Space elevator in the media - dÃ©jÃ vu?

ANTIcarrot. · 2004-07-01 16:56:05

GCNR, please provide rough engineering specs and cost estimate for a ground based solar array capable of producing 43,830,000kwh per year. I am not familiar with any such project.

S = 3.6*10^7 meters
T = 86400 seconds (one day)
s = 1/4at^2 (If you want to stop at your destination)
a = 4s/(t^2)

A constant acceleration car could get to GEO in one day if it accelerated at 0.02m/s^2. I'd say that was well within our capacities, even on top of gravity. You might have to accept some loss in payload, but I see no reason why this couldn't be done.

Getting the power back to earth is difficult, but prolonged study indicates it is *only* that, not impossible. On the other paw there may be real and insurmountable problems with transmission though the atmosphere, but no one knows for sure. And after all, I did say, 'maybe'.

ANTIcarrot.

GCNRevenger · 2004-07-01 19:40:54

Sure thing, just as soon as you provide figures for all the rest of the cost of such a system...

-Designing a monsterous solar array to keep alligned with the sun

-In space assembly costs, maintence costs

-Amoratized replacement costs (from radiation/space debries damage)

-Transmitter(s) for multigigawatt energies 40,000km to the ground station you have to build, and the cost of upkeep at the station, without frying anything on or above the Earth.

-Transmitting energy from the ground station, which will occupy square kilometers, and the profit lost by transmission inefficencies versus insitu solar arrays

-Profit lost due to inefficency by atmospheric scattering

The advantage of SSPS is only about 6-8 times less area (7x in Kansas says the DOE) than regular regular, non-space-hardend, non-tracking, inexpensive, simple solar cells on the ground. And that isn't accounting for any transmission losses that an SSPS would surely incur, which will surely be on the order of 25-50% from power line resistence and beam scattering, so now you only need about 4-6x the area on the ground. The DOE figure takes into account atmospheric absortion, weather, seasonal varience, and day/night cycles

Now, I don't think a calculation of the cost comparison is really nessesarry... SSPS only saving you 4-6x the array area, for all that mess and expense of making it in space?

John Creighton · 2004-07-01 23:29:46

The really good space elevators should be like conveyer belts, continuously going up and continuously going down. Of course this would probably mean considerably more weight. Maybe if each container was spaced a mille apart it wouldn’t be so bad.

Free Spirit · 2004-07-02 04:07:02

The really good space elevators should be like conveyer belts, continuously going up and continuously going down. Of course this would probably mean considerably more weight. Maybe if each container was spaced a mille apart it wouldn’t be so bad.

It wouldn't work because the ribbon has to be tapered in order to hold itself up. There's no way to maintain the taper and have the ribbon moving in the way you describe at the same time. Anyhow, it would be a mechanical nightmare to have that thing in constant motion because the ribbon has to be moved out of the way of orbital traffic not to mention that having moving parts at the counterweight is going to cause a lot of headaches if they break down. If you want the climbers to come back down to Earth, just build a parallel se dedicated for downward traffic and an extra powerbeaming station to power the motors on the downward climbers.

Rxke · 2004-07-02 05:18:47

BTW: Great to see you back, Free Spirit!

ANTIcarrot. · 2004-07-02 06:00:23

A 1kw array in New York (or any similar location) will produce 1,300kwh in a year. In orbit, that same array will produce 8,766kwh in a direct illumination. With mirrors is can produce much more. Concentrate ten times as much solar energy and you get 87,660kwh per year. Suddenly that 6-8 increase you claim jumps to 60-80! - or more!

In space you get 144% as much sunlight, for 600% as much time, and can concentrate many times the sun's intensityon it with cheep and lightweight mirrors.

Now a 1kw panel costs $6k-$8k. But even if the space version costs another $8k to launch, and another 8k to assemble, and the ground station costs another $8k/kw to build, and half it's power gets lost in transmission, the price increase does not matter because the space panel still generates ten times as much power for eight times the cost.

You're right that power transmission and large scale space construction are unsolved problems, but that works both ways. You don't know they're impossible any more than I know they're possible.

And to ask a dumb question, if you don't think anything in space is worth doing or even remotely practical (which you seem to) what the hell are you doing here?

ANTIcarrot.

