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No antennae radiate all the power fed to them!
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No antennae radiate all the power fed to them!
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No antennae radiate all the power fed to them!
rickman wrote in :
Hmmm... All things emit energy according to their temperature and their surface emissivity. All things also absorb energy according to their surface emissivity. Both processes are going on at all times. So an object loses or gains heat depending on its temperature and the temperature of the environment. That delta temperature sets the rate along with the surface emissivity. Ok, that works for me. I guess the rate of change is exponential just as energy loss in a fading note from a stretched string, roughly reaching equilibrium when it can't lose more energy to ambient conditions. About warming of superconductors out there, I may be wildly underestimating the effect of a difference of 77K. What's I'd thought of was that if a supeconductor can only operate at a very low temperature, its thermal emission will be low; perhaps so low that it might take very little input (from whatever, I know not what, and especially so if its emissivity is high making absorbtion easy) to balance that and stop it staying cold enough. My difficulty comes from not being sure whether a difference of 77K means the same thing at cryogenic temperatures as it does around room temperature, because it's not an infinite continuum of temperature. I was thinking that because it is so cold, that small amounts of heat lost from other equipment, might find their way to a superconductor and cause bother in the absence of forced cooling. I can't really imagine any use of superconductors in space that would not include the risk of local heat sources. |
No antennae radiate all the power fed to them!
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No antennae radiate all the power fed to them!
"Brian Reay" wrote in message
... I doubt the casual reader would give his muddled nonsense the time of day, especially if they read the other stuff he posts. Although you try to lay the blame at my door, there can be no doubt that it is from your own keyboard that the gratuitous abuse originates. |
No antennae radiate all the power fed to them!
On 11/3/2014 4:24 AM, Lostgallifreyan wrote:
wrote in : It would be called a scene from The Big Bang Theory; a speaker covered with plastic wrap with a water and corn starch mixture. That's no answer. It describes a method already decribed by me, not a result, let alone a conclusion. I've thought about it a bit though, last night waiting to sleep. I'm guessing that the static patterns formed are not the standing wave itself, but redistributions of the particles in the fluid into nodes in the wave due to differences in pressure. Uh... "The Big Bang Theory" is a television show... -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote in news:m37qbe$pgl$1@dont-
email.me: Uh... "The Big Bang Theory" is a television show... I discovered that much. But only after I'd searched a bit for Faraday waves. |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote in news:m37qbe$pgl$1@dont-
email.me: Uh... "The Big Bang Theory" is a television show... Btw, I don't watch TV. :) I just got done telling the TV license people that too. Every two years or so they decide not to beleive me despite the fact that any time they visited over 15 years, the cut cable has been plastered by the same old paint on the outside front wall every time. I'm fine with radio (and first thought that Big Bang thing might have been a movie. I don't see many of those either. The last several show series I have came off eBay on disks.) |
No antennae radiate all the power fed to them!
On 11/3/2014 8:53 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:m37qbe$pgl$1@dont- email.me: Uh... "The Big Bang Theory" is a television show... Btw, I don't watch TV. :) I just got done telling the TV license people that too. Every two years or so they decide not to beleive me despite the fact that any time they visited over 15 years, the cut cable has been plastered by the same old paint on the outside front wall every time. I'm fine with radio (and first thought that Big Bang thing might have been a movie. I don't see many of those either. The last several show series I have came off eBay on disks.) I don't watch The Big Bang Theory, but I do enjoy some of the old shows. The 60's "Man from U.N.C.L.E." is on Sunday nights now. And we enjoy a movie now and then. At around $50 for two to go to a movie (parking, admission, popcorn, drinks) here, we don't go to many theater movies. Although I wish we had seen "Gravity" in 3D. Saw it on HBO a couple of weeks ago and, while I didn't think the story was that good, the special effects were great. Would have been even better in 3D. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote in news:m38235$pqa$1@dont-
email.me: Although I wish we had seen "Gravity" I so want that one! It's one of the few on my imaginary list of must haves. Add to that all the Doctor Who shows since series four of the new ones, plus the Tom Baker and Jon Pertwee shows, and the last series of House. Last time I saw a movie in a thetre, it was Matrix II (packed) and a week earlier, Johnny English (empty but for two people other than me). Johnny English was the better show. :) |
No antennae radiate all the power fed to them!
