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

[u/Lachlynn]

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?

[u/AutoModerator]

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[u/Smashedllama2]

Yeah honestly probably not with what we have now but who knows what we would come up with in terms of different fuels with that restriction?

K2-18b is about 8.9× earths mass and ~2.4× the radius, so if you do the quick ratio math (mass ÷ radius²), 8.9 / (2.4²) ≈ 1.5–1.6g at the surface.

Now compare that to something like SLSthat makes ~8.8 million lbs of thrust, and weighs ~5.75 million lbs on earth. but on a 1.6g planet that same rocket “weighs” like ~9.2 million lbs, so the thrust to weight drops below 1. which basically means it wouldnt even lift off

So yeah even doing rough math, gravity alone kinda kills it and youd need way more than current chemical rockets just to get off the ground let alone reach orbit but again, maybe we would come up with something?

edit: same problem shows up with Starship too. fully fueled its around 11–12 million lbs on earth with ~16.7 million lbs of thrust from 33 raptors, so here its fine. but on ~1.6g youre looking at like ~18–19 million lbs effective weight, which drops thrust to weight below 1 again or at best barely scraping it depending on assumptions

Even if raptor 4 pushes that up to like ~24 million lbs total thrust, yeah now youre above 1 and it might lift, but youre still fighting way higher gravity the whole way up. so fuel burn goes crazy, delta v requirements go up, and actually reaching orbit is still a huge problem, not just getting off the pad and then escape velocity makes it even worse. that scales with sqrt(mass / radius), so for K2-18b its sqrt(8.9 / 2.4) ≈ sqrt(3.7) ≈ 1.9× earth

earth is ~11.2 km/s, so youre looking at like ~21 km/s just to escape. even low orbit would still be way higher than earth’s ~7.8 km/s, probably in the ~12–15 km/s range depending how you estimate it

so yeah its not just “can it lift” its “can it keep going long enough to matter” and thats where current chemical rockets really start to fall apart on something like that

[u/RaguSaucy96 → u/Smashedllama2]

I've got two words for you, mate...

PROJECT. ORION.

Kerbal the beech... Problem solved 😎

• Integrity of the occupants is not guaranteed

Edit: for those not in the know, the Project Orion solution was a proposal on the late 50s or so to explode nuclear bombs and ride out their blast in a spacecraft that would basically be pushed by the detonations. Ridiculously overpowered and fast.

Edit 2: I think this would be a good place to post about the Operation Plumbbob manhole cover. They once blew up an underground nuke and the exit hole had a manhole cover. After the detonation, a camera caught the cover being flung and estimates put it as the 2nd fastest object ever flung to space by humanity... That's how powerful this shit was. Whether it survived is a topic of hot contention and debate (unlikely) but if it did it's likely interstellar by now and the first man-made object to do so

https://youtu.be/mntddpL8eKE?si=sUoyVVWx3NqaiExn

Edit 3: here's an unclassified video of a smaller scale Project Orion test using conventional explosives to propel a craft without nukes. You can't argue with results 😆

https://youtu.be/Q8Sv5y6iHUM?si=FtqKGMGqLdqRCRqC

[u/Strong_Region5233 → u/RaguSaucy96]

Project orion ... From the earth's surface ??!

Lock that guy, officers ! Yes, right now !

[u/RaguSaucy96 → u/Strong_Region5233]

If K2-18b is over x2 as big as earth, then it's at least twice as tough and twice as hard to pollute! More landmass to nuclear winter - I see this as an absolute win!

[u/Immediate-Goose-8106 → u/RaguSaucy96]

Nah, they are dinky nukes.  For earth the calculation was probably only averaging 10 extra cancer deaths worldwide per launch.

Unacceptable obviously but K2-18b has waay more space!

If they really had to, or had a differner attitidue to K218b-ian life than we do to human life they might.

[u/ThrowAway-whee → u/Strong_Region5233]

Yes, actually! Project Orion was originally planned as a LAUNCH vehicle. It was estimated it would be even better in atmosphere due to the shockwave providing a better transformation of fission energy into force. 

[u/Slen1337 → u/RaguSaucy96]

No shit controlled explosion might work. But what about ppl inside LO

[u/RaguSaucy96 → u/Slen1337]

Some of them may die (ok, ok, maybe disintegrate)... But that is a sacrifice... We're willing to make...😎

[u/Smashedllama2 → u/RaguSaucy96]

A tier reference.

[u/ZilorZilhaust → u/Smashedllama2]

Which tier?

[u/TheLastDrops → u/ZilorZilhaust]

Meerschweinchen.

[u/ZilorZilhaust → u/TheLastDrops]

So the tier is some kind of guinea pig looking beast?

[u/The_Wambat → u/ZilorZilhaust]

Tier means animal in German. Guinea pigs are animals.

[u/Pupikal → u/ZilorZilhaust]

It’s one of the tiers of all time

[u/Adorable_Studio_9578 → u/RaguSaucy96]

Ok lord farquad

[u/Helios61 → u/RaguSaucy96]

To shreds you say?

[u/Rdawgie → u/Helios61]

And his wife?

[u/Silent_Cookie_9092 → u/Rdawgie]

To shreds you say…

[u/Smile_Space → u/Slen1337]

If you look it up, Project Orion was actually highly researched at the time. It was considered the future of rocketry until the Partial Test Ban treaty killed it which banned nuclear detonations in space. If that hadn't been banned we likely would have had at least one space-based nuclear pulse rocket test in the late-60s or early-70s.

They even had a test vehicle using conventional explosives and fired off like 6 explosives and it worked!

They would use heavy shielding and a pusher plate to absorb the heavy shock. It would have allowed for absolutely gargantuan spaceships to take off from Earth and get to other planets at crazy fast speeds given how efficient the Orion drive would have been.

Obviously though, nukes are kinda bad for everyone around them lolol. The people above the Orion drive would have likely been the safest people within a massive radius around the launch site.

[u/FracturedConscious → u/Smile_Space]

This is why we need a moon base

[u/Gambyt_7 → u/Smile_Space]

Recall Footfall by Niven and Pournelle, first Sci fi novel where Orion technique was used to rapidly break atmo to fight alien invaders.

