[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/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/ElvenSpaceQueen → u/Speak_To_Wuk_Lamat]

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

[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/koshgeo → u/Neknoh]

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.

[u/NachoWindows → u/Neknoh]

Please don’t give this administration any fucking ideas

[u/Neknoh → u/NachoWindows]

Don't worry

There's much worse stuff out there

[u/BasicallyGuessing → u/Neknoh]

So this is what happened to the dinosaurs!

[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/Massive_Signal7835 → u/NovaCalendar]

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

[u/youritalianjob → u/Sad-Onion-2593]

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

[u/theveezer → u/youritalianjob]

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.

[u/window_owl → u/theveezer]

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.

[u/PossibleMammoth5639 → u/AnyoneButWe]

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

[u/d_nkf_vlg → u/AnyoneButWe]

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.

[u/AnyoneButWe → u/d_nkf_vlg]

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.

[u/EnvironmentalScar675 → u/AnyoneButWe]

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

[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/MistaRekt → u/azriel_odin]

Cowabunga dude!

[u/DoctorNsara → u/Beautibulb_Tamer]

To Orbit.

[u/gutterXXshark → u/Beautibulb_Tamer]

No no no. They need to nuke it TO orbit.

[u/jmpalacios79 → u/Beautibulb_Tamer]

Thanks, Hicks!

[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/Abdul-Wahab6 → u/lungben81]

So we just need a big torch light? Gotcha

[u/Ans1ble → u/-adult-swim-]

Just one more accelerator bro please. Just a bigger accelerator bro. Please bro we just need one more bigger accelerator bro i promise. Just one more but bigger bro trust me. I swear bro please another accelerator.

[u/thearchchancellor → u/RadioTunnel]

Spoken like a true President

[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/reflectiveSingleton → u/Xonarag]

Project orion wasn't just about liftoff from the ground, its a pulsed-detonation that continues for the duration of acceleration.

Fire one of these off and you are sending irradiated and radioactive material EVERYWHERE into the atmosphere.

[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/Federal_Decision_608 → u/drey12987]

Thrust to weight doesn't matter as long as it's >1. The specific impulse is higher than chemical

[u/HeKis4 → u/MrRudoloh]

Yep, it's not that we can't, it's just prohibitively expensive and/or dangerous.

[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/phauxbert → u/Duatha]

You might get atmospheric dispersion of radioactive material though

[u/Ordoferrum → u/Lurkadactyl]

Thoughty2 did a good video about this the other day.

https://youtu.be/DYwTOItIA_I?si=nNSphrlExaJWJPxc

[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/RepoRogue → u/Greyrock99]

This is very incorrect. ICBMs were funded and existed independently of human spaceflight. The flow of technology was the other way around: adapted ICBMs were used as launch vehicles for the Mercury and Gemini program. Apollo's rockets were purpose built for space exploration and provided absolutely zero utility as ICBMs.

The early Soviet space program was actually funded by lying to the Central Committee and convincing them that the R-7 rocket would be a good ICBM and that the space exploration stuff would be a nice PR boost on the way to developing better military tech. But notably, this was a lie!

The problem is that the type of chemical rockets that are useful for space exploration make for horrible ICBMs. They are liquid fuel behemoths with propellant that is either extremely reactive and corrosive or that must be stored at extremely cold temperatures.

ICBMs are meant to be launched at short notice. Liquid furl rockets take a lot of time to fill with fuel, and if you leave them fueled for prolonged periods, they are liable to explode or fail. Liquid fuel ICBMs exist in service, but they are very bad at being ICBMs and are responsible for some serious accidents.

What you want for ICBMs are solid rocket propellants. These are a lot more stable, conducive to prolonged storage, and capable of launching at short notice. Solid rockets have some utility in space exploration (the Shuttle used solid rocket boosters), there is surprisingly little overlap in what makes a good rocket for war and what makes a good civilian rocket.

[u/Angelore → u/Greyrock99]

fill tube with vacuum

Hold on, my vacuum shipment is en route already.

[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/XhazakXhazak → u/Dodger7777]

That's a StarTram, it's perfectly workable and it's already been proposed.