TwinBeam · 2004-07-02 21:48:18

What if space solar power were beamed down with microwaves that are easily absorbed by water, to a sealed-over artificial lake? Let the steam rise through insulated pipes, high up a mountain. Cool the steam into a man-made lake. Use the lake to generate hydropower.

CON: You lose some energy to the atmosphere
PRO: You can potentially concentrate the beam more - allowing smaller ground area
CON: Planes must not fly through the concentrated beam
CON: Possible effects beyond slight warming for birds
PRO: Built in energy storage allows 24-7-365 electricity generation, without additional loss stages.
PRO: cheap ground construction - sq meter of glass is FAR cheaper than sq meter of solar cells, should be cheaper than a rectenna array, due to smaller area.

If you chose the right area, with near continuous winds coming in off the ocean next to high mountains, you could probably just heat up a small patch of ocean, and let the moisture naturally rain out on the mountains, increasing natural hydropower to existing installations, AND helping solve water shortages. Or just use mirrors to focus a little added energy onto a very large patch of ocean where winds commonly blow on-shore. That should be quite inexpensive - though I'm sure the Greens would go nuts hearing about it.

A similar approach, over land, could be used to help boost more moisture over mountains to deserts beyond.

ANTIcarrot. · 2004-07-03 16:00:04

What if space solar power were beamed down with microwaves that are easily absorbed by water, to a sealed-over artificial lake?

That would be possible. It would be a toss-up over whether any power efficiency increase justified the additional maintinance costs.

As to the pros and cons,
You'll always loose some energy to the atmosphere. A lake won't help you concentrate the beam, that's a matter of transmitter size on the sat. Direct conversion can recieve high power/area consentration anyway. No, planes won't fly though, but there are many places where planes can't fly. A few more won't be hard to add to the navigation systems. Birds is an issue. Wind farms have reciently illustrated the need not to place obstructions on migration routes. And normal glass probably won't cut it, not if you want it to work at pressures high enough to turn turbines.

ANTIcarrot.

GCNRevenger · 2004-07-04 17:44:23

Ah yes the ol' "giant space mirrors(!!!)" argument... uh huh. Frankly, I don't buy it, I don't think that a mirror of that magnetude yet which will stand up to the harsh conditions of space for that long and be practical to operate.

Oh, and that "600% as long" thing isn't accurate, the 4.3kWh/day figure for an average cheap fixed solar panel already takes day/night cycles into account. So, the giant huge mega space SSPS system just got 600% less good...

Frankly, until somebody proves that transmission can be done with efficency, and assembly isn't going to break the bank, and you can fix the thing up there, and it will last for decade(s), and you can convince investors and insurers, then you might just have a chance... but just for the risk involved, just building it on the ground is a hard deal to beat.

Using a big dome to intentionally absorb the energy will cost you about 80-90% of the energy transmitted, since so much heat will escape the dome and a turbine arrangement is only about 30-40% efficent for thermal energy watt.

You are correct, I don't think there is anything signifigantly profitable for the people of Earth to gain in space... and the sooner people get this into their heads, the sooner the sci-fi "giggle factor" is gone.

Euler · 2004-07-05 00:47:09

Oh, and that "600% as long" thing isn't accurate, the 4.3kWh/day figure for an average cheap fixed solar panel already takes day/night cycles into account. So, the giant huge mega space SSPS system just got 600% less good...

The 600% as long is accurate, in Earth orbit you would get about 34 kWh/day of sunlight compared with 4.3 kWh/day on the ground.

Frankly, until somebody proves that transmission can be done with efficency, and assembly isn't going to break the bank, and you can fix the thing up there, and it will last for decade(s), and you can convince investors and insurers, then you might just have a chance... but just for the risk involved, just building it on the ground is a hard deal to beat.

NASA estimates that with current or near term microwave transmission, you should be able to transmit power from orbit to Earth with about 40% efficiency.

I think that if thin film solar cells are all that they are cracked up to be and if the costs of getting to orbit go down significantly, then SSP would be profitable. However, if one or both of these things does not happen, I don't see SSP being profitable.

One strategy to increase the space solar power's performance compared with ground based solar power would be to place the solar panels in close solar orbit rather than in geostationary orbit. This would make transmission of power even more difficult, but as long as it is done on a large enough scale, it should be possible to overcome this difficulty.

You are correct, I don't think there is anything signifigantly profitable for the people of Earth to gain in space... and the sooner people get this into their heads, the sooner the sci-fi "giggle factor" is gone.

