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...-- dbsousa, Aug 28 2003 Solar Chimney http://www.wired.co...,1282,46814,00.htmlmay 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.htmNotice this heliostat field uses thermal storage. [rpardell, Oct 04 2004, last modified Oct 06 2004] Orbital Motion explained http://www.physics....ys2081/circular.htmLots 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.htmThings every 1/2baker should know, F=ma etc. [BunsenHoneydew, Oct 04 2004, last modified Oct 06 2004] 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.-- kbecker, Aug 28 2003 maybe turn this into a half-bake idea on how to solve the side-whack problem:
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....
Think of pushing a piece of flat paper 100 meters in the air, and as if falls down, it can float @ 50 meters sideways.
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....-- sophocles, Aug 28 2003 [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.
Hurry up, get a half patent and charge NASA half an arm and half leg for half royalties (would that be duchies?).-- kbecker, Aug 28 2003 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)?-- Katt, Aug 29 2003 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?-- phoenix, Aug 29 2003 --how much stuff can withstand being blown out of a cannon....
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.
I think Wile E Coyote must have done something quite similar...-- sophocles, Sep 02 2003 In the article attached on the solar chimmney it stands an output of 200MW for a 2,5 miles diameter plant.
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.
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!).
I even don't opine about the spacecraft side of this idea.-- rpardell, Sep 03 2003 <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?-- stupop, Sep 03 2003 (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).-- dbsousa, Sep 03 2003 How do conventional satellites get a side whack? Those Titan rockets look like all the whack they provide is straight down.-- bungston, Sep 03 2003 [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.-- Worldgineer, Sep 03 2003 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.
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.
Alternativelly the greenhouse biomass product could be orientated to human consume, and this might be competitive in certain areas of the planet.
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.
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?-- rpardell, Sep 04 2003 [stupop] and [dbousa] the turbines are at the base of the tower.
[kbecker] "Result: You can generate the energy in about 5:30 minutes."
But where am I going to find a 66 gigajoule capacitor... leftover from a Tokamak?
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.
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.
[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.
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.
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.
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.
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.
I've got a feeling this tower is going to be a magnet for gliders, hang gliders and paragliders. Can you imagine the thermal?-- BunsenHoneydew, Dec 20 2003 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
Power (2x10^8 W) x time (0.25s) = kinetic energy (Ek) imparted to payload = 5x10^7 Joules
Ek = mv^2/2 (from other link), solve for m:
m = 2Ek/v^2 = 1x10^8/(8000*8000) = 0.78125 kg
So roughly a two-pound payload could reach the ISS's orbit, if it could withstand 6,400 Gs of acceleration.
Note I'm making no allowances for inefficiency or for converting all that vertical motion to horizontal.
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.
But then you've just got another railgun to space which could be sited anywhere and powered from any large power station.
I think the SCSL would be most useful for sub-orbital payloads, like high altitude scientific instruments, where sounding rockets are used today.
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.
The thing I personally most want to launch from the solar chimney is myself on a paraglider.-- BunsenHoneydew, Feb 28 2004 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?).-- Ling, Mar 01 2004 [BunsenHoneydew] I think you're right, somebody should post a link to a basejumping site. Not me, I'm tempted but too scared.-- normzone, Mar 01 2004 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?-- JNK, Jun 22 2005 But that would just spin you, not kick you sideways.-- Worldgineer, Jun 22 2005 random, halfbakery