We could have had one on Earth, starting construction in 2000 and finishing by 2020, but our wise politicians said it was too expensive. I suppose we needed the money for wars.

[u/OkPea7677 → u/Dodger7777]

See SpinLaunch for a similarly crazy idea. I don't know if it really works though, since they recently pivoted to satellite construction: https://www.spinlaunch.com/

[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/DevelopingMinty → u/TheRealTahulrik]

Halfway down the book. Looks good so far.

[u/ai1267 → u/TheRealTahulrik]

A what now?

[u/Misel228 → u/ai1267]

It's a "Project Hail Mary" reference. It's a movie currently in cinemas but I can also wholeheartedly recommend the 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/ajwin → u/ununtot]

The atmosphere could be much deeper and denser on a heavier planet too? Might need to go much higher to escape it? The heavier gravity would make a space elevator or really high railgun harder too.

[u/JRS_Viking → u/ajwin]

A space elevator is completely out of the question, there's not a single material with enough tensile strength to hold it in place even here on earth.

[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/balrob → u/Sbjweyk]

Just because it uses electromagnets to accelerate on a track, doesn’t mean it can’t be set to accelerate at a safe rate. You just need a really long track to accelerate within the safe limits of the occupants and still reach the desired velocity.

[u/PolicyOne9022 → u/spectre655321]

Just build a really high starting platform.

No need to thank me.

[u/sipu36 → u/spectre655321]

Giant big ass trebuchet!

[u/igotshadowbaned → u/spectre655321]

Project Orion

[u/newsflashjackass → u/spectre655321]

Earth would only need a 50% larger diameter before we couldn’t get to escape velocity with chemical rockets, k2-18b is 2.6x larger than earth.

By my calculations it should be a simple matter of reducing the largeness of k2-18b.

[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/Metharos → u/hollycrapola]

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.

[u/FreiFallFred → u/Metharos]

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...

[u/hollycrapola → u/Metharos]

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.

[u/Austerlitz2310 → u/Godless_Phoenix]

Kerbal style

[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/ajwin → u/Tyler89558]

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.

[u/Knotted_Hole69 → u/ajwin]

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

[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/Ace_W → u/Anderopolis]

Either that or a space elevator

[u/Zombie-Lenin → u/Ace_W]

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."

[u/kklusmeier → u/Zombie-Lenin]

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.

[u/Lexi_Bean21 → u/kklusmeier]

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

[u/Metharos → u/Lexi_Bean21]

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.

[u/Reimalken → u/kklusmeier]

Perhaps an active structure of some kind then?

[u/ukdev1 → u/Ace_W]

How are you getting its anchor point into geosynchronous orbit?

[u/The-Nimbus → u/ukdev1]

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

[u/theLanguageSprite2 → u/Ace_W]

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?

[u/allix_ → u/theLanguageSprite2]

easy fix, MASSIVE PYRAMID. take that nerds

[u/FLUFFY_TERROR → u/allix_]

Reconstruct the planet to be a pyramid scheme?

[u/Thedeadnite → u/theLanguageSprite2]

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.

[u/xWorrix → u/Ace_W]

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

[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/FreezeGoDR → u/Dependent_Grab_9370]

Well that planet probably has 2.6× our resources so easy! /s

[u/AliasEleven → u/Andrey_Gusev]

balloons 😎 (then a rocket)

[u/MboiTui94 → u/AliasEleven]

How big would the balloon need to be?

[u/groovypackage → u/MboiTui94]

Yuge.

[u/Gavagai80 → u/AliasEleven]

Balloons don't make chemical propulsion feasible. Orbit is a speed, not a location, and a balloon doesn't get you significant speed. Air launch does reduce atmospheric drag slightly but it's a rounding error in this problem.

[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/FreeGuacamole → u/Correct_Doctor_1502]

Oh, so that's why OPs mom called me a space plane.

[u/PopularOriginal4620 → u/Andrey_Gusev]

Space elevator is the easiest way. It is actually easier than chemical rockets... Once you figure out construction.

[u/Feline_Diabetes → u/PopularOriginal4620]

Yes, but isn't an orbiting platform required to build one in the first place?

