so what kind of force does it exert on earth's rotation

3/8/2006 12:29:26 PM

one of my favorites..."We aint found shit"

3/8/2006 3:01:33 PM

earth radius:
12,756.270 km = 7908 miles

7908 miles * (1/16) =/= 62,000miles

Quote :

"it is like 1/16 the diameter of the earth! of course it is going to be an eyesore!"

but it also makes me think.. thats a long ass distance to put the top of the elevator! 8 Earths away! doesnt seem right

3/8/2006 4:14:43 PM

Quote :

"earth radius: 12,756.270 km = 7908 miles 7908 miles * (1/16) =/= 62,000miles"

I think he was referring to the diameter of the platform, not the length of the tether.





and he was joking, anyway.

Quote :

"so what kind of force does it exert on earth's rotation"

The change in angular velocity of the earth due to the mass of the satellite/tether would come from the conservation of angular momentum.

A few assumptions:
1 - Satellite is taken to be a point mass. (not a bad assumption at all)
2 - Tether is taken to be a point mass at its halfway height point. (not bad, either)
3 - Earth's moment of inertial is that of a constant density sphere. (maybe a little iffy, but at this large of scale, it's not that big of a deal)
4 - Satellite's mass is 60,000 kg. (communications satellites seem to run around 3,000 kg, so this is 20x bigger)
5 - Tether's mass is calculated at .2 kg/km = about 20,000 kg.

A few givens:
1 - Radius of Earth = 6,378,000 m
2 - Geometric height of Satellite = 99,758,000 m (above earth surface)
3 - Absolute height of Satellite = 106,136,000 m (above center of earth)
4 - Angular velocity of Earth = 7.27220521664304 e-5 rad/s (assuming exactly 24 hr day)

Conservation of angular momentum:
L(i) = L(f)
L = Iw : I == Moment of Inertia, w == angular velocity
I = m*r^2 (point mass)
I = 2/5*m*r^2 (constant density sphere)

L(i) = I_Earthw_Earth
L(f) = [ I_Earth + I_Satellite + I_Tether ] w_System

Therefore,

w_System = I_Earthw_Earth / [ I_Earth + I_Satellite + I_Tether ]


Working out all that math with the numbers provided above yields us:

w_System = 7.27220521664304 e-5 rad/s


Which means that the change in angular velocity due to the satellite is at most:

0.00000000000000000001 rad/s

In other words, negligible.




And just for fun, let's make the Satellite's mass = 60,000,000 kg

Now our new Final Angular Velocity
w_System = 7.27220521664299 e-5 rad/s

Thus, the difference in Angular Velocity created by the satellite is:
-5.14996 e-19 rad/s

So the earth has slowed down by:
8.08954 e-19 seconds/day
2.95268 e-16 seconds/year
1 second/3 quadrillion years

with some shady math, of course...






[Edited on March 8, 2006 at 5:29 PM. Reason : ]

3/8/2006 5:19:07 PM

this is why i'm conflicted...i love the math above (the implications, etc)...but i really HATE doing it, it makes my head hurt

3/8/2006 6:35:03 PM

Someone give me a graph that shows the change in rotation with increasing satellite mass.

I'm to lazy to figger out if its linear or geometric.

3/8/2006 6:39:11 PM

according to tl's equation for Moment of Inertia (MOI), I = m*r^2, MOI increases linearally with mass and exponentially with radius.
So increasing the mass of the satellite would not be very interesting. Increasing the length of the tether, however, could give some cool results.

3/8/2006 6:45:23 PM

we need graphs.

many more graphs.

3/8/2006 6:46:21 PM

ha, i bet we have some program at work that does this with nice pictures





I think it's called "Matlab"

3/8/2006 6:56:25 PM

i had a recurring nightmare as a kid that i was in a regular elevator that was going up, but didnt stop at the top of the building. it just burst through the roof and kept going into space. it was horrifying. this, however, seems cool.

3/8/2006 8:52:41 PM

man, I would LOVE to see a project of this magnitude happen in our lifetimes.

3/8/2006 9:00:24 PM

^50 years. It will easily happen by then. Just imagine the technological change that people have witnessed over the last 70 years.


