Solar panels of the future, design aspect

[PB666]

http://www.engadget.com/2014/08/18/nasa-origami-solar-panels/

I was going to add this to a pre-existing thread that would have been perfect for this topic, but for some reason moderator locked it, if said moderator feels the urge to unlock the thread, then please merge this post with that thread.

[PB666]

http://maslam.net/australian-engineers-edge-closer-to-the-theoretical-limits-of-sunlight-to-electricity-conversion/

New three frequency top later allows a broader band of absoption. 

[PB666]

http://www.sciencealert.com/scientists-have-developed-solar-cells-100-times-thinner-than-a-human-hair

100 times Thinner than a human hair panels.

OK so lets do the math. lets say they are 2 micrometers thick, and lets say the density is 3000 kg per meter cubed. 
So 1m x 1m x 0.000002 m = 0.000002 cu. meters. That times 3000 equals 0.006kg or 6 grams. Lets say you had this on a roll.

At one end you attached a pole and the other is rolled up into a long column, say a couple hundred meters and you simply roll out several 100 meters of panels in space, pushing the pole away from the ship, in theory you have a really great thing.

OK, so then lets talk about problems.

1. Efficiency, we can't let efficiency fall off.
2. Lifespan, falling lifespan not so cool either, but for some deep space craft may be ok
3. Heat tolerance.
4. How to push the pole out, there are locking chains that can do this be at certain length segmental flexibility kicks in and these lack structural rigidity. You would need to engineer some sort of system of locking chains that roll out and then hold the distal pole in reference to the ship this adds weight
5. So in space, because of the stability of ions high voltages create problems, you can only step the voltage up so high before you have to carry the current back to the ship. You could have several columns each column attached to the end of the previous roll. as the current goes back to the roll it is transferred axially to a bus that then conducts the power back to the core.

OK, lets speculate on  weight, lets say we can get the weight down to 12g per meter square. I think this is highly unlikely but for the sake of arguement lets just say that this is the minimum weight per panel.

Lets say the panel+structure+wiring = 1/2 the weight of a vessel and less say the collection efficiency is 25% of surface area. If we then take these numbers we can estimate how useful this might be as a space tug.

Our ISP is set at 100,000 (ISP = 10,200), thruster efficiency is set at 80%. Since our power is tied to weight we can estimate power production per kg of ship mass. 25% * 1300 w/sq. meter * 1000/24 sq.meter/kg = 13.4 kw per kilogram. Not bad.

how much ion drive thrust can we produce. 2 * 0.8 * 13,400 / 100,000 = 0.0214 N per kilogram or a = 0.002 gs of thrust.

Now lets suppose that 10% of our crafts weight is fuel.

X

10%  10500 m/s = 100,000 * ln(1.0/0.9)
20%   22300 m/s = 100,000 * ln(1.0/0.8)
30%   35700 m/s = 100,000 * ln(1.0/0.7)
40%   51100 m/s = 100,000 * ln(1.0/0.6)
45%   59788 m/s = 100,000 * ln(1.0/0.55)

In each of the above the payload could be no more than 40%, 30%, 20%, 10% and 5% of the weight of the vessel. To achieve a higher payload ratio the amount of panel would still need to be reduced, and therefore the amount of acceleration reduced.

But lets say that we desperately needed the acceleration, and lest say that in order to leave earths LEO we kicked for a period of 36 degrees.
So thats 8.8 minute burn per kick. 8.8 x 60 = 528 seconds, 528 seconds x 0.0214 meters per second is 11.28 m/s per kick.

The orbital periods will shrink as the orbit become more eccentric, starting at 7800 meters per second we need double the energy to exit, so that represents 11030 m/s on the perigee velocity (although practically speaking reaching about 10030 m/s will provide sufficient quantity of momementum to push out with ION drive and lose some efficiency. That's about 200 kicks. less because we would gradually begin raising perigee and increasing the allowable burn time, but orbits become considerably longer, the time to push out would be more than 12 days. However  3300 spent to enter circumsolar orbit. In the several days required to reach apogee the craft can burn toward a radius that intercepts mars, taking an additional  260 days to reach mars so at maximum efficiency it would take 280 days to reach mars, again the revers process would have to occur, another 20  days or so spend neutralizing that velocity in a counterclockwise orbit about mars. So that makes 300 days. 

Because of the high dV we have other options for shrinking the time, but not down to 39 days. This is because the insolance is lower as we approach mars, and the ion drives are starting to degrade with constant use (but if this were a manned vessel astronauts could replace the gratings), and because you really have about a 50 day transfer window to play with before dV cost get really high. So at least we could consider a transfer time of 250 days or so using ION drives.

Some things that could make the process cheaper, booster vehicle on earths orbit that is all drive and thruster that double or triples thrust at the expense of ISP, but since you are LEO and you have a very cheap gas (argon) and a very inexpensive source (SpaceX delivery services) you don't mind and inefficient system just to trim a few days off. Alternatively you could opt for a hydrolox driven system, or even methane drive LEO booster (these would have to be expendible because of LOX).

 

 

[magnemoe]

16 hours ago, PB666 said:

http://www.sciencealert.com/scientists-have-developed-solar-cells-100-times-thinner-than-a-human-hair

100 times Thinner than a human hair panels.

OK so lets do the math. lets say they are 2 micrometers thick, and lets say the density is 3000 kg per meter cubed. 
So 1m x 1m x 0.000002 m = 0.000002 cu. meters. That times 3000 equals 0.006kg or 6 grams. Lets say you had this on a roll.

At one end you attached a pole and the other is rolled up into a long column, say a couple hundred meters and you simply roll out several 100 meters of panels in space, pushing the pole away from the ship, in theory you have a really great thing.

Yes the deployment and support is likely to be heavier than this panel, however light solar panels will make it easier with ion engines. 
Looks like even an LEO to GEO ion tug start making sense. here xenon for the probe would be part of the docking adapter. 
 

[PB666]

On 6/22/2016 at 3:52 AM, magnemoe said:

Yes the deployment and support is likely to be heavier than this panel, however light solar panels will make it easier with ion engines. 
Looks like even an LEO to GEO ion tug start making sense. here xenon for the probe would be part of the docking adapter. 
 

http://phys.org/news/2016-07-discoveries-photosynthesis-solar-cells-future.html