X-Message-Number: 32702
From: Roko Mijic <>
Date: Mon, 12 Jul 2010 19:38:48 +0100
Subject: A proposal for a cryonic grave

Dear Cryonauts,

This is my first post to the cryonet list, and my subject is a
proposal for a cryonic grave to improve the probability of revival of
cryopatients.

I'd welcome any comments or criticisms, especially from those on this
list who are involved running CI or Alcor. Does it sound like
something we as a community ought to pursue further?


A proposal for a cryonic grave

The probability that cryonics organizations fail for some reason in
the next 100 years is non-trivial, even with the very best management
and organization. There are various modes of failure:

- The organizations are closed down by hostile legal action

- The organizations run out of money, for example due to a severe recession

- Society as a whole breaks down or is severely retarded by a disaster
of some kind, but eventually rebounds



If this happened, cryopreserved patients may be left to die at room temperature.

Furthermore, it seems that with the development of cryoprotectant
perfusion and the successful preservation and reanimation of animal
organs, the weakest link in the cryonics chain is now the possibility
of re-warming in between preservation and "the future".

The ideal solution to this problem is a way of keeping bodies cold
(colder than -170C, probably) in a grave. Our society already has
strong inhibitions against disturbing the dead, which means that a
cryonic grave that required no human intervention would be much less
vulnerable than a cryonics company. Furthermore, such graves could be
put in unmarked locations in northern Canada, Scandinavia, Siberia and
even Antarctica, where it is highly unlikely people will go, thereby
providing further protection. If modern society collapses reversibly,
then the cryopatient will stand a chance of revival if (and only if)
the grave can sustain them for longer than it takes for society to
bounce back.

An engineering case is put forward claiming that such a system could
be built for less than $1,000,000, with some uncertainty as to whether
a more efficient system with a higher vacuum and smaller size/cost
would work. Split between 10 or 20 patients, this cost level is highly
feasible, even if these estimates are optimistic by a factor of 2 or
even 4.

Most importantly, the "peace of mind value" of a 90% chance of
reanimation is much more than twice as great as the "peace of mind
value" of a 45% chance of reanimation. A cryonic grave would provide a
second layer of defence beyond the cryonics organization responsible
for the patient: both would have to fail for the patient to be
re-warmed.


An insulated cryogen grave: preliminary engineering case

One way to make a cryonic grave of sufficient endurance would just be
a tank of LN2 (or some other cryogen) of sufficient volume and
insulation.

A preliminary engineering case is presented as follows:

Consider a spherical tank of radius r with insulation of thermal
conductivity k and thickness r (so a total radius for insulation and
tank of 2r) and a temperature difference of deltaT, the power getting from
the outside to the inside is approximately

25 * k * r * deltaT

If the insulation is made much thicker, sharply diminishing returns
are encountered (asymptotically, only another factor of 2 is
achievable). The volume of cryogen that can be stored is approximately
4.2 * r^3, and the total amount of heat required to evaporate and heat
all of that cryogen is

4.2 * r^3 * (volumetric heat of vaporization + gas enthalpy)

The quantity is brackets for Nitrogen and a deltaT of 220C is
approximately 346,000,000 J m^-3. Dividing energy by power gives a
boil-off time of

1/12,000 * r2 * k^-1 centuries

Setting this equal to 1 century, we get:

r^2/k = 12,000. (1)

Can this constraint be satisfied without an exorbitant price tag?

A primitive way of estimating the cost of a large cryo-tank is to
scale up the costs of existing dewars and liquid nitrogen tanks, which
indicates that

Cost in dollars ~ (Volume in litres) * 20 + 5000

so that a volume of 50 cubic meters, i.e. a radius of 2.3 meters would
cost on the order of $1,000,000.

To get a system that cost less than $1M, one would therefore want a
thermal conductivity of or better than

0.0004 W/m-K

To attain thermal conductivities in the desired range, there seem to
be two routes: Multilayer Insulation (MLI) at high vacuum, or aerogel
granules at medium vacuum. It should be noted that this level of
thermal conductivity is not "breaking new engineering ground", low
temperature systems and satellites routinely achieve values in this
range.

5 cubic meter system, high-vacuum multilayer insulation

MLI is a sandwich of ultra-thin layers of aluminized mylar
interspersed with a low conductivity spacer grid. Its performance
relies on a relatively high vacuum in order to cut out gaseous thermal
conduction. Suppose that MLI is used at a higher vacuum of 10-5
atmospheres. We might expect a k value of 0.00005 W/m-K, almost an
order of magnitude better than what is required, meaning an r of
approximately 1 meter could be used. At r=1.06m, the cryogen volume
would be 5 m^3, leading to a tank-cost estimate of $90,000. Other costs
would dominate in this case (e.g. cost of engineering a reliable
vacuum, cost of insulation materials, etc.) meaning that the total
system cost would be at least n*$100,000 for some small n. However, it
is not clear whether such a vacuum could feasibly and reliably be
maintained for 100 years. Further investigation is required.

50 cubic meter system, low-vacuum aerogel insulation

The other option is aerogel granules, where a less extreme vacuum is
required. Aerogel granules at a rough vacuum yield a good degree of
insulation for the following reason:

When the mean free path of a gas increases significantly beyond the
characteristic dimension of the space that encloses it, the thermal
conductivity drops linearly with pressure. If the space is just an
evacuated gap of size ~10cm, the required pressure to begin seeing
decreased thermal conductivity is one millionth of an atmosphere, 10-6
atm. However, for tiny voids between grains of aerogel of size 0.01mm,
the required pressure is a mere 0.01 atmospheres, a very rough vacuum.

Figures of 0.0007 W/m-K for perlite powder in vacuum have been quoted,
though this is at high vacuum. Fine granules of aerogel would probably
outperform this in terms of the vacuum required to get down to < 0.001
W/m-K. On the other hand, aerogel at 0.1 atmospheres can have a
thermal conductivity of just 0.004 W/m-K, with approximately linear
improvements in k with decreases in pressure, until radiative thermal
transport dominates at very low k.

A system at 0.01 atmospheres might therefore have a k of 0.0004.

The remaining question is whether a sufficiently good vacuum can be
maintained for the required period of 100 years. Note that cryogenic
dewars maintain a high vacuum for periods of a year at low cost. It
seems that maintaining a much rougher vacuum for 100 times longer is
very feasible, especially given that the vacuum space and space
available for getters and sorbs (which scour incoming gas particles
and counteract leaks) scales with r^3, whereas leak rates scale at
lower powers of r (linearly for welds, ports, etc.).

Further improvements are possible, such as

- the use of dry ice to maintain a shield at dry ice sublimation
temperature (-78C), as dry ice has 4 times the volumetric heat
capacity of liquid nitrogen, and most of the radiative heat transfer
will occur at higher temperatures due to the T^4 scaling of blackbody
radiation. In fact, this may yield a factor of nearly 4 increased
performance, since almost all of the heat loss would be to the dry
ice.

- installation in cold permafrost at -20C, or installation in
Antarctica where winter temperatures reach -80C (though only a
relatively light system could get there economically). This would
combine well with a heat pipe/thermal reservoir to maintain the system
at winter temperature.

- the use of liquid oxygen as the main cryogen (1.4 times higher
specific heat capacity and latent heat of vaporization than nitrogen)

Development costs would have to be amortized, and as with any new
piece of equipment these are uncertain. Costs would almost certainly
drop with increased demand for such graves, perhaps to the point of
one patient per grave being feasible.

Roko Mijic

2010




Roko Mijic


07958582685
www.rokomijic.com

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