From: vince@offshore.ai (Vincent Cate)
Newsgroups: sci.space.tech
Subject: Re: Heat Sink Heat Shields
References: <5dcb47db.0310011151.51d744ce@posting.google.com> <9186edb5.0310012120.758e3a2a@posting.google.com>
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I got a new book and learned some more. First I have added 2 lines
for ablatives to the most interesting parts of the table earlier in
this thread:
Material Conductivity Density Specific Melting HeatSink
Heat Point
W/m-C kg/m3 J/kg-C C Joules/Kg
Beryllium 175 1,859 1885 1278 2,409,030
Aluminum 220 2,707 896 660 591,360
Copper 386 8,954 380 1085 412,300
If steam used in transpiration x4 13,005,600
Phenolic-nylon Charing Ablative 15,000+ BTU/lb (p. 127) 34,890,000
Apollo Total heat/heat shield weight (p. 133) 13,886,220
The book says that for Apollo to have used Beryllium, the heatsink
would have to have been about half the total mass (page 120). With
the ablative they show the heat-shield weight as 1300 lbs out of
a total of 9500 lbs or 13.7%. It has 5,970 BTU/lb as the
total heat / heat shield weight which I converted to 13,886,220
Joules/Kg. No doubt there is some margin there. It is dated 1968
(i.e. before landing on the moon) so there is some chance some
Apollo numbers changed after ths book came out.
The book is "Re-entry and Planetary Entry Physics and Technology -
II / Advanced Concepts, Experiments, Guidance-Control and Technology"
By W. H. T. Loh
There is also a volume I, but II has been more interesting so far.
My attempts to simulate the Apollo reentry are not working well
so far. The book describes the Apollo computer's guidance logic
during reentry but my simulator does not have that. I may try
to put the logic in just so I can get some validation of my
simulator.
If I scale the heat I get at 7.7 km/sec to 11.3 km/sec I get
close to their numbers. The kinetic energy goes up with the
square of velocity, this would be about 2.15 times the heat
(we are assuming the same fraction of the heat goes into
the capsule, which is only an approximation). If you take
2.15 times the heat I get for a 7.7 km/sec reentry you are
about at the heat the book says for Apollo reentry. So my
similator may be close to reality on reentry heat!!!!!
-- Vince
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Vincent Cate Space Tether Enthusiast
vince@offshore.ai http://spacetethers.com/
Anguilla, East Caribbean http://offshore.ai/vince
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You have to take life as it happens, but you should try to make it
happen the way you want to take it. - German Proverb