Today’s guest video is from Amy at Vintage Space,
who has brought along one of the greatest
and also the tiniest props that I have ever seen
Amy, it’s all yours.
One of the benefits to being a professional space history nerd
is you get to add some amazing artefacts to your private collection.
My latest addition is this tiny piece of Kapton foil from Apollo 11.
This tiny piece of foil went to the moon and came back through the earth’s atmosphere
to be put on to this piece of paper, so I can hang it on my wall.
But if you look closely at the piece, you’ll notice that it’s sort of silvery
and it looks like it’s been scratched off and there’s gold underneath.
So, what’s going on with this piece of foil?
What exactly was that silvery stuff?
And the larger question is, why does the Apollo spacecraft look white when it launches,
silver when it’s around the moon,
and a dirty gold once it’s come back to earth?
Well, it’s all part of the thermal protection system.
Thermal protection was a huge engineering challenge for the men and woman who designed
and built the Apollo spacecraft.
Not only was the vehicle going to be flying through the vacuum of space
where it would be exposed to raw, unfiltered sunlight
and also in the shadow behind the moon, where there would be no light hitting it at all:
it also had to return through the earth’s atmosphere at lunar re-entry speeds.
This is an insanely fast re-entry through the earth’s atmosphere.
In the case of Apollo,
this re-entry speed was 24,677 miles per hour or 36,194 feet per second.
That translated to a heat during re-entry of over 4,000 degrees Fahrenheit.
That meant the Apollo spacecraft was going to need
a very specific thermal protection system
to not only get the spacecraft through the earth’s atmosphere in one piece,
but to protect the three astronauts inside it.
The thermal protection system actually involved a number of different elements.
First was the boost protective cover.
This is the white covering that fits over the command module
that you see as being white when the spacecraft has made it to its launch vehicle
on the launch pad, ready to go to the moon.
This protected the spacecraft from the heat associated with launching through the atmosphere,
but it didn’t last very long.
The boost protective cover was separated from the spacecraft
when the launch escape tower jettisoned 200 seconds after launch.
Once the boost protective cover was clear, the spacecraft looked silver.
That’s because the entire Apollo command module was covered with a pressure sensitive
Kapton polyimide tape.
This tape was made of coded aluminium and oxidized silicon monoxide.
The tape was applied to the entire external structure of the command module
with the gold side down and the silver side facing out.
That’s why,
when you see pictures of the Apollo spacecraft in orbit around the moon,
it looks like it’s reflecting space in a mirror.
It’s beautiful.
Now, when it came time for the Apollo spacecraft to re-enter the atmosphere,
this Kapton tape wasn’t exactly enough to protect it from the searing heats of re-entry
and it wasn’t designed to.
The Apollo spacecraft,
like the Mercury and Gemini vehicles before it, was a blunt body design.
It had a rounded bottom and a conical after body,
designed to minimize convective heating during re-entry.
The centre of gravity in the vehicle was also offset from the axis of symmetry
in order to generate a very small amount of lift.
This meant that the spacecraft had a little bit of controllability during re-entry.
So, the blunt underside of the spacecraft was taking the brunt of the heat
and that was where the last piece of the thermal protective system was housed.
That of course is the ablative heat shield.
The heat shield was a honeycomb structure bonded to the stainless-steel body of the
spacecraft
and each little honeycomb was individually filled with an ablative material
that would burn away as it was heated
thus protecting the spacecraft from the worst of heat of re-entry.
But, the heat shield and the bow shock generated by that blunt body of re-entry
couldn’t entirely protect the outer structure of the spacecraft.
As it went through that fireball phase of re-entry the Kapton was burned away a little bit,
revealing the golden underside of the tape.
But how is it that I’m able to actually own a piece of the Apollo 11 spacecraft?
Well, it turns out that recovery crews and pretty much anybody
who could get within arm’s reach of the spacecraft,
and this doesn’t just go for Apollo 11,
this applies to all the vehicles that went to the moon,
they would reach up and just take off a tiny piece of that foil as a souvenir.
So, even if at first glance it looks like a tiny insignificant dime-sized portion of foil,
it’s actually amazing to think that that little dime-sized piece of foil
helped to protect the Apollo 11 astronauts on the way to the moon
and their re-entry back through the earth’s atmosphere.
Go subscribe to Amy’s channel for all sorts of videos about space flight!
I would recommend starting with her one on how the Saturn V got to the launch pad.
Next time, we have a video about linguistics and music all in one.