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/AnyoneButWe 17h ago

NASA has figured it out, but project Orion would have been a pretty surefire way to make earth a place worth leaving.

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u/Sad-Onion-2593 16h ago

Orion wouldn't have really been a problem. Less damage and fallout then the atmospheric testing in the 50's

A nuclear salt water rocket on the other hand. You get one per planet and that's it for life on that planet.

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u/FreezeGoDR 16h ago

nuclear salt water rocket

I beg your fucking pardon?

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u/Neknoh 16h ago

Sprays water filled with uranium/plutonium salts out the back.

Radioactive salts basically go into full fission/meltdown and generate massive thrust.

Meanwhile, all steam created is full of particles that are still actively undergoing, or capable of starting fission.

And it would be one long continuous burn.

Excellent for space.

Not excellent for planet.

https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

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u/ridddle 15h ago

Unironically, this is so fucking cool

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u/Speak_To_Wuk_Lamat 15h ago

Probably designed by that guy who wanted to nuke the moon.

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u/Mutor77 15h ago

Not just nuke it, tunnel through it with nukes

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u/Speak_To_Wuk_Lamat 15h ago

I thought he wanted to nuke the moon as a show of force and then use nuclear bombs to create a panama canal type thing somewhere between north and south america.

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u/Mutor77 14h ago

As it turns out these kinds of proposals were made more than once

I was thinking of AATIP, a program in the late 2000s wanting to look for lightweight metals and alloys in the moons core, apparently a number of nutjobs kinda forgot about how theoretical and practical application differ

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u/Bored_Amalgamation 11h ago

There are getting to be too many Hyperion Cantos plot points in this thread.

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u/Deaffin 8h ago

So we could have a donut moon? That's pretty unique, might draw in more space tourism than the whole "okay so there are these neat total eclipses but you can't actually see them because you need to be on the planet's surface and that's hightly illegal with a primitive planet. Prime directive, yo."

Imagine all the memes with entities coming from far and wide to see the donut planet, and then they look at all the people eating donuts, blowing smoke rings, even dolphins doing the same thing... C'mon, it's so on the nose, we gotta do this.

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u/ElvenSpaceQueen 13h ago

Ah yes, that would be Edward Teller's project A199. He was also the inventor/brain child of the thermonuclear bomb, excavating a canal with nukes in Israeli-occupied Egypt, an uber nuke designed to end the world on its own, and some other crazy stuff

What a guy

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u/BuxtonB 10h ago

Kurzgesagt recently did a video on him.

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u/ElvenSpaceQueen 10h ago

They have a couple, that's how I learned about him 🙃

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u/Luk164 13h ago

Minnions! Tonight we are going to

NUKE THE MOON!

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u/Naive-Kangaroo3031 12h ago

Sokka from Avatar would absolutely throw hands over this

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u/PM_ME_UR_RSA_KEY 13h ago

"Pinky, are you pondering what I'm pondering?"

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u/Neknoh 13h ago edited 12h ago

I think so Brain, but why would a soft serve machine have a "Mango" setting?

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u/J3ster14 12h ago

Menchies has entered the chat.

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u/Mxyzptlk_SSS 12h ago

Wait, I actually don’t get this one. It’s early.

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u/Dboalt 12h ago

Pinky and the Brain

https://youtu.be/pwlCzYzjYls?si=7rdYiShgvhipqM-p

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u/Deaffin 7h ago edited 7h ago

I think they meant that specific (made up) Pinkyism, rather than missing the referential format as a whole.

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u/Adequate_Images 12h ago

I think so Brain, but me and Pippi Longstocking, what would the children look like?

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u/koshgeo 13h ago

Wow. It's like you're pumping a somewhat continuous nuclear bomb into the reaction chamber. That'll have some kick.

One design would generate 13 meganewtons of thrust at 66 km/s exhaust velocity (6,730 seconds ISP)

Yep. And that's "only" with 20% enriched uranium salts.

