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gami@piefed.social ⁨3⁩ ⁨weeks⁩ ago

(Not a rocket scientist or mathematician, but I spent 100s of hours playing KSP RP-1)

Just doing some estimates using data from the wikipedia page:

The dV (delta-V) needed to get into low Earth orbit is around 9.4km/s.
The dV for K2-18b might be around 19km/s, more than double that of Earth’s.

It’s practically impossible I think, you would need such a massive launch vehicle. For double the dV, you would need exponentially more fuel assuming current rocketry tech (fuel+oxidizer tanks and engines). There wouldn’t be any single-stage or two-stage rockets that could do this. With a 3 or 4 stage rocket maybe? But you would be sending nearly 100% fuel off the launchpad with virtually zero payload.

I tried to factor in:

spoiler

  • Atmospheric drag - K2-18b’s atmosphere is quite dense with a huge radius:

The density of K2-18b is about 2.67+0.52/−0.47 g/cm3—intermediate between that of Earth and Neptune—implying that the planet has a hydrogen-rich envelope. […] Atmosphere makes up at most 6.2% of the planet’s mass

  • Since the atmosphere is so thick and takes up a lot of mass, I’ve picked 500km as the low orbit altitude (comparing to Earth’s ~100km Karman line, it makes you appreciate how thin our atmosphere is ).

  • Rotational assist - I’m assuming it’s tidally locked since it orbits so closely to its star (33 day years), and so you wouldn’t get the assist from rotation like you do on Earth:

The planet is most likely tidally locked to the star, although considering its orbital eccentricity, a spin-orbit resonance like Mercury is also possible.

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