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By the Numbers: Reference Material
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Brian Turner
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« Reply #30 on: May 12, 2006, 05:53:23 AM »
Quote from: neil
I'm having some trouble with 20% of the laser energy converted to heat. Since the photovoltaic panel converts 59% of the laser energy to electricity. Does that mean 21% of the laser energy is reflected by the photovoltaic panels? Perhaps some laser energy passes thought the panels?  Neil
I also have this concern. It is my understanding that Photovoltaic cells are typically designed to minimize reflectance. 21% reflectance is believable but I would like to see the data from the tests that showed 59% conversion to see if heat gain was calculated. The power densities in Edwards book are not connected to the conversion efficiency.  I suspect that the cells were massively heat sinked and maybe even artificially cooled. Both of which are not likely on the elevator. We need all three data points, efficiency, temp, and power density at constant rates.

Also cell and panel efficiency are not the same thing.
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Brian Turner
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« Reply #31 on: May 31, 2006, 04:44:57 PM »
http://www.spectrolab.com/DataSheets/TerCel/PV_Concentrator_Module.pdf

In this test they used a chiller. And rate power in Suns.
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A_M_Swallow
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« Reply #32 on: April 06, 2007, 11:37:21 AM »
This is a table of the net gravitational acceleration on climbers at various heights.


Height (km)       net gravity (m/s/s)          acceleration in (g)

0                9.76916                1
50               9.61704                0.98104
100              9.46841                0.96588
150              9.32318                0.95106
200              9.18124                0.93658
250              9.04250                0.92243
500              8.39345                0.85622

1000             7.28725                0.74338        (three-quarters weight)
2000             5.63778                0.57511
3000             4.48554                0.45757        (half weight)
4000             3.64852                0.37219

5000             3.02097                0.30817
6000             2.53802                0.25890
7000             2.15811                0.22015        (quarter weight)
8000             1.85361                0.18909
9000             1.60555                0.16378

10000            1.40058                0.14287
11000            1.22908                0.12538
12000            1.08396                0.11057
13000            0.95992                0.09792        (one tenth weight)
14000            0.85293                0.08700

15000            0.75987                0.07751
16000            0.67832                0.06919
17000            0.60634                0.06185
18000            0.54240                0.05533
19000            0.48525                0.04950        (one twentieth weight)

20000            0.43388                0.04426
21000            0.38748                0.03952
22000            0.34534                0.03522
23000            0.30690                0.03130

23551.655        0.28710                0.02928        (Drop height for 140 km LEO orbit)
24000            0.27168                0.02771

25000            0.23928                0.02440        (one fortieth weight)
26000            0.20935                0.02135
27000            0.18160                0.01852
28000            0.15578                0.01589
29000            0.13168                0.01343

30000            0.10910                0.01112
31000            0.08789                0.00896         (one hundredth weight)
32000            0.06792                0.00692
33000            0.04905                0.00500
34000            0.03118                0.00317

35000            0.01420                0.00144

36000           -0.00200               -0.0002         (GEO)
37000           -0.01736               -0.0018
38000           -0.03210               -0.0033
39000           -0.04622               -0.0047

40000           -0.05977               -0.0061
50000           -0.17262               -0.0176
60000           -0.26048               -0.0266
70000           -0.33553               -0.0342
80000           -0.40333               -0.0412
90000           -0.46674               -0.0476
100000          -0.52732               -0.0538         (Counter weight)


Andrew Swallow
« Last Edit: June 26, 2007, 08:54:52 PM by A_M_Swallow » Logged
Andrew Swallow
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« Reply #33 on: April 06, 2007, 01:53:36 PM »
My modified HyperPhysics page will do those calculations for you.  It's here.  The calculations seem to be fairly accurate, even though I'm doing them in Javascript.
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Merlynx
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« Reply #34 on: December 17, 2009, 09:53:01 AM »
Can someone tally for me the energy required to get the lifter from the ground to above atmosphere? (say 200 km)
How much more energy is required to reach GEO?

I can't help but wonder if solar or solar-thermal might not be a better power supply outside the atmosphere than a ground based laser.

Merlnx
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Merlynx
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« Reply #35 on: December 18, 2009, 09:36:08 AM »
Quote from: Merlynx on December 17, 2009, 09:53:01 AM
Can someone tally for me the energy required to get the lifter from the ground to above atmosphere? (say 200 km)

E = mgh
Where:
E is energy in joules
g is the acceleration due to gravity (9.81 m/s2 at the Earth's surface, less higher up)
m is mass in kilograms
h is height in metres

To lift out of the atmosphere each kg needs E = 1 * 9.81 * 200,000 = 1,962,000 J (or 1.962 MJ)

A 20 tonne climber would need 39,240 MJ

The solar-thermal power supply question does not belong in a reference thread.
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Andrew Swallow
Merlynx
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« Reply #36 on: December 20, 2009, 06:45:13 AM »
Right, gravitational potential energy.
How about the kinetic energy of the climber at that point?
Any estimate on energy lost to drag passing through the atmosphere?

Still,
Allowing for the variation in gravity by height, how much additional energy is required to get to GEO?
How far could the climber coast if it left the atmosphere at 200 kph?
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Merlynx
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neil
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« Reply #37 on: December 22, 2009, 05:01:39 PM »
Hi Merynx: I don't know the numbers, but I don't think a square kilometer of solar panels could power the climber up the ribbon at 200 kilometers per hour. That is because the air resistance of a square kilometer at 200 kilometers per hour would be huge. Perhaps not even 20 kilometers per hour which would take perhaps 8 hours for the first 200 kilometers. Worse a square kilometer of solar panel would have more mass than the climber and payload, and the ribbon needs to hold all the weight. Even a slight breeze would stress the ribbon to failure. Launches from an hour before sun set to an hour after sunrise, typically would not move the climber even 1 kilometer per hour even though the square kilometer of solar panel could be angled for minimum air resistance. Solar thermal would produce about the same air resistance as PhotoVoltaic. It might be practical to use ship electricity through a long extension cord for the first 30 meters, but there is likely no alternative to laser power the rest of the way to 39,000 kilometers.
The net gravity at 6000 kilometers is still about 1/6 th g, because the climber is sub orbital until it reaches GEO altitude, so only about 3% of the energy to GEO is used for the first 200 kilometers. Cutting the power and pinch roller resistance to zero at 200 kilometers would allow the climber to coast about as far as a canon ball aimed straight up would coast from a muzzle velocity of 200 kilometers per hour = maybe 50 meters.
At 200,000 meters altitude, a ten ton climber would have a kinetic energy of two million meter tons (almost 7 billion foot pounds)   Neil
« Last Edit: December 22, 2009, 06:39:51 PM by neil » Logged
Merlynx
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« Reply #38 on: December 27, 2009, 08:44:03 AM »
Where exactly did a square kilometer of solar cells come from?

<Borrowing from AM>
The difference in potential energy for 200 km vertical is 39,240 MJ (20 ton climber)

So to raise the lifter at 200 kph, requires 39,240 MJ per hour, or 10.9 MegaWatts.

Solar Insolation above the atmosphere is roughly 1.366 kw per square meter.  Assuming 100% efficiency that would require 7980 sq. meters of panels.  This would be a square approx. 89 meters on a side.
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Merlynx
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