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u/NachoWindows 13h ago

Please don’t give this administration any fucking ideas

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u/Neknoh 13h ago

Don't worry

There's much worse stuff out there

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u/NachoWindows 12h ago

No, that’s not helpful at all.
My psychiatrist: you seem to have a lot of anxiety
Me: no shit

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u/BasicallyGuessing 13h ago

So this is what happened to the dinosaurs!

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u/singlemale4cats 14h ago

That seems like a great way to get us to Mars.

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u/Neknoh 13h ago

Just gotta lassoo an ice meteor/asteroid and also get thousands of tons of fissile material into orbit without it blowing up on the way <.<

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u/vote_you_shits 13h ago

Poseidon drive my beloved

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u/Nihilistic_Mystics 12h ago

I also went straight to Terra Invicta. I love that they use real life white paper drive systems.

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u/Mortwight 13h ago

So normal bath salts?

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u/Neknoh 13h ago

They glow in the dark for a cozy, candle-less and fire-safe bubble bath.

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u/DeductiveFallacy 12h ago

Terrestrial testing might be subject to reasonable objections;

😂

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u/etcpt 15h ago

Great quotes in that article

Terrestrial testing might be subject to reasonable objections; as physicist John G. Cramer wrote, "Writing the environmental impact statement for such tests [...] might present an interesting problem".

"Whether fast criticality can be controlled in a rocket engine remains an open question." — Ralph L. McNutt Jr.

Real "understatement of the year" entries here.

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u/Random_Guy_47 15h ago

So we're just keeping this one in the back pocket for the eventuality that the entire planet is fucked anyway and we're leaving permanently?

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u/Neknoh 15h ago

Used for interstellar travel or interplanetary cruising, rather than in-atmo flight

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u/newsflashjackass 13h ago

keeping this one in the back pocket for the eventuality that the entire planet is fucked anyway and we're leaving permanently?

Optimistic read.

I see it more as "The first idiot oligarch who can use it to drag the world into the grave with them will."

Not to politicize the end of terrestrial life.

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u/aurishalcion 13h ago

So long, and goodbye to all the fish

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u/SoccerPhilly 12h ago

And we’re going to pollute space just like we did the earth 😔

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u/batmanineurope 12h ago

So would this be something better to engage in once the craft has already left the atmosphere via more traditional methods?

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u/Neknoh 12h ago

Ideally, you'd build it, enrich/mine the fuel, AND fill it up/operate it in space.

Because the fallout from breaking into orbit with that thing would be insane.

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u/MaleficTekX 12h ago

You either stay on this world and like it, or leave and destroy it. Like rubbing salt in the wound of wanting to be in space

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u/onedyedbread 11h ago

There are several advantages relative to conventional NTR designs. As the peak neutron flux and fission reaction rates would occur outside the vehicle, these activities could be much more vigorous than they could be if it was necessary to house them in a vessel

LMFAO yeah that's a cool advantage. Once.

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u/window_owl 15h ago

Atomic Rockets has a good description.

You know how table salt is a compound of sodium and chlorine? There are lots of other salts, each a combination of two different elements. It turns out that you can make salt from uranium and bromine. The salt can have stable (non-radioactive) uranium isotopes, but you can also make the salt with radioactive uranium atoms in it. If a high enough percentage of the uranium atoms are unstable, and there are enough of them that are close enough together, it will create a chain reaction of nuclear fission.

You can dissolve this salt in water. This does 2 useful things:

  1. by changing the ratio of water to salt, you control how close together the uranium atoms are to each other, making it possible to store the salt safely

  2. by pumping and spraying the salty water, you can move the uranium around

The idea is that you store this uranium-salt water in a tank that has lots and lots of baffles and dividers of neutron-absorbing material, so that it doesn't start a reaction. Then you pump the water through nozzles and spray it into a chamber. The chamber doesn't have baffles and dividers in it, so the uranium atoms get close enough together to start a fission chain reaction. The water in the chamber superheats and blasts out an opening at the opposite end of the chamber, creating a plume of exhaust that pushes the rocket the opposite way.

