Re: why people pretend that the moon landing was for real

Koobee Wublee:
>
>"Bilge" <dubious@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
>news:slrnd8v6mr.ii.dubious@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> >> >Now, another mystery deals with the temperature of an enclosed bubble
>> >> >of
>> >> >air
>> >> >in vacuum. According to the 1st law of thermodynamics, energy must be
>> >> >conserved. However, due to black body radiation, the temperature will
>> >> >slowly decrease. So, what is the mechanism to allow this bubble of
>> >> >air
>> >> >to
>> >> >lose 20 degrees C in a few hours?
>> >>
>> >> Radiation.
>> >
>> >That type?
>>
>> Do you mean ``What type?'' Electromagnetic.
>
>Yes, I meant "what type". Now, how do you figure the ambient temperature of
>Apollo 13 would lose 20 degrees in a few hours due to electromagnetic
>radiation?

I didn't ``figure'' anything regarding apollo 13. I answered the
question you asked. You haven't supplied the data required to answer
any question at all regarding apollo 13.

>What spectrum of the electromagnetic radiation do you have in mind?

A blackbody spectrum would be a decent first approximation.

>In the meantime, the spacecraft is still receiving a lot of energy
>from the sun.

That happens to be a rather crucial piece of information that you
haven't supplied. How much is ``lots?'' In numbers. A spacecraft
has to survive re-entry without frying the astronauts or the
electronics. How do you suppose the capsule is designed to
accomplish that? It receives ``lots more'' energy during re-entry
than it does tooling around out in space. (An insulator would
be a decent first guess - but you might consider the ability to
conduct heat around the capsule hull.)

>Have you tried to get into your car in a hot day with all the
>windows closed?

Have you ever tried to keep warm in your car on a cold day using only
the heat from the engine compartment being conducted through the firewall?

Use your head. The obvious answer to any such question requires
knowing more than just ``lots of energy from the sun hits the
spacecraft.'' However, none of this is so mysterious that one
could not calculate the answer if one really wished to do so
(with emphasis on the ``really''), as opposed to offering biased
speculation aimed a furthering a preconception.

The solution boils down to how much heat is transferred into or out of
the capsule. The total power incident on the capsule is just the total
solar output/4 \pi r^2, which turns out to be 5 kw/meter^2. You can easily
determine that the capsule can't be very hot at any point by the fact that
it doesn't melt. It doesn't even become red hot. Space capsules are mostly
made from titanium, so that sets an upper limit of 3000 K, which is the
melting point. However, any surface that is in contact with air can never
reach 900 K or it will burn. So, even on re-entry, the exterior of the
capsule never reaches 600 C. In space, the exterior is nowhere near the
temperature attained on re-entry. Do a detailed calculation using some
extreme limits.

.

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