Author Topic: Space application of very high structures  (Read 4497 times)

Online Eerie

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Space application of very high structures
« on: 01/25/2011 07:37 PM »
Some theoretical musing.

How high a structure can we build, using existing materials? Current record is just 828m, but no one ever tried to do "height for height's sake".

For example, if we can reach 50km, the atmosphere is almost negligible, 0.1% atm. Launching rockets from such structure won`t give much benefit, if you count the trouble of lifting one to the top, but how about putting a telescope on top of it? I suppose you could put Hubble out of business.

Offline rklaehn

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Re: Space application of very high structures
« Reply #1 on: 01/25/2011 07:45 PM »
Some theoretical musing.

How high a structure can we build, using existing materials? Current record is just 828m, but no one ever tried to do "height for height's sake".

For example, if we can reach 50km, the atmosphere is almost negligible, 0.1% atm. Launching rockets from such structure won`t give much benefit, if you count the trouble of lifting one to the top, but how about putting a telescope on top of it? I suppose you could put Hubble out of business.

If you would be able to launch a rocket from 50km, you would be able to use higher expansion ratio and thus get better specific impulse. You would also not have to care about aerodynamics, so your vehicle could consist of spherical tanks and have no payload fairing.

But compared to building a 50km high structure, even an SSTO RLV development program would be pocket change.
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Offline KelvinZero

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Re: Space application of very high structures
« Reply #2 on: 01/27/2011 09:10 AM »
One thing I have wondered about, Could we use lighter than air techniques to construct buildings with the exact density as their surrounding air. The bottom layers could be quite study and the top somewhat akin to weather balloon structures.

It seems to me the larger you build a balloon, the better the ratio between volume and surface which helps with retaining heat for lift, allows heavier materials and makes leaks less fatal.

Offline jee_c2

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Re: Space application of very high structures
« Reply #3 on: 01/27/2011 10:08 AM »
Actually there is a developement, what is described by KelvinZero.
I find the link...
Now, I don't find it, but here is another link:
http://www.universetoday.com/72317/astronomy-without-a-telescope-space-towers/

Offline jee_c2

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Offline mdo

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Re: Space application of very high structures
« Reply #5 on: 01/27/2011 01:11 PM »
[...] how about putting a telescope on top of it? I suppose you could put Hubble out of business.

While it would be a great viewing spot above the weather and for the public it would not necessarily be so attractive to professional astronomers. Space observatories not depending on the Shuttle moved further and further away from Earth's background noise/radiation to GEO (SDO), L1/L2 (Soho, Herschel/Planck, JWST etc.) and even solar orbit (Kepler). Also, the next class of ground based optical telescopes is in the 20-40 meter range weighing many 1000s of tons. They make up for many disadvantages by means of adaptive optics, interferometry, high mountain sites and sheer size of collecting area. Regarding Hubble: It is specifically known for its high pointing accuracy (a few milliseconds of arc). That is tough to achieve on a moving platform like the top of a tall building. Meteorologists, on the other hand, might love to put their sensors up along the structure to measure vertical profiles.

Offline agman25

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Offline mdo

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Re: Space application of very high structures
« Reply #7 on: 01/27/2011 01:56 PM »
http://www.sofia.usra.edu/index.html

So, how does SOFIA compare to Hubble's 7 mas rms system requirement?

Offline agman25

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Re: Space application of very high structures
« Reply #8 on: 01/27/2011 02:40 PM »
http://www.sofia.usra.edu/index.html

So, how does SOFIA compare to Hubble's 7 mas rms system requirement?

The point was that useful science can be done at high altitudes. Not everything has to match the Hubble.

