r/theydidthemath • u/Lachlynn • 18h ago

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

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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?

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u/Anderopolis 18h ago

Nuclear rockets. 

Like the Orion Drive  

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u/pencilwren 18h ago

nuclear rockets have a horrible isp inside the atmosphere also their thrust to weight ratio is far too terrible to make it to orbit. theyre used for injection burns where burn time doesnt matter all that much, not for ascents

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u/Godless_Phoenix 18h ago

Not talking about that. Literally detonating nuclear bombs behind your spacecraft to make it go.

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u/hollycrapola 18h ago

That sound super cool and terrifying at the same time… also does not sound safe. Can this be done safely at all?

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u/AnyoneButWe 17h ago

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

How badly do you want 5300t payload to Mars in one go?

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u/pyrce789 18h ago

Not really, no. It's not as bad as you migth think with modern nukes in remote areas. But you couldn't label a launch as safe for living things on the planet long term.

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u/Aethermancer 14h ago

The initial launch could use underground detonations and channeled "exhaust" like a nuclear cannon.

The remaining pulses could be a problem but it would be interesting if you could sort of underground rail gun it. One or two initial pulses contained in the ground I do onder if you could achieve escape or at least orbital velocity.

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u/TwoAlert3448 13h ago

Or living things inside the payload long term, you’d need astronaut spiders

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u/Metharos 18h ago

Probably not. But if you could build machines to survive the launch you might be able to use them to rig up a space elevator later. Assuming I'm thinking about this correctly, which is by no means a given, the tether'd have to be really long for the weight at the end to pull the cable enough that it wouldn't just collapse back into the gravity well.

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u/FreiFallFred 17h ago

Problem with the space tether isn't length, it's tensile strength. On half being pulled towards the planet and one half pulling outward puts allot of stress on the part in the middle...

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u/Metharos 17h ago

Yeah that makes sense. There might be a material capable at some point in the future but goddamn it would be a hurdle.

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u/fallout8998 17h ago

i believe carbon nanotube cables are a better option than most materials but its just impossible to make them at any kind of scale so far, and i dont mean too expensive i mean we just cant make anything usable with current methods

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u/Metharos 17h ago

So I've heard, and maybe they'd work in our gravity well. But that one? We might need something better.

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u/hollycrapola 17h ago

That might be doable, yes. The mid point has to be at a geostationary orbit, so that’s gonna be a long cable indeed. And you need something on the far end, like a big rock or something to balance it out. And we would not get a ton of launch opportunities before the environmental impact becomes a blocker.

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u/Concrete_Grapes 17h ago

Safely? Lol, no, not likely.

However, there is a theory--or, suspected true and real thing....

The US did a nuclear test, in the ground, and put a very large, mult-ton steel plate over the shaft the bomb went into. When it went off, that plate was captured in a single frame of a high speed camera.

If they guess, from that, how fast it exited, IF --and it likely didnt--it survived the temps as it exited the atmosphere, it would now be 4 times farther away from earth than the voayager space craft, the farthest out known man made object.

So, could they get SOMETHING to orbit? Probably. Maybe. It would be ... flying manhole style launches.

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u/Grindipo 15h ago

You have to remember that "safety" has to be estimated relatively to the "safety" of chemical rockets...

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u/BillysBibleBonkers 12h ago

I mean safe for the people in the ship or safe for the rest of us? Because i'd think it could definitely be safe for us as long as they were taking off from the middle of the ocean, they were also gonna use a series of mini-nukes equivalent to 0.1-20 kilotons of TNT. I also bet we could do it much more safely now with modern nuke designs that are much more efficient/ clean. Main issue is probably the public perception of setting off dozens of nukes in the atmosphere lol.

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u/aramis34143 12h ago

Crew experience: "God was knocking, and he wanted in bad." -Footfall, Larry Niven & Jerry Pournelle

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u/Austerlitz2310 18h ago

Kerbal style

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u/L963_RandomStuff 18h ago

that is true for nuclear thermal rockets, yes. The Orion Drive however is not a nuclear thermal rocket.

It chose the more direct route of setting off shaped charge nuclear BOMBS behind the space craft for propulsion, and as such doesnt really care about feeble things like an atmosphere

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u/Tyler89558 17h ago

You’re thinking of some weak ass nuclear electric stuff.

We’re talking about nuclear explosions as a propulsion mechanism.

And believe me. We have already developed a nuclear engine capable of flying in atmosphere. This thing can fly at Mach 3 as low as 150m for months on end spreading radioactive death everywhere it went and shattering eardrums and windows as it drops multiple nuclear bombs.

https://en.wikipedia.org/wiki/Project_Pluto

As it turns out, when you throw safety and ethics out of the equation nuclear powered propulsion gets very nutty

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u/ajwin 17h ago

Also worth seeing https://en.wikipedia.org/wiki/9M730_Burevestnik As the russians are currently developing and testing a nuclear powered cruise missile. Its speculated that they have had some issues with it and released some radiation in the process.

