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Comment by azernik | Hacker News Reader

One of the interesting ones I've heard talk about lately is the "interstellar travel" step - Earth is on the lower end of the size range for rocky planets that can support an atmosphere and magnetic field to shield surface life from radiation. And because of the tyranny of the rocket equation, life developing on larger rocky planets may have a much harder time reaching orbit.

A good demo video: https://www.youtube.com/watch?v=amjuJJwI3iM

On a planet with twice the Earth's mass, it would take a larger-than-Saturn-sized rocket to put a Mercury-sized payload into orbit.

EDIT: And said Mercury-sized payload would have to spend more of its mass on heat shielding than the human Mercury capsule if it's intended to come back down.

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Just to clarify for anyone unfamiliar with the US space program in the 50s-70s, or those just briefly confused by the discussion about planet sizes using planet names for things that aren't planets...

Mercury was a small space capsule containing 1 person designed to last a few hours in space. The Saturn V rocket was until recently the most powerful rocket ever launched, and took 3 crew, a crew module, a lander module, and payloads, to the moon.

This wouldn't stop von neumann probes https://en.wikipedia.org/wiki/Self-replicating_spacecraft

The upmass requirement for bootstrapping that kind of system would be quite large.

Yes but the rocket equation wouldn't stop intelligent species from going "loud" with radio signals.

The rocket equation itself, no, but the planet mass would also have drastic effects on the evolution of species. On our planet, high density fibrous plants like trees have an advantage when it comes to access to the sun but what if on a bigger planet, that advantage goes to plants than can emit a spidersilk-like material to float on the wind in colonies? There goes a practically infinitely renewable building material that can be used for almost anything until the industrial age. How can a civilization get to the electronic age when they spend all their time between extinction events hauling rocks and mining ores to build 2 story dwellings?

There's just so many unknowns.

Not only dwellings but fuel as well. I mean, if you don't have trees how are you going to invent fire...

Some people consider cooking a critical step in our evolution (cooking enables harvesting more calories from food).

With no good fuel available cooking could also be ... off the menu.

Dry grass catches fire quite easily and high gravity shouldn't hinder the growth of low grass.

If not grass, dried escrements are also good fuel. People use them in areas of this world with little or no trees.

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