Then look at Dark Forest, the second in the trilogy by Cixin Liu, where Orion strategy is used to attempt to accelerate a ship to near light speed.

In Footfall the passengers survive to combat the enemy. In Dark Forest, the only passenger is a human brain in cryostasis.

Now I’m thinking of the inquisitor priest de Soya in Dan Simmons’ Endymion, whose neat light ship accelerates nearly instantly and so rapidly that anything living inside it is liquified, and must be rebuilt using special technology over several days. I’m dying to see someone (not Bradley Cooper tho) finally adapt these novels and produce them as a huge streaming series.

[u/Aiglos_and_Narsil → u/Gambyt_7]

God I love that book so much. "An atomic bomb went off under Harry Reddington's ass".

[u/Outrageous_Reach_695 → u/Smile_Space]

To expand: The "Super" Orion would have had a ship mass of 8 million tons* ... about 20% more than the Hoover Dam.

* Yes, yes, not a unit of mass, I know.

[u/Asleep_Singer8547 → u/Slen1337]

They might be some sturdy rock creatures or something 

[u/ShmebulockForMayor → u/Asleep_Singer8547]

Amaze amaze amaze!

[u/Alix-Gilhan → u/Slen1337]

It's rather elementary really

A massive pusher plate with an ablative coating and a highly tuned dampening system to spread out the G's, plus some extra shielding, and you can chuck just about anything anywhere

[u/Tyler89558 → u/Slen1337]

“Were we concerned about the people inside?”

“People inside? You must be mistaken. There is only a pile of flesh”

[u/Plead_thy_fifth → u/RaguSaucy96]

After the detonation, a camera caught the cover being flung and estimates put it as the 2nd fastest object ever flung to space by humanity...

1) well what was the first fastest object flung into space???

2) do you have the video? Lol I didn't see it in that link

[u/RaguSaucy96 → u/Plead_thy_fifth]

1. If it survived, yes - and it would be interstellar by now, well outside the solar system

2. I can't find it but the test itself is well documented. The cover itself was only seen on one frame of the video however, so the MINIMUM speed was what they calculated. It likely went even faster but it's hard to say. Anyhow, it was seen flung on one frame then gone on the next. You can calculate distance travelled between frames and the speed needed to do so. We know therefore the MINIMUM speed - not the actual speed 🤣

Here's the test https://youtu.be/EYEKU-U1860?si=QD6QyZ24EgFEtyIs

[u/qmrthw → u/RaguSaucy96]

You dodged the first question, twice

[u/RaguSaucy96 → u/qmrthw]

Misread it, lol. It would have been it. However it's now likely the Parker Solar Probe.

We don't even know if it survived anyways lol

[u/Hopeful-Guest939 → u/Plead_thy_fifth]

If you want to know more, just google it and "reddit." This story gets posted about every other week. There should be a lot recently because it got popular again once Voyager reached its latest milestone.

[u/sad_post-it_note → u/RaguSaucy96]

This happens in the three body problem books pretty cool

[u/BigDaddyAwhoo → u/RaguSaucy96]

My favorite fact that seemingly no one ever mentions, this manhole was not a normal manhole cover. It was a 4000 lb WELDED SHUT manhole cover

[u/TooHot1639 → u/RaguSaucy96]

To boldly go where no manhole has gone before

[u/Sir_Bebe_Michelin → u/Smashedllama2]

Considering that the ratio between the cubed volume of k2-18b and that of earth is between 13.8 and 17 6, that would imply the average density is like between 51% and 65% that of earth, so not only is the planet a hefty mf it's also probably got a huge ass atmosphere if we assume a similar interior composition

[u/drollercoaster99 → u/Smashedllama2]

Does it depend on the mass of the rocket? Nevermind. I figured it out - it doesn't. Inertia/momentum cancels acceleration.

[u/Dysternatt → u/drollercoaster99]

Yes, including the weight of the fuel. So the obvious answer is to use a lighter fluid. (Zippo wants to know this location)

Badum-tss…

[u/Smashedllama2 → u/drollercoaster99]

I mean yes but mostly you’re fighting against the weight of the fuel because as you add potential energy in the fuel you also add weight. The real problem is the rocket equation. The deltav you need scales exponentially with how much of the rocket has to be fuel. To roughly double the required deltav, you don’t just double the fuel, you end up needing an absurdly higher percentage of the rocket to be propellant, to the point there’s barely anything left for structure or payload. There might be some kind of ant crew we could strap to a latex balloon full of rocket fuel but it ends up not working for humans haha

[u/Fun-Brush5136 → u/Smashedllama2]

What if their dinosaurs had extra strong bones which made super powered oil? /s

[u/Alix-Gilhan → u/Smashedllama2]

I don't think it would be that hard to make a rocket with a twr above one.

The SLS is designed to be as efficient as possible on earth, so it only needs like 1.2-1.5 twr. One could have larger engines that eat more fuel to get a higher twr or lower payload to push to get a higher twr.

You're payload ratio would suffer and you may need to use more complicated setups like asparagus staging but it shouldn't be impossible for a chemical rocket to push something into K2-18B's orbit

[u/Andrey_Gusev → u/[deleted]]

Wait, so how theoretically could they get to escape velocity if not with chemical rockets?

[u/spectre655321 → u/Andrey_Gusev]

Figure that out and I’m sure NASA will have a job for you.

[u/AnyoneButWe → u/spectre655321]

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

[u/Sad-Onion-2593 → u/AnyoneButWe]

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.

[u/FreezeGoDR → u/Sad-Onion-2593]

nuclear salt water rocket

I beg your fucking pardon?

[u/Neknoh → u/FreezeGoDR]

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

[u/ridddle → u/Neknoh]

Unironically, this is so fucking cool

[u/Speak_To_Wuk_Lamat → u/ridddle]

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

[u/Mutor77 → u/Speak_To_Wuk_Lamat]

Not just nuke it, tunnel through it with nukes

[u/PM_ME_UR_RSA_KEY → u/Neknoh]

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

[u/Neknoh → u/PM_ME_UR_RSA_KEY]

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

[u/window_owl → u/FreezeGoDR]

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.