On 11/3/2014 3:36 AM, Lostgallifreyan wrote:
rickman wrote in : Recorded temperatures have always set new records. Just considering one location, there are 365 days in a year and so 730 high and low records to test. We have been recording temperatures for roughly 200 years. What are the chances we *won't* set a new record for one of those dates in a given year? True, it's no great deal intself. And given the Maunder Minimum soem big excursions can be expected, especially as the sun isn't following its usual 11-year pattern. On the other hand I remember people asking me in 1983 about glonal warming, and me insisting that it did not just mean warmer, but wetter, stormier, as well. There's no doubt that compared to thiry years ago this has happened across most of thwe world. There is tons of doubt. Considering your "impression" of what you have heard about is not science. For a real balance of 'records', we need to know how often the record for quietest, or closest approach to average, conditions occured, and I have never heard the like. :) Generally, if news is not exciting, it is not considered as news. Also, even when we had unusual cold recently, it is arguable that climate conditions don't cause a strong enough gradient to keep a strong division of temperature with lattitude, and similar things can be said about the wandering of the jet stream. Too many things look new, an the rate of broken records is increasing when it ought to be decreasing if things were generally stable. I think you are talking through your hat. Let the scientists analyze the data and come up with facts. -- Rick |
No antennae radiate all the power fed to them!
rickman wrote in :
I think you are talking through your hat. Let the scientists analyze the data and come up with facts. I do. Those are where I get that impression. Many people ignore them, but they will keep saying it. |
No antennae radiate all the power fed to them!
On 11/3/2014 4:19 AM, Lostgallifreyan wrote:
rickman wrote in : Hmmm... All things emit energy according to their temperature and their surface emissivity. All things also absorb energy according to their surface emissivity. Both processes are going on at all times. So an object loses or gains heat depending on its temperature and the temperature of the environment. That delta temperature sets the rate along with the surface emissivity. Ok, that works for me. I guess the rate of change is exponential just as energy loss in a fading note from a stretched string, roughly reaching equilibrium when it can't lose more energy to ambient conditions. Equilibrium is when the temperatures are equal. Of course this is a bit of a cyclic definition because of how we define temperature. Still, that is the point, equilibrium means equal heat exchange in both directions. About warming of superconductors out there, I may be wildly underestimating the effect of a difference of 77K. What's I'd thought of was that if a supeconductor can only operate at a very low temperature, its thermal emission will be low; perhaps so low that it might take very little input (from whatever, I know not what, and especially so if its emissivity is high making absorbtion easy) to balance that and stop it staying cold enough. My difficulty comes from not being sure whether a difference of 77K means the same thing at cryogenic temperatures as it does around room temperature, because it's not an infinite continuum of temperature. Trouble is you don't really think like a scientist or engineer. Temperature *is* a continuous function and each degree is the same. If you want to understand it, look at the math. There are no step functions in the equations for heat exchange. Remember what I wrote, "delta temperature" determines the rate of heat exchange. Nowhere did I say depending on if you are in "cryogenic" ranges. The equations don't know what we consider "cryogenic". It takes the same amount of heat to raise a substance 1 degree at 77 °K as it does at room temperature. Also remember that I only picked 77 °K as a convenience (boiling point of N2) as we know there are a number of superconductors with their transition temperature well above that. The key is "well above". I was thinking that because it is so cold, that small amounts of heat lost from other equipment, might find their way to a superconductor and cause bother in the absence of forced cooling. I can't really imagine any use of superconductors in space that would not include the risk of local heat sources. An antenna is also subject to EMC. It is not uncommon to mount them clear of the rest of the craft. It's easier to insulate them from heat sources than it is to isolate them from EMC from the rest of the craft. -- Rick |
No antennae radiate all the power fed to them!
