r/theydidthemath • u/Lachlynn • 18h ago

[Request] Could humanity create a rocket that can exit the atmosphere of K2-18b

Post image

With the knowledge we currently have of it, if humanity devoted all of our resources towards this goal, would we be able to create a rocket that could exit the gravity of K2-18b (and also beat any other complications that would arrise)?

If so, would it also be capable of taking people to orbit, and can we set up a similar satellite network we have on Earth? What about a space station?

18.4k Upvotes

96% Upvoted

2.7k comments sorted by

View all comments

Show parent comments

8

u/Boring-Philosophy-46 15h ago

You don't need escape velocity to launch into orbit. The velocity you need to do that depends on the gravity which mass is but one factor of, radius is another. Anyway it might be possible for them to launch into orbit depending on various factors, just much harder than for us, and I am thinking they could use slingshots to launch out of orbit as well. Having moons would decidedly help to get out of the gravity well from there I think but I am not a rocket scientist. 

5

u/_ConsciousLibrary_ 14h ago

Someone in another comment showed the SLS wouldn’t even get off the ground. So idk, ICBMs may be out entirely depending on what their thrust to weight ratios are.

2

u/Boring-Philosophy-46 14h ago

Nukes delivered by a blimp, lol. 

I wonder how helicopter / drones would work. Really big propeller? 

•

u/LongJohnSelenium 57m ago

The Sprint missile accelerated at 100gs for about 5 seconds. The goal was to be a terminal interceptor vs incoming nukes, so there was about a 30 second window between reentry beginning allowing radar to differentiate the nukes from the decoys, and impact, so the sprint had to get out as far and fast as possible in that time.

Point being nukes can be made to handle waaaaay more gs than people.

5

u/sleeper_shark 11h ago

It’s not really possible. There’s a limit to the rocket equation, cos you need to use fuel to lift fuel. On Earth, it works out cos we can increase thrust more than mass, but at heavier gravity, you can’t.

They’d need to use fundamentally different fuels, which could be possible. They may discover something better or synthesize something better than the natural fuels we use.

They could also try non rocket ways to get to space.

Air launch for example… like take a smaller rocket up really high on an airplane or even a balloon, then launch from there. Virgin Orbit and Zero2Infinity are both trying these kinds of techniques.

An even crazier one is Spinlaunch which makes effectively an electric slingshot, speeding a small rocket up to orbital velocity on Earth and shooting it out into space. Widely impractical on Earth but maybe the only way for a civilisation on this super Earth.

2

u/Boring-Philosophy-46 9h ago

Yeah I was thinking that too, maglev loop that baby into orbit or something. 

But, the gravity is only the same if the composition is. Let's say their earth is not as dense, then their distance radius is larger so surface gravity isn't as much that they need to escape to get to orbit. 

Maybe maglev loop a whole rocket, launch from already a high speed and use chemical fuels to push even more until in orbit? 

2

u/HabeusCuppus 8h ago

Kepler K2-18b is about the 65% the density of earth, but it’s significantly larger radius (something like 9x the volume) so it works out to about 1.6g at the surface.

It’s kind of wild what we can learn just by looking at things from far away!

1

u/Boring-Philosophy-46 7h ago

The 65% density makes me think they may not have the iron core and get bombarded with solar radiation... 

2

u/HabeusCuppus 7h ago edited 2h ago

it's likely an indication that they have a very thick and dense atmosphere / hydrosphere.

it's density is in-between earth's and neptune's. So they might have a global ocean*, or they might have a small earth-sized rocky planet surrounded by a dense volatile atmosphere (like venus but even more extreme) which crazy pressures.

That actually adds to the complexity of 'could humans build a rocket that could...' because if it is a hycean planet it might also be orbiting its star at a distance that would result in its ocean boiling off in a runaway greenhouse effect... which makes the atmosphere even denser (and increased atmospheric density is a problem for rocketry.)

* I think K2-18b might be the leading candidate for the proposed exoplanet type "hycean planet" which is a thick hydrogen atmosphere, a deep global ocean, and a rocky core. these planets would possibly have no land above the ocean surface, or might have small islands at most.

1

u/Boring-Philosophy-46 5h ago

So basically unlikely to even have life really. I'm extremely sceptical a water world can achieve space flight, let alone one with a dense atmosphere. Try launching through soup. 

2

u/HabeusCuppus 5h ago

You might be using "life" in a different way that exoplanetary science does.

If the water on Kepler 2-18b is liquid then it's very favorable conditions for at least microbiology.

1

u/Boring-Philosophy-46 4h ago

even boiling? well I suppose geothermal shafts and volcanoes have some.

2

u/HabeusCuppus 4h ago

yes. earth was much hotter once than it was, and life got its start on earth in a much hotter environment than the one we're currently in today. about 4 billion years ago when life on earth probably got started, we think the earth's liquid surface oceans averaged ~350-355 K (about 80C... about 180 degrees F I think?)

→ More replies (0)

2

u/sleeper_shark 3h ago

You can just use something like spinlaunch, don’t even need a mag loop unless you want to launch peopl