Planetary Spaceships


So, yes this is out there, but I have been thinking. Sure, the scale is ridiculous, but if you had to live on an intergenerational spaceship…what would the best one be? A planet, right? I know, the temperature on the surface would drop and it wouldn’t be habitable to humans on the surface, but we could live underground and there would be plenty of heat energy from Earth’s core. Or like Mars…instead of moving a spaceship to Mars, why don’t we move the Earth to a closer Mars orbit? How big would the solar sail or ion engine have to be? Don’t even ask about how we attach a planetary-scale propulsion system to a rotating planet, but I’m sure there is a way. Anyhow, I’m curious…


You could try looking at some of Issac Arthur’s videos on Youtube, they sometimes reference moving planets and other hypothetical super advanced technologies (he was also on orbit 11.23 if your havent watched it). As for moving Earth closer to Mars orbit if you had the technology to somehow accomplish this i think that moving Mars closer to Earth would be far more interesting, you could increase the amount of sunlight reaching Mars which would make solar more efficient. If you were moving entire planets around i feel like it’s a safe assumption that they have terraformed Mars, so the increased light could also be quite nice as Mars’ surface would be receiving even less light after travelling through an atmosphere.


Good points. However, as the sun heats up gradually over time, wouldn’t it also make sense to move the Earth further out? For now sure, move Mars closer and Venus further out, keep Earth where it is.

I mean heck, for that matter, if we can move a planet, then why not just move the entire solar system from one part of the galaxy to another, or from one galaxy to another? An entire solar system is an awesome intergalactic spaceship for humanity.Thanks for the info, I’ll check the videos and TMRO episode out.


I like the idea of moving an entire solar system to another galaxy. The amount of energy needed would be mind-boggling, but we’ve found hypervelocity stars moving fast enough [1500km/s, 0.5% the speed of light] that you could cross the distance between the Milky Way and Andromeda in a reasonable amount of time for the life of a star like our Sun [a transit time of roughly 500MY]. Pick a target like the Large or Small Magallenic Clouds, and suddenly you could get there very comfortable within the length of the existence of a species [40MY].


So, to start “small” (lol), what would it take to move the Earth further out? Could we…(and forgive the simplicity of my thoughts, but they arrive like butterflies :slight_smile:) make a ground mounted chemical rocket engine big enough (like Sea Dragon OTRAG!) to conceivable do this? I mean, weight doesn’t matter, it’s anchored to the Earth, and at some point even inefficient chemical rockets COULD add delta-v and move the planet around. Talk about complicated and controversial space law! Imagine trying to get everyone on board to move the planet around…


What you’re looking for is called a Fusion Candle:

You take a gas giant and stick a pair of giant two-sided rockets in either end and use them as thrusters to move the planet. One side thrusts down and keeps the candle aloft, the other side thrusts out and pushes the planet from place to place. The gas giant’s hydrogen/helium atmosphere gets used as the fuel, creating energy through fusion. Then you use its gravity to capture your habitable planet. Once your living space is in tow, you use the light of the engines to keep the planet warm as you switch between stars. Travel time is on the order of millions of years. Or you can just use it to move your world from a lower solar orbit to a higher one.


Haha! Read the strip from the link. I know this is mostly ridiculously theoretical, but COULD we build a rocket or cluster of big chemical rockets big enough to essentially make the Earth into a moving spaceship? Fusion candle sounds awesome, but how would we attach the rockets to the gas giant? I guess if we had the technology to use the fuel on a gas giant, we’d be able to attach it to the solid core somehow. We’d have to be careful with towing the planet with a gas giant, of course. I like where it says “Steer carefully, and signal your turns WELL in advance…this is a big vehicle…” Might end up at its core…seems like attaching the gas giant to rockets would be harder than simply making a huge rocket anchored to the Earth and splitting ocean water to make the rocket fuel. There’s a lot of water…


The rocket burns from both ends… One side fires down, keeping the rocket from sinking. The other side fires into space, proving thrust.


Does it go completely through the core of the gas giant? Like a rocket shiskabob?


Hopefully not… Them’s crush depths. If you want to thrust out the other side, you’ll either have to move the candle or have another one on the other side.


Oh wait, it provides thrust…like a fusion version of Project Orion? It doesn’t HAVE to be attached to the planet somehow, because the fusion thrust is planetary scale, and having that on one pole is enough to move the gas giant…right?


Over long enough timescales yes. The bottom side rocket’s exhaust transfers momentum to the planet’s atmosphere, which mixes to produce a whole-of-planet change in speed.


I say we build Sea Dragon OTRAG, or just build an Earth anchored rocket. I suppose I could calculate the rocket we’d actually need to do this…maybe later.


Think I understand now. The rocket is pushing against the gas giant from the underside, and the thrust from the outward facing end pushes the candle against the gas giant, so overall you get thrust in the other direction. Did I get that right?


Sounds about right, it’s a bit of a balancing act. If you had something solid you could anchor to, you wouldn’t need to have the underside rocket since you could transfer the force directly to the solid surface. But since you’re on a gas giant, you’re typically miles and miles from anything solid. So the underside rocket both keeps the candle up and transfers force to the planet.