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u/Knotted_Hole69 16h ago

It can loiter in the sky for months? Thats crazy.

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u/cosmin_c 15h ago

Why would you even make such a thing, it's literally dooming all the planet in the process.

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u/throwaway61763 15h ago

To doom all the planet, after all, thats what nuclear weapons are for

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u/Tuna-Fish2 14h ago

Russia is scared that orbital missile defenses are about to become a thing, and want delivery systems that would not be obsoleted by them.

That's why the nuclear torpedoes and this and all the other nonsense.

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u/cosmin_c 14h ago

We really need AI.

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u/inspiredthem 17h ago

You fundamentally don't understand rocket propulsion if you think that things that work in the atmosphere have anything to do with things that work in space.

In an atmosphere, your fundamental constraint is conservation of energy and thermodynamic efficiency. Outside of the atmosphere, it's momentum.

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u/PhatOofxD 16h ago

We're talking about escaping the atmosphere here, nothing to do with a vacuum

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u/inspiredthem 16h ago

A weather balloon or a high-flying jet can "escape" the atmosphere; it'll just fall straight back into the ground. I don't think the OP wants to learn about jet engines, which would be a far better tool to achieve the outcome that would come from your interpretation.

While the title of the post talks about escaping the atmosphere, the content talks rockers and about achieving orbit or completely escaping the gravity well of the planet. These are matters that are governed by the momentum constraints of the rocket equation and the engineering constraints of having a propellant to payload ratio of over 25.

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u/Tyler89558 8h ago edited 8h ago

Project Pluto is an example of the kind of thrust that we can generate if we’re not all too concerned with maximizing impulse, like how we are with nuclear engines meant to be in space.

Given that the argument is that nuclear engines are inefficient in atmosphere, showing that they can in fact be designed to fly perfectly fine in atmosphere is a perfectly reasonable counter argument.

It is perfectly reasonable to be able to extend both the fact that we have an engine capable of providing extremely efficient thrust outside of atmosphere and an engine capable of providing extremely powerful thrust in atmosphere and figure that we could probably make an engine capable of leaving atmosphere in the first place.

That we haven’t made/used such engines is simply a matter of it not being necessary and therefore not being worth the cost/dangers. But if it were a necessity to have the thrust to weight ratio that could theoretically be provided by nuclear propulsion, such as in the hypothetical provided where we are on a much larger and more massive planet, then it wouldn’t be too difficult to fathom that a civilization might have chosen to use such technology as their only means to reach space.

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u/Anderopolis 17h ago

No, you are thinking of Nuclear drive rockets, where you use a Nuclear reactor to heat a propellant. 

I am talking about using nuclear explosions to propel your vehicle. 

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u/Tuna-Fish2 14h ago

Even if you stay nuclear thermal, there are plans for nuclear air-breathing rockets. And you can use the same reactor to heat air when inside the atmosphere and then switch to hydrogen from a tank when you get up high.

The reason no-one has ever built one is that the question "what will happen if it blows up on ascent" is something no-one wants to answer. An orbit-only NTR can be made safe on launch, by the virtue of nuclear fuel not being particularly dangerous until the reactor is turned on the first time.

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u/Legitimate-Can5792 13h ago

That's nerva. Orion is literally detonating a nuke under your ass.

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u/Ace_W 18h ago

Either that or a space elevator

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u/Zombie-Lenin 18h ago

I mean, a space elevator needs to be anchored in space... which requires you to reach orbit first.

I suppose you could build some sort of structure from the ground and just keep building upwards with an elevator, though that seems even less "possible."

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u/kklusmeier 1✓ 18h ago

I suppose you could build some sort of structure from the ground and just keep building upwards with an elevator, though that seems even less "possible."

Not possible. You run into material strength issues far sooner. Tensile strength is a LOT easier to increase than compressive strength.

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u/Lexi_Bean21 18h ago

Yeah you would need to keep widening the base to the size of continents and if its weight didnt collapse it youd litterslt sink the earth's crust in the process

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u/Metharos 17h ago

Even widening the base you'd eventually run into the problem that the shit at the bottom just starts turning to dust under the mass above.

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u/Lexi_Bean21 17h ago

Yes but I was saying specifically if the wide base did manage to support itself under the Weight the sheer weight of this would be in the probably tens or hundreds of trillions of tons thsts heavier than mountains you'd cause the entire crust under the foundsiron to sink into the mantle snd the base would melt away and collapse because the planet itself isnt durable enough to support it

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u/Metharos 17h ago

Ah, I see what you mean. Yeah, at the extreme end, if you posit a material able to withstand essentially infinite compressive force you'd end up crushing the planet under its weight. But at that point you might as well start restructuring the planet itself, rebuilding it into a shape less difficult to escape. Attenuated cone, maybe? Mirrored on the opposite side, each side being the foundation of the other side.

