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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Message-ID: <9186edb5.0310091009.118d0d4c@posting.google.com>

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


 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Vincent Cate                           Space Tether Enthusiast 
  vince@offshore.ai                      http://spacetethers.com/
  Anguilla, East Caribbean               http://offshore.ai/vince
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 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