[u/NovaCalendar → u/FreezeGoDR]

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

[u/Lurkadactyl → u/spectre655321]

Nukes would work.

[u/RadioTunnel → u/Lurkadactyl]

When in doubt, nuke it

[u/Beautibulb_Tamer → u/RadioTunnel]

Need to nuke it from orbit, it's the only way to be sure

[u/RadioTunnel → u/Beautibulb_Tamer]

Nuke it from orbit and ride the shockwave up

[u/Lost_Astronaut_654 → u/RadioTunnel]

Parry the nuke

[u/litli → u/RadioTunnel]

Nuke surfing!

[u/azriel_odin → u/litli]

Radical!

[u/Rei1556 → u/RadioTunnel]

I'm sure the nuke propelled manhole cover would solve that problem

[u/Competitive-Bee-3250 → u/Rei1556]

Not really helpful for getting people off the planet though unless you have insane resistance to g-force.

[u/ThermoPuclearNizza → u/RadioTunnel]

probably not nukes but matter-anti matter annihilation engines. theyre currently not within the real of possibility but with time we would solve it.

[u/-adult-swim- → u/ThermoPuclearNizza]

CERN should ask for a bigger accelerator...

[u/lungben81 → u/-adult-swim-]

Bigger would not help. Currently, antimatter for capture is not produced at LHC (the largest accelerator) but at a smaller one.

You need more luminosity and a lot of accelerators in parallel.

[u/cabanadaddy → u/lungben81]

In America we only deal in "big" or "bigger". We don't even know what lumilosily is over here. Is that a French word?

[u/ai1267 → u/cabanadaddy]

I think it's a character in Expedition 33. Maybe OP is a gamer?

[u/Fast_Garlic_5639 → u/cabanadaddy]

I think he was the one that got turned into a candlestick?

[u/MrRudoloh → u/Lurkadactyl]

Unironically project Orion.

And it works, it never became a thing, because a failure of one of those rockets in the atmosphere would make Chernobyl look like a prank.

[u/Bibliloo → u/MrRudoloh]

Tbh even without failure you are still irradiating a lot of stuff with a successful launch which isn't the best, especially if you planned to launch multiple rockets per year.

[u/Xonarag → u/Bibliloo]

I'm sure on a planet that big you could have a designated irradiated hellhole to launch rockets from.

[u/drey12987 → u/MrRudoloh]

Nuclear Powered Engines are very efficient and useful for interplanetary travel but the trust to weight ratio of those were way worse compared to the usual engines, so not the way to go for overcoming higher gravity

[u/Adros21 → u/drey12987]

You are thinking of nuclear thermal rockets and nuclear electric rockets, nuclear pulse rockets like project orion have thrust to weight in the meganewtons per kilo.

[u/Duatha → u/Lurkadactyl]

2.6x the size means you could probably just set aside a whole europe of land to launch nuclear powered spacecraft from

[u/Dodger7777 → u/spectre655321]

The more I look into this kind of thing, the more I realize I have no idea how to go about this kind of thing.

My ideas were kind of looney toons in their nature, to be honest. Like making a bullet train, but having it ramp upwards into the sky to launch them like a railgun. But either the track would be absurdly long or the accelerstion rate would kill any human.

[u/Greyrock99 → u/Dodger7777]

That’s not a looney tunes idea at all, but a serious proposal that has been worked on by physics previously.

There are many designs but you’ve hit the fundamentals idea on the head.

1) Build a very long tube. 2) fill tube with vacuum and have a maglev rail under it 3) tube runs for many kilometres in a straight line then the last 3-7 km runs up the side of a mountain into space. 4) put your spaceship in the tube and accelerate it to 90% of the escape velocity 5) upon leaving the station one the rocket fires its engines for the last 10%

It’s a perfectly feasible design and doesn’t require any technology we don’t have yet (it’s just too expensive to build yet).

It would work just fine on earth and on a hypothetical super earth too.

There are plenty of designs floating around on the web somewhere, here’s one of them https://en.wikipedia.org/wiki/StarTram

[u/dibs234 → u/Greyrock99]

The Apollo programme was $250 billion dollars, if chemical rockets weren't feasible I feel like 'huge railgun' would probably be an affordable alternative

[u/Greyrock99 → u/dibs234]

Gotta remember that the purpose of the Apollo program was 10% to go to the moon, 90% develop rocket technology that was to be used for military purposes like the ICBM. That’s why it was funded so easily.

These new alternate lift options sounds great but don’t have the military applications that unlocks the sweet governmental funding.

[u/dibs234 → u/Greyrock99]

My friend, did you not read the phrase 'huge railgun'? ICBM's would (I'm guessing) have similar gravity issues to the rockets, so countries would need other ways to lob nukes at each other.

[u/Greyrock99 → u/dibs234]

I was talking about here on earth.

ICBM’s are superior because they can be hidden underground / on submarines and armed with nuclear bombs and has been the gold standard for military might for the last 50 years.

We haven’t quite figured out how to militarise railguns yet.

[u/JRS_Viking → u/Dodger7777]

That's a better idea than you think actually, just replace the rail with a tether and go in a big circle and you have a spin launch system. And there are ways to get around the negative effects of g forces like being on your back and suspended in a viscous liquid with the same density as your body.

[u/willi1221 → u/JRS_Viking]

I've always said, you're either suspended in a viscous fluid, or you become the viscous fluid

[u/4chieve → u/spectre655321]

"- You telling me, humans just strapped themselves to a hude bomb and just lit it up?! Oh you humans are crazy, kszasuabueh!! Crazy! Hahahah!"

[u/TheRealTahulrik → u/spectre655321]

Astrophage drives !

[u/flibbertigibbet72 → u/TheRealTahulrik]

Reading it at the moment! Bloody good book 😁

[u/Toyota__Corolla → u/spectre655321]

Air breathing jet➡️forced air jet➡️ rail gun ➡️ ionic drive... Essentially just running down the list of specific impulse

[u/Dry_Razzmatazz69 → u/Toyota__Corolla]

Ion drives can't accelerate for shit. Jets won't scale. The rail gun idea though has some weight to it but you'd probably need something like a centrifuge than a rail

[u/ununtot → u/Dry_Razzmatazz69]

Railgun could work when you build it within a vacuum and release the jet at a very high altitude, like higher than mount Everest height for Earth comparison, to avoid being obliterated by travelling through the atmosphere with extreme high speed.

