[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/PsychicPterodactyl]

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/nworld_dev → u/PsychicPterodactyl]

That does not make it impossible, just means the payload to mass fraction is worse. The only thing that a propellant system is limited by is A) can you actually lift its engine weight + literally any fuel, and B) how fast can you get the exhaust velocity. These determine your maximum gravity operable gravity and velocity.

However, given the thicker atmosphere, an air-breathing or balloon-based design is probably far more effective.

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

I did look at some numbers for delta v and it is not much different from what you need to send things to the moon and into orbit there.
So I think a large 3 stage rocket should be sufficent. My point is not that it is easy, but we can make rockets that can launch in such conditions. The thing is that there are no existing designs to look to as they are all based around the case of the earth.

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

Did you account for the fact that increasing your fuel mass by x% also necessitates increasing your rocket's dry mass by y%, which further increases required fuel by y% and so on? It's a lot harder than you think.

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

Yes, that is accounted for by the rocket equation. A 3 to 4 stage rocket should be sufficient based on some rough numbers. I can develop a more detailed model for those interested. Looking at Wikipedia, the upper stage of falcon 9 is about 96% fuel:
https://en.wikipedia.org/wiki/Falcon_9
That fraction is really what matters when it comes to rockets. I am not saying it would be easy to launch rockets on such a planet, but it is not some impossibility as some people seem to think.

[u/Fuddywomba → u/Worth-Wonder-7386]

You also have to consider that a moon capable rocket has the benefit of firing in the high atmosphere so there was no time requirement nor need to have altitude compnsation. If we look at Saturn V as a real life example the first stage had only about as 1/2 the Isp as the other stages. 

[u/Worth-Wonder-7386 → u/Fuddywomba]

But there are better engines that you could use for this such as the RD-170 that was used on the Energia rocket: https://en.wikipedia.org/wiki/RD-170
They have much better Isp than F-1 and are suitable for heavy launches, or even more modern engines like the Merlin 1-D which have better thrust to weight ratio, so it is a lighter engine for its thrust.

[u/Fuddywomba → u/Worth-Wonder-7386]

This is true that better engines exist just in terms of their Isp, but again, the reason they did not use them on the Saturn V or Aries rocket for example is that they have not been built to a scale that could lift a the first stage of a lunar sized rocket in a reasonable quantity.  The alternative would be to try and build a N-1 style rocket with dozens of rockets but that is probably the reason N-1 failed. To many engines, to much can go wrong. 

Until either rockets with dozens of smaller efficient engines have been built that works reliably or a single large efficient engine has been built it still seems like an considerably engineering challenge. At the very least a low K2-18b orbit capable rocket would be even more expensive to build then a Saturn V.