Explaining How Astronauts in Low Earth Orbit Stay Cool

[CitronBleu]

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

 

[russ_watters]

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?

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.

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

Don't ever apologize for that: choosing to be open about it so you can learn is a virtue.

 

[Drakkith]

Russ, just for clarity, is that the energy difference in the total spectrum, or just the visible portion?

 

[CitronBleu]

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?

 

[rcgldr]

Link to NASA article about the space station thermal regulation.

nasa/2001/ast21mar_1.htm

Link to Yahoo answer about thermal issues on the lunar missions:

https://answers.yahoo.com/question/index?qid=20081006022021AABwsaD

 

[russ_watters]

Russ, just for clarity, is that the energy difference in the total spectrum, or just the visible portion?

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.

 

[russ_watters]

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?

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.

 

[davenn]

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."

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

 

[davenn]

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

 

[Meson080]

Washington:

What would threaten astronauts who are part of a manned mission to the red planet the most? Space radiation.

According to a study, astronauts on the International Space Station (ISS) receive medications against cosmic ray radiation that exceed their lifetime after just 18 months for women and two years for men.

In case of Mars mission, a reality in next two decades, astronauts would spend at least this long in the harsh radiation of deep space.

"The tumours that cosmic radiation make are more aggressive than what we get from other radiation," Francis Cucinotta, a radiation expert at University of Nevada, Las Vegas, was quoted as saying.

He has recommended that NASA gather far more data about the health risks their astronauts are exposed to.

Astronauts are exposed to galactic cosmic rays.

If they hit an important cellular structure like DNA, they can generate mutations.

Because they move so fast, galactic cosmic rays can not being stopped much by shielding, said the authors in a report published in the journal, PLoS One.

According to the report published in LiveScience, "one way to reduce astronauts' exposure to galactic cosmic rays could be to send only during the peak of the sun's natural 11-year solar cycle".

In this period, the sun's radiation blows counter actively against the cosmic rays streaming the cosmic rays streaming into our solar system, reducing an astronaut's exposure.

The astronauts, however, have to be saved against deadly solar flares during this time.

NASA is also planning a longer stay for astronauts on the ISS. Currently, astronauts take six-month shifts.

The space agency also plans to send humans to an asteroid or beyond to understand health hazards of longterm spaceflight, the report added.

By this you would had understood, how complex things are than what you had thought.

 

[dauto]

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

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.

 

[enorbet]

<snip>
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?

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.

 

[BruceW]

(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)