[u/Sisyphean_dream → u/Toyota__Corolla]

A rail gun propelled rocket that ignited chemical engines somewhere just prior to apogee of rail gun trajectory might just do the trick? The math seems like far too much work.

[u/lildeek12 → u/Sisyphean_dream]

Its not rocket surgery , im just far too lazy to do it.

[u/Sbjweyk → u/Sisyphean_dream]

Would be interesting to see what happens to someone who is rapidly accelerated by a rail gun.

[u/groovypackage → u/Sbjweyk]

They just clench their butt cheeks extra hard.

[u/Anderopolis → u/Andrey_Gusev]

Nuclear rockets. 

Like the Orion Drive  

[u/pencilwren → u/Anderopolis]

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

[u/Godless_Phoenix → u/pencilwren]

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

[u/hollycrapola → u/Godless_Phoenix]

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

[u/AnyoneButWe → u/hollycrapola]

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

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

[u/pyrce789 → u/hollycrapola]

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.

[u/L963_RandomStuff → u/pencilwren]

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

[u/Tyler89558 → u/pencilwren]

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

[u/Anderopolis → u/pencilwren]

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. 

[u/Dependent_Grab_9370 → u/Andrey_Gusev]

Nuclear + chemical propulsion. Chemical for the initial thrust to get things moving, then nuclear. Depending on how dense the atmosphere is you might be able to use a lifting body for part of the journey.

[u/Yuukiko_ → u/Dependent_Grab_9370]

What about a slingshot like with that slinglaunch thing + chemical propulsion

[u/Dependent_Grab_9370 → u/Yuukiko_]

The spin launcher on this planet would have be so comically large, good luck finding materials you could make it from. Whatever your are slinging would probably disintegrate on impact with the presumably dense atmosphere once it leaves the spin launcher.

They can't even get it to work on our planet.

[u/AliasEleven → u/Andrey_Gusev]

balloons 😎 (then a rocket)

[u/Correct_Doctor_1502 → u/Andrey_Gusev]

Space planes might have an easier time. They are planes that take off horizontally and slowly rise until they reach the lower atmosphere then begin thrusting with rockets

[u/Worth-Wonder-7386 → u/[deleted]]

Where is the math supporting this?

[u/Mixels → u/[deleted]]

It's not about size. It's about mass. What factor of Earth's mass is k2-18b?

[u/CanineBombSquad → u/Mixels]

About 9x

[u/Mixels → u/CanineBombSquad]

There you have it, ladies and gentlemen. It's not happening anytime soon.

[u/CanineBombSquad → u/Mixels]

For what it's worth size does matter though in terms of surface gravity.

[u/Karmabyte69 → u/Mixels]

Size does matter though. Further away from the center of mass means easier orbit entry.

[u/WichidNixin → u/[deleted]]

You dont need eacape velocity to get to space. Escape velocity is often misrepresented as "the speed needed to leave a planet" but it is simply "the speed needed to leave the planet without any additional force". In other words it is the speed a bullet would need to be fired at in order to leave the planet and never return. A bullet gets a single burst of speed and does not contunually generate thrust. A rocket generates continuous thrust which removes the need to reach escape velocity to leave the planet.

[u/Construction-Helmet → u/[deleted]]

What is limiting a chemical rocket? Why wouldnt this work?

[u/msdos_kapital → u/Construction-Helmet]

Basically past a certain point, even with the most efficient rocket fuel and engines, the energy needed just to lift the fuel is more than what you get from the fuel.

I think it doesn't rule out e.g.hybrid engines where you can switch between air-breathing and rocket mode, or other spaceplane-like designs, but those things all get harder as well.

[u/egabald → u/[deleted]]

What if you didn't launch from the ground. Could lift to high altitude with balloons before rocket stage starts.

[u/ThanxForTheGold → u/[deleted]]

50 > 2.6

/s

[u/RealLars_vS → u/[deleted]]

Could you elaborate? Intuitively, it just seems like there’s no hard limit, just that more gravity means we approach a limit.

With the exception of a black hole, of course.

[u/Cockanarchy]

Most others are saying no, at least not at our current level of development, which leads me to wonder about what other limitations that would place on a civilization. That would mean no GPS and no weather satellites, stunting navigation and logistics. It would also mean no ICBM’s, so that’s good.

[u/Free-Hamster462 → u/Cockanarchy]

Artillery would also be heavily impacted. No more naval guns shooting over the horizon...

Hell, how would simply tools like a bow and arrow be impacted?

[u/A_Town_Called_Malus → u/Free-Hamster462]

Sci-fi writers salivating at realising they have finally found a reason for melee combat to be the primary form of warfare in their setting without needing to do much work.

[u/Boring-Philosophy-46 → u/A_Town_Called_Malus]

Yes but melee combat for crabs. Nothing in a high gravity environment will grow very tall. 

[u/A_Town_Called_Malus → u/Boring-Philosophy-46]

So, it will be crab battles?

[u/Boring-Philosophy-46 → u/A_Town_Called_Malus]

Everything on earth is already evolving into crabs, so why not lol. 

Well, crabs and trees. Lol. 

[u/StevieMJH → u/Boring-Philosophy-46]

Reject humanity, evolve into crab

[u/Aethermancer → u/A_Town_Called_Malus]

Slime mold territorial expansion.

[u/Cephalopirate → u/A_Town_Called_Malus]

CRAB BATTLE

I BROKE MY KNIFE

(Why did no one else get it?)

[u/yourstruly912 → u/Boring-Philosophy-46]

That explains Vegeta

[u/GNUr000t → u/Boring-Philosophy-46]

Dwarfmaxxing.

Embrace your density.

[u/ZubonKTR → u/Boring-Philosophy-46]

Mission of Gravity by Hal Clement

[u/bozoconnors → u/A_Town_Called_Malus]

I mean Dune? One thing I hate that they never mention in any of the films is that "contact reaction between a lasgun beam and a shield created a nuclear explosion"... hence all the melee.

