Space Elevator

[Aeronaut]

The Japanese research story that Brian linked to above doesn’t seem to think that impact is going to be a show-stopper. Tethers.com uses a hybrid approach similar to launching and recovering small planes from a blimp. And unless they use a rigid tether, I don’t understand how their tether could restore the momentum transferred to the payload.

[Brian H]

Aeronaut wrote: That could shield the tether, but how would the drive wheels get their traction?

No, no; the aerogel is a hollow tube with the ribbon well inside. I specified a .5km dia. space in the center for the actual cable, etc. The function of the aerogel is just to intercept debris, and is never in contact with the core ribbon except for anchoring fibers/cords that hold it at a fixed distance. Or SLT (insert hand-waving here. 😉 )

Traction is its own issue, altogether. Electromagnetic, ratchets, whatever works. :cheese:

[Breakable]

I would like to point out that the only reason a space elevator makes sense is due to the inefficiency of current rocket engines and the total costs (environmental and energetic) of producing rocket fuel. Space elevators purpose is just to reduce the price of delivering loads to orbit.
In case we have cheap energy and/or reaction-less drives and/or cheap easy to produce environmentally friendly fuel (aluminium rockets are being tested now) space elevator becomes more of a attraction than practicality. Yes it would be nice for kids to take an excursion to, but in case you could buy semi-orbital flight for ~1000 usd, it becomes less of an interest.

[Aeronaut]

What does SLT stand for, Brian? The aerogel tube sounds like a great start. Especially if they can deflect most junk.

Breakable, I agree that the goal is to reduce the cost of getting a specified amount of freight to and from orbit- which can and should be interpreted as an orbit relative to at least our sun, to enable the system to initiate ballistic transfer orbits. But until a ship’s drive can eliminate the need for rockets and heat shields, I doubt they’ll be really useful for anything other than really heavy lifting and or 8 minute access to orbit due to the enormous mass handicaps that they leave the drawing board with.

[Brian H]

Aeronaut wrote: What does SLT stand for, Brian? The aerogel tube sounds like a great start. Especially if they can deflect most junk.

Breakable, I agree that the goal is to reduce the cost of getting a specified amount of freight to and from orbit- which can and should be interpreted as an orbit relative to at least our sun, to enable the system to initiate ballistic transfer orbits. But until a ship’s drive can eliminate the need for rockets and heat shields, I doubt they’ll be really useful for anything other than really heavy lifting and or 8 minute access to orbit due to the enormous mass handicaps that they leave the drawing board with.

SLT is web-acronymics for “Something Like That”. YCLIU (You Can Look It Up). :cheese:

Aerogel wouldn’t deflect, it would collect, absorb. One concern I have, tho’, is that it is gas-filled, and I wonder how it would fare in vacuum. Would the gas simply leak away, leaving it limp and flimsy? Would it expand hugely and burst? Perhaps if it was “inflated” in orbit with just enough gas to give it shape …

IOW (In Other Words) it may not be suitable for naked exposure, without being contained in some kind of sealant, etc.

[Brian H]

Breakable wrote: I would like to point out that the only reason a space elevator makes sense is due to the inefficiency of current rocket engines and the total costs (environmental and energetic) of producing rocket fuel. Space elevators purpose is just to reduce the price of delivering loads to orbit.
In case we have cheap energy and/or reaction-less drives and/or cheap easy to produce environmentally friendly fuel (aluminium rockets are being tested now) space elevator becomes more of a attraction than practicality. Yes it would be nice for kids to take an excursion to, but in case you could buy semi-orbital flight for ~1000 usd, it becomes less of an interest.

Tourism is not the point. Projections suggest a marginal cost to orbit (not just sub-orbit) of as low as $20/lb (and FF could seriously slash that). That is orders of magnitude lower than even optimistic fueled boost projections. Energy-wise, “Once you are in orbit, you are half-way to anywhere”.

As for reactionless drives, that’s way too deep in free energy perpetual motion territory for my mind. The Mach Effect is pure physics bootstrapping. IBIWISI (I’ll Believe It When I See It).

[Aeronaut]

I was wondering if I’d missed a jargon term. Been a while since I’d actually looked into how an elevator might be built, deployed, and operated, and I never did see anything reasonably current.