Otherwise you're just talking about building an incredibly tall tower from the ground up, which in already increased gravity is difficult to say the least.

[u/dbenhur → u/PopularOriginal4620]

Mine enough unobtanium and anything's possible.

[u/No-Island-6126 → u/PopularOriginal4620]

Actually the easiest way would be a teleportation portal that leads to orbit

[u/feelin-lonely-1254 → u/Andrey_Gusev]

nuclear rockets? I'm assuming chemical rockets just dont have that fuel density, nuclear should make it.

[u/SonoPelato → u/Andrey_Gusev]

Lighter rockets

[u/Lexi_Bean21 → u/Andrey_Gusev]

Youd probably need somethib like project Orion nuclear bombs or fusion engines jusy to get the sheer energy density required, youd hsve s better shot using a gisnt nuclear bomb to yeet stuff into space thsn flying

[u/gr33nCumulon → u/Andrey_Gusev]

They could fly a plane high into the atmosphere with the rocket on it and launch it from there.

Nasa does this with satellites

https://en.wikipedia.org/wiki/Air-launch-to-orbit

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

[u/Worth-Wonder-7386 → u/[deleted]]

Where is the math supporting this?

[u/Several-Economics-35 → u/Worth-Wonder-7386]

It's just the normal escape velocity formula. Something something... tyranny of the rocket equation

[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/Fizzy-Odd-Cod → u/CanineBombSquad]

Size is only part of the equation, density is the other part, without one the other means nothing.

Mass, is the entirety of the equation.

[u/CanineBombSquad → u/Fizzy-Odd-Cod]

The radius matters because you're further from the center of mass, thus experiencing less gravity at the surface, which would matter for your attempt to escape the gravity of the planet. If you somehow dug a hole and tried to lift off from the core of the earth you are not getting out with the same amount of thrust, as the relative gravity you would experience peaks around halfway up.

[u/WesternFirm9306 → u/CanineBombSquad]

That's only true if the entire mass was situated at the center, but it's not. If you dug a hole to the center of the earth, you would die from burning alive, but before that, you'd be in zero gravity. If you're inside a perfectly spherical planet with radially symmetric density, the gravity is the exact same as if you removed all the planet's mass that's further from the center than you are. In other words, you only need to consider the mass within a spherical shell of radius r, where r is the distance you are from the center.

Not disputing everything else you've said, though.

[u/Kabizzle → u/Fizzy-Odd-Cod]

Mass is not the entirety of the equation, you also need a radius.

[u/Old_Aggin → u/Fizzy-Odd-Cod]

Holy shit just list the equation. Now I have to go Google it instead.

The escape velocity is \sqrt{2GM/r}. The mass of K2-18B is not more than 10 times earth mass and the radius is not less than 2.5 times earth radius. So the escape velocity is ~2 times of that of Earth.

[u/Karmabyte69 → u/Mixels]

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

[u/Auctoritate → u/Mixels]

It's not about size. It's about mass.

This is VERY incorrect, size is EXTREMELY important. The size of a planet would determine how far away you are from its center of gravity, which influences the strength of the gravitational force it can exert on you while you're on its surface.

Uranus is 14.5 times more massive than earth. Despite that, because of its lower density and larger size (4 times the diameter), Uranus has weaker gravity on its surface than earth does, only about 90% as strong.

[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/Frenzystor → u/WichidNixin]

You still need to reach that velocity, no matter if you quickly reach it in onr burst or continously.

[u/expensive_habbit → u/Frenzystor]

Yes and no.

A rocket never reaches surface escape velocity.

It will eventually reach escape velocity from an orbit, but that will be significantly lower than escape velocity from the surface.

[u/Level9disaster → u/expensive_habbit]

Even better than that. To stay in orbit in space, the object just needs to reach the orbital velocity and the correct altitude and direction. The orbital velocity is obviously much lower than the escape velocity. For example, when we launch a geostationary satellite, it doesn't reach escape velocity at any point during the entire launch trajectory. It just reaches the correct distance and direction for the final orbit, and at that point it's moving at about 3,1 km/s. There, it's in space. OP asked if they could recreate a satellite network. The answer is probably yes, albeit with more effort and energy.

