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Old August 29 2015, 06:26 PM   #1
Rear Admiral
Flyby asteroid rotovator

One of the problems with space elevators will be the constant attack by atomic oxygen--not to mention icing loads near the ITCZ. (Convection is deeper near the equator)

One concept I had was an asteroid bola with a tail that could fly by Earth, deposit a large load, and yank a load upward.

Doctor Pat from Next Big Future was kind enough to supply the math: (Scroll down)

Minimum velocity of the center of mass of the rotovator is the minimal orbital velocity of 7.8 km/s
Velocity of rotor tip at pickup from the ground needs to be about 0, or close enough to make no difference to this level of calculation.
Minimum rotor length is going to be the height of LEO, so about 100 km.
Maximum velocity of the rotor tip in the atmosphere should be lets say no more than mach 6 (~2 km/s) until it reaches at least 20 km in altitude. Based on the articles about hypersonic aircraft and what they can handle.

Let's put that together.

If we assume the tip of the rotor is sort of accelerating straight up with respect to the earth's surface, that means that the tip goes from 0 to 2000 m/s in 20 km.
v[sup]2[/sup] = 2 x Acceleration x distance
4 000 000 = 40 000 x Acceleration
Acceleration = 100 m/s/s = 10g (actually, that turned out rather reasonable)

Accel. = v[sup]2[/sup] / R (note, now V is relative to rotor center, not Earth)
V = twice the rotor center speed = 15.6 km/s
R (rotor radius) = 2.4 million meters = 2400 km.

OK, that's a lot higher than our original Minimum rotor length, so it meets that limit too.

But a rotor that long does not need to going to not be travelling at LEO speeds, so we can slow everything down a bit. But the minimum is still 6.7 km/s, so it isn't enough to make much difference.

Anyway, the real problem is that to have a reasonable speed through the thick parts of the atmosphere, your rotor needs to be so long that you are looking at a 2400 km long rotor. Not quite a space elevator cable, but it would be a serious material strength problem."

That's only 1,500 miles--not 22,500--to--60,000.

Lunar Elevator meeting

Supertall towers

Misc SLS art
Magnetic hole
Light fibers

ISS seen from the ground http://0e33611cb8e6da737d5c-e13b5a91...1440524457.jpg

Last edited by publiusr; August 29 2015 at 09:40 PM.
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Old August 29 2015, 10:16 PM   #2
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Re: Flyby asteroid rotovator

Here's a vid about something very similar. I like the idea! It seems more feasible than a space elevator.

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Old Yesterday, 03:24 PM   #3
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Location: Perpetually being chased by airplanes
Re: Flyby asteroid rotovator

^, Was that video narrated by Krepky?
No Where to be found, but everywhere you are - I'll be there looking for ways to save your life.
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Old Yesterday, 08:09 PM   #4
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Re: Flyby asteroid rotovator

They do sound similar. He even acknowledges it in one of his other videos.
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