Was Apollo's heat shield segmented?

[ This is a repost of the following article: ]
[ From: Rick Jones ]
[ Subject: Was Apollo's heat shield segmented? ]
[ Newsgroups: sci.space.tech ]
[ Message-ID: ]

I just went to http://www.spacex.com/updates.php and their update for
May 14 2009 has some pictures of Dragon:

http://www.spacex.com/assets/img/200...ragontrunk.jpg

shows Dragon maded with the trunk section, and:

http://www.spacex.com/assets/img/20090514_picax.jpg

shows the heat shield. The image and text suggest that the heat
shield is in tiles rather than one cohesive unit. Was that the case
with Apollo? My recollection is was not but thought I would ask.
Also, some of the wording states:

"The gap between the capsule and trunk in the photo above will be
filled by our lightweight, high performance PICA-X heat shield panels
which will protect the capsule during reentry."

From the images and the description, does that mean that the edges of
the heat shield are going to be "exposed" during launch?

rick jones
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On Tue, 19 May 2009 23:55:54 +0000 (UTC), Rick Jones
wrote:

I just went to http://www.spacex.com/updates.php and their update for
May 14 2009 has some pictures of Dragon:

http://www.spacex.com/assets/img/200...ragontrunk.jpg

shows Dragon maded with the trunk section, and:

http://www.spacex.com/assets/img/20090514_picax.jpg

shows the heat shield. The image and text suggest that the heat
shield is in tiles rather than one cohesive unit. Was that the case
with Apollo?

No.

http://history.nasa.gov/SP-4205/ch4-2.html

Scroll down for pictures of the heat shield being installed.

Brian

shows the heat shield. The image and text suggest that the heat
shield is in tiles rather than one cohesive unit.

I wonder if that means there will be "gap fillers" on Dragon?

Was that the case with Apollo?

No.
http://history.nasa.gov/SP-4205/ch4-2.html
Scroll down for pictures of the heat shield being installed.

Thanks.

rick jones
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Process shall set you free from the need for rational thought.
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On May 19, 9:59*pm, OM wrote:
On Tue, 19 May 2009 23:55:54 +0000 (UTC), Rick Jones

wrote:
shows the heat shield. *The image and text suggest that the heat
shield is in tiles rather than one cohesive unit. *Was that the case
with Apollo? *My recollection is was not but thought I would ask.

...Nope. One solid shield consisting of Hexcell filled with ablative
resin.

* * * * * * * * * * * * * * * *OM

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I just looked at an Apollo shield at the Smithsonian. It was a single
large honeycomb-like structure filled with an ablative material.
Different shields showed diff ablative patterns too. Dont know what
that means.

Brian Thorn wrote:
http://history.nasa.gov/SP-4205/ch4-2.html

Scroll down for pictures of the heat shield being installed.


I saw the Columbia CM when they took it to all the states after it returned.
The honeycomb structure was very noticeable on the burnt heatshield.
Imagine trying to form honeycomb structure around the X-23's belly for
its ablative heatshield:
http://www.ninfinger.org/models/x_planes/x23_01.jpg
....that must have been fun. :-)

Pat

Frogwatch wrote:
I just looked at an Apollo shield at the Smithsonian. It was a single
large honeycomb-like structure filled with an ablative material.


Every single individual honeycomb cell on those Apollo heatshields was
filled by hand using something like a oversized hypodermic syringe to
avoid bubbles (by women, IIRC). If one showed any bubbles in tests after
it was filled, then it had to be cleaned out and refilled.
Once they were all filled up to spec with no bubbles in any of them,
then the heatshield was heated to cure the rubber-like ablative material
and then machined down to final shape.
I forget how many total woman-hours of work it took to make one
heatshield, but IIRC, it was up in the thousands.

Pat

I saw the Apollo 7 CM on display at an aviation museum in Dallas recently
and you can definitely see the honeycomb structure of the heat shield on
that. Reminded me of a burnt beehive.

Matt J. McCullar wrote:
I saw the Apollo 7 CM on display at an aviation museum in Dallas recently
and you can definitely see the honeycomb structure of the heat shield on
that. Reminded me of a burnt beehive.


The reason that bubbles were bad news is that they could cause turbulent
airflow when one was exposed via ablation...and that could cause the
cells surrounding it to also start burning away at a uneven rate - till
it burnt clean through the heatshield as the heating got worse via even
more unevenness in the aerodynamics of the heatshield as the damaged
area grew in size.
The Shuttle can also suffer from this problem if an irregularity in the
belly TPS causes the spun silica tiles to start heating to the point
where they melt rather than just soaking up the heat - due to
non-laminar airflow over them during the highest-heat point of the
reentry - which is why NASA has been so concerned about doing any
repairs to damaged tiles on-orbit... you get the surface too uneven via
a repair and the cure could be worse than the problem.
I don't know if anyone ever checked to see if the dread "zipper effect"
occurred during the Columbia reentry... this was a scenario where a
missing tile caused the adhesive that binds the tiles aft of it to the
airframe to overheat from turbulent superheated airflow, and more and
more tiles to begin to detach in rapid succession.

Pat

"Matt J. McCullar" wrote:

I saw the Apollo 7 CM on display at an aviation museum in Dallas recently
and you can definitely see the honeycomb structure of the heat shield on
that. Reminded me of a burnt beehive.

That's a one piece honeycomb filled with ablative, not hexagonal tiles
assembled into a honeycomb.

D.
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Oct 5th, 2004 JDL

Why the honeycomb structure? How did it improve the performance of the
heat shield?

I can see that casting the shield as a single piece, like a giant
contact lens, might make it very hard to get a bubble-free shield, so
that that breaking the casting process into a bunch of smaller cells
might make sense from a manufacturing perspective. But was that the
only reason for the honeycomb?

David

OM wrote:

On Tue, 19 May 2009 19:11:12 -0700 (PDT), Frogwatch
wrote:

I just looked at an Apollo shield at the Smithsonian. It was a single
large honeycomb-like structure filled with an ablative material.

...As I said. Hexcell filled with ablative resin.

OM

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