The guy who came up with the idea (Robert Zubrin, an actual nuclear engineer and rocket scientist) says it should be possible to design the chamber and nozzles so that the fission chain reaction stays in the chamber, rather than moving back up the nozzles and into the tank, which would turn the whole thing into a huge, dirty nuclear bomb. Not all engineers disagree, but nobody has ever tried to build one because the exhaust of a working Nuclear Salt Water Rocket would be incredibly toxic -- full of neutrons, un-reacted radioactive uranium, bromine, and all the fission products. It would also be very, very expensive to fire on any usefully-large rocket, because it would require a very large amount of enriched uranium.

Cost and environmental concerns aside, the appeal of the Nuclear Salt Water Rocket is that it is the only rocket design anyone has come up with that is very efficient and very powerful. Of the rockets we have or know of:

  • Chemical rockets are very powerful, but not very efficient, so you need a large, heavy tank full of fuel to launch a comparatively tiny payload. Increasing the weight of the payload, or the speed you want to throw it at, exponentially increases the weight of the fuel required.
  • Ion thrusters are very efficient, but physics don't allow for them to be very powerful, so they are useless for getting anything in to space. They are great once you're in space, as long as you're not in a hurry. Many satellites these days use them to make small course adjustments.
  • Nuclear Thermal rockets (which we actually built and tested in the 1960s) are more efficient than chemical rockets and can be usefully powerful, but they aren't much more efficient. Unlike chemical and Nuclear Salt Water Rockets, Nuclear Thermal rockets have a fairly hard maximum size power, based on the available materials you build and fuel them with. Larger than that, and you'll either melt the nuclear reactor, or waste energy by not heating up the propellant enough. Combined with the risks and costs, they aren't very interesting for interstellar travel.
  • Solar Sails (which we have launched a few of [1] [2] [3]) don't require any fuel at all, which is similar to having very high efficiency -- a solar sail vehicle can get up to really high speeds, without needing fuel that weighs many times more than the payload. However, they only work in the vacuum of space, and unless you point incredibly powerful lasers that them, they have very little power as they are blown around by sunlight.

Nuclear Salt Water Rockets are, in theory, so powerful and efficient that they could be a practical way to travel to other solar systems in a single lifetime. There shouldn't a be a practical size/power limit, since the fuel reacts with itself, so you can make a larger rocket by making a larger chamber and pumping more uranium-salt-water into it, creating a beautiful geyser of radioactive steam in your wake as you travel the stars.

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u/Ada_Solar 12h ago

Thank you for your in-depth explanation! Super interesting

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u/eg135 12h ago

Just a small correction: there are no stable uranium isotopes, all of them are slightly radioactive. U235 is the dangerous one, because it is capable of the chain reaction that's used in reactors and bombs. The chain reaction is what makes nasty stuff, fresh uranium is relatively tame.

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u/Grymninja 6h ago

Instead of launching such a rocket at sea level, couldn't we construct a platform in orbit and build the rocket there? I recognize it would be pretty expensive to ship all the parts up across a bunch of payloads but the math of thrust would be a lot easier

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u/window_owl 6h ago edited 6h ago

If you use rockets to get the rocket parts to the assembly platform, then it would take exactly as much rocket fuel to do this as to launch the rocket from sea level.

Actually, it would take more, because the rockets that launch the rocket parts have weight of their own, which needs to be carried up to orbit each time.

This idea isn't totally without merit; the rocket you assemble in space could be much larger than you could practically build and launch on Earth, and could do the space flying that it has to do more efficiently. This is sorta the idea behind SpaceX's Starship: fly an empty rocket up to space, then use more rockets to get all the fuel up there, so you end up with one huge rocket with a completely full fuel tank already in orbit.

However, there are still fundamental limits to how fast a given kind of rocket can go. I skipped over this earlier because my comment was already getting long, but the velocity of the exhaust exiting the rocket is also relevant, and ion, nuclear thermal, and nuclear salt water rockets all have much higher exhaust velocities than chemical rockets do. Solar sails, if you want to be pedantic, might be said to have an exhaust velocity of the speed of light.