Had a tour of my workplace this week, and they are doing advanced shit like this everyday all over the lab. It's extremely easy for me to imagine technology advancing well beyond what it is now within my lifetime.

I expect advanced robotics and cyborg shit as well as all kinds of genetic engineering. Nanotube shit everywhere, ridiculous computing power, intelligent, wirelessly networked stuff everywhere. That's not even being imaginative.

history channel recently mentioned the speeds at which people entered each century. We entered the 20th century at 60 mph (trains), 21st at 600 mph (planes), 22 will be 6000 mph (hypersonic suborbital), 23 will be 60000 mph (space).
-----------------

The political situation will also be very different just as it has been over the last 100 years. All this cool shit wont happen under our watch if we are indeed wavering on math and science education and endeavors. It's crazy to think how excited people were about science in the 50s and 60s.

--------------

We will also burn 1 million chinese alive.

[Edited on March 8, 2006 at 9:51 PM. Reason : sdf]

3/8/2006 9:40:22 PM

only a million?

3/8/2006 10:25:31 PM

This should have been done sooner

3/8/2006 11:19:35 PM

on a more serious note....

wouldn't the "elevator" be able to travel faster the further it got from the earth, seeing as there would be less gravitational pull...

d'you think the speed of the elevator is determine by the strain on the ribbon, or the energy required to move it?

also, I'm kinda confused how the elevator moves... is it attached to the ribbon, and it works like a pulley, or is it launched and just kept in an upwards trajectory (like a rocket with a guide wire... which doesn't seem like a big improvement), or does it use the ribbon to pull itself up somehow??

3/9/2006 12:20:22 AM

from what I've read, the elevator platform would be moved using an attached accender (sp?). Sorta like it'd pull itself up the ribbon. It's supposed to get power from the bottom platform I think.

My question is.. what happens when a big fucking storm comes through the pacific where this thing is at?? would that fuck with the ribbon? The platform? It's not like you can just detatch the cable.. or move the platform...

[Edited on March 9, 2006 at 12:24 AM. Reason : hmm..]

3/9/2006 12:22:47 AM

http://www.newscientistspace.com/article.ns?id=dn8725&feedId=online-news_rss20
http://groups.google.com/group/space-elevator
http://www.siliconbeat.com/entries/2005/09/19/space_elevator_might_really_happen.html

[Edited on March 9, 2006 at 12:28 AM. Reason : ]

3/9/2006 12:26:51 AM

2018? that would be rather impressive...i'll be, what? almost 36? wonder if i can take the first ride...

3/9/2006 12:39:34 PM

Shit like this makes me wish I could live for a few hundred years.

3/9/2006 12:59:49 PM

cryo yourself.

have them wake you up 300 years from now.

3/9/2006 4:06:25 PM

with my luck it would just be a big joke to leave me frozen

3/9/2006 4:08:52 PM

Is that even possible?

3/9/2006 4:43:59 PM

I dunno,

ask Ted Williams.

3/9/2006 5:55:21 PM

Just his head is frozen. Well, at least it's separated from the rest of his body if indeed his body is frozen also.

3/9/2006 10:43:18 PM

yeah... so i'm still excited about this....

is that sad??

3/17/2006 12:59:05 AM

yes

3/17/2006 2:13:22 AM

OK, going waaaaaayyy back to when somebody said this was going to be an eyesore.....

I don't know about you guys, but when it's just me running around the house, I don't care if my hair isn't brushed or if I have holes in my shirt. It's just me, nobody's gonna see me, who cares?

In this case, Earth is me. What does it matter if we have a hundred thousand kilometers of nanotubes sticking out into space? It's just us! Who is going to make fun of us, the Klingons? The Mooninites?

Besides, it's so thin...

And I, for one, am putting functionality over fashion. Well, if going out into space in an elevator somehow had a purpose, then yeah.

3/18/2006 4:06:24 AM

3/18/2006 4:09:14 AM

Quote :

"wouldn't the "elevator" be able to travel faster the further it got from the earth, seeing as there would be less gravitational pull..."

Think i saw that they were gonna beam energy to it via a laser on earth, so the farther away it got, the less energy would make it to it (unless they could make a laser with a wicked spot size), so yes and no...

I say a bigass storm comes through and rips that shit down...