What about communications satellites, Earth observation satellites, and GPS? Those are all profitable uses for space that are currently being exploited. Are they not "significant" enough for you?

ANTIcarrot. · 2004-07-05 05:43:53

Ah yes the ol' "giant space mirrors(!!!)" argument... uh huh. Frankly, I don't buy it, I don't think that a mirror of that magnetude yet which will stand up to the harsh conditions of space for that long and be practical to operate.

An optimised solar-sail is reflective, and there don't seem to be any significant problems building those. You're effectively using material that ammounts to very thin tin-foil. The mirror would be a parabolic version of that, attached to a ring of girders and kept in shape by a combination of structural support and solar wind.

Oh, and that "600% as long" thing isn't accurate, the 4.3kWh/day figure for an average cheap fixed solar panel already takes day/night cycles into account. So, the giant huge mega space SSPS system just got 600% less good...

4.3kwh is the amount of electricity generated per day (in a sunny country) based upon the fact that the sun isn't overhead all the time. For an SSPS, the sun is always 'overhead' and hence it can produce more electricity.

Maybe you should run for congress? You seem to have the required understanding of physics and mathematics.

ANTIcarrot.

GCNRevenger · 2004-07-06 12:26:14

Sounded alot like you were stating that a panel on Earth with a 4.3kWe/day capacity really only did 0.72kWe/day since it gets "600% less sun," you should be more precise.

Giant mirrors + girders = in space easy construction, light weight, high reliability. Riiight, sure thing, let me just get my checkbook out and invest in your idea right now!

Thin film solar cells? I guess you are referring to the organic ones being cooked up Euler? Trouble with those is that they can't stand up to heavy doses of radiation, and will even break down from Earth's modest UV dose after a decade or two.

40% from orbit huh? Which orbit? 200-400km LEO, or 36,000km GEO? And how much will the reciever station cost?

And I stick by my assertion that space travel is essentially without profit; communications satelites aren't really nessesarry anymore, advances in fiber optic transmissions could do the same job, plus weather or GPS satelites aren't really profitable either... The GPS system was paid for by the military, the EU/ESA/Chinese Galileo system will be gov't funded too, and so on.

clark · 2004-07-06 12:43:14

Fiber optics can't keep up with advances in technology. Every mile you lay down is another mile you have to tear up. In the big cities (which are growing), it leads to infrastructure nightmare- ownership hassles, etc.

It also dosen't solve the rural problem. Try getting a decent conncetion out in the boonies.

Don't get me wrong, fiber optics have room to grow, but the sats are unlimted. Eventually, the fiber optics is going to hit a ceiling, then sats will take over.

BWhite · 2004-07-06 13:28:13

Fiber optics can't keep up with advances in technology. Every mile you lay down is another mile you have to tear up. In the big cities (which are growing), it leads to infrastructure nightmare- ownership hassles, etc.
It also dosen't solve the rural problem. Try getting a decent conncetion out in the boonies.
Don't get me wrong, fiber optics have room to grow, but the sats are unlimted. Eventually, the fiber optics is going to hit a ceiling, then sats will take over.

Large balloons doing figure 8's at 100,000 feet offer wireless telecom without the need for satellites. Easier to repair, also.

GCBRevenger's main point is one I have agreed with for quite a while. Profit motive, in any narrow sense of that phrase, is not sufficient to justify expansion into space.

Over time (decades, centuries) expansion into space will very greatly grow the total human economy, but that is something different, IMHO.

Rxke · 2004-07-06 13:46:29

http://www.mit.edu:8001/people/gassend/ … html]Notes on the 3rd conference

Weathersats not profitable?

Try to imagine life w/o them, no long term predictions, no storm-warnings, this alone is billions worth for insuance etc...

GCNRevenger · 2004-07-06 14:45:30

I think you (vastly) underestimate the capacity of fiber optics, with the coming optical switches and multi-wavelength/multi-beam trancievers... the amount of bandwidth FO cable can push is vast compared to bouncing radio waves off birds at GEO.

Weather satelites? And how big of a market is there for them? How many do we need? How often are they replaced... and so on. They are a small subset of an already small market.

