Would it be possible to create a planet sized space station, with technology levels close to Star Trek TNG, if so, how long would it take to make it? Think the Death Star and starkiller based from Star Wars, how long would that take to make? If it was possible? Thanks
First thing I see- making a planet sized anything requires a planet sized pile of materials. So either you're completely upgrading earth or using a whole system of planets to build your planet-spacecraft.
With that out of the way-
I forget where I saw it, but someone did some estimates on the Death Star and decided it was overly expensive(If you can find that, please put it in the comments), and even just firing the death laser costed a lot of money. so your first problem will be the money.
To build a planet sized thing, you have to either;
A- build it on the surface of a planet and then send it up in spacecraft. this will cost a lot of money, and is probably not all that good for your spacecraft. the more joints, the more places it could leak.
B- build it in space, which will require some smaller spacecraft with tool attached and very precise servos to put it all together. still, you need to get the supplies there unless you have refineries nearby making the pieces as you go.
C- modify an existing planet. this is probably the best option, but will still require tons of work. The other options allow for just building it, but this one requires you to dig through the planet and hollow out your fuel source, living quarters, and other things. at least it comes with an atmosphere.
To use this craft, you need to move it, which needs some big engines. not to mention, moving a planet will almost certainly distort the local orbits, and possibly cause the entire system to slowly orbit into the sun if you're not careful.
All in all-
Yes it is possible, but no, it is not feasible. even without a death laser, you could doom planetary systems just by passing through the neighborhood.
Let me preface this by saying that anything is possible if one is willing to imagine sufficiently powerful technology. But there are problems with a planet-sized station that need to be overcome. The first and foremost problem is gravity.
A space station the size of a planet would have a mass roughly corresponding to a planet's mass, which would create corresponding gravitational effects. This presents a significant problem in structural engineering, since the center of the station would be subject to extreme pressures as it tries to prevent the entire station from collapsing in on itself. Remember, the Earth's core is molten iron in large part because of the pressure of (more than trillions) of tons of material trying to fall inward under its own weight. By the time the station reached 'dwarf planet' size — i.e., a planet that has sufficient gravity to bend its constituent rock and metal into a rough sphere — the internal pressures would be far beyond the strength of any materials we currently know of. If materials that could survive those pressures existed, gravity would still cause problems. As one goes deeper into the station, both air pressure and ambient temperature would increase, so without sophisticated airlocks and cooling systems most of the station would be uninhabitable.
And then there's the other question: how many people would be required to run such a thing? There are currently seven billion people on the surface of the Earth; if the Earth were a sphere filled all the way down with rooms and passages and workshops, etc, how many trillions of people would be needed to functionally manage it? How would those trillions be fed, where would they get their water, what would happen to their waste products?
These are not trivial problems. Most of the SciFi/Fantasy world ignores them, but if you want to take them seriously you'll need some serious scientific advancements.
Generations, not dollars:
If you were building such a thing, you would need a reason for it to exist. So my first thought is that your builders are homebodies. They've decided there's no reason to go running all over, and slowly consume their world until it's an enormous, continuous habitat. The total mass of the world wouldn't change, but as they hollowed it out and converted rock to buildings and tunnels, 10,000 story high rises would be buried under 50,000 story high rise buildings. The support systems would evolve with the building, and the tech would transform the world as science allowed new techniques. Eventually, the planet would be reshaped for new functions, like absorbing sunlight for power.
Alternatively, you start building space stations and just keep adding and adding endlessly until you have a giant conglomeration of stations. This would probably look like an immense ring orbiting the planet. Eventually, you might not even be able to SEE the planet under the mass of orbiting stuff. Space elevators would terminate in a giant orbital rail system where train-like assemblages take you to which station you want to go to. Again, the systems would evolve in time with generations of tech. Or instead of elevators, buildings a mile wide and 100 miles high do the same job. On that scale, why not?
These kinds of developments would be the poor-civilization's equivalent of a ringworld or Dyson Sphere. They would less be built and more evolved along with a civilization. The construction would take thousands (more likely 10's of thousands) of years. Now if such a civilization decided they needed to move from their home to go elsewhere, then they could apply intelligent design to the project and consume a planet somewhere with a huge engineering project. The timeline for something like that would depend on lots of variables with the people and their tech. It would likely take a fraction of the time than for the original, and operate more smoothly once inhabited.
I could imagine such a station orbiting a dead star, stripped of much of it's tech, a slowly collapsing testament of a culture that has moved on to a new world and left the old one behind. For humanity, it could be a goldmine of resources, tech, and even habitable space (humans might have low standards compared to the aliens). Or maybe it would hold the devolving remnants of the alien's culture, with wild aliens as a menacing threat to explorers. It's the stuff of good storytelling.
Depends on the meaning of "planet-sized".
For example, we could imagine an array of space telescopes or omnidirectional sensor array; the individual units might be lashed together with very thin carbonan and fiberoptic filaments, thousands of kilometers long. The whole ensemble might well be spherical, and having the farthest units at some 6500 km from the center of the array would make it "planet-sized" (specifically, approximately Earth sized).
Time to build: months, depending on the number of individual units. Then you'd have a large sphere made up of mainly nothing.
If you wanted a solid space station, big as a planet, then things change - a lot. I don't think it's even doable using TNG technology; you'd need a Kardashev level II or above civilization.
Yes it should be doable with Federation level technology, a spare planet or two, and a lot of patience. With automation, you can build robots that replicate themselves and break down a planet by drilling and mining it, reshape the material into useful forms, and then begin building the planet.
You can send a swarm of small robots to a planet that take the local material and setup a processing facility and a factory to create more robots. You would just need a planet or planetoid that has enough ore to break down and fabricate. Take our own solar system for example. Mercury's core has TONS of iron, albeit in molten form most likely, that could be cooled down and fabricated for different parts.
#1. Send robots to Mercury. #2. Robots take local materials and build a factory to produce specialized robots. Some robots drill, some mine, some fabricate specialized computer chips and electronic equipment, some robots send back status reports, others collect energy, etc. There is plenty of iron and silicon. #3. Robots replicate themselves and begin disassembling the planet. #4. If more material is needed, robots can find suitable asteroids and comets to get other materials needed and deliver them to the staging site at Mercury. #5 Wait a few decades and voila! A Death Star!
This would require quite a few advances in AI, but they're not all THAT difficult given how far image recognition and neural nets have come just in the last decade. At the beginning of the project a remote human team could assist the robots in making decisions. It would most likely require one robot team on Mercury as well as several in the asteroid belt, transiting material and refabricating it to whatever use you need!