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Author Topic: Why don't materials sheer in space due to the cold?  (Read 3198 times)

Offline walterCbx

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Walter Bubie asked the Naked Scientists:

Thank you all for newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive]!

My question: What is the risk of breakage of some exterior part of the space station being repaired by astronauts, considering the super cold temps of space?

I have seen those lab demos where tough objects are dipped in liquid nitrogen and then easily shattered with a good whack.

I imagine it is as cold in space - at least in the 'shade'.  Or are all space repairs done in sunlight so  the repair area warms up before any bolts are turned (without being snapped)?  

Thanks!

What do you think?


 

Offline lightarrow

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Why don't materials sheer in space due to the cold?
« Reply #1 on: 17/06/2008 12:50:39 »
Walter Bubie asked the Naked Scientists:

Thank you all for a very enlightening and entertaining show!

My question: What is the risk of breakage of some exterior part of the space station being repaired by astronauts, considering the super cold temps of space?

I have seen those lab demos where tough objects are dipped in liquid nitrogen and then easily shattered with a good whack.

I imagine it is as cold in space - at least in the 'shade'.  Or are all space repairs done in sunlight so  the repair area warms up before any bolts are turned (without being snapped)? 

Thanks!

What do you think?

Spacesuits are thermoregolated with many little pipes near the astronaut's body through which flows a cooled or heated liquid.
 

Offline LeeE

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Why don't materials sheer in space due to the cold?
« Reply #2 on: 17/06/2008 16:08:56 »
That's a good question Walter.  I imagine the ISS generates a fair amount of heat, which can only be radiated away - no conduction - so that might help keep the temps up a bit, but the HST operates at very low temps, so I would guess that the nuts and bolts etc. are made from stuff that isn't effected by the temps.
« Last Edit: 17/06/2008 17:40:52 by LeeE »
 

lyner

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Why don't materials sheer in space due to the cold?
« Reply #3 on: 19/06/2008 10:34:29 »
Because a space station is, essentially, in a vacuum, energy gain and loss are by radiation, as you say LeeE.
There is plenty of Solar Energy for an object at the same distance from the Sun as we are.
The core temperature of a  'black' sphere made of a good conducting material will stabilise at about 300K in Earth orbit. (The occasional eclipse doesn't have much effect  on average)
This is because the radiation from a body at about 300K (peak wavelength in the Infra Red region) will balance the energy received from the Sun (peak wavelength in the visible region of the spectrum) .  This accounts for the Earth's average temperature although there is a contribution from heat sources in the core too.

If the body in space is not a good conductor, the 'dark side' can get very cold (same effect as in the Sahara Desert on a clear night). If  space station is kept in the same orientation wrt the stars, the dark side would be dark for six months at a time so parts could get v. cold.

Satellites, HST and Space Stations have to do a lot of  thermal control to balance the temperatures of the different parts.
This is done using insulating / reflective coatings, heat pipes and air blowers (unfortunately you can't get any natural convection in microgravity).
The permitted range of temperatures depends on what you are trying to protect. Humans are very fussy, electronic equipment is a bit less fussy, telescope mirrors could be very sensitive to temperature gradients but nuts and bolts might not be too fussy and conduction through the structure should prevent serious excesses in temperature. There is one thing in their favour and that is the mechanical stresses are pretty low (after launching) so they may not need to be tightened too much. But,  OTOH, you can get things welding themselves together in a vacuum.
I do remember a fantastic (live  TV) sequence on the HST in which a maintenance  engineer was  struggling  to remove a bolt. The success of the whole mission hung on this particular procedure, I seem to remember. A lot of relief when it came apart! WD40 in space? Does anyone else remember it?

I guess there is no one who would claim that was done at Universal Studios?
 

Offline walterCbx

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Why don't materials sheer in space due to the cold?
« Reply #4 on: 20/06/2008 02:34:09 »
Thanks for the thoughtful, detailed answers. I like your explanations.  I have imagined that the ISS was super insulated, so I was surprised by the explanation that a significant amount of the internal heat would 'leak' out into space.  I was also surprised to know that the 'skins' of the spacecraft are engineered, with heat/cooling coils, conductive blankets, and blowers (sort of like human skin), It makes sense now, realizing that there is virtually no convection in micro-gravity. 
A "living" spacecraft skin probably explains a related question I had - how does the ISS tolerate, what I imagine are significant thermal expansion/contraction gradients created when "half" the craft is in a cold shadow and the other half is in the direct heat of the sun.

Cheers!
 

lyner

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Why don't materials sheer in space due to the cold?
« Reply #5 on: 20/06/2008 07:55:33 »
Quote
A "living" spacecraft skin probably explains a related question I had - how does the ISS tolerate, what I imagine are significant thermal expansion/contraction gradients created when "half" the craft is in a cold shadow and the other half is in the direct heat of the sun.
An interesting question.
Imagine not being able to shut the door behind you when you leave because of distortion. Perhaps they are all issued with sandpaper!
 

Offline RD

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Why don't materials sheer in space due to the cold?
« Reply #6 on: 20/06/2008 09:05:02 »
The real problem with astronauts turning bolts in space is low torque: without gravity the astronaut just rotates in the opposite direction. 
http://www.ingentaconnect.com/content/hfes/hfproc/1994/00000038/00000010/art00011
 

lyner

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Why don't materials sheer in space due to the cold?
« Reply #7 on: 20/06/2008 09:46:43 »
I believe that workers on oil rigs use special tools - reactionless designs - to work on heavy nuts and bolts because they have a similar problem.  They use a number of divers(e) methods to overcome it.Owch.
 

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Why don't materials sheer in space due to the cold?
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