rickman wrote in :
Trouble is you don't really think like a scientist or engineer. I'm neither. I managed to build a phase modulation synthesiser despite that. I get by. :) And I usually do that by being willing to go beyond my 'comfort zone'. How many other people who are not engineers or scientists do you see posting around here? |
No antennae radiate all the power fed to them!
"Lostgallifreyan" wrote in message
. .. How many other people who are not engineers or scientists do you see posting around here? In discussions about short antennae, quite a few from Yankland. |
No antennae radiate all the power fed to them!
rickman wrote in :
It takes the same amount of heat to raise a substance 1 degree at 77 °K as it does at room temperature. Ok, but when I read (or hear on BBC radio science programs) that it takes FAR more effort (energy) to pump from 2K to 1K than it does from 300K to 299K, what am I supposed to make of that given what you just said? |
No antennae radiate all the power fed to them!
On Sunday, November 2, 2014 6:51:50 PM UTC-6, Jerry Stuckle wrote:
Which means it rolls once per orbit. Otherwise it wouldn't be able to keep the same side facing the earth. I'll take you all's word for it.. I was pondering it as you would a matchbox car rolling across a globe.. ?? If it's rolling, it must be real slow about it, as it's not really detectable on the cameras. |
No antennae radiate all the power fed to them!
On 11/3/2014 3:36 AM, Lostgallifreyan wrote:
rickman wrote in : Recorded temperatures have always set new records. Just considering one location, there are 365 days in a year and so 730 high and low records to test. We have been recording temperatures for roughly 200 years. What are the chances we *won't* set a new record for one of those dates in a given year? True, it's no great deal intself. And given the Maunder Minimum soem big excursions can be expected, especially as the sun isn't following its usual 11-year pattern. On the other hand I remember people asking me in 1983 about glonal warming, and me insisting that it did not just mean warmer, but wetter, stormier, as well. There's no doubt that compared to thiry years ago this has happened across most of thwe world. For a real balance of 'records', we need to know how often the record for quietest, or closest approach to average, conditions occured, and I have never heard the like. :) Generally, if news is not exciting, it is not considered as news. Also, even when we had unusual cold recently, it is arguable that climate conditions don't cause a strong enough gradient to keep a strong division of temperature with lattitude, and similar things can be said about the wandering of the jet stream. Too many things look new, an the rate of broken records is increasing when it ought to be decreasing if things were generally stable. The problem is the Earth's climate is a very complex system. You can't take a small area and project what's happening world-wide; things are too interconnected. This would be like taking one street in a big city and count cars going by. If the number of cars goes down, you can't say "traffic in the city is lighter" because there might have been an occurrence such as an accident on a feeder road which is blocking up traffic. At the same time, if the number of cars increases, you can't say "traffic is heavier" - there might have been an accident in another location and people are getting around it by using this street. It's all tied together. A perfect example with the weather is last winter. North America had one of the coldest winters in recent years (due to the polar vortex moving our way). But Europe and Asia had one of the warmest winters in recent years; world-wide the average temperature increased. The last figure I heard was that 95% of climatologists (people who should know better than anyone else) agree that global warming is occurring, as indicated by world-wide average temperatures. There is still debate, even amongst them, how much man is responsible for this warming. But still the vast majority believe that man is responsible for at least some of the warming. So, as rickman pointed out, (paraphrasing) with only 200 or so years of tracking temperatures (even less than that in much of the Americas), there is almost a certainty some locations will report record highs, and some locations will report record lows. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
No antennae radiate all the power fed to them!
