🚀 go-pugleaf

>
>
>        For Christmas I received a Space Shuttle model with instructions to
>paint the underside black.  This brought up the question "Why is the
>bottom of the Shuttle black?"  It occurred to us that a black surface might
>absorb a lot more radiation and that in space there might be greater
>exposure to radiation than on earth, so why isn't the whole shuttle white
>or perhaps silver to reflect as much as possible?
>
>        Perhaps a simple posted response would be better than everyone
>sending mail to me, only to have me follow up with a post.
>
>--
>/*______________________________Jeff Tannehill_______________________________*

    The shuttle uses many different types of thermal insulation. There
    are tiles and thermal blankets, and there are varieties of each.
    The black tiles are rated for the highest temperatures and are used
    where the shuttle gets the greatest heating (the underside, the nose,
    and the leading edge of the tail). White tiles are next, with the
    second-highest rated protection, and are used on the forward fuselage,
    the aft area, and the tail. The lowest temperatures on the shuttle
    are experienced on the upper surfaces, i.e., the tops of the wings
    and the tops of the payload bay doors. In this area, NASA switched
    from white tiles to thermal blankets in 1984, so Discovery, Atlantis,
    and Endeavour have blankets while Columbia still mostly has tiles.
    Both are white, but you can see the differences in good photos.
    
    That's a simple, but not complete or 100% accurate description. The
    Shuttle also uses a grey thermal insulation on the wing leading
    edges, but I'm not sure which category they belong to.
    
    Please note that the tiles and blankets have proven very effective
    in the years since the 1981-82 test flights, despite their
    reputation for being a maintenance nightmare. The average flight
    requires the replacement of only a half-dozen tiles (more on the
    dry-lake runways at Edwards, less on the concrete at the Cape.)
       
    -Brian

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Brian S. Thorn                                    "If ignorance is bliss,
BrianT@cup.portal.com                               this must be heaven."
                                                -Diane Chambers, "Cheers"
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In article <725334983@romeo.cs.duke.edu> jwt@duke.cs.duke.edu (Jeffrey W. Tannehill) writes:
>...paint the underside black.  This brought up the question "Why is the
>bottom of the Shuttle black?"  It occurred to us that a black surface might
>absorb a lot more radiation and that in space there might be greater
>exposure to radiation than on earth, so why isn't the whole shuttle white
>or perhaps silver to reflect as much as possible?

As Brian pointed out, the difference in colors reflects differences in
materials resulting from different heat loads during reentry.

A black surface will generally absorb more light and heat, but it will
also radiate heat better.  Choice of materials for spacecraft thermal
control is complex and much depends on detail.  Actually, it probably
*would* be preferable, strictly from a thermal viewpoint, to have the
shuttle belly painted white... but I doubt that paint would survive
reentry on the high-temperature areas.
-- 
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  henry@zoo.toronto.edu  utzoo!henry

In sci.space.shuttle, BrianT@cup.portal.com (Brian Stuart Thorn) writes:
>     The shuttle uses many different types of thermal insulation. There
>     are tiles and thermal blankets, and there are varieties of each.
>     The black tiles are rated for the highest temperatures and are used
>     where the shuttle gets the greatest heating (the underside, the nose,
>     and the leading edge of the tail). White tiles are next, with the
>     second-highest rated protection, and are used on the forward fuselage,
>     the aft area, and the tail. The lowest temperatures on the shuttle
>     are experienced on the upper surfaces, i.e., the tops of the wings
>     and the tops of the payload bay doors...
>     
>     That's a simple, but not complete or 100% accurate description. The
>     Shuttle also uses a grey thermal insulation on the wing leading
>     edges, but I'm not sure which category they belong to.

  The grey insulation is a composite material called RCC (reinforced
carbon-carbon).  It is used only on the nose of the orbiter, and the leading
edges of the wings - the two places where the orbiter gets hottest during
descent. RCC can withstand much higher temperatures than the black tiles can.

  The principal drawback of RCC is the price - I heard once that, to replace a
half-meter strip on one of the orbiter's wings cost somewhere around $6 million
bucks...

Ty Willis
Stephen F. Austin State University
a_willisgt@ccsvax.sfasu.edu

jwt@duke.cs.duke.edu (Jeffrey W. Tannehill) writes:
: 
: 
: 	For Christmas I received a Space Shuttle model with instructions to
: paint the underside black.  This brought up the question "Why is the
: bottom of the Shuttle black?"  It occurred to us that a black surface might
: absorb a lot more radiation and that in space there might be greater
: exposure to radiation than on earth, so why isn't the whole shuttle white
: or perhaps silver to reflect as much as possible?


	Colour affects heat absorption in cases where the heat is being
radiated. The shuttle experiences heat absorption due to friction.
The SR-71 is black. The skin of the plane is aligned perfectly so
that when the skin begins to ripple (sortof like coorogated sheet
metal), the ridges and valleys are set up so that they are in line
with the air flow.    If you take a sheet of white paper and a
sheet of black paper and rub each on a smooth surface they should
both heat at the same rate....

				Ryan

Ty Willis, Stephen F. Austin State University <a_willisgt@ccsvax.sfasu.edu> writes:
> The grey insulation is a composite material called RCC (reinforced
> carbon-carbon).  The principal drawback of RCC is the price - I heard once 
> that, to replace a half-meter strip on one of the orbiter's wings 
> cost somewhere around $6 million bucks...  
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Ah, the mysteries of government procurement contracts!
If you start with thousand-dollar hammers, yea, it's possible!   :-)

klassen@sol.UVic.CA (Melvin Klassen) writes:

>Ty Willis, Stephen F. Austin State University <a_willisgt@ccsvax.sfasu.edu> writes:
>> The grey insulation is a composite material called RCC (reinforced
>> carbon-carbon).  The principal drawback of RCC is the price - I heard once 
>> that, to replace a half-meter strip on one of the orbiter's wings 
>> cost somewhere around $6 million bucks...  

Yes, it does. Because it has to be moulded to fit, and NOT CUT. And it has to be ac close to aerodynamically smooth to avoid local hot spots.

-- 
Edward C. Otto III			* e-otto@uiuc.edu
No one really knows...                  * edotto@ux1.cso.uiuc.edu
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