Imagine a terrestrial planet that is Earthlike in all respects, but it simply has more persistent cloud cover, such that seeing an open cloudless sky is miraculously unlikely, as unlikely as humans seeing an asteroid impact.
No ground based astronomy.
No technological discoveries or culture that derives from ground based astronomy.
No celestial navigation on the ground.
Very different / stunted / more difficult cartography.
Technological civilization is capable of emerging, but it would not be able to well understand anything beyond the terra firma, not untill it generated aircraft capable of breaching the cloud cover layer, and thrmen developed airborne observatories.
turdas@suppo.fi 3 weeks ago
According to Wikipedia this planet has an estimated surface gravity of 12.43 m/s^2 with a margin of error of about 2 m/s^2. That’s only up to 50% higher than Earth’s 9.8 m/s^2 (on the high end of the error margin) so it probably would be possible to get into orbit.
That said we don’t actually know much about it for sure. We don’t know if it’s a terrestrial planet for example. It could be composed mostly of gases and liquids like Neptune.
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
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:
jballs@sh.itjust.works 3 weeks ago
Kerbal Space Program is such an amazing game that secretly teaches you physics.
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PabloSexcrowbar@piefed.social 3 weeks ago
With a denser atmosphere, wouldn’t that mean that you could get more lift from a traditional aerofoil than on earth? And if so, wouldn’t that technically make it easier to start from a high enough altitude that at least some of the gravity is mitigated?
matsdis@piefed.social 3 weeks ago
Or ask Randall Munroe How many model rocket engines would it take to launch a real rocket into space?
ColeSloth@discuss.tchncs.de 3 weeks ago
Build a large enough magnetic rail launcher and you could save shit tons of fuel. Get a ship doing 2000 mph before it leaves the ground and needs its rockets and you’ll have a pretty good head start.
M137@lemmy.world 3 weeks ago
You don’t have to launch from the ground, there are many things that can be done to allow them to reach orbit. It’ll be an enormously bigger undertaking but the physics doesn’t make it impossible. No reason to think of it in terms of our current situation either, what we are behind our current science when it comes to rocket science, due to waves at everything else
Not_mikey@lemmy.dbzer0.com 3 weeks ago
Wouldn’t that be a non starter for life? One side would be perpetually baked and the other would be frozen.
sylveon@piefed.blahaj.zone 3 weeks ago
It’s probably still a lot harder though. You’re not just heavier, but also slower which means you’ll spend more time fighting gravity. And all the extra fuel you bring for that makes the rocket heavier which means you need even more fuel to launch the fuel. Higher surface gravity likely means a thicker atmosphere too which is a big issue and a more massive body also has a faster orbital velocity. Although in this case the larger diameter might counteract that a bit because higher orbits have slower velocities.
My point is that this would probably still be a lot harder than just building a 50% bigger rocket. If you’ve ever tried launching from Eve in Kerbal Space Program you know the pain. Although in that case you also have to fly the entire rocket there first which is its own challenge.
crank0271@lemmy.world 3 weeks ago
Aw man. This is already a significant portion of my day.
Speculater@lemmy.world 3 weeks ago
It would actually be impossible for them to get to orbit using chemical rocketry, like we use. The could theoretically do it with nukes.
Chemical rocketry limits
Nuking your way to orbit
expr@piefed.social 3 weeks ago
I assume it’s not just about the gravity, but also the much larger radius of the planet would mean much larger distance from the surface, and thus much more fuel needed.
potatopotato@sh.itjust.works 3 weeks ago
That’s how how…what???
F = G * (m1 * m2) / r^2
turdas@suppo.fi 3 weeks ago
That’s, uh, not really how that works. A taller atmosphere would mean you have to go through more of it, but unless it’s not a terrestrial then the atmosphere won’t be that much taller.
If it is a non-terrestrial planet, it’s unlikely anyone would be building rockets on there to begin with.
degenerate_neutron_matter@fedia.io 3 weeks ago
You're sort of right. The change in distance from the surface is insignificant, but a spacecraft orbiting a bigger planet has to travel further with each orbit so its speed must be faster to avoid falling out of orbit, even if the gravitational acceleration at its orbital height is the same.
cogitase@lemmy.dbzer0.com 3 weeks ago
I’ve been wondering what a hypothetical perfect habitable planet for spacefaring would look like. Could you have one where a plane line the SR-71 Blackbird or an even less capable aircraft could simply “fly” into orbit? Or what about something Earth-like but with a flat plateau at 15,000 m where you could launch rockets from?
turdas@suppo.fi 3 weeks ago
I think Mars, assuming you terraform it, would be pretty close to that on both counts. Space planes might still be difficult, but the delta V is much lower and Olympus Mons would pretty much sit above the atmosphere.
wonderingwanderer@sopuli.xyz 3 weeks ago
Classic planes require an atmosphere to generate lift. There’s an outer limit where that would be a viable mechanism, and on Earth it’s still far below LEO. Still too deep in the gravity well for ion thrusters to ve viable.
It requires chemical rocket fuels to bridge that gap. Maybe someday fusion propulsion will break that limitations, but for now the best you can do is reduce the amount of fuel needed by flying to the upper atmosphere and reaching hypersonic speeds before kicking into rocket fuel propulsion.
Then after orbital injection, switching to ion thrusters to move around, and solar sails for exiting orbit into interplanetary/lunar routes.
gandalf_der_12te@discuss.tchncs.de 3 weeks ago
Mars is better for launching rockets into deep space than Earth because it has a lower gravity field and also thinner atmosphere.
suodrazah@lemmy.world 3 weeks ago
Orbital speeds would be very hard to reach compared to low Earth orbits.
JasonDJ@lemmy.zip 3 weeks ago
Or Uranus.
AugustWest@lemmy.world 3 weeks ago
Or your mother’s.