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From: (Henry Spencer)
Subject: Re: Another tank question
Date: Fri, 19 Feb 1999 01:06:36 GMT

In article <>,
George C. Mantis <> wrote:
>Which begs the question: Why in the heck did they place this line there? Since
>it's just a purge line, not connected to anything on the exterior, could they
>not place this line out of harm's way? I imagine repairing all those TPS
>impacts after every flight must cost a GREAT deal of time and money.

The fast answer is:  because they did not realize that falling ice would
be a problem until quite late in development.

This shows up in other ways, too.  The reason why on-pad LOX venting is
done through that odd-looking "beanie cap", rather than through a simple
and inconspicuous umbilical, is that originally the LOX boiloff was simply
vented into the open air at the top of the tank.  When they realized that
the resulting local icing was unacceptable, it was too late to move the
venting plumbing to a proper umbilical, so they ended up improvising an
umbilical that would sit over the existing vents.  The shuttle program
was very short of money when it went through puberty (the stage before
maturity, when the facts of life become apparent :-)), and a number of
problems had to be patched over rather than fixed properly.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: Causes of low flight rate for shuttle
Date: Fri, 9 Apr 1999 15:15:34 GMT

In article <>,
Greg Moore (Strider) <> wrote:
>> You can be too modular....
>	And some of the modularity WAS in the original design.  The problem is
>the interfaces between modules drives up the dry mass of the vehicle.
>And usually one of the first things to go in a new vehicle is the dry
>mass margin.  So, you start looking for places to save a few kilos and
>decide that the modules weigh to much and would weigh a lot loss if they
>weren't modules.

And the shuttle had a major weight squeeze early in its development, when
(as I recall) it became clear that the takeoff gross weight of the orbiter
had to be reduced.  The rational approach would have been to either scale
the rest of the system up slightly to eliminate the need to reduce orbiter
weight, or scale the orbiter down slightly.  But neither was considered
acceptable:  the latter would have reduced the payload, which was deemed
politically unacceptable, and the former was considered too big a change.
So the orbiter had to lose quite a bit of weight no matter how much it
The good old days                   |  Henry Spencer
weren't.                            |      (aka

From: (Henry Spencer)
Subject: Re: solid rocket steering
Date: Sun, 18 Apr 1999 01:15:09 GMT

In article <7fa9ch$16s$>,
Magnus Redin <> wrote:
>Btw, were there any plans to do an "Atlas" kind of stack? To have a
>jetissonable pod with SSME:s below the external tank and recover it in
>the same way as the SRB:s. Its halfway to the original idea of having
>two manned fully recoverable vehicles.

There was talk of such things for cargo variants which would delete the
orbiter, but not for the orbiter configuration.  (Also, late in the
evolution of the series of stillborn projects that started with ALS, there
were several Atlas-style stage-and-a-half concepts using an ET as their
tankage.  No orbiter or SRBs.)

Basically, NASA started with two manned fully-reusable stages, conceded
that it was better to add drop tanks to the upper stage, gradually moved
more and more of the upper-stage tankage into the drop tank(s), and
finally was forced to replace the reusable lower stage with something
cheaper to develop.  Studies of alternative configurations tended to get
no more than lip service at all phases of this process.

In particular, NASA originally rejected the drop-tank concepts, such as
Lockheed's Starclipper, because they had expendable components.  When NASA
finally conceded that expendable tanks were inevitable, no attempt was
made to study how this affected overall configuration -- NASA clung to the
two-stage concept, even though drop-tank systems designed from scratch,
like Starclipper, typically got by with one stage.
The good old days                   |  Henry Spencer
weren't.                            |      (aka

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