On Monday, November 3, 2014 11:05:11 AM UTC-6, gareth wrote:
"Lostgallifreyan" wrote in message . .. How many other people who are not engineers or scientists do you see posting around here? In discussions about short antennae, quite a few from Yankland. I'm just a regular ole ham here. Never studied any of this stuff in school, and don't work in any related field. Everything I've learned, I learned on my own. Mainly from books, of which I have several. I trust good textbooks a lot more than I trust usenet jibber jabber. Usenet jibber jabber is only as good as the qualifications of the one jabbering. Some info is good, some is bad, and some is pure unadulterated bafflegab. |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote in news:m38cv9$9g2$1@dont-
email.me: The problem is the Earth's climate is a very complex system. You can't take a small area and project what's happening world-wide; things are too interconnected. Ok, I'll buy that. I'll let the matter rest. I actually have no axe to grind either way. I just found it odd that people I knew did not realise that 'warming' could likely mean 'more dynamic'. Whatever the outcome or cause, we have to adapt to changes or we're stuffed. |
No antennae radiate all the power fed to them!
wrote in message
... On Monday, November 3, 2014 11:05:11 AM UTC-6, gareth wrote: "Lostgallifreyan" wrote in message . .. How many other people who are not engineers or scientists do you see posting around here? In discussions about short antennae, quite a few from Yankland. I'm just a regular ole ham here. Never studied any of this stuff in school, and don't work in any related field. Everything I've learned, I learned on my own. It shows. Mainly from books, of which I have several. I trust good textbooks a lot more than I trust usenet jibber jabber. Usenet jibber jabber is only as good as the qualifications of the one jabbering. Some info is good, some is bad, and some is pure unadulterated bafflegab. |
No antennae radiate all the power fed to them!
On 11/3/2014 12:07 PM, wrote:
On Sunday, November 2, 2014 6:51:50 PM UTC-6, Jerry Stuckle wrote: Which means it rolls once per orbit. Otherwise it wouldn't be able to keep the same side facing the earth. I'll take you all's word for it.. I was pondering it as you would a matchbox car rolling across a globe.. ?? If it's rolling, it must be real slow about it, as it's not really detectable on the cameras. Take an experiment. Go to your dining room table, opposite the door to the kitchen. Face the table (and the kitchen door). Now, walk around the table, trying to keep facing the table without rotating your body. You can't do it. The ISS is the same. You don't see the rotation because the ISS is stationary (rotation-wise) relative to the earth, and you are observing the earth. But if the cameras were pointed into space, you would see the stars move as the ISS rotates. The moon is the same way. It makes a complete rotation once every orbit, thereby keeping the same face pointed at the earth. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
No antennae radiate all the power fed to them!
wrote in news:215ae22b-4725-454d-9b7a-
: I trust good textbooks a lot more than I trust usenet jibber jabber. Me too. I'm, mostly self taught, and try to find those internet pages that look most like the old texts I found in libraries. Putting that better, I look for those that look like I can get a grip on it and verify with other efforts. I have to take some on trust, because I can't do that much for myself, alone, and I'm no mathemetician either. :) (regarding trust, I hear several times a month that even scientists can be very selective of their facts. This observation coming from actual scientists too.) Best bit of wisdom I heard recently was that the way to peace is to admit that 'we do not know'. Works for me, as it;s true more often than not. |
No antennae radiate all the power fed to them!