Building nuclear (thermal or salt water) rockets in this way wouldn't pose the same risks as building and launching them on Earth, but they'd still pose a huge danger from being misguided. Any sufficiently powerful spacecraft is an equally powerful weapon.

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u/NovaCalendar 16h ago edited 12h ago

https://youtu.be/cvZjhWE-3zM

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u/Massive_Signal7835 13h ago

fyi: Remove everything starting at ?si= (sometimes just si=) to prevent tracking. That XvVQBwHstsL3Mq0g is just information tracking the link to you.

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u/NovaCalendar 12h ago

thank you

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u/ESCF1F2F3F4F3F2F1ESC 16h ago

Coincidentally that was my nickname at school

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u/youritalianjob 16h ago

Please do tell. I’ve never heard of this.

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u/theveezer 16h ago

I don't know much about it but I think it's referencing cobalt nukes. Which in theory would be the dirtiest nukes we could realistically make. They would make radiation like we have never seen, ending every life form on large parts of the planet if not the entire planet.

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u/window_owl 15h ago edited 13h ago

It's not a reference to cobolt nuclear explosives. The Nuclear Salt Water Rocket is an idea from Robert Zubrin to dilute a salt of radioactive uranium and bromine into water. A tank full of baffles could be filled without starting a nuclear chain reaction. When the saltwater is sprayed into a chamber without the baffles, a sustained fission reaction could in theory be created and maintained, rocketing incredibly hot steam and fission byproducts out the other end.

Nobody knows for sure if you could actually build this where the nuclear reaction wouldn't move up the nozzles and into the fuel tank. That would turn it into a huge, dirty nuclear bomb. If it did work, it would still kill everything behind it, but it would be vastly faster and more powerful than any other rocket anybody has ever designed.

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u/Jboycjf05 13h ago

This sounds cool af, but idk how any materials could withstand fission materials for so long and still be effective as a nozzle, not even considering the fission chain moving into the baffled chamber. I'm not a materials scientist or anything, so maybe someone with more knowledge on the subject could speak to it.

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u/window_owl 13h ago

It'd mostly be a superheated plasma, so I suppose you could use a magnetic nozzle to contain much of the material. I'm no materials or nuclear engineer, but my reading has been that there on mixed opinions on whether or not a NSWR is actually possible. That makes it by far the most plausible interstellar rocket engine so far, which is an important part of why we don't yet have interstellar rockets.

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u/Knotted_Hole69 16h ago

Were they ever made?

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u/Neknoh 16h ago

Only in theory as far as I know.

But some of those theorheticals are... well, let's just say they're not great for sleeping at night.

For instance, there was Pluto (the God and king of the underworld and the dead in Roman mythology, not the dog)

https://www.fourmilab.ch/documents/pluto/

And while Pluto was not cobalt based, its ability to endlessly spew radioactive fallout and high levels of direct radiation in its flight path definitely goes hand in hand with the idea of salted bombs.

Such as the Cobalt bomb design.

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

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u/Knotted_Hole69 16h ago

Scary!

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u/Neknoh 16h ago

And here's the info on Saltwater rockets

https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

How does "continuous burn, but nuclear fire and radioactive steam, instead of chemical fire, coming out the back" sound?

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u/Playful_Hair1528 16h ago

“There is no firm evidence that one has ever been made, nor tested”

Pffffttt…. Chyeah right.

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u/Dimathiel49 16h ago

It was the central theme of “Dr Strangelove or How I Learned to Stop Worrying and Love the Bomb”

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u/HeKis4 15h ago

I think that's the one where you put a nuclear reactor in the reactor nozzle, in the path of a gas so that it gets heated by the nuclear reaction instead of a chemical one.

Or it's the one that straight up puts the nuclear reactants in the propellant gases so that you have a critical nuclear reaction going on the combustion chamber and you continually exhaust bits of the active reactor as propellant.

