
Ask HN: How do instructions on opening the Soyuz capsule survive reentry? - chungleong
I saw a Soyuz reentry vehicle today at the cosmonaut museum in Zhytomyr. At the bottom of the capsule there&#x27;re instructions in both Russian and English for opening it. That makes sense since the thing could land far beyond the designated landing zone. What I don&#x27;t get is how the text could survive reentry since it&#x27;s printed where the heat shield is.<p>Here&#x27;s a picture: https:&#x2F;&#x2F;ibb.co&#x2F;RgfZfPR
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Someone
I would think your question boils down to “how do these layers of paint
survive reentry?”

Firstly, they aren’t on the heat shield, but on the part of the capsule it
shields.

[https://en.m.wikipedia.org/wiki/Atmospheric_entry#Ablative](https://en.m.wikipedia.org/wiki/Atmospheric_entry#Ablative)
explains how that shielding works:

 _”The ablative heat shield functions by lifting the hot shock layer gas away
from the heat shield 's outer wall (creating a cooler boundary layer)”_

So, it’s not only that insulation layers in the heat shield slow down direct
heat transfer to the capsule. Also, evaporation of the heat shield pushes the
place where heat is produced away from the heat shield.

The shape of the capsule also helps, as it prevents (most of) the hot gases
from coming close to the wall of the capsule.
[https://blog.scienceandindustrymuseum.org.uk/re-entry-
gettin...](https://blog.scienceandindustrymuseum.org.uk/re-entry-getting-home-
safely/):

“ _WHY IS THE CAPSULE BLUNT?

When we think of vehicles that are designed to go fast, they are usually sharp
and slender to minimise the drag. However, with a space capsule we want to
maximise drag to slow down for a safe landing. The blunt capsule design was
first proposed by Harvey Julian Allen in 1953 at NASA Ames research centre. It
had two advantages—not only the high drag needed to reduce speed but also the
blunt shape, which resulted in the shock wave detaching from the surface of
the vehicle. This helped to reduce the very high temperatures (around 1,648°C
for the space shuttle nose) from directly contacting the surface, which would
otherwise melt.“_

(That page has a photo of the shock waves around a Soyuz during recently)

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sawaruna
That part is underneath a primary heat shield:
[https://i.imgur.com/CovYbor.png](https://i.imgur.com/CovYbor.png)

You can see it dropping off @ 5:20 here:
[https://www.youtube.com/watch?v=GWusG5EW3dU](https://www.youtube.com/watch?v=GWusG5EW3dU)

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gus_massa
Clicky: [https://ibb.co/RgfZfPR](https://ibb.co/RgfZfPR)

