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Comment by rplnt | Hacker News Reader

You have to consider how low that orbit is. ISS is closer to earth than SF is to LA for example.

Skyscrapers aren't that tall either. Burj Khalifa is only 830 meters tall, which is about half the distance from here to the neighborhood store.

At 21,000 meters, the U-2 didn't fly that high. That's only a half marathon, and many people can run that distance easily.

In other words, I fail to understand your point, even omitting the 7.9km/second sideways velocity for LEO.

It doesn't speak to the technical difficulty, but his example, and all of yours, help put the distance into context that we can intuitively understand. It's definitely helpful.

The kinetic energy of 1 kg moving at orbital velocity is about 31 megajoules. The potential energy of the same kilogram suspended 100km overhead is less than a megajoule.

Most of the difficulty to orbit isn't distance, it's the amount of energy it takes to get something moving that fast.

Actually it's much, much worse than that, because it's actually the change in momentum involved.

http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

The point is it's less far than it looks (humans are bad at judging vertical distances), and giving a real-world comparison makes the real height easier to conceptualize than an abstract number.

Humans are also bad at comparing horizontal differences to vertical ones. Switching from one to the other obscures the difficulty of going higher. If the peak of Everest were 8,848 meters in distance rather than height, it would be an unremarkable hike.

That makes sense; it's easier to take a horizontal step than a vertical one. Someone should do up an infographic showing the effect of gravity on work required for horizontal versus vertical movement.

I think it's logarithmic, but my math is bad.

The work required to move horizontally is zero (ignoring friction)

I was under the impression that we walk primarily by applying friction?

http://news.ycombinator.com/item?id=4010640

The problem is the rocket equation. Yes, there's a natural log in there, but working against our favor.

It still requires travelling at mach 25, that's a lot of velocity to put under the belt in such a short amount of time.

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