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I was looking at the solar chimney pictures, and thought that if you ran a track from the base to the tip, and used the 200 Megawatts the chimney produced to power a magnetic mass driver, you could concievably lift payloads into orbit. Does anyone know how to do the math on this?
After some thought,
I realised that the Solar Chimney Satellite Center has two functions.
1) to replace the first stage of a rocket
2) to turn water into hydrogen, to fuel subsequent stages of the rocket.
Alternately, you could use these chimneys simply to produce hydrogen for rockets, and the hydrogen economy in general...
Solar Chimney
http://www.wired.co...,1282,46814,00.html
may become the world's tallest structure... [dbsousa, Oct 04 2004, last modified Oct 06 2004]
potential of heliostat fields
http://www.meike.co...um/papers/Schr1.pdf
[rpardell, Oct 04 2004, last modified Oct 06 2004]
figures for an heliostat field in Spain
http://www.solarpaces.org/ps10.htm
Notice this heliostat field uses thermal storage. [rpardell, Oct 04 2004, last modified Oct 06 2004]
Orbital Motion explained
http://www.physics....ys2081/circular.htm
Lots o' math, git yer orbital mechanics heyah [BunsenHoneydew, Oct 04 2004, last modified Oct 06 2004]
Basic physical formulae
http://thinkzone.wl...m/Physics/Units.htm
Things every 1/2baker should know, F=ma etc. [BunsenHoneydew, Oct 04 2004, last modified Oct 06 2004]
[link]
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Launch to lift load into orbit:
mass 2000 kg
orbit height 320000 m
gravity 10 m/sec^2
energy lift to orbit 6400000000 Joule
energy lift to orbit 6400 MegaJoule
Once in orbit it needs a whack from the side
to start spinning around earth and stay up there:
orbit time 5400 sec
orbit length 42000000 m
orbit speed 7778 m/sec
kinetic energy in orbit 60493827160 Joule
kinetic energy in orbit 60494 MegaJoule
total energy 66894 MegaJoule
solar power plant 200 MegaWatt
time to generate the energy 334 seconds
Result: You can generate the energy in about 5:30 minutes.
But: Most energy would have to go into the side whack.
Problem: How do you get the whack energy up there?
As far as I know the side whack problem has gotten in the way of many cannon launch projects. You could launch at a low angle instead of vertical, but then you would have a lot more air drag on the way. |
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maybe turn this into a half-bake idea on how to solve the side-whack problem: |
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overshoot the height you're looking for.
on the way back down, you're going to build up a lot of kinetic energy that you might be able to use to go off to a side. There likely wouldn't be much fluid available for it, but with very little other forces available... hmmm.... |
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Think of pushing a piece of flat paper 100 meters in the air, and as if falls down, it can float @ 50 meters sideways. |
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If you don't have enough fluid forces, you might use magnetic forces. If there's no fluid friction at the height you're working, then turn on an electric-driven magnet to polarize your satellite and then be blown to a side by the earth's magnetic field.... |
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[sophocles] That could actually work, skim off the upper layer of the atmosphere. You would need a lot less energy to give the vehicle the final touch to move into a stable orbit. |
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Hurry up, get a half patent and charge NASA half an arm and half leg for half royalties (would that be duchies?). |
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Why not just add a bottle of compressed air to the satalite to push it off to the side? Isn't that how the space shuttles maneuver (more or less)? |
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We've done cannon-to-space ideas before. The general concensus is that it's possible, but how much stuff can withstand being shot out of a cannon? |
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--how much stuff can withstand being blown out of a cannon.... |
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well if that's the problem, then how about shooting a cannonball out of the cannon, and attaching a less-forgiving payload to the cannonball with an energy-storing/absorbing cord (ok, bungee cord). Once high enough, you can sever the cord for better control. |
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I think Wile E Coyote must have done something quite similar... |
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In the article attached on the solar chimmney it stands an output of 200MW for a 2,5 miles diameter plant. |
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This points to a very low output/surface ratio compared to any solar conversion technology. The theoretical maximum for such a hugue surface is around 20GW. Given present standard "low" efficiency figure for photovoltaics of 10% you would get 2GW, and if using a field of heliostats and a hot tower this would increase to at least 4GW. |
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Looks like much more realistic (and cheap and enviro friendly) covering such a surface with heliostats and obtaining 4GW instead of 200MW (20 times more!). |
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I even don't opine about the spacecraft side of this idea. |
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<gross error check> The track is fixed to the outside of the chimney right? So that the rocket doesn't crash into the turbine on the way up? |
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(rpardell) I would like to look at the solar information you mentioned. Please provide a link. I was under the impression that the solar chimney would provide constant power day and night, making it more useful as a power plant than a solar array, but I would like to read an opposing viewpoint...