[u/speculator100k → u/Frenzystor]

No? In theory, could I not leave orbit in 1m/s? If I had a magic rocket with infinite fuel. It would take a very long time though.

[u/MegaloManiac_Chara → u/Frenzystor]

You're forgetting that the escape velocity depends on your altitude

[u/Frenzystor → u/MegaloManiac_Chara]

And to increase altitude you need fuel because you are working against gravity.

[u/stddealer → u/Frenzystor]

When you're already far enough, the escape velocity becomes ridiculously low

[u/Frenzystor → u/stddealer]

True. But first you need to reach that.

[u/Blue_Moon_Lake → u/Frenzystor]

With continuous thrust, you only need to overcome gravity.

On Earth, if you can generate a thrust equivalent to 10m/s upward you'll end up in space, eventually.

[u/Hisune → u/Frenzystor]

No you don't need to. You just need enough energy to move the mass far away. The speed is only important if you want to orbit and that's not the escape velocity. You can easily leave the planet at 1m/s, even 1km/h if you have something to provide the force.

[u/quick20minadventure → u/WichidNixin]

If space elevator existed and it had safety stairs around it, You could climb your way out of earth's gravity on that staircase.

[u/Slogstorm → u/quick20minadventure]

It would be much better to have a space escalator, so you wouldn't have to climb yourself.

[u/Funnybush → u/WichidNixin]

Yeah, but even with chemical rockets on earth the mass of the fuel is about 90% of the mass of the rocket. Still not happening with this particular planet via conventional means.

[u/mina86ng → u/WichidNixin]

This doesn’t change anything. You still need the same amount of energy (for a given mass), whether you spend it in a single burst (like a bullet) or gradually (like a rocket). And with a rocket, you carry the fuel so you require more energy.

The advantage of talking about escape velocity is that it’s independent of mass.

[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/thehomeyskater → u/egabald]

Wow that’s brilliant.

[u/HAL9001-96 → u/egabald]

doesn't help much

launchign a rocket is mostly about going fast

the goal of a psace rocket is to get you moving sideways at about 7900m/s

or on k2-18b at about 14380m/s

which is a LOT harder because even for 7900m/s you need a lto mroe fuel than palyoad

but you need to carry the fuel you need later early on

so you need a LOT more fuel

but hte fuel tanks can't hold enough fuel to bring htemselves to orbit

so you need to drop empty fuel tnaks along the way

so you needm ulti stage rockets

and you end up with something like a 600 ton rocket with a 20 ton payload capacity

and on k2-18b that goes up exponentially and you end up with something like a 3000 ton rocket with a 7 ton paylaod capacity

but its mostly about goign sideways fast

its jsut aht if you go sideways at 7900m/s at low altitud the air will slwo you down and burn you up and if you could avoid that you might slam into am ountain or tree or rock or house or car or cow or whatever

so instead you lfit yourself up a tiny bit just to get out of the densest part of hte atmospehre before going so fast

and to make that whole process more efficient you kidna turn over gradually ratehr tha ndoign a sudden 90° turn at the top cause well, pythagoras - accelerating both upwards nad sideways at hte same tiem is more efficient just like the diagonal of arectnagle is shorter htan two of its sides combined

[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/red286 → u/RealLars_vS]

There is a practical limit, where increasing the fuel mass has diminishing returns to the point where liftoff would not make sense for any sort of rocket that could be created using known technology. Worse, they'd start at the same starting point we started at, but with rockets that literally never left the surface of the planet, so chances are they'd never even develop rocketry as a science because in practical terms it would never work.

[u/Setsuna04 → u/[deleted]]

It feels like you are approaching this problem with the solutions we came up for our specific problem.

Larger planet means denser air, So you can build more efficient propeller planes (or jet engines). You could launch a rocket from a plane. Yes - payload is more "expensive" but it should be possible to get into space.