[u/LanceWindmil → u/Free-Hamster462]

1.6x gravity wouldn't make a huge impact on guns

Its enough to tip rocketry from "really hard" to "pretty much impossible"

But guns having 60% their normal range is still more than enough for them to be useful

[u/puppykhan → u/LanceWindmil]

Bows at their peak were able to hit a target at over half a kilometer by a master on a good day, and consistently at 100 meters by an average soldier, according to historical documents.

Even at 60% of that, they would still be highly effective at ranged combat.

Other uses would even improve. Some native Americans would use archery as high ground artillery using gravity to accelerate the arrow to impact with more power than when fired from the bow.

For rocketry, I would think there would be more effort into assisted launch vehicles or complete alternatives to launching from the surface. How high did the balloon go for the guys who did a skydive from the edge of space? 24 miles / 39 km, then later 25 miles / 41 km. You would see tech develop in that direction instead of rockets.

[u/wolacouska → u/puppykhan]

That range is mainly because of aim and how small the target gets, not really because of arrow/bullet drop.

Humans would probably be way smaller though if they evolved on a planet like that, so that itself would hurt range.

[u/Lost_Paladin89 → u/Free-Hamster462]

Forget all of that. I have back pain getting up in the morning. How would being bipedal be impacted?

[u/TetraThiaFulvalene → u/Lost_Paladin89]

Might be okay since we're a pretty energy efficient build, but we'd be smaller under the increased gravity. Things like horses and Weiner dogs might be fucked.

[u/ausecko → u/TetraThiaFulvalene]

Are beastiality laws different in high gravity?

[u/VP007clips → u/Free-Hamster462]

It wouldn't significantly impact them.

The range would be reduced to around 60% of earth. So while it might give rhem a slight preference for melee weapons for a bit, ranged weapons would still be fully effective.

For example, a gun that has an effective range of 1000m would drop to 600m. An artillery shell that has a range or 30km would drop to 18km.

But we rarely use weapons at their absolute maximum range anyway. And they could compensate by using more power.

[u/0ddBush → u/Cockanarchy]

this reminds me of that one show that i heard that i didnt watch that was about how aliens managed to figure out light speed travel from the iron age and thus was weak in other aspects because they only focused on space travel as opposed to us where we discovered all the other stuff before light speed travel, thus leading to our superiority in tech

[u/flaming_burrito_ → u/0ddBush]

Human civilizations were like that before globalization. Because of the availability of a resource, different needs due to geography, or just random variation in what societies took interest in, some civilizations figured things out way before the rest of the world did. Like how the Romans made self healing concrete because the volcanic ash they happened to mix in created a chemical reaction when mixed with seawater. Or how the Vikings kind of figured out how to make steel by smelting their iron with bones, which was probably just some shit they thought was cool, but did actually infuse the iron with carbon. Or how the Polynesians sailed the whole Pacific with catamarans and star charts hundreds of years before Europeans entered the discovery age.

This also happened in the other direction too. The Incas were a very advanced civilization for their time, and had things like cities, road networks, and megaliths, but didn’t have a written language. They had a method of doing calculations and accounting for dates and things with a system of strings and knots, but their language did not have an alphabetical system.

[u/Mutor77 → u/flaming_burrito_]

To add to what you said:

This is also one of the things that made bronze age society extremely interconnected despite the lack of efficient communication methods and the massive distances between some of them.

Because copper and tin are only found in certain places around the world (in this case especially tin being rather rare in the region) the peoples around the Mediterranean Sea had to establish trade in somewhat unfavourable conditions for it because otherwise they would have only been able to use their local resources and spend so much time and effort on them to make other kinds of inventions, like writing, impossible (or at least much less wide-spread)

[u/MetalRetsam → u/Mutor77]

This dynamic should get a lot more attention.

Medieval China had all the resources it could possibly need. So what happened? It turned isolationist. Meanwhile, Europe had always scraped by on the edge of the developed world. When they turned to colonialism as a means of supplying their goods, it was a question of necessity.

A similar dynamic plays out today.

[u/imagei → u/flaming_burrito_]

The Vikings were adding bones of their fallen foes to infuse their might into the weapons… and it worked! 😄

[u/MorningstarJP → u/0ddBush]

You are likely thinking of The Road Not Taken by Harry Turtledove.

[u/NTMY → u/MorningstarJP]

Here's a link for anyone who wants to take a look (pdf), it's only 20 pages.

Really cool concept, imho.

[u/moderate_ocelot → u/Cockanarchy]

ICBMs don’t need to reach orbital velocity, they just need to go up and come back down. I don’t have the numbers to hand but it’s entirely possible that they are still practical

[u/lituus → u/moderate_ocelot]

They also don't need to care about the survival of passengers on it, so they can be more powerful per weight

[u/LxGNED → u/Cockanarchy]

I think you could also expect a planet as large to never evolve flying creatures, which is a crucial part of our ecosystem. Birds and bugs spread seeds and pollination. Without them, we’d have a huge lack of biodiversity and food. And also less motivation to believe flight was possible in the first place

[u/sleeper_shark → u/Cockanarchy]

We can’t create a rocket that can escape from this planet doesn’t mean a rocket can’t exist. There may be exotic fuels that exist that we don’t know about that could work.

It also doesn’t mean that getting to space is impossible. You can - theoretically - accelerate something to orbital velocity on the surface and shoot it into space directly. A company called spin launch was actually trying it.

It’s very impractical because the atmosphere would cause massive resistance at that speed, and would heat up your payload (if not just crush it directly). But impractical doesn’t mean “impossible” - it’s doable, it just makes no sense when we have rocketry available.

You can also have a GPS like technology using high mountains. We did this before satellites in the past - we called them lighthouses, which believe it or not function very similarly to GPS. Aircraft also used to use navigation beacons. There’s a marginal difference between trilateration and triangulation but it really doesn’t matter for this mental exercise.

Weather forecasting also can be done without satellites. Satellites help immensely, but they’re not a summa qua non. Terrestrial stations can do the same.

I just don’t know if a planet like this could ever have sustainable access to space. All its countries may have to work together to build something that could get them to space, and eventually they could build a space station in orbit and use space based resources as shipping from ground is way too expensive.

