That was the what my link said. The German's were expert at optics maybe even the experts, I find it hard to believe they were not totally versed in f ratios, image scale, etc. That stuff came from the late 20's and the author himself gave a 50-100yr timeframe for it being possible.
Still are thanks to Carl Zeiss and Ernst Abbe and what they did 150 years ago.
They were nice people and extremely good at their job.
Thanks largely to Abbe Carl Zeiss AG is fully owned by the Carl Zeiss Foundation who regularly audits that the businesses it owns adhere to the Foundations principles:
Economic security of both firms owned by the foundation
Social responsibility to the employees
Advancing the interests of precision industries
Involvement in community facilities for the good of the working people of Jena
Advancing natural and mathematical science in research and teaching
(as far as I know the 4th was extended to every place they have a plant. They have to show that the presence of Carl Zeiss is beneficial to the entire community in question, not just their employees.)
At the moment they are making the optical parts for the Hubble replacement so I think they are still quite good at it.
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The rule of thumb is focal_length*2*tan(theta/2) for image size at focus. the sun subtends the same angle as the moon or 1/2 a degree so the image size for the 5100mi focal length would be 46mi across. So I guess at no loss you could take the radiant energy from the mirror size and spread it over that area. The flux of the sun is ~1400W/sq meter at 1AU. So a 2000 meter mirror would increase the flux at the surface by ~30%.
Repeat that for a 6" magnifying glass with a 12" focal length. 6" gives about 18W in on a bright sunny day i.e. ants are burnt.
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Thanks Scott. Typical hand held magnifying glasses are 3X and about 3 to 4 inches in diameter. Focal length around 3.3". How big is the hot spot of the focused sun?
May I remind everyone to abide by the 'no politics rule', otherwise this thread will be very short lived.
Offending posts have been deleted.
0.03" and sorry I slipped on a metric conversion the 2000m mirror would only increase the insolation by 1W/sq. m. where at the surface we have at best around 1000w/sq. m.
0.03 inches? That's tiny. So we have taken sunlight energy that is spread across an area of about 7 sq inch and concentrated it down to an area of about 0.28 sq inch. Do we have 25X more energy at the focal point than under normal sunlit illumination?
Real world "testing" with a lens out of a circular magnifying desk lamp reveals about a 1/4 inch burn spot in a 2X4. It took minutes (maybe 5 or 10) to make smoke and never made flame.
I took a 6 foot parabolic dish that was once used in a 12GHz microwave point to point link, and covered the entire surface in shiny grocery store grade aluminum foil. The coating was not perfect, but contained no major errors. The spot at the focal point was about 2 inches in diameter, and time to flame was under 1 minute with serious smoke in seconds. Attempts to make a solar cooker with an automotive heater core at the focal point, and 4 cores for the "grill" was met with hose and pump failures, and a steam explosion that convinced me to abandon the idea.
All testing was done in summertime Florida sun on a clear day. I already had the dish for watching the blacked out Miami Dolphins games, but dismantled that system when they quit blacking out the games.
I took a 6 foot parabolic dish that was once used in a 12GHz microwave point to point link, and covered the entire surface in shiny grocery store grade aluminum foil. The coating was not perfect, but contained no major errors. The spot at the focal point was about 2 inches in diameter, and time to flame was under 1 minute with serious smoke in seconds. Attempts to make a solar cooker with an automotive heater core at the focal point, and 4 cores for the "grill" was met with hose and pump failures, and a steam explosion that convinced me to abandon the idea.
All testing was done in summertime Florida sun on a clear day. I already had the dish for watching the blacked out Miami Dolphins games, but dismantled that system when they quit blacking out the games.
.03" circle is .0007 sq. in. so that's a lot of concentration but the conversion to heat depends on absorption and other things. The French solar furnace facility reaches 3500C in a 40cm circle.
Ah yes, so it is. Tiny area. My mistake on the area calculation. Soooo.... solar death ray a possibility?
George, have you seen any of the stuff where the big lenses out of old projection TVs are used to make a solar furnace? For melting aluminum and such.
George, have you seen any of the stuff where the big lenses out of old projection TVs are used to make a solar furnace? For melting aluminum and such.
Sure at 5100mi the mirror would probably need to be 100's of miles wide. You have a 46mi wide spot now you need to compute how many W/sq. m constitutes a death ray. The concept was debunked as soon as it was first published.
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Thank you all for the great information, however, the answer to my original question is not clear.
How is the heat dissipated from a vacuum tube operating in space? The tube would be inside an enclosure with no atmospheres around the tube.
I worked on troubleshooting a communication satellite PCB in 1975. The board was covered in thermally conductive RTV. We only had the PCB, so I did not see how heat was dissipated in the satellite.
Vacuum Tube Liquid Cooling System
http://www.realhamradio.com/liquid-cooling.htm
How is the heat dissipated from a vacuum tube operating in space? The tube would be inside an enclosure with no atmospheres around the tube.
I worked on troubleshooting a communication satellite PCB in 1975. The board was covered in thermally conductive RTV. We only had the PCB, so I did not see how heat was dissipated in the satellite.
Vacuum Tube Liquid Cooling System
http://www.realhamradio.com/liquid-cooling.htm
Quite. The payload is on a conductive area, often a panel, with active or passive cooling to get the heat out. And of course to get heat in where needed for startup. And of course bad things happen if the propellant freezes.
I saw a home made hot dog cooker made from the lens out of a TV set or an overhead projector maybe 20 years or so ago at the tailgate party of an NFL football game of all places. Somewhere I have a picture of it, on film.
I never experimented with those lenses, but as soon as someone puts one of those TV's outside on trash day, the lens is gone. Somebody is using them. After living through the aftermath of hurricane Wilma where we had no power for 22 days, I could see where a solar cooker could be handy. We had a gas grill and two full tanks of propane.
I have successfully melted small pieces of aluminum wire with a 100 watt tubular ceramic resistor, and a 1000 watt power supply. The resistor was glowing red, almost white inside, and the brown coating was melting. This went on for about half an hour until a good bit of the brown stuff dripped off, leaving an area of the wire exposed to air, where it quickly fried, then burnt open. Aluminum ground wire would melt within a minute or two of being placed inside the resistor.
Lead, and solder melts with Sterno.....makes for some cool "popcorn sculptures" when poured into cold water......DON'T be near the point of contact!
Apparently solar death rays exist for birds.
At Ivanpah and similar solar facilities they call birds who fly into the ray 'streamers' because they die in flight leaving a trail of smoke behind them.
They get one streamer every two minutes.
The space mirror was debunked not solar furnaces the lens looks to be about f1 so that makes the equivalent space mirror 5100mi. in dia.
https://en.wikipedia.org/wiki/Odeillo_solar_furnace
"you need to conduct the heat to an effective black body radiator" How is the accomplished?
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