they must be able to calculate mass from orbital physics?
so you'd need a rocket 6x the size of SaturnV or whatever they are using for Artemis to escape it and most of that rocket is to lift the weight of the fuel for said rocket so it might be physically impossible to build such a creature at current level of tech
(might be yet another angle to "why no ETs" unless they are WAY more advanced)
Impossible to tell how much extra mass you need but it's exponential. Adding a unit of v_e [effective exhaust velocity] to escape velocity means you need 2.717 times as much fuel in an ideal rocket.
Earth escape velocity is 11000m/s ignoring atmosphere (which is not ignorable). If the new planet is 6x mass and 2x radius then √3 times escape velocity (about 1.73) would be about 8000m/s extra velocity which is about 3 times a random v_e which means you need about a 25 times bigger rocket. Ignoring the denser atmosphere which makes it even worse.
And related...
https://worldbuilding.stackexchange.com/questions/178131/wha...
https://physics.stackexchange.com/questions/117347/when-a-pl...
> Up above 10g, something really interesting happens that is kind of a theoretical limit. The mass of the rocket reaches a measurable fraction of the mass of the entire planet it's launching from.
been diving into PBS-Space-Time and DrBecky past few years as distraction from the endless nightmare of the world we are living in
this has been a great educational thread on HN too, I knew rockets would have to be bigger but didn't realize exponential and the 10g upper-limit
also puts the "Mars sample return" mission into perspective, very difficult
https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NE...
The "view" at the bottom has an animation of the various routes. They're all EM-ME though...
If you pick some other interesting targets you can get EVJS or something like that (launch from Earth, Gravity assist at Venus, Gravity assist at Jupiter, rendezvous with Saturn)... and then the trajectory animations are much more interesting.
Unless you skip chemical rockets altogether there is a pretty hard cap on how much bigger a planet can be than earth before a space capable civilization becomes almost impossible.