1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Astronauts in Space

  1. May 5, 2014 #1
    Hello,

    Can someone please explain to me how Astronauts in Low Earth Orbit do not instantly fry up when in direct sunlight?

    How does the International Space station, for example, not become a torch-lit super-oven when the sun's rays hit its walls?

    Thank you for helping me understand, and please forgive my ignorance in this matter!

    CB
     
  2. jcsd
  3. May 5, 2014 #2

    russ_watters

    User Avatar

    Staff: Mentor

    The sun is only about 36% more intense when you're in orbit than when sitting on Earth. The atmosphere only absorbs a third of the energy.
    Don't ever apologize for that: choosing to be open about it so you can learn is a virtue.
     
  4. May 5, 2014 #3

    Drakkith

    User Avatar

    Staff: Mentor

    Russ, just for clarity, is that the energy difference in the total spectrum, or just the visible portion?
     
  5. May 5, 2014 #4
    Thank you, however I am still confused.

    The International Space Station orbits around 400 km above the Earth's surface. According to Wikipedia this would put the ISS in the Thermosphere, which extends from 85 KM to 500-1,000 KM above Earth atmosphere.

    Again according to Wikipedia temperatures rise in this zone, and can reach up to 2,500 degrees Celsius.

    http://en.wikipedia.org/wiki/Thermosphere

    But if my finger was in this zone, I would not feel heat "because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat."

    This is because "the energy lost by thermal radiation would exceed the energy acquired from the atmospheric gas by direct contact."

    But I don't get hot because there is a continuous chain of atoms in contact from the sun to my finger. If the object is in front of the sun, with nothing to block it, won't it heat up, such as an ISS, or an astronaut?
     
  6. May 5, 2014 #5

    rcgldr

    User Avatar
    Homework Helper

  7. May 5, 2014 #6

    russ_watters

    User Avatar

    Staff: Mentor

    Total. 1366 w/sq m at the top of the atmosphere, 1000 at the surface, average:
    http://en.wikipedia.org/wiki/Insolation#Earth.27s_insolation

    Obviously, it depends on how clear a day it is.
     
  8. May 5, 2014 #7

    russ_watters

    User Avatar

    Staff: Mentor

    Definitely. Just like you do if you go out in the sun right now. It just isn't as intense as you appear to think.
     
  9. May 6, 2014 #8

    davenn

    User Avatar
    Science Advisor
    Gold Member

    but you didn't read quote the whole section.......

    The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) 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. A normal thermometer would read significantly below 0 °C (32 °F),

    so no confusion needed

    Dave
     
  10. May 6, 2014 #9

    davenn

    User Avatar
    Science Advisor
    Gold Member

    and did you read the first link that rcgldr gave ?

    it gives the temp range that astronauts and the ISS etc are subject to

    Dave
     
  11. May 6, 2014 #10
    By this you would had understood, how complex things are than what you had thought.
     
  12. May 6, 2014 #11
    Actually, the atmosphere does block some of sun's radiation but it is even more effective at blocking the Infrared radiation produced by the earth. That keeps the Earth's heat in having a warming effect (That's the essence of the greenhouse effect). In the ISS due to the absence of an atmosphere the loss of Infrared radiation is much more effective and measures must be taken to keep it properly warmed.
     
  13. May 6, 2014 #12
    Correct. That would be Conduction. Remember there are also Advection, Convection, and Radiation all of which contribute to thermal effects in the ISS or an astronaut. Space Capsules of any kind carrying living things and that includes Space Suits and Planet Earth, "guard" against these with insulation, reflective material and cooling (heat transfer) engines.

    That said, our Moon has none of these mitigating circumstances/devices yet it is cold as are parts of our Earth. Venus is so hot, not because it is so much closer to our Sun, but mostly because of it's atmosphere's thermal effects. Each is a complete system. Even some of the radiation that the sun creates never gets past the interior as it is converted within. Others never are converted so low as InfraRed.
     
  14. May 6, 2014 #13

    BruceW

    User Avatar
    Homework Helper

    (I think) the danger to astronauts is from high-frequency radiation from the sun. but still, the danger is not from overheating, but is risk of illness due to high-frequency radiation. (as meson's quote says). Anyway, if the ISS is only 400km above the earth's surface, I would guess the magnetosphere will protect those astronauts from the high-frequency radiation. (I don't know much about this kind of stuff, so don't take me too seriously)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook