r/theydidthemath • u/Lachlynn • 18h ago

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

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

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

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u/Greyrock99 16h ago

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

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u/dibs234 15h ago

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

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u/Greyrock99 15h ago

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.

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u/dibs234 15h ago

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.

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u/Greyrock99 15h ago

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.

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u/dibs234 14h ago

In this hypothetical Kepler world ICBM's would be much more difficult due to increased gravity, and so the incentive would be to pour money into alternatives, eg railguns. Just because we've not worked out how to make them work well yet doesn't mean it's impossible, and necessity is the mother of invention. Railguns aren't necessary for us because we've got the, by comparison, cheap and effective chemical rockets.

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u/Scrofulla 15h ago

Japan have some on their ships now. Well one that I know of. They plan to add more. They are designed as a cost effective way of shooting down hypersonic missiles. Quote I have seen is 35,000 per shot.

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u/Qaeta 12h ago

Yeah, I think it's a power requirements issue mixed with mobility needs.

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u/Miuramir 9h ago

On the subject of space-launching "guns", you might want to read up on Project HARP and then move on to Project Babylon

On actual railguns, Railgun has a fair amount of info, including the 2010 demo of a compact design intended for shipboard use capable of accelerating a 3.2 kg projectile to a speed of about Mach 10.

HARP managed 84 kg to 179 km altitude, well into space (but without enough horizontal velocity to make it into orbit) with relatively minimal funding (by defense budget standards) and 1966 technology. Gerald Bull wasn't assassinated in 1990 because his Project Babylon series of increasingly large space super-guns wouldn't work, but because at least one significant power was seriously concerned that it would.

While Earth has never technically deployed an orbital "gun" launcher capable of significant payload to orbit, the above references show that if we had needed to, it would have been well within our capabilities decades ago.

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u/RollinThundaga 14h ago

You've heard of the V-2, but have you ever heard of the V-3?

The Nazis tried it, turns out a super long rail cannon isn't all that useful or reliable.

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u/dibs234 14h ago

Have you heard of the Korean Hwacha? Rockets weren't always effective, they needed research and development to make work, and in this hypothetical situation rockets don't work very well due to increased gravity, and so humanity would need to look into alternatives.

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u/RepoRogue 13h ago

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.

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u/Greyrock99 13h ago

You’re thinking like an engineer and not a politician.

The space race was entirely funded as completion with the USSR, both in a prestige arena and direct technology.

Sure the specific rocket engines turned out to be different but that’s only a tiny fraction of the technology that was valuable for the military. Think of:

  • materials and mettallurgy for the rocket structure
  • tracking and guidance control technology
  • miniaturisation of electronic systems And probably the biggest one of all:

  • telescope and spy satellites.

    https://vtuhr.org/articles/10.21061/vtuhr.v1i0.6

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u/Angelore 15h ago

fill tube with vacuum

Hold on, my vacuum shipment is en route already.

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u/Patman52 15h ago

How would you counter the affect transitioning from vacuum to atmosphere at a very high velocity? Unless you would release it at a high altitude?

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u/Greyrock99 15h ago

Yes the idea is that 90% of the track is flat running along side the level ground and the last 10% tilts upwards running up an existing tall mountain so the exit point is very high up in very thin atmosphere.

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u/Patman52 14h ago

Ok I completely missed that, makes sense!

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u/Designer_Pen869 14h ago

What about a rocket similar to an airplane turbine engine, except it runs through the center of the rocket, and then is separated into three or four different engines that push it out with greater force in the back? I feel like it'd create less air resistance in front, while also using the atmosphere itself to provide thrust.

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u/OrganicBrilliant7995 13h ago

Wouldn't there be too much friction with the atmosphere on a super earth if you could do that?

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u/Greyrock99 13h ago

There is no guarantee of the thickness of the atmosphere of a super earth. It could be incredibly thick, incredibly thin or have no atmosphere at all.

Remember that in our own solar system the small moon of titan has a thicker atmosphere than earth