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Thread: Why don't satellites burn up?

  1. #1 Why don't satellites burn up? 
    New Member Mouthwash's Avatar
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    Taken from here, a website arguing for a concave Earth:

    At about 85km altitude temperatures start to rise until they hit the Krmn line which is 100km high. After this line, the heat abruptly increases rising rapidly to 200km whereby it starts to level off (100km is the very start of the radiation belts as well which become full strength at 200km funnily enough), although other sources say it continually rises. Temperatures can vary, depending on sun activity, but can reach as high as wait for it

    2500C!

    I kid you not.


    In case you dont know how hot 2500C is. Your oven in your kitchen can hit 240C max. A ceramic laboratory oven for jewelers and dentists to melt gold can reach 1200C. Temperatures in a blast furnace for melting iron can go as high as 2300C.


    The only elements in the periodic table that can withstand 2500C are carbon, niobium, molybdenum, tantalum, tungsten, rhenium, and osmium. Except for carbon, these metals are very, very heavy and are of course extremely conductive to heat and most are very ductile when heat treated meaning they bend and coil. Carbon even has the highest thermal conductivities of all known materials! So, if you want to cook someone very efficiently and quickly, there is nothing better than a space capsule made out of graphite.


    Now, admittedly, it is not always 2500C. In fact the temperature range is usually between a mere 600 to 2000C! depending on sun activity and if it is day or night, with these temperatures usually reserved for altitudes of 300km and above; the upper boundary of which is unknown.


    Now guess what altitude all the NASA machines are supposed to orbit Earth?


    We are told most satellites orbit the Earth at altitudes of over 500km to avoid atmospheric drag, with a few circling in Medium Earth Orbit which goes up to 35,786km!


    As you can see, all three objects above are in the seriously ferocious hot zone. Apart from nothing working at the minimum 600C due to thermal expansion of the materials (iron glows red hot at 500C), some of the electronic components like lead, zinc, and epoxy resin would not just burn out, but melt.


    The solar panels which adjorn these machines would barely function even if they could keep it together long enough. A British company found a drop of 1.1% of peak output for every increase in degrees Celsius of photovoltaic solar panels once the panels reached 42C, and of course at 1414C silicon actually melts. But wait the Hubble Telescope and satellites uses gallium arsenide instead of silicon which melts at an even lower temperature of 1238C. I could go on, but you get the picture.
    So how do those solar panels work? How does anything work and why do satellites, the Hubble Telescope, ISS etc. not melt during a day of high solar activity?

    Aha, dont worry, Im sure the apologists have come to the rescue of this laugh-in-your-face contradiction; and they have, or rather have tried. Excuse number one comes from a few websites such as Wikipedia who wish to insult our intelligence to the max. Here is the main explanation for why satellites arent converted into man-made meteorites:
    The highly diluted gas in this layer can reach 2500C (4530F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat.
    Errr wait a minute. I thought it is the sun that causes those few atoms of gas to heat up to 2500C? Oh, it is.
    Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation.
    So, do you think if NASA put a Hubble Telescope up there, it also might absorb highly energetic solar radiation exactly like those few atoms of gas to a maximum of 2500C? You think!!!!

    The source of the heat of the thermosphere is not a few atoms of gas.


    It is the sun!

    I am not a concave-Earther. But I haven't found an explanation for why satellites do not burn up as he says they would. The upper atmosphere may not have many particles, but solid matter is extremely dense compared to it, no? Why wouldn't solar radiation heat it up as well?


    Last edited by Mouthwash; July 22nd, 2017 at 11:22 AM.
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  3. #2  
    Genius Duck Moderator Dywyddyr's Avatar
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    The simplest answer is that temperature is not heat (alluded to in one of his quotes from Wiki).
    While individual molecules may have a high temperature that doesn't mean that the heat is high at those altitudes.
    With regard to "if NASA put a Hubble Telescope up there, it also might absorb highly energetic solar radiation exactly like those few atoms of gas to a maximum of 2500C?" is less simple.
    The fact is that heating of satellites does not approach any where near that value. I'll quote a reply to this question from elsewhere: So the radiation flux of the sun (1,4 kW/m2) will easily heat up the few molecules that are behind every m2 when it reaches the thermosphere, but behind a [multiple] m2 satellite there are a billion times more molecules to heat up. Apart from the fact that the satellite will reflect most of the incoming radiation. And from here: Objects in space (that is, in the absence of air) are heated by radiation on their Sun-facing side and then, because there is nothing (like air, which acts as a "blanket") to reflect and reradiate the heat back toward the side facing away from the Sun, most of that heat escapes into space.
    The smaller an object (e.g. individual molecule) the less surface area to radiate heat away. The larger (e.g. satellite) the more surface area (especially in shade) to radiate heat away.
    IIRC (with regard to heating of a solid object in direct sunlight) a typical temperature is actually closer to 30C rather than 2500.


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  4. #3  
    Moderator Moderator Janus's Avatar
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    Quote Originally Posted by Mouthwash View Post
    The upper atmosphere may not have many particles, but solid matter is extremely dense compared to it, no?
    Therein lay your answer. The density difference between the exosphere and solid matter. The approximate density of the exosphere is 1.72e-7 kg per m3. It is also ~600 km thick. It absorbs the vast majority of high energy photons passing through that thickness. So if we consider column of exosphere 600 km high and with a 1 square meter base, it would mass something like .1 kg. A 1 square meter of aluminum would only have to be 38 microns thick to have an equal mass. So to look at it one way, it takes 600 km of exosphere to absorb the same amount of high energy photons as 38 microns of aluminum. After passing through either little to no high energy photons are left.

    Now that 600 km of exosphere represents all of the mass to be heated by those photons. But the first 38 microns of an aluminum casing of a satellite represents a mere fraction of the total satellite's mass. Distributing the energy absorbed by that 38 micron thick layer throughout the satellite results in a much lower average temp than for the surrounding exosphere.
    Last edited by Janus; July 24th, 2017 at 10:10 AM.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
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  5. #4  
    New Member Mouthwash's Avatar
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    Fantastic answer, thanks!
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  6. #5  
    Forum Professor Zwolver's Avatar
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    I do have an additional question though. It could be hogwash, but it may be a bigger issue than the heat.

    Photons usually release a partial charge, so they sometimes kick electrons out of the structure of the spacecraft/satellite. This in turn makes for a charge difference between plates in the sun, and plates in the shade. And because it is a vacuum, it is very difficult to get these electrons back. How do they prevent sparks flying from components in the sun and components in the shade?

    Or isn't this an issue in space?
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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