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Matter Beam
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Hello everyone.
Can someone check if the Rocketpunk-Manifesto blog is unavailable for them as well? I keep getting a blank page with an 'unavailable' error message.

rocketpunk-manifesto.com

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Part II of the discussion on materials, this time based on solar system availability.

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Biological nano-machinery can solve many of our global warming and energy problems.

Imagine this: a sugar-solar panel.

This panel looks like a solar panel, but does not contain rare metals or semiconductors. Instead, it contains sheets of carboxysomes in water.

These carboxysomes are the critical organic machines that convert CO2 into sugars during photosynthesis. Maybe they are exploited directly, copied artificially or function inside independent organelles, but their function is simple: convert sunlight and CO2 into sugar.

Sugar is a biofuel. Photosynthesis is exceedingly efficient. It absorbs CO2, solves energy storage and gets rid of the expensive part of solar power all at once.

Unlike plants, a sugar-solar panel requires much less resources and space, does not take time to grow, is much more resistant to damage or adverse environments and is simply more effective at converting sunlight into a storable form of energy.

https://phys.org/news/2017-06-nanotechnology-reveals-hidden-depths-bacterial.html

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Follow-up from discussions under the Casaba Howitzer post.

Windows crashes and gets stuck in an infinite (tested 20 hour) reboot loop if you try to update it. Windows has superviruses (ETERNALBLUE ect.) running in the wild that antiviruses cannot do anything about.

Damned if you do, damned if you don't.

Suggestions?

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A look at the construction materials that will be used in space, derived from ISRU.

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Hi!

I've been looking at nuclear-heated thermophotovoltaics.
The current concept is the following: a nuclear source of heat raises the temperature of an intermediate element to about 1200K. This element emits infrared light. The light is absorbed by a thermophotovoltaic cell and converted into electricity.
The high operating temperature of the thermovoltaic cell and the long wavelengths (low photon energy) combine to produce a system with very low efficiency. It is difficult to get rid of the heat produced, as it comes out at 600-800K (massive radiators). The total efficiency gain when combined with traditional thermoelectrics is 8%...

http://i.imgur.com/zq23K0b.png

Another version tries to overcome the Shockley-Queisser Limit, which is the maximum energy a solar cell can capture from sunlight. For silicon-based n-p junction gaps, this is about 32%. Using thermophotovoltaics allows the capture of the spectrum wasted by a solar cell, but n-p junction gap efficiency fall sharply with higher temperatures and real-world performance is less than 10% efficiency, compared to the 80%+ theoretical maximum.

http://i.imgur.com/CSKbd0z.png

[gcep.stanford.edu/pdfs/CTlSZRP4nww_77Shjd-A2g/ShanhuiFan_Symposium2009.pdf]
I was wondering if it were possible to improve upon this concept. Shorter wavelength from higher temperature emitters allow for more efficient thermophotovoltaic cells to be used. A 6000K emitter can replicate the full spectrum of sunlight. A 25000K emitter emits the vast majority of its energy in a very narrow ultraviolet band (https://astrogeology.usgs.gov/tools/thermal-radiance-calculator/).

http://i.imgur.com/5AItHYp.png

It is not a coincidence that 25000K is the temperature of uranium gas in a nuclear lightbulb. We can do away with intermediate emitters and work directly with the high-energy photons emitted by the uranium gas. The photovoltaic cells can be tuned to work specifically at this wavelength, but I need examples of such materials. Maximum Carnot efficiency between a 25000K heat source and a 300K PV cell is 96%, so the efficiency of the system is simply how effective the PV cell is at absorbing and converting ultraviolet light.

Temperatures from the PV cells absorbing the incident ultraviolet light must be dealt with by either active cooling, distance between the emitter and the cells or a combination of both.

Here is a simple schematic for a distance-reliant no-active-cooling reactor. It has a massive weight.

http://i.imgur.com/WVobKay.png

If a cooling system is used to remove 1kW/m^2 from the solar cells without raising their temperature, then the radius can be decreased to 470m. At 2kW/m^2, it can be reduced to 332m and so on.

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Raw, unprocessed view of Saturn from the Cassini probe during its final spirals.

Photo

An optics question:

This is NOT about lasers, but regular light.

How do you determine the 'spot size' of a regular emitting blackbody source of light focused by an optical element of known diameter?

The objective is to compare just how much worse regular light is than lasers with regards to focusing ability.

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I've had to update the effective ranges in the Casaba Howitzer post.
http://toughsf.blogspot.com/2016/06/the-nuclear-spear-casaba-howitzer.html
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