Timeslicer · 2004-07-07 00:36:00

As to the pros and cons,
You'll always loose some energy to the atmosphere. A lake won't help you concentrate the beam, that's a matter of transmitter size on the sat. Direct conversion can recieve high power/area consentration anyway. No, planes won't fly though, but there are many places where planes can't fly. A few more won't be hard to add to the navigation systems. Birds is an issue. Wind farms have reciently illustrated the need not to place obstructions on migration routes. And normal glass probably won't cut it, not if you want it to work at pressures high enough to turn turbines.

I agree that the CONs seem weaker than the PROs. What I'm not sure of is whether this approach would in some way be better than conventional space solar power concepts, or an equal area of ground solar cells. The main advantages seem to be that it uses cheaper materials in the collector and has built in energy storage. So if you had a city that used solar power to run things during the day, you could use a system like this to provide power at night, without needing to use electricity to pump water up the mountain at a considerable additional energy loss.

I would not expect it to use steam pressure to turn turbines - the main proposal is simply to let the hot moist air rise up a mountain through convection, cool off, condense, and fill a lake for hydropower production.

Algol · 2004-07-07 09:07:46

If you combined it with a http://www.enviromission.com.au/index1.htm]Solar Power Tower then youd definately be onto something. EnviroMission, through this project, would validate most of the concepts and technologies - all youd need to do is 'extend' the tower up the side of a mountain and add cooling facilities at the top.

An added bonus is that moist air is denser than dry air and would as such deliver more power to the turbines on the way up.

EDIT:

BTW, im not envisaging using SPS in this arrangement - just the power of the sun. Whilst im not sure of the efficiencies of incorporating SPS im sure it would work to boost the power - but at what cost.

John Creighton · 2004-07-07 09:15:12

I think you (vastly) underestimate the capacity of fiber optics, with the coming optical switches and multi-wavelength/multi-beam trancievers... the amount of bandwidth FO cable can push is vast compared to bouncing radio waves off birds at GEO.

What about sat phones, sat internet and cable for the pack seat of the car. Granted one can use micro waves or fiber optic rf links but this requires much more infrastructure to reach all the rural areas.

ANTIcarrot. · 2004-07-08 06:23:14

I'd agree about the 'narrow definition of profit' bit. SPS construction *would* be profitable, but building the first one would cost somewhere in the reigon of $75B. Building 4 would cost $120B total, and they would pay for themselves after 24 SPS-years of operation. With an average SPS life of ten years, the four of then would produce $80B profit. After that an SPS would cost $25B and generate roughly the same amount of gross profit.

So yes, it can be 'profitable', but the sums involved are way outside the range of current industry. The government could, with some commercial participation. And IMHO, it's a better way to spend money than $300B for mars, or $70B for Iraq, or $60B for the F22 for that matter.

ANTIcarrot.

Euler · 2004-07-08 20:56:03

Thin film solar cells? I guess you are referring to the organic ones being cooked up Euler?

I think so. They are supposed to be less than 10% efficient, but still have a specific power more than 10 times greater than conventional solar cells.

40% from orbit huh? Which orbit? 200-400km LEO, or 36,000km GEO? And how much will the reciever station cost?

From GEO. Actually, it is probably easier to transmit power efficiently from GEO than from LEO becuase it is still not really that far away and targeting is easier due to being at rest with respect to the surface of the Earth.

It is hard to find a good estimate on the cost of the receiving station. However, even if it is fairly cheap, you still need much lighter solar cells and significantly lower launch costs for solar cells at GEO to be cost effective in supplying power to Earth.

I think that it would probably be more cost effective to put the solar cells in a close solar orbit rather than at GEO due to the much greater intensity of the sun's light there. The main question is how much heat and radiation can the solar cells be made to withstand. The easiest way to transmit power would send laser light or microwaves to mirrors/lenses in GEO that would redirect it to a receiver on the Earth. The optics at both the transmission station and GEO must be very large (100+ meters diameter) and their size is dependent on the wavelength of light being used and the Raleigh Criterion. Fortunately, the lenses can be very thin and light, and their size is independent of the amount of light being transmitted. This means that you could not start on a small scale for a project like this (the lenses would make up to large of a portion of the total mass), but if there is a really large investment it could be practical. The requirements of generating power in close solar orbit are also very similar to what you would need to launch a beam-propelled sailcraft, so working on this technology could also lead to interstellar probes.

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Re: Space elevator in the media - dÃ©jÃ vu?

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