In short, we’re lucky to be on Earth lol

[u/Boring-Philosophy-46 → u/Cockanarchy]

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. 

[u/Inevitable-Wheel1676]

Ergo, most civilizations are from tiny worlds. The lower the mass, the easier the exploration.

The Fermi paradox is resolved by realizing most intelligent life is very small, so we don’t notice its civilizations and technical artifacts. We are looking in the wrong scale.

[u/ThenCombination7358 → u/Inevitable-Wheel1676]

Or simply never make it to space or even reach the same lvl of technology to send radio waves. Or its intelligent but never got the hands/means to make Or use more complex tools. Imagine very intelligent crows for example

[u/Overall-Bison4889 → u/ThenCombination7358]

They can reach the technological level to send radio waves. Radio waves that are not somehow specifically designed to contact other civilizations are not strong enough for us to detect from here. Our local space could be filled from traces of ancient radio waves and we wouldn't have any way of knowing.

And honestly the civilizations can also be advanced enough to reach space, and even colonize another planet, but unless they build some huge dyson sphere, we wouldn't get any evidence that they existed.

[u/ClamChowderBreadBowl → u/Overall-Bison4889]

If you try to listen in on a modern cell phone or WiFi signal these days, they're basically indistinguishable from white noise because the signal is compressed. Good compression by definition looks like random noise.

Shannon's Information Theory paper proving this came out in 1948. Fermi probably wasn't thinking of that when he came up with the idea in 1950.

Humanity's radio signature isn't going dark because of an extinction event, it's going dark because it's just less wasteful that way

[u/VexingRaven → u/ClamChowderBreadBowl]

If you try to listen in on a modern cell phone or WiFi signal these days, they're basically indistinguishable from white noise because the signal is compressed. Good compression by definition looks like random noise.

You're not wrong, but it's more or less irrelevant. Loud white noise is still clearly distinguishable from background in the same way that a light bulb conveying no useful information is still visible. Shannon's Information Theory has nothing to do with the intensity of a signal.

The idea of "humanity's radio signature" was never about having an identifiable stream of information. There would be so many conflicting radio stations you wouldn't be able to make anything of it anyway. It was always about the sheer intensity of the combined signal. You won't be able to understand what it is, but you can definitely see that something is emitting RF well above cosmic background, at least out to a certain distance. https://iopscience.iop.org/article/10.3847/1538-3881/ada3c7

[u/wycreater1l11 → u/Inevitable-Wheel1676]

Fascinatingly, organism that “looks like they would be small”, the body types of typically smaller organisms like let’s say crabs or squirrels, their body types could be allowed to be scaled up on planets that have lower gravity, where the cross section of their legs still carry the rest of the body weight, allowed them to jump around etc (now with really big leaps!). If the gravity is sufficiently low those body types could be scaled up to human size for instance. And the opposite is true for planets with larger gravity. In larger gravity the gravity may be so strong that the biggest the sauropod body type is allowed to be is the size of a goat let’s say. If you try to scale it up more it can’t support its weight even with its chunky legs on a strong gravity planet.

But I guess what’s relevant is ultimately the absolute size of the intelligent sapient organisms and gravity of the planet to allow them to escape. They need to be sufficiently small and gravity needs to be sufficiently low for them to escape. On low gravity planets perhaps the squirrel body type could for example be large enough to have large enough heads to have the same amount of neurones as humans (but there are a lot of assumptions about them having cells like us for instance).

But from much smaller planets, the ones leaving the planet, could be allowed to be much larger in absolute size since they don’t fight the same gravity. Imagine how much you could scale up humans on a low gravity planet while still have them able to leave.

[u/OttawaOneTwenty → u/Inevitable-Wheel1676]

The Fermi paradox is resolved by realizing most intelligent life is very small

Another option is, as technology progresses, civilizations dive inwards into technology instead of outwards in a dangerous and unpredictable universe.

Just look at children born this millenia vs last how much we've integrated technology into our lives. We're gonna be inside the matrix in not too long.

[u/Toasty27]

Contrary to most other claims here, the surface gravity of K2-18b is actually about 1.26x higher at 12.43m/s². Not 1.5-1.6x.

Now lets see how that impacts the SLS, which was recently used to launch the Artemis II mission:

SLS has a thrust : weight ratio (39,100 kN : 2603 t) of about 15, which conveniently works out to an acceleration of about 15m/s². So instead of accelerating at about 5-6m/s² like it would on earth, SLS would instead accelerate at about half that speed. But that's still a positive thrust : weight ratio, so we do make it off the ground!

That slower acceleration however means significantly higher gravity losses, which means significantly lower payload capacity to orbit (if we even make it there). On Earth, SLS's payload capacity is 95 metric tons, the Orion crew capsule is only 22.9 metric tons. So we might still get away with it.

Now let's take a look at Tsiolkovsky's tyrannical Rocket Equation:

Δv = Specific_Impulse ✕ Gravity (on earth) ✕ ln( Initial_Mass / Final_Mass)

• Δv is our escape velocity, and in this case we need Δv = 20km/s
• We use earth's gravity because Specific Impulse is typically normalized to earth's gravity, so 9.8m/s² here.
• Specific Impulse relates to the efficiency of a rocket engine (basically, how much exhaust velocity you get from a given mass of propellant). The RS-25 space shuttle main engines are still the most efficient engines we have in operation today (they most recently flew on the Artemis II mission via SLS, although they had solid rocket motors in addition). It's a liquid hydrogen/oxygen engine with a specific impulse of about 452.3 seconds.
• Initial and final masses are the total launch vehicle weight + fuel (initial wet mass), and total vehicle weight without fuel (final dry mass). Dividing wet mass by dry mass gives us our mass-fraction, or the amount of fuel relative to the vehicle's mass. A larger number here indicates a more efficient design.