Offline gospacex

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Re: Space application of very high structures
« Reply #9 on: 01/27/2011 07:22 PM »
I believe with today's tech it's possible to build 10 km high structures. No exotic materials needed: only 1% of the area at the bottom will be used up by supporting metal structure if you'd use steel. (In ordinary skyscrapers the proportion is much, much smaller than 1%)

Offline kkattula

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Re: Space application of very high structures
« Reply #10 on: 01/28/2011 06:09 AM »
I believe with today's tech it's possible to build 10 km high structures. No exotic materials needed: only 1% of the area at the bottom will be used up by supporting metal structure if you'd use steel. (In ordinary skyscrapers the proportion is much, much smaller than 1%)

Tough gig for the construction workers as it starts to get into thin air. They'd have to carry oxygen and dress like Everest climbers.

My idea is to build from the top down.  i.e. Build a high altitude platform and all the buildings/facilities it needs, on the ground first, then jack it up 10 m and add the first layer of open framework supports. Repeat 3000 times.

I like 30 km as the height. From there a rocket can have a high expansion nozzle, and stiil be non-aerodynamic since it will be at 50+ km before it aquires significant velocity.

The big issue is, how do you stabilise the tower during construction as the base gets wider as it goes higher. Some sort of massive, sliding foundation blocks? Spreading out like spokes from a central point for kms, adding new ones as the diameter of the base increases.

Offline A_M_Swallow

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Re: Space application of very high structures
« Reply #11 on: 01/28/2011 01:29 PM »
{snip}

The big issue is, how do you stabilise the tower during construction as the base gets wider as it goes higher. Some sort of massive, sliding foundation blocks? Spreading out like spokes from a central point for kms, adding new ones as the diameter of the base increases.

It is a bad idea to move the foundation blocks whilst they are under load.  As the tower gets taller add more foundation blocks to the outside of the base.  To take the extra weight the foundations may need to get deeper.

It may be possible to reuse the inner blocks when they are no longer under load, that will be a cost of new blocks Vs. cost and risk of reuse trade off.

Offline jee_c2

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Re: Space application of very high structures
« Reply #12 on: 01/29/2011 10:37 AM »
...
My idea is to build from the top down.  i.e. Build a high altitude platform and all the buildings/facilities it needs, on the ground first, then jack it up 10 m and add the first layer of open framework supports. Repeat 3000 times.
...
Not that good - and possible idea: just think, what should be the mass to lift, when the tower is almost ready? How would you solve that?

What I linked was the idea of building the structure from higher pressure inflated walls, which are lighter than air (or about the denisity of air).

For telescope such a tower it is not usable (because of the movements of the top), I think.

Offline frobnicat

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Re: Space application of very high structures
« Reply #13 on: 01/31/2011 09:53 AM »
Some theoretical musing.

How high a structure can we build, using existing materials? Current record is just 828m, but no one ever tried to do "height for height's sake".

For example, if we can reach 50km, the atmosphere is almost negligible, 0.1% atm. Launching rockets from such structure won`t give much benefit, if you count the trouble of lifting one to the top, but how about putting a telescope on top of it? I suppose you could put Hubble out of business.
If it's possible to reach such altitude with a pipe evacuated from ground to top, why not build a high throughput (contactless) ultra small payload  electromagnetic gun that shoots "pellets" of usefull bulk material above 8km/s? With a ground based space catapult one has to send relatively big payloads with thermal shield to cross atmosphere : huge investment for the catapult and lost energy. Maybe it's possible to economically integrate navigation hardware and MEMS microthrusters into cheap, lighter that 1kg, nanosats able to "dock" (be grabbed) to high orbit stations. Or even smaller, passive pellets < 1gram, maybe sent in clusters linked by a thin thread to be retrieved by on orbit small fleet of robots. The thread is used only to keep pellets linked while in ballistic trajectory, though it has to accomodate its own weight while unfolding between two successive pellets in the accelerating part of the gun, which means no more than a few tens of meters between pellets, at least 100 pellets a second. The electromagnetic gun would be mainly ground based, only a very thin evacuated pipe has to reach 50km (but has to remain very straight, probably needs active control against wind...).