On Monday, November 3, 2014 11:17:26 AM UTC-6, gareth wrote:
wrote in message ... On Monday, November 3, 2014 11:05:11 AM UTC-6, gareth wrote: "Lostgallifreyan" wrote in message . .. How many other people who are not engineers or scientists do you see posting around here? In discussions about short antennae, quite a few from Yankland. I'm just a regular ole ham here. Never studied any of this stuff in school, and don't work in any related field. Everything I've learned, I learned on my own. It shows. Big talk from rraa's new purveyor of bafflegab... I've forgot more than you know, and you can take that to the bank. |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote:
On 11/2/2014 6:11 PM, wrote: Jerry Stuckle wrote: On 11/2/2014 3:58 PM, wrote: Lostgallifreyan wrote: wrote in : Apples and oranges; we already know what will happen if one were to build an antenna from a superconductor. Fire up EZNEC and set material loss to zero; done. Yeah, anyone with a map could say a great deal about the shape of West Africa based on ocean travel. Again, apples and oranges as we know EXACTLY and in DETAIL what would happen. My point isn't so much about antennas, as about exploring the easy availability of cold environments for superconductors in space. Easy availability measured in thousands of dollars an ounce to get stuff there. Not having to lug heavy coolers up there might be an offer someone cannot refuse, and that someone might come back with all kinds of discoveries, things no models or predictions are going out there to find. The only thing that makes a superconductor different is the lack of resistance. We already know exactly what that means and what we would do with them if room temperature superconcductors were available. Here are a couple of things: electric motors and generators that would be very close to 100% efficient, small, light, and lossless power transmission lines, lossless transformers, big honking magnets. It's a little more than just no resistance. For instance, superconductors will "reflect" (for lack of a better word) a magnetic field. That's now a superconducting disk will levitate over a magnetic field. So just setting the resistance to zero doesn't necessarily cut it. There are other things to consider which EZNIC may not handle properly. Such as? In regards to magnetic levitation, a super conductor is a perfect diamagnet due to the Meissner effect. None of that has anything to do with antennas. http://hyperphysics.phy-astr.gsu.edu...ds/maglev.html http://en.wikipedia.org/wiki/Magnetic_levitation Are you sure? I haven't seen anything one way or the other on it - although I'm sure it's been studied. Can you point at some studies to that effect? Start with the two links, follow the internal links. -- Jim Pennino |
No antennae radiate all the power fed to them!
rickman wrote:
On 11/2/2014 3:58 PM, wrote: Lostgallifreyan wrote: wrote in : Apples and oranges; we already know what will happen if one were to build an antenna from a superconductor. Fire up EZNEC and set material loss to zero; done. Yeah, anyone with a map could say a great deal about the shape of West Africa based on ocean travel. Again, apples and oranges as we know EXACTLY and in DETAIL what would happen. My point isn't so much about antennas, as about exploring the easy availability of cold environments for superconductors in space. Easy availability measured in thousands of dollars an ounce to get stuff there. Not having to lug heavy coolers up there might be an offer someone cannot refuse, and that someone might come back with all kinds of discoveries, things no models or predictions are going out there to find. The only thing that makes a superconductor different is the lack of resistance. That is far from true. There are all sorts of magnetic effects. All of which are due to the lack of resistance which results in enormous eddy currents. Are you familiar with the eddy current dampers found on some balance scales consisting of a piece of aluminum between two permanet magnets? If the scale is see-sawing up and down, the eddy currents induced in the aluminum generate a small magnetic field in oposition to the motion, thus damping the motion. Replace the aluminum with a superconductor and the scale is no longer damped, it is locked into position because of the huge eddy currents from even the slightest movement. -- Jim Pennino |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote:
On 11/2/2014 6:17 PM, wrote: Jerry Stuckle wrote: On 11/2/2014 4:55 PM, wrote: Lostgallifreyan wrote: wrote in : There is no undiscovered magic in superconductors. There was no magic in any of the materials used for Gemini and Apollo either, but countelss things were learned just by using them out there. Care to name a few specifically from Genini and Apollo? And BTW, 99.9% of the materials used is aluminum. Much of the medical monitoring technology came out of the early space program, for one thing. So did advances in propulsion systems and remote controls (more than just model planes and cars) for another. True, but none of that came from throwing the stuff up into space just to see what would happen. No, but they all came from the space race (Mercury, Gemini and Apollo programs) - which was your question. Nope, my question was what came from throwing the stuff up into space just to see what would happen. Perhaps I should have phrased it more clearly. And since then, there have been all kinds of experiments on various orbiting objects such as MIR, Skylab, the space shuttle and ISS. Many discoveries are coming out of it - although I don't know offhand what's been put to use yet, since there is no manufacturing in space. But thinks like perfectly round ball bearings and new ways to make pharmaceuticals come to mind. All of which revolve around the concept of doing something dynamic in a zero gravity environment. None of it has anything to do with some material showing some new and hitherto unknown property simply by being in such an environment. Take ball bearings for example. It has long been known that absent an external force, i.e. gravity, that a liquid will form into a sphere due to surface tension. -- Jim Pennino |
No antennae radiate all the power fed to them!
