Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pulling External Tank into orbit (summary so far)
Date: Fri, 6 Aug 1999 14:48:06 GMT

In article <7od3fa$2gc$1@nnrp1.deja.com>, gbaikie  <gbaikie@hotmail.com> wrote:
>If you are going to redesign ET why not leave the foam off the ET- put
>it into orbit without foam- put a jacket around the ET and remove say
>an hour before launch- or fuel up just before launch.

Unfortunately, the foam is not really optional.  The foam on the LH2 tank
really has to be there throughout, or you get excessive LH2 boiloff and
formation of liquid air on the tank surface.  LH2 tanks simply *must* be
insulated.  (The foam on the LOX tank is probably optional after liftoff;
the main concern there is ice buildup causing tile damage at launch.)
Previous experience with jettisonable insulation has not been good.

>That or simply use a "better foam".

Wishing for it doesn't necessarily make it available.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Pulling External Tank into orbit (summary so far)
Date: Sun, 8 Aug 1999 00:21:47 GMT

In article <37ACA835.A1A8087B@greenms.com>,
Greg Moore (Strider) <mooregr@greenms.com> wrote:
>> Unfortunately, the foam is not really optional.  The foam on the LH2 tank
>> really has to be there throughout...
>
>	Didn't the S-II stage use insulation INSIDE the tank?  Would that
>perhaps be a possibility here I wonder.

The S-IV and S-IVB had internal insulation.  The S-II originally had an
external insulation jacket purged with helium, which was a huge headache
and never worked as well as hoped; midway through, it switched to spray-on
foam insulation (sound familiar?), still external.

Converting the ET to internal insulation would not be impossible, but
would be a major engineering job.  It has ramifications far beyond the
insulation itself; for example, metals are generally stronger at low
temperatures, so putting the insulation inside makes the ET structure
weaker.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)