Offline Nomadd

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Re: Space application of very high structures
« Reply #14 on: 01/31/2011 11:27 AM »
 I think you might want to think about the loads when the jet stream hits that sucker ata 45,000 feet. Try Googling "Archimedes"

Offline frobnicat

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Re: Space application of very high structures
« Reply #15 on: 01/31/2011 01:37 PM »
I think you might want to think about the loads when the jet stream hits that sucker ata 45,000 feet. Try Googling "Archimedes"
Archimedes ? You mean buoyancy ?
Wind loads are obviously big problem with tall structures. Dont know much about very thin very tall guyed masts but with a 1cm diameter pipe 1mm walls in Al alloy and assuming 30m/s winds @ 10km altitude approximate figures yield : 90g/m linear mass of tubing, 1.6N/m of lateral force that can be guyed at 45░ with 60Ám kevlar thread (including safety margin >x3) that weighs around 50g (down to the ground). To acomodate winds, guy lines would represent a significant mass ratio of the whole structure but it is not orders of magnitude out of range. Not yet speaking of wind drag of the guy lines themeselves though... moreover it might not take bad wether (irregular gusts of wind, rain, and lightning). A very light very thin structure might be rolled/unrolled ? With guy lines anchoring points runing on 3 or 4 railways extending 50km sideways on the ground ??

Offline Nomadd

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Re: Space application of very high structures
« Reply #16 on: 01/31/2011 02:07 PM »
 I mean leverage. Both on the tower and the guys, if you used them. No concievable guy would be anything like taut at that length. They'd be blowing all over the place. And if it wasn't guyed, you'd be able to tilt Texas with a lever that height. No practical base could be that strong.

Offline gospacex

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Re: Space application of very high structures
« Reply #17 on: 01/31/2011 02:42 PM »
I think you might want to think about the loads when the jet stream hits that sucker ata 45,000 feet. Try Googling "Archimedes"

Anything that high will probably need to be built in the shape of the letter A (3D of course...)

Offline frobnicat

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Re: Space application of very high structures
« Reply #18 on: 01/31/2011 03:30 PM »
I mean leverage. Both on the tower and the guys, if you used them. No concievable guy would be anything like taut at that length. They'd be blowing all over the place. And if it wasn't guyed, you'd be able to tilt Texas with a lever that height. No practical base could be that strong.
Ok that a thin structure is clearly not rigid enough to cope with the lever, it would bend and collapse no matter the base. So it's necessarily guyed, at closely spaced intervals. Agree that it puts the problem on the guy lines and I haven't say this would be a piece of cake. Very rough estimates give a Reynold number ~100 for a 50Ám wire in 30m/s wind, hopefully that's laminar flow and if we are out of the quadratic wind speed formula to the viscous linear one thats on the order of (again very roughly because I dont master the subject) 10N lateral which means even more in tension depending on sag. And my line was supposed to cope with 1.6N (+ its own weight). Yet it's not orders of magnitude out of range. For compensating the problem of sagging lines blowing everywhere some carefully thought geometry (triangulated meshwork?), trying a freely rotating streamlined profile around the pipe to reduce drag in the first place (a factor of 5 might be possible), an optimal place with stable winds (and few people in a 100km radius)...

That and my 1cm pipe is supposed to be actively controlled within a millimeter of a laser straight line on its 50km length, maybe with fast ultralight shape memory alloy local actuators + slower guy lines length/tension control. Mmh. Isn't it "advanced concepts" ?

Offline frobnicat

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Re: Space application of very high structures
« Reply #19 on: 01/31/2011 04:00 PM »
I think you might want to think about the loads when the jet stream hits that sucker ata 45,000 feet. Try Googling "Archimedes"

Anything that high will probably need to be built in the shape of the letter A (3D of course...)

Eiffel tower ? 300m is a bit short of stratosphere, though it might reach that with very high specific strength materials... But it's a huge mass, why I suggested a more 1D structures with only guy cables as lateral stabilizers. A needle like structures could puncture the atmosphere for less than 10 tons total weight and still inject 100s tons of (admittedly hard to use) millions pellets at escape velocities at the price of kWh.

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