Lostgallifreyan wrote:
wrote in : True, but none of that came from throwing the stuff up into space just to see what would happen. Do you think that 'experiment' is a switch, not a continuum? You write as if it's either a forgone certainty, or total whimsy. You write like a starry eyed dreamer that believes long established principals are going to go away simply by putting something in space. The effects of temperature, air pressure, radiation and gravity have been well known for a very long time and are the only things that change by putting something in space. -- Jim Pennino |
No antennae radiate all the power fed to them!
rickman wrote:
On 11/2/2014 4:11 PM, wrote: Lostgallifreyan wrote: wrote in : The only external heat source in space is the Sun; solution, sun shade. Maybe not. I just did a bit of Googling for 'superconductors in space' minus quotes. There's a lot of statements abotu space missions ended because required helium or hydrogen coolant ran out, Yeah, the coolent ran out for the things that GENERATE a lot of heat and need to be cooled more than radiation can provide. Radiative cooling does not provide for a lot of cooling. and also of space having latent temperatures up to 100K, so a sun shade won't help a lot there with current materials. There really is no such thing as temperature in space as it is a vacuum. That is a gross oversimplification. The temperature of space is the temperature of the background radiation, even in a near vacuum. That is also an simplification. -- Jim Pennino |
No antennae radiate all the power fed to them!
Jerry Stuckle wrote:
On 11/3/2014 8:53 AM, Lostgallifreyan wrote: Jerry Stuckle wrote in news:m37qbe$pgl$1@dont- email.me: Uh... "The Big Bang Theory" is a television show... Btw, I don't watch TV. :) I just got done telling the TV license people that too. Every two years or so they decide not to beleive me despite the fact that any time they visited over 15 years, the cut cable has been plastered by the same old paint on the outside front wall every time. I'm fine with radio (and first thought that Big Bang thing might have been a movie. I don't see many of those either. The last several show series I have came off eBay on disks.) I don't watch The Big Bang Theory, but I do enjoy some of the old shows. The Big Bang Theory is one of very few shows which actually get science right. -- Jim Pennino |
No antennae radiate all the power fed to them!
wrote in message
... On Monday, November 3, 2014 11:17:26 AM UTC-6, gareth wrote: wrote in message ... On Monday, November 3, 2014 11:05:11 AM UTC-6, gareth wrote: "Lostgallifreyan" wrote in message . .. How many other people who are not engineers or scientists do you see posting around here? In discussions about short antennae, quite a few from Yankland. I'm just a regular ole ham here. Never studied any of this stuff in school, and don't work in any related field. Everything I've learned, I learned on my own. It shows. Big talk from rraa's new purveyor of bafflegab Read and learn a bit more. |
No antennae radiate all the power fed to them!
On 2014-11-03 17:06:02 +0000, Lostgallifreyan said:
rickman wrote in : It takes the same amount of heat to raise a substance 1 degree at 77 °K as it does at room temperature. Ok, but when I read (or hear on BBC radio science programs) that it takes FAR more effort (energy) to pump from 2K to 1K than it does from 300K to 299K, what am I supposed to make of that given what you just said? That's energy to keep all the heat from the surrounding environment out. In a system completely separated from hot material or radiation, such as space, the energy is exactly the same, because of the way temperature is defined. -- Percy Picacity |
No antennae radiate all the power fed to them!