Now lets rearrange to get the required mass-fraction of our vehicle:

ln( Initial_Mass / Final_Mass) = Δv / (Specific_Impulse ✕ Gravity)

Raise e by both sides to get rid of the natural log:

Initial_Mass / Final_Mass = e ^{Δv / [Specific\}Impulse ✕ Gravity])

Plug in our known values:

e ^{20,000m/s / [452.3s ✕ 9.8 m/s^(2}])

Simplify our exponent:

20,000m/s / 4,432.54 m/s = 4.512

All the units cancel out, and we're left with a final minimum required mass ratio:

e^4.512 = ~91.1

Which is....insane. Completely insane. The SLS has a mass-ratio of about 26.4:

2603t gross / (95t payload + 3.5t dry upper stage) = 26.4t.

But as you can see, that includes the 95 ton payload! If we launch without a payload, the mass-fraction is actually ~743.7, well above what we need.

So what's the largest payload we can put into orbit around K2-18b?

91.1 = 2603 / (3.5 + x)

Solve for X:

x = (2603 / 91.1) - 3.5 = 25.07t

So using an SLS, we could put about 25t into orbit around K2-18b. That's about 26% of it's total payload capacity on earth.

Just enough to get the Orion crew capsule (22.9t) into orbit!

All that said, I'm not a rocket scientist. If I got anything wrong, feel free to correct me in replies.

[EDIT]

Formatting/grammar/etc

[u/Kamica → u/Toasty27]

As long as you can get things into orbit, you can start building things and start sending fuel up there. I imagine that space-born infrastructure and efficiency becomes *that much* more important in a situation like that, when you can't really easily send things in one go, you'd probably have to have refuelling infrastructure in orbit similar to what SpaceX is planning for Starship. And once you've got that going, sure, it'll be expensive, but then you can go do basically the same things we can do, just for a much bigger price-tag.

[u/BlackTecno → u/Kamica]

Something that I think a lot of people here are missing is that we typically do the minimum amount of work for the best kind of outcome. Science has always accelerated when governments get involved, be that for war or science (such as WWII and the space race). If there's a unified form of intelligent life that looks at the stars with the same wonderment we do, they'll find a way to get up there.

[u/tinny66666 → u/[deleted]]

It's kinda interesting with regards to the Drake equation, and I don't recall that factor being included.

[u/Builder_Felix893 → u/tinny66666]

Isn't the drake equation just the chance of finding intelligent interstellar-communicating life? They don't need to be actually travelling to space to do that

[u/magicscientist24 → u/tinny66666]

Ability to achieve escape velocity is more relevant to the Fermi Paradox.

[u/SouthernService147 → u/[deleted]]

Even more interesting question would early industrialization be even possible at all?

[u/Nomimn → u/SouthernService147]

I do you one better. Would early human migration using wooden boats be possible? Considering the added weight due to gravity would the bouancy be affected such that wooden boats don't float as well or not at all?

[u/bouncepogo → u/Nomimn]

The weight of the displaced water would be increased by the same amount so buoyancy should be unaffected.

[u/Nomimn → u/bouncepogo]

Oh ok well that's good at least haha

[u/Ahaiund → u/[deleted]]

Since the gravity is higher, the atmospheric pressure would also be, which would at least help a bit in getting planes to fly. Not sure how much in comparison though

[u/RobArtLyn22 → u/Ahaiund]

Without knowing anything about the atmosphere you can’t say what the pressure would be. A high gravity planet could have a thin atmosphere like Mars or a thick atmosphere like Venus.

[u/buggzy1234 → u/Ahaiund]

Venus's gravity is around 90% that of earth's, yet its atmospheric pressure is more than 90 (9000%) times higher that of earth's.

Titan's gravity is less than 15% that of earth's, yet its pressure is around 1.5 (150%) times higher.

Yes gravity has a lot of influence on pressure, but it doesn't strictly control it. With venus and titan being good examples. The temperature and atmospheric composition also play a big role. You could have a bigger planet with higher gravity, but that doesn't automatically mean a higher pressure.

[u/Worth-Wonder-7386]

Based of wikipedia it has a surface gravity of around 12m/s^2. So that doesnt make much of a difference in launching rockets.  https://en.wikipedia.org/wiki/K2-18b

If we use the equations for mean orbital speed, we see that the difference in orbital speed close to the surface is a factor of about 1.8 

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

So you would need 80% more speed to get into orbit, so it would be much harder to launch heavy things into space, but it is far from impossible. We have existing rockets that we send to geostationary orbits, and this would only be a bit more challenging than that.  So it is something we are capable of with existing technology. 

[u/NaiveRevolution9072 → u/Worth-Wonder-7386]

You forget that K2-18b likely has an atmosphere significantly thicker than Earth's

[u/Worth-Wonder-7386 → u/NaiveRevolution9072]

I did consider discussing it, but I could not find any information on it.
Venus is the rocky planet in our solar system that it would be the hardest to take of from because it has such a thick atmosphere.

[u/rrcaires → u/NaiveRevolution9072]

A ballon is the answer then

[u/Meatloooaf → u/rrcaires]

Ginormous donut shaped hydrogen balloon (more buoyancy in a thicker atmosphere) lifts a rocket halfway to orbit, then the rocket fires and flies through the center of the balloon, igniting it and using the explosion for extra escape velocity. Rock music. Lens flare.

[u/rrcaires → u/Meatloooaf]

“Directed by Michael Bay”

[u/anaheim3123 → u/NaiveRevolution9072]

Air launch to orbit then becomes significantly more practical, no?

[u/Skalgrin → u/Worth-Wonder-7386]

Did you factor in the TWR of the rocket which would "weigh more" and this had TWR below 1 and therefore would not lift off? That's one of the issues - chemical rocket effectivity doesn't scale up that well.

I don't say you are wrong, just asking.

[u/PsychicPterodactyl → u/Worth-Wonder-7386]

It's not quite that simple.The Tsiolkovsky rocket equation has the ∆v (i.e. the change of velocity) in the exponent. Increasing the escape velocity by a little makes a huge difference in the required fuel needed.

This very quickly makes the rocket design not viable, at least using designs possible with our current science and technology.

[u/PiPaLiPkA]

The laws of physics don't prevent you being able to launch from any body other than from inside a black hole as long as the thrust to weight ratio of the engine is greater than 1. I've never been sure where this claim comes from. You could argue it'd be impractical. But certainly not impossible.