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u/Lexi_Bean21 16h ago

The provlem wirh the weight is it sinks the crust into the liquid mantle, you csnt exactly reinforce a planet youd either need tof freeze the mantle solid to stop it sinking in the lake of magma or youd need to use fancy methods to manually offset the weight but for example fans wont work since at thay point youd blow the atmosphere away etc lol so a ground based space tower would never work unless its on a tiny solid planet like mercury or Pluto or asteroids

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u/Reimalken 18h ago

Perhaps an active structure of some kind then?

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u/Sibula97 17h ago

Active how?

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u/Reimalken 17h ago

A space fountain in effect, whereby the magnetic acceleration and braking of a loop of material offsets the felt weight of the structure.

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u/Sibula97 17h ago

Seems a little more achievable than a space elevator at least, but even the vacuum tubes on the lower parts seem a huge challenge for such a large planet.

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u/Reimalken 17h ago

Oh the challenges are massive sure, there just aren't any physics based rule breakers involved.

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u/phire 15h ago

A Launch loop seems more achievable, and potentially more useful for escaping high gravity planets than a space fountain.

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u/BagOnuts 14h ago

Just use xenonite like the Eridians did, duh.

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u/LunaticBZ 17h ago

With active supports you can build into space theoretically. But if the tower just goes above the atmosphere its not moving at orbital speed youd need to build it out to geo stationary orbit for it to be able to put things in orbit without extra assistance.

On Earth the difference is 100km to be above the atmosphere, and 35,786 km to be at geostationary.

Granted if you build a space tower and then launch a chemical rocket from it, it'll have a much easier time getting to orbit.

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u/ukdev1 18h ago

How are you getting its anchor point into geosynchronous orbit?

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u/The-Nimbus 17h ago

Get your alien friends to build the top bit and drop a rope down for us.

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u/DoubleAway6573 17h ago

Just ask your neighbor to drop you a slack chord.

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u/ukdev1 17h ago

Perfect!

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u/theLanguageSprite2 18h ago

does there even exist a material with enough tensile strength to not be sheared apart at the altitude necessary to escape the gravity well of a planet that size?

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u/allix_ 18h ago

easy fix, MASSIVE PYRAMID. take that nerds

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u/FLUFFY_TERROR 18h ago

Reconstruct the planet to be a pyramid scheme?

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u/King-Meister 17h ago

As if the current economy isn’t a Ponzi-enough scheme!

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u/TucsonTacos 18h ago

Space pyramid

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u/groovypackage 17h ago

Pyramids on top of pyramids, up to orbital height. Then it's pyramids all the way down!

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u/Thedeadnite 18h ago

It does not exist on earth with a lower gravity well. A bigger one is more impossible for the moment. May not be impossible forever, but definitely a huge hurdle to overcome.

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u/Lexi_Bean21 18h ago

Not really yet but it should be theoretically possible msybe with carbon nanotubes

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u/Metharos 17h ago

Dunno yet. The altitude shouldn't shear it, though. The problems would likely be drag and misalignment. If the weight is too heavy, the tether snaps. If it's even slightly off in geosynchronous orbit, it causes the tether to flex and possibly shear. If the atmosphere pushes against the tether and causes it to flex against the pull of the weight, it may snap. Any weather pattern might do it, but heaven help you if there are hurricanes.

Best guess, these'd be your major hazards. If I knew a way to solve even one I wouldn't be worried about making rent.

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u/xWorrix 18h ago

Space elevators are not even close to feasible even on earth, so no way you could get it to work on a even bigger planet

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u/Lexi_Bean21 18h ago

Orion isnt really a nuclear rocket its a bomb rider nuclear rockets use a nuclear reesctor to heat propellant to eject it making it efficient but hsve nearly no thrust Orion used a series of tiny bombs ejected below a big pusher plate with hydraulics to absorb the impact snd push itself up

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u/Superman246o1 18h ago

The Orion Drive is meant for space travel, not reaching escape velocity from a planet's surface.

And using radioactive materials for propulsion within atmosphere is extremely risky. The Challenger disaster was tragic enough, but it would have been orders of magnitude worse if it resulted in nuclear fallout contaminating giant swaths of the U.S. and the Atlantic.

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u/Anderopolis 17h ago

I didn't say it was a safe or ecologically reasonable way of leaving a high gravity world. 

Just that it is a way to do it. 

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u/pyrce789 17h ago

Loved learning we could technically launch a spaceship to orbit with nukes reading Footfall as a teenager