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I was surprised to find out from @JohnnyRobinson's new answer that China's series of Fanhui Shi Weixing spacecraft (FSW) used impregnated oak heat shields. I found this in astronautix:

The capsule for the FSW, like that of the US Discoverer/KH-1 spy satellite, was mounted heat shield-forward on top of the launch vehicle. The ablative impregnated-oak nose cap covered electrical equipment. The spherical aft dome contained the recovery parachute. (emphasis added)

Question: Did these spacecraft re-enter narrow-end or "nose" first? If so, was this aerodynamically stable? Most re-entry spacecraft (manned capsules for example) tend to be larger, blunt-end first. Why would nose-first have been chosen early-on?

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above: Labeled "JB-2" in astronautix, presumably a FSW spacecraft.

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above: "Recovery of FSW-17 photoreconnaissance satellite." From astronautix.

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above: Image of FSW-3 or FSW-4 from globalsecurity.org.

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above: "FSW reconnaissance satellite in assembly." From astronautix.

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above: Screen shot from China's Space Program - From Conception to Manned Spaceflight by Brian Harvey, 2004, Springer-Verlag London, 978-1-85233-566-3, (also here)

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above: Screen shot from CORONA: America’s First Satellite Program Kevin C. Ruffner, Ed., Center for the Study of Intelligence, Central Intelligence Agency, Washington, D-C. 1995

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uhoh
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    @OrganicMarble not sure what I was thinking re the original (sic) spelling, possibly a series of 21st century SF novellas? – uhoh Jan 17 '17 at 04:07

1 Answers1

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The advantages of the blunt end first design were known well before either vehicle was launched (1958, a few years earlier for spy satellite designers). However, pointy end first is the simplest design that works.

  • Falling objects generally want to go heavy end first, draggy end last. With a heavy heat shield on the front and a light but bulky parachute in the back, pointy end first is more stable.

  • Most rockets provide a cone shaped space for the payload. Launching blunt end first would need a large fairing, and putting the heat shield at the back makes connections to the rest of the spacecraft a whole lot more complicated.

That makes it perfect for early designs or when reliability is more important than launch mass. However, there are a couple of issues that make it impractical for large / manned capsules.

  • It requires significantly more thermal shielding. Part of this is simple geometry - the blunt end has less area to cover. On top of that the shockwave from a blunt object keeps most of the heat away from the vehicle, so a blunt end first shield can be thinner as well.

  • Acceleration and deceleration are in opposite directions. Equipment can be secured in all directions easily enough, but an astronaut would experience reentry as 8 g while tied to the ceiling, which seems distinctly unpleasant.

Quentin Clarkson
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  • A very clear and well written answer as was this one as well - thanks! – uhoh Jan 16 '17 at 08:38
  • Concerning "simple geometry - the blunt end has less area to cover". Does not the "pointy end", being at a slant, incur less air resistance (per area) than the blunt end? I would think that would reduce some of the "pointy end" thermal shielding needs. Do not both ends have the same sized air resistance profile - a circle. – chux - Reinstate Monica Jan 17 '17 at 06:47
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    @chux That part is assuming equal shield thickness. Although both ends do need to move the same volume of air, a sharp cone allows hot gases to flow along the surface of the vessel, increasing the thermal load. – Quentin Clarkson Jan 17 '17 at 07:08
  • Perhaps I'm ignorant here, but wouldn't experience the 8g of forces in a forward direction be safer than the current way during reentry? (8g of "backwards" acceleration)

    The opposite being true during liftoff, obviously. Seems they need swivel chairs.

     – Ezra Bailey Aug 16 '17 at 17:58
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    @SarahBailey The forces are all in the same direction that the capsule is designed for - backwards deceleration during reentry is equivalent to forward acceleration during launch. – Quentin Clarkson Aug 16 '17 at 22:23
  • @QuentinClarkson Ah, I forgot that they'd feel the "push" in the opposite direction because of deceleration! Thanks! :) – Ezra Bailey Aug 17 '17 at 12:35