On 11/3/2014 12:19 PM, Jerry Stuckle wrote:
The ISS is the same. You don't see the rotation because the ISS is stationary (rotation-wise) relative to the earth, and you are observing the earth. But if the cameras were pointed into space, you would see the stars move as the ISS rotates. As I read this and pictured cameras pointed to the earth as the "space" station orbits the earth while ignoring the vastness of *space*, it seems to be that humanity is obsessed with selfies. -- Rick |
No antennae radiate all the power fed to them!
On 11/3/2014 1:07 PM, wrote:
rickman wrote: On 11/2/2014 4:11 PM, wrote: Lostgallifreyan wrote: wrote in : The only external heat source in space is the Sun; solution, sun shade. Maybe not. I just did a bit of Googling for 'superconductors in space' minus quotes. There's a lot of statements abotu space missions ended because required helium or hydrogen coolant ran out, Yeah, the coolent ran out for the things that GENERATE a lot of heat and need to be cooled more than radiation can provide. Radiative cooling does not provide for a lot of cooling. and also of space having latent temperatures up to 100K, so a sun shade won't help a lot there with current materials. There really is no such thing as temperature in space as it is a vacuum. That is a gross oversimplification. The temperature of space is the temperature of the background radiation, even in a near vacuum. That is also an simplification. But not a gross oversimplification. -- Rick |
No antennae radiate all the power fed to them!
|
No antennae radiate all the power fed to them!
|
No antennae radiate all the power fed to them!
rickman wrote:
On 11/3/2014 1:07 PM, wrote: rickman wrote: On 11/2/2014 4:11 PM, wrote: Lostgallifreyan wrote: wrote in : The only external heat source in space is the Sun; solution, sun shade. Maybe not. I just did a bit of Googling for 'superconductors in space' minus quotes. There's a lot of statements abotu space missions ended because required helium or hydrogen coolant ran out, Yeah, the coolent ran out for the things that GENERATE a lot of heat and need to be cooled more than radiation can provide. Radiative cooling does not provide for a lot of cooling. and also of space having latent temperatures up to 100K, so a sun shade won't help a lot there with current materials. There really is no such thing as temperature in space as it is a vacuum. That is a gross oversimplification. The temperature of space is the temperature of the background radiation, even in a near vacuum. That is also an simplification. But not a gross oversimplification. True. Shall we go into why an ordinary thermometer exposed to the Sun at about Earth's distance from the Sun allowed to stabilze will read the tempurature of space as about 7 C and what are the unstated assumptions for this to happen? -- Jim Pennino |
No antennae radiate all the power fed to them!
|
No antennae radiate all the power fed to them!
On 11/3/2014 12:06 PM, Lostgallifreyan wrote:
rickman wrote in : It takes the same amount of heat to raise a substance 1 degree at 77 °K as it does at room temperature. Ok, but when I read (or hear on BBC radio science programs) that it takes FAR more effort (energy) to pump from 2K to 1K than it does from 300K to 299K, what am I supposed to make of that given what you just said? Ok, I'll grant that few who have not had thermodynamics really understand heat. Thermo was not an easy part of the curriculum in school. The reason why cooling something gets harder as it approaches absolute zero is because the heat flow is proportional to the difference in temperature. Even if your pump is perfect and acts as if you put the thing being cooled in contact with a heat sink at 0 °K, the rate of heat flow decreases as that temperature delta diminishes. The reality is that thinking 77 °K is especially cold is a bit of an exaggeration. Yes, it is cold by human experience, but in the world of cryogenics it is just a step stool to board the rocket. Thinking that any little heating effect would warm a high temperature superconductor is thinking with your feelings and not your brain. Not that we don't all do that. But you need more experience with this stuff to let your instinct guide you. -- Rick |
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