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mmmmmmBacon12345 t1_j29d9xj wrote

The rocket equation is a butt and as mass/gravity scale up you start needing a rocket the size of the Saturn V just to put Sputnik into orbit

Earth having a 50% greater diameter means it has 3.375x the mass because mass scales with volume and that results in a surface gravity about 50% higher (~14.7 m/s^2 )

That higher gravity means that you need stronger(heavier) rocket engines since a rocket needs a Thrust to Weight ratio of at least 1 to leave Earth and if we still with Earth weights it'd need a TWR of 1.5 to leave the bigger Earth. The Saturn V rocket had a TWR of 1.02 at launch so it'd never make it, and the Falcon 9 is pretty zippy off the pad today but it only has a TWR of 1.4 so it would also never make it.

This then pairs with the tyranny of the rocket equation where the higher gravity means we need to go faster which means we need more fuel which needs to be lifted with more fuel and you need to lift that fuel with more fuel. Today the ISS orbits at a speed of 7.66 km/s, but around our new Earth even at the same 400 km up it'd need to be going 11.6 km/s and it'd take a bit more to get to orbit

Today it takes about 10 km/s of DeltaV(how much a rocket can change its speed, basically range) to get from the surface to the ISS, that means lifting 1 ton requires 29 tons of fuel so the rocket is 96.66% fuel. If you need to get up to 14 km/s then the rocket needs to have 115 tons of fuel(99.1% of overall mass)

So we start needing more fuel just to get to orbit and stronger rocket engines which require yet more fuel which means stronger heavier engines and more fuel and more fuel for the fuel....

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