(stupop) The launcher would be on the outside, carefully positioned so as not to collide with the roller coaster (link). |
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How do conventional satellites get a side whack? Those Titan rockets look like all the whack they provide is straight down. |
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[UB] I believe the "whack" issue discussed is the energy required to accelerate a ship in a horizontal direction up to a speed where it will attain orbit. If you shoot it straight up it will fall straight down. |
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The day and night problem is better solved by converting excess power into hydrogen by day and coverting hydrogen back to electricity by night through fuel cells. Standard efficiency of hydrolisis is 70% and efficiency of best fuel cells is near 60%, so this way you still get near 50% of surpluss day energy by night. Using an heliostat field of 20% efficiency you still have an all around efficiency over 10%, and this is an order of magnitude better than the meagre 1% figure that the greenhouse system offers. |
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I think the greenhouse system could only make sense when you consider it together whith its biomass generation ability, in this case figures may change dramatically, but i don't have any information on this. If you would burn the generated biomass retrofeeding the resulting CO2 to the greenhouse you would have more electrical output and an even better biomass growth rate. |
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Alternativelly the greenhouse biomass product could be orientated to human consume, and this might be competitive in certain areas of the planet. |
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Imagine it in Mauhrithanian Sahara, near the sea, and well provided of seawater: You produce crops for Africa and bottled energy in the form of hydrogen for Europe. |
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What is not clear to me is if there is an scale effect on efficiency. I mean, apart from the space ramp idea, why should the greenhouse be so gigantic? (and therefore unrealistic) Would it not be better the possibility to create many medium sized systems? |
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[stupop] and [dbousa] the turbines
are at the base of the tower. |
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[kbecker] "Result: You can
generate the energy in about 5:30
minutes." |
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But where am I going to find a 66
gigajoule capacitor... leftover from
a Tokamak? |
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Let's say we do away with the two-
tonne payload, and aim for much
smaller microsatellite missions.
Say a 200kg solid fuel sounding
rocket with a 2kg payload. The
power station could supply
the railgun/maglev thingy in
realtime (launching at night for an
offpeak discount), and the
sounding rocket would act as the
second/third stage to provide that
lateral orbital velocity. The track
and associated infrastructure
could be a lot lighter too, and
easier to design as a bolt-on for
the tower. |
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A third approach would be to start
from the power available in
realtime, and work backwards to
the possible payload. Back of the
envelope, here I come. |
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[rpadell] The light plastic or glass
covering of a greenhouse is a lot
cheaper than PV panels, probably
powers of ten cheaper than 20%
efficiency cells, and you
can grow plants under it. And PV
will only work during the day, so
you'd need expensive storage
infrastructure rather than the
cheap dirt thermal mass under the
greenhouse. |
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One thing we have plenty of out
here is land, so it doesn't really
matter if it is big, just so long as
it's cheap. It could also be one of
those things which actually gets
more economic the bigger it is. |
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The people putting this project up
must have done their sums.
According to their website, some
bank must have done them too,
because they've just received
funding. It's based on a previous
80 megawatt station in Spain
which ran for many years. |
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As to the spaceship, I say hang it
under a parachute and send it up
the inside of the chimney. It won't
get you all the way to orbit, but a
conventional second or third stage
should do it. |
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Or use the track to launch a glider,
whose wings pop out when it
reaches azimuth. It won't be
orbital, but it should glide a hell of
a long way. |
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I've got a feeling this tower is
going to be a magnet for gliders,
hang gliders and paragliders. Can
you imagine the thermal? |
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Near-earth orbital velocity (from
link): 8000m/s (7900 rounded off)
Track length: 1000m
Initial velocity: 0m/s
=> Average velocity = 4000m/s
=> Time on track = 0.25s |
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Power (2x10^8 W) x time (0.25s)
= kinetic energy (Ek) imparted to
payload
= 5x10^7 Joules |
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Ek = mv^2/2 (from other link),
solve for m: |
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m = 2Ek/v^2
= 1x10^8/(8000*8000)
= 0.78125 kg |
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So roughly a two-pound payload
could reach the ISS's orbit, if it
could withstand 6,400 Gs of
acceleration. |
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Note I'm making no allowances for
inefficiency or for converting all
that vertical motion to horizontal. |
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If you could build a long almost-
horizontal track you'd be better off
because you could apply the
200MW to the payload for a much
longer time. It seems payload
and length are directly
proportional, all else being equal.
IE a 10km track will launch a 7.8kg
payload at a mere 640 Gs. |
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But then you've just got another
railgun to space which could be
sited anywhere and powered from
any large power station. |
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I think the SCSL would be most
useful for sub-orbital payloads,
like high altitude scientific
instruments, where sounding
rockets are used today. |
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Reaching 100km straight up and
down would require leaving the
tower at 2000m/s. Dropping that
in, I get a 100kg payload
subjected to 200 Gs, using all the
station's available power for one
second at 100% efficiency. |
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The thing I personally most want
to launch from the solar chimney
is myself on a paraglider. |
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Is this correct?
When the mass rises, it initially starts off with a horizontal velocity which is the same as the earths surface. When it is elevated, it is still travelling with a horizontal velocity which is the same as the earth. But now, it has further to travel, so it will trail behind the earths rotation. As the mass reaches the top of the elevator, it will drag the elevator over.
The shape would look something like those night sky photographs where the material spirals out.
So for an elevator to work, doesn't it have to accelerate the mass in a horizontal direction as it is lifted?
Assuming this problem could be solved, I have a proposal:
The "chimney" is high enough so that the top is in a partial vacuum (320km or so). So evacuate the air! When it is empty of air, insert your object. Then let the air in the bottom as quickly as you can. The air will rapidly travel up the chimney, pushing the object in front of it. Like an air rifle, except no air is in front of the "pellet" to give friction.
Terminal velocity, I suppose, would only be the speed of sound. (Correct?). |
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[BunsenHoneydew] I think you're right, somebody should post a link to a basejumping site. Not me, I'm tempted but too scared. |
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If you are looking for a sideways kick. Would it be possible to have some rifling in Your canon Like in a gun where the bullet comes out spinning? |
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But that would just spin you, not kick you sideways. |
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