working copy even if something went wrong with the copy.

This is what you want to do.

Create the copy using material from the asteroids, the Moon, Mars, the martian moons and so on. Transfer the minimum needed biosphere from Earth and let life spread. While this might be difficult and even not work at all, that is irrelevant. If we cannot make it work with all the resources of Earth available to us, we are all doomed as soon as we lose access to Earth anyway. Might as well get it to work when failing won't kill us.

Fail often, fail fast totally works for building gigantic space habitats.

I think the simplest construct to use would be a O'Neill cylinder but instead of two cylinders, you would want a much larger number. The correct number would probably be time to build one divided by available time as having insufficient space to be self-sustaining might be lethal while building too many only costs the opportunity cost. And building cylinders out of material mined from space probably will not compete with anything else you need after the initial investment.