but do you need to reach geostationary? couldn't you just switch to a rocket at this stage? Maybe a small one to bridge the gap? I would have thought that the first kilometres are the ones where you have to invest the most work so if you just bridge them using the space elevator it would be still an improvement.
Maybe for cargo the 20 days are not really important
Getting to 100km or even 200km is easy. Staying there is hard.
80% of the energy in a rocket goes to adding sideways motion.
An elevator upto GEO adds enough energy (taken from the earths rotational energy) to your payload to get it into orbit. If you let go lower down you need to add sideways velocity.
In LEO you on an elevator would be travelling about 1,400mph and need to get to 18,000 to get into orbit. Sure there’s no atmosphere to work against but it’s still a lot of fuel to use in a rocket.
> In LEO you on an elevator would be travelling about 1,400mph
That's a pretty significant speed already and it helps that you are already in space. See how tiny a Pegasus rocket is, and that one is launched from aircraft, slower, and nowhere near as high as what we are discussing.
Getting to 100km from ground requires beefy first (even second) stages because you need to accelerate further stages plus the fuel, inside the atmosphere. We can basically pretend we are starting at the second or third stages. It now up to the rocket equation.
So, to recap, there's already 1400mph of sideways motion, at a negligible air resistance, 100 to 200km up with vacuum optimized nozzles. It is a massive win.
The question is if we could hoist what are still relatively heavy payloads.
> 80% of the energy in a rocket goes to adding sideways motion.
I have not researched this at all, so I'm not doubting you, but doesn't most of the energy go into accelerating the remaining fuel? So, by the rocket equation, shouldn't you be way ahead of the game by starting at the edge of space?
Maybe for cargo the 20 days are not really important