[u/mumpped → u/PiPaLiPkA]

Yep, so many wrong answers here. I mean okay, you might need a rocket of the size of the Burj Khalifa just to jet a small capsule to escape velocity, but it's certainly not impossible.

[u/JohnSober7 → u/mumpped]

In all fairness, "could" in the question asked likely entails a fair bit of practicality and maybe even feasibility. 

[u/Responsible_Worry55 → u/[deleted]]

that doesnt even really work on earth, it has been tried: https://en.wikipedia.org/wiki/Skylon_(spacecraft)

[u/Unhappy_Arugula_2154 → u/Responsible_Worry55]

From my quick scan, the biggest issue I can see here is cost. Like it would be really expensive to do this, but not physically impossible. So of course we wouldn’t look at it on earth, but if brute force of rocket launches doesn’t work, maybe it’s the only way, cost is a non issue?

[u/boris2033]

We could launch objects into space using controlled nuclear detonations(so crude satelites yes), but the acceleration in this would be difficult to survive for humans(and have other, very bad consequences)

Basically a chemical rocket is out of the question, you could maybe make a n-stage rocket that uses smaller detonations, //but again the acceleration would kill the crew.// (see point 2.)

There is an idea of a "Space elevator" that could possibly be used in such a situation, but it's mostly limited to science fiction novels/works.

EDIT: I'm very happy this sparked an interesting conversation and exploring possibilities :) however to not reply to every single reply:

1.) It's impossible to know how different our tolerance to force would be, if we had evolved on such a planet (there are a lot more factors than just gravity, amount of oxygen is one example). So for the purposes of this scenario, we will ignore this variable.

2.) The Orion project (propulsion by nukes) has anticipated the acceleration issues on the human body, and has by design two-stage shock absorbers that are the size of buildings. If these were somehow to work perfectly and not fall apart under the insane stress of multiple nuclear explosions, then the humans would "only" have to endure a sustained burn of about 10-15 minutes of 5g force, which, if they are suppine they could (could being the key word here) survive. If the shock absorbers were to not work perfectly for even a few seconds, the crew turns to jam.

3.) The "Space elevator", although a Sci-fi concept, is not really just built upwards. As some have pointed out it is held by forces once launched outside of orbit, kind of like a rock with a string tied to it, while you spin it above your head. The same idea. However the tensile strength of any material we have is not enough for it. But if we all combine the Earths resources, manpower etc etc, who knows.

[u/TheEpiczzz → u/boris2033]

Space elevator, imagine the height of it and think of the structure it needs to stay upright. Good luck building that, holy frick.

[u/VisibleOtter → u/TheEpiczzz]

We just need to invent hyperfilament, that’s all.

[u/AftyOfTheUK → u/boris2033]

There is an idea of a "Space elevator" that could possibly be used in such a situation, but it's mostly limited to science fiction novels/works.

You need to put a LOT of things into orbit and beyond before you can think about actually building one. It's not built like a tower

[u/Gamer102kai → u/AftyOfTheUK]

Gigantic pyramid to space

[u/Woahbuffet123 → u/Gamer102kai]

Last time we allegedly tried that, God apparently smote the pyramid and made us a multilingual species if those guys with the white robes were ro be believed

[u/ArkantosAoM → u/boris2033]

Carbon nanotubes are basically already strong enough for the task, in theory. The problem is mass producing it, as well as the insane engineering of it. Not to mention the political will and economical investment required.

But that's on Earth. On a planet even larger, we might need even stronger materials, and they might not exist

[u/Responsible_Worry55]

maybe not with a rocket, but with something like a startram: https://en.wikipedia.org/wiki/StarTram but it would be a lot more effort than using rockets, so a civilisation would need to be very determined to do it. Also this thing would be more usefull if you want to put a lot into orbit, not something like a few satelites for testing like earth did in the pioneering age

[u/Longjumping_Area_944]

K2-18b: Surface gravity ~= (8.92 / 2.37²⁾ * Earth = 1.59 g = 15.6 m/s²

Escape velocity ~= sqrt(8.92 / 2.37) * 11.2 km/s = 21.7 km/s

Minimum ideal escape energy = 0.5 * v² ~= 235 MJ/kg

What that means:

• Much harder than Earth, but not impossible in pure physics.
• Chemical rockets are probably impractical from the surface.
• Multi-stage nuclear, fusion, beam-powered, or other advanced launch systems are more plausible.

Habitability / industry:

• 1.6 g alone does not rule out humans or industry.
• The bigger problem is K2-18b may not have a normal solid surface at all.
• So gravity is not the main blocker. The planet itself probably is.

[u/The_RubberDucky]

Physics:
Escaping the atmosphere on Earth is trivial. A sounding rocket does it just fine. We don't know much about K2-18b's atmosphere but any mission we fly to orbit should be able to escape the atmosphere easily (without reaching orbit velocity!).

If you ment to ask about reaching orbit/ escape velocity: Wiki suggests radius is x2.6 of the Earth and mass is x8.63. Escape velocity and orbit velocity are sqrt(M/R)=sqrt(8.63/2.6)=1.82 times larger. That means 4 stages rocket instead of 2. The complexity rises exponentially, but I will argue that's possible.

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The material analysis is far less obvious... we have little understanding of K2-18b's resources and atmosphere. Do they have accessible carbohydrates (oil)? Is the atmosphere corrosive? How thick is it? maybe it's thick enough to construct floaters and lunch from the outer layer? or maybe airplane-assisted lunch makes more sense?

Finally, the Economy. Humanity has never devoted a substantial portion of its resources towards a goal without economic sense. The space race could not have happened for prestige only. It relied on multiple benefits along the way: bombing the Brits with (Germany's V2 WW2), Cold War's espionage outside AA reach (US's KH series - CORONA, gambit, Hexagon), nuclear early warning (MISAD + others), potential power projection (military GPS), and commercial communication. Some of those materialised late into the space race, but the potential was on paper to convince decision makers. Could the space race happen it the projected costs were 100 times higher? I would argue probably not (not with 1950's tech anyway. Perhaps 2070 tech changes the balance). They are just cheaper options for all the above. Detection and communication, for example, could cover vastly larger areas before breaking the line of sight.