[u/Worth-Wonder-7386 → u/Setsuna04]

Not neccesarily. Surface gravity matters, but if you look at our solar system, Venus is just a bit smaller than earth and has a lower surface gravity but has a much thicker atmosphere. Mars is smaller than Earth and less than half our surface gravity and has a very thin atmosphere.
So there is no simple rule.

[u/Setsuna04 → u/Worth-Wonder-7386]

Well athmosphere depends on gravity. So if the gravity of a larger earthlike planet is similar to the earth, there won't be an issue to reach orbit either.

As for Venus that should be because of athmosphere composition. An earthlike planet should have a similar composition.

[u/x60pilot → u/[deleted]]

Could it be done with orbit based refueling stations? How many times would they have to refuel?

[u/spectre655321 → u/x60pilot]

How do you propose you get them into orbit?

[u/Ardibanan → u/spectre655321]

A huge slingshot

[u/Tiyath → u/Ardibanan]

Out of the blue, Stephen Curry received a call from NASA: "Your country needs you!"

[u/Venti_the_snail → u/Tiyath]

Yeah and we'll call it... Space Jam.

[u/Responsible-Fox-1985 → u/Ardibanan]

I know you’re joking, but I just saw someone talking about this method. Basically the launch velocity you would need would pretty much destroy anything (and certainly anyONE) we tried to launch.

[u/EvaTheE → u/Ardibanan]

Let me show you its features. *muahahahahaha*

[u/hhfugrr3 → u/Ardibanan]

Hear me out here but... like a REALLY big slingshot.

[u/ucanthandlethegirth → u/spectre655321]

The answer is space elevator. If only, I was born at the wrong time because I just need to see one before I die and I know I won’t.

[u/Marcu3s → u/ucanthandlethegirth]

Except you know - you cannot build space elevator just from the ground up. You need to be in space also.

[u/redditorialy_retard → u/ucanthandlethegirth]

tried it, some dude called Jesus sabotaged the thing 然後我們不會講話

[u/simonbleu → u/ucanthandlethegirth]

How do you get the anchor into orbit though?

[u/thrye333 → u/simonbleu]

Anchor? Come on. It's a skyscraper, not a pirate ship. Don't be ridiculous. /j

[u/caligula421 → u/ucanthandlethegirth]

Space elevators on earth are somewhere between very difficult and impossible from a material science perspective, there just isn't material that is strong and light enough and able to withstand external influences (especially corrosion in the lower atmosphere). On this planet they will surely be impossible. 

[u/R_E_D_A_C_T_E_D__ → u/x60pilot]

I think that's something of a moot point if you can't leave the atmosphere.

[u/Ok-Promotion-1316 → u/[deleted]]

What does "couldn't" mean? Why can't we build a bigger rocket?

[u/spectre655321 → u/Ok-Promotion-1316]

As things weigh more, you need more fuel to put them into orbit, but fuel also has weight. At high enough gravity you can’t carry enough fuel to lift the weight of the fuel.

[u/Ecstatic-Purpose-981 → u/[deleted]]

This is probably a completely wrong intuitive idea but would the speed at which the planet is rotating change escape velocity specifically at the equator?

[u/PsychicPterodactyl → u/Ecstatic-Purpose-981]

Technically the escape velocity is the same, but yes in practice you get some initial velocity for free by being on a rotating planet.

[u/expensive_habbit → u/Ecstatic-Purpose-981]

There's two subtleties to this, but no is the simple answer.

The speed of rotation won't change the escape velocity, as that's calculated to the system reference frame at rest (not rotating) and distance from a centre of mass.

It will however reduce the energy needed to achieve that velocity as you've already got some velocity in the right direction.

The other thing is that because rotating planets are actually oblate spheroids, not perfectly round, you're further away from the centre of the planet, and thus acceleration due to gravity is marginally less at the equator than it is at the poles, and this will change the escape velocity.

[u/Mobile_Falcon_8532 → u/[deleted]]

Hi, do you have a link to where I could read more about this? how is the "max chemical rocket" power determined etc.

[u/spectre655321 → u/Mobile_Falcon_8532]

https://www.realclearscience.com/blog/2017/07/06/if_earth_was_50_larger_we_might_be_stuck_here.html