3/20/2006 11:52:29 PM

Quote :

"Well, if going out into space in an elevator somehow had a purpose"

How about the progress of science?

Just struck me as a surprising criticism from an engineer.

3/20/2006 11:58:57 PM

Don't get me wrong, I think that space exploration is very interesting, but I don't think that this space elevator will provide us with the opportunity to gain more knowledge about space. In particular, going into outer space in an elevator will result in a zero-g environment and the opportunity to peek at stars without our atmosphere in the way (which, we are already doing with hubble and other space telescopes anyways).

While this has SOME potential for science, I think it is going to wind up being Carowind's "Space Needle" to the extreme. People will pay to hang out in space more than goverments will pay to have a few scientists grow plants and raise mice in a weightless environment.

To get to the true point of "scientific exploration", we are going to need to learn how to bend the laws of physics so that we can go farther/faster, more adequately sustain life where there are no resources, and then figure out what we really plan on doing when we land people on Pluto or wherever we land them. Rocks are only so interesting, no matter where they are from.

The preparation we need for this isn't going to come from a tourist attraction, it is going to come from the expenditure of EXTREME levels of time and money, levels which nobody is willing/able to sustain.

This IS exciting. I WANT to ride this thing. But as far as really using this to make major moves into space? I'm not fully convinced.

3/21/2006 1:10:46 AM

from the article in the original post:

Quote :

"And no wonder: A working elevator would reduce the cost of launching anything into space by roughly 98 percent."

^this isn't a "tourist attraction" ... it's not the size of a building's elevator. we'll be able to launch things into space faster, easier, cheaper, and safer.

3/21/2006 1:35:34 PM

right - to expand on that ^
as has been repeated many times, this isn't an 'elevator' in any normal sense of the word. Perhaps the name is a misnomer - maybe it should just be referred to as Space Ribbon, or Space Tether or something, although both of those are probably even more confusing.

But this is NOT just to serve as a 0-g environment where you can ride up, float around, snap some picks, then ride back down. This will replace all current methods of getting people and objects into space. Something like 98% of all the fuel needed for an entire space mission is used in the first 5 or 10 minuts. That's why you see a huge rocket type machine taking off from Ft. Lauterdale with 3 gigantic fuel tanks, but then only see a significantly smaller, plane-type machine landing when it returns to earth. This elevator would eliminate the need for the huge booster rockets on the shuttle. Not to mention, if you don't have to deal with all those peskey aerodynamics and drag caused by the atmosphere and gravity of the earth, you can probably build much more efficient space explorers. You put a big sphere on the elevator, ride it up a few hundred miles beyond the pull of the earth's gravity, then let it drift off into space with tiny gas propellants for steering, but hardly any needed for propulsion (at least hardly any when compared to what's needed to escape the gravitational pull of the earth).

If you don't think this can/will revolutionize space exploration, terrestrial communications, lunar colonization, etc, then you don't truely understand how it works (not that I do, but i'd like to think i'm trying).

3/21/2006 2:27:34 PM

actually,

its cape canaveral.

Not ft. lauderdale.

The yuppies in FL wouldn't want their beach view obstructed by a ball of fire and smoke.

3/21/2006 3:16:26 PM

How would you keep the thing from sheering due to horizontal moment forces?

3/21/2006 4:28:09 PM

Quote :

"we are going to need to learn how to bend the laws of physics so that we can go farther/faster, more adequately sustain life where there are no resources,"

Kind of like by building a spaceship with a big fucking nuclear reactor strapped to the back? And a ship that's big enough to sustain life for extended periods of time?

There are two things holding those back right now:
1 - Big ships are heavy. Heavy ships are too expensive to get off of earth. Solution: Some cheap way to get off earth.
2 - Nuclear reactors are full of radioactive material. When spaceships explode 5 miles up, that radioactive material gets dropped all over Florida. Solution: Some safe way to get off earth.

The Space Elevator solves both of these issues pretty damn well. (of course, we have yet to prove the safety thing, but being able to go into orbit without a gazillion pounds of liquid fire strapped to your back is a good step forward.)

3/21/2006 4:44:26 PM

[Edited on March 21, 2006 at 4:46 PM. Reason : n/m]

3/21/2006 4:46:14 PM