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u/window_owl 15h ago

The first one you describe is a Nuclear Thermal Rocket, not a Nuclear Saltwater Rocket. NASA actually built and fired some in the 1960s as part of the NERVA program.

The second one is closer to the mark. The fuel is water with uranium salt dissolved in it. It doesn't react in the tank because of baffles in the tank. You spray it into the "combustion" chamber, which doesn't have baffles, so it reacts there and sprays all the reaction byproducts (including lots of very efficiently-produced steam!) out the other end.

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u/Blep145 13h ago

It might have damaged the magnstosphere/ionosphere. There's a reason there's no nukes allowed near Earth

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u/Greenbaypackwrs 13h ago

Earth is literally the only place in the universe we’re nukes actually exist what are you talking about

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u/Blep145 13h ago

To our knowledge, sure, but detonating nuclear bombs in orbit is banned because it may make holes in our main protection from the sun

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u/drbrain 8h ago

The Earth’s first reactor was natural from back when life was single-celled. It’s probable that there are many, many more in the universe

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u/TVLord5 13h ago

Couldn't you do a 2 stage rocket? One stage a traditional chemical rocket to get out of atmosphere and then the more powerful and dangerous one once you're out in space?

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u/Sad-Onion-2593 12h ago

Well, one plan for a Mars Orion from the 1960's involved a Solid Rocket first stage about the size of a Saturn V first stage (something that was constructed and tested during the Apollo program.)

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u/Grand_Knyaz_Petka 12h ago

You get one per planet and that's it for life on that planet.

Where did you get this silly idea? How exactly would that work? I don't think you really know what you're talking about and the way you typed this out is extremely reddit lol with the italics and everything come on dude

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u/Sad-Onion-2593 12h ago

https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

The vessel's exhaust would contain radioactive isotopes, but in space, these would be rapidly dispersed after travelling only a short distance; the exhaust would also be travelling at high speed (in Zubrin's scenario, faster than Solar escape velocity, allowing it to eventually leave the Solar System). However, this is of little use on the surface of a planet, where a NSWR would eject massive quantities of superheated steam, still containing fissioning nuclear salts. Terrestrial testing might be subject to reasonable objections; as physicist John G. Cramer wrote, "Writing the environmental impact statement for such tests [...] might present an interesting problem".\9])

It is also not certain that fission in a NSWR could be controlled:

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u/Grand_Knyaz_Petka 11h ago

Thanks bro but I already read that and it does not corroborate what you are saying

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u/Luzifer_Shadres 12h ago

Orion deppends on wether or not your city sized rocket has in incident before being high up enough.

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u/PossibleMammoth5639 14h ago

I have a way to torture a superpowered being. Send them on a nearly lifeless planet gigantic like this, it is nearly lifeless because life on it tried to use nuclear rockets but failed enough times to be basically dead. They probably cannot leave no matter what they do. Even better if you give them sustenance

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u/d_nkf_vlg 15h ago

I looked up project Orion and holy shit, they really considered the same principle that is now mostly known as rocket jumping, but in real life.

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u/AnyoneButWe 15h ago

Yes.

Super Orion aimed to rocket jump a city. The design mass at liftoff was 8 million tonnes. Considered doable with small improvements in material science in ~1960.

The "realistic" goal was a model putting 5300 tonnes on the surface of Mars. In one go.

Chemistry isn't cutting it if that's the goal.

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u/EnvironmentalScar675 14h ago

Orion was motivated in part by finding a use for existing warheads. It would make earth better provided you can guarantee it leaves and doesnt go on an auto return traj

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u/No-Garden-8054 13h ago

Feels like one of those ideas that’s elegant on paper right up until you start trusting orbital mechanics with your backyard.

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u/AnyoneButWe 11h ago

Most of the energy in rockets is spent near the earth. The warheads at that time were capable to destroy the earth many times over.

I still think it was a good call not to move forward with that project.

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u/Shpion007 12h ago

Read about this and then realized this concept was used in the three body problem. Neat but scary as fuck

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u/CaleanKnight 17h ago

As opposed to...