X-Message-Number: 25989
From: "Basie" <>
Subject: Rotating cryostat
Date: Fri, 8 Apr 2005 23:15:48 -0400

 I wonder how long it would take for the ice in the body to migrate to the 
head in a cryostat. It would be expensive and risky but ideally the patient 
should slowly rotate.


This is a quote!

"Another way to slow chemical activity is by lowering the temperature. The 
problem here is that some materials go through a significant phase change as 
temperature is lowered, water being the most obvious example. Not only does 
water freeze to sharp-edged ice crystals, but these expand to a larger 
volume than that occupied by the original water. Also, over time, the 
crystals - as crystals do - consolidate, moving water molecules from one 
place to another. So you eventually wind up with a dehydrated material 
having a few large pieces of ice dispersed through it. There would be, of 
course, major changes in the texture and perhaps of the chemistry of the 
preserved material during this process.
     The lower the temperature the slower this migration. At cryogenic 
temperatures it is pretty much - though not completely - stopped. Still, 
material stored in liquid helium would probably keep a long time before this 
process caused a significant amount of damage. The problem is that - on 
Earth, at least - maintaining such low temperatures requires a highly 
technical infrastructure. If you really want to preserve something a long 
time by freezing, you'd have to leave the planet. (The Antarctic ice caps 
are only a few million years old at most. Even without warming periods 
melting them, the pressure of new snow on top slowly squeezes the lower ice, 
causing physical deformation. Much of the ice is eventually pushed out onto 
the ocean by slow creeping due to the weight of ice above it and further 

     For really long term storage you definitely want cryogenic 
temperatures, whatever else you may do to preserve your material. Burying 
something in an icy planetesimal well out in the Oort Belt or Kuiper cloud 
would do for at least a few hundred million years. The temperature would be 
a few Kelvins, plenty cold enough. But there's one small problem. When other 
stars pass by, every few million years, their gravity affects the orbits of 
these bodies, sometimes sending one or more careering through the inner 
solar system. The chance of any one particular body having this happen is 
remote, but still... Even using a free body, one which orbits the galaxy 
independently of a parent star, runs this risk. And there's also a chance of 
collision, as well as cosmic rays. If you want to keep something frozen for 
billions of years this just won't do.

     Interestingly, there's a place much nearer to Earth where a 
low-maintenance cryogenic facility capable of holding a very low temperature 
for a few billion years and providing better protection from cosmic 
radiation could be built. Find a crater at one of the Moon's poles. Dig a 
narrow, vertical shaft. Insulate the bottom and sides with multiple, waffled 
layers of something appropriate. (Aluminized or silverized mylar, for 
instance.) Place your object there. The deeper the shaft the lower the rate 
of micrometeoroid impacts and the lower the amount of outside radiation 
(including thermal) which makes it to the bottom. However, the Moon does 
generate some internal heat, so the hole can't be too deep. Half a kilometer 
or so should work fine. With the object insulated from the surrounding rock 
and open to empty space in a vacuum, temperatures will soon be down to not 
far above the microwave background. Devices of this type are known as Ruzic 
Cryostats. Of course, at the most, this will only last until the sun enters 
its red giant phase... No matter how hard you try, nothing lasts forever.

     So, let's accept and value impermanence, and appreciate things for the 
few billion years they'll be around."

     This work is Copyright 2002 Rodford Edmiston Smith. Anyone wishing to 
reprint this material must have permission from the author, who can be 
contacted at: 

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