If aerogel’s a good electrical conductor, a mag field effect might keep it up.

[Brian H]

Aeronaut wrote: I was wondering if I’d missed a jargon term. Been a while since I’d actually looked into how an elevator might be built, deployed, and operated, and I never did see anything reasonably current.

If aerogel’s a good electrical conductor, a mag field effect might keep it up.

The solids used in aerogels vary widely. They range from silicon with or w/o fibreglass, etc., to carbon. No metals, AFAIK.

[emmetb]

The Japanese research story that Brian linked to above doesn’t seem to think that impact is going to be a show-stopper.

Do they also say why not? 😉

Tethers.com uses a hybrid approach similar to launching and recovering small planes from a blimp. And unless they use a rigid tether, I don’t understand how their tether could restore the momentum transferred to the payload.

Now that you mention it, i must admit that when i posted the link i hadn’t the foggiest idea how their system really works. 8-/

So i took a second look at it: they certainly don’t seem to be using a rigid tether, instead it is two masses connected by the tether that form a rotating two-body system. Then when they grab something at the base of the rotation and let it go at the apex momentum gets transfered from this two-body system to the payload. They say they can boost the orbit of the facility by simply riding the earth’s magnetic field by running a large current through the tether itself.

Now i wonder if another way to boost the facility orbit would be for the facility to climb the tether when it is at the base of the rotation. Maybe this way momentum can be transfered back into orbital velocity while shortening the cable (and the time it is exposed to debris).

[Aeronaut]

The tether needs to be at least 100 times stronger than steel (I know this lacks precision in defining which characteristics- sorry) and apparently the carbon nanotube weave can or will soon be able to do that, according to the article.

One issue that hasn’t been pointed out, since nobody details their SWAGs (Rematog’s term Silly Wild Asked Guess), is the cost of the tether itself and the various overhead involved in replacing it on a regular basis. I’m guessing that the real budget-busters are freight aboard the chemical rocket required to loft the first tether, along with the structures at both ends and the incremental research programs. Replacing the tether every year or few might turn out to be cheap insurance.

[zapkitty]

… er…

… 30 short tons to orbit would be 60000lb @ $20/lb = $1.2 million… fusion SSTO costs to orbit should be cheaper than that and with a vastly less expensive infrastructure.

My stated reservations about the viability of fusion SSTO will only be valid for the short term after the introduction of fusion powerplants… and even the most optimistic beanstalk is a long term project…

[Brian H]

zapkitty wrote: … er…

… 30 short tons to orbit would be 60000lb @ $20/lb = $1.2 million… fusion SSTO costs to orbit should be cheaper than that and with a vastly less expensive infrastructure.

My stated reservations about the viability of fusion SSTO will only be valid for the short term after the introduction of fusion powerplants… and even the most optimistic beanstalk is a long term project…

That’s quite a “should be”. But very positive, if true. OTOH, the infrastructure costs should also take a big hit (drop) if power gets nice and cheap.

For an even funner possibility, look up “rotovator”. Dramatic!

[vansig]

the material to use is Colossal carbon tubes. these macro-scale fibres have the longest known breaking length. they are stronger, by weight, than nanotubes.

http://www.mse.ncsu.edu/research/zhu/papers/CNT/PRL-CCTs.pdf
http://physicsworld.com/cws/article/news/35364

[Breakable]

Another major issue I see with Space Elevator besides the tether material is its throughput. What is the planned speed and the amount of payload it can deliver?
If we say that it can deliver a few tons of payload per day,
then the infrastructure costs (especially with alternative cheaper-than-currently methods) will be a very long term investment
and might not even pay for itself.

[Aeronaut]

Breakable wrote: Another major issue I see with Space Elevator besides the tether material is its throughput. What is the planned speed and the amount of payload it can deliver?
If we say that it can deliver a few tons of payload per day,
then the infrastructure costs (especially with alternative cheaper-than-currently methods) will be a very long term investment
and might not even pay for itself.

My understanding is moving 30 ton loads (probably gross earth weight) at 120 mph most of the trip, for a 30 to 45 minute trip each way. Say 720 gross tons per day for a guesstimate…

[Author]

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