Newsgroups: sci.space.history,soc.history.what-if
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Dyna-Soar (was Re: What would it have taken to go...)
Date: Sun, 30 Nov 1997 22:31:19 GMT

In article <65sct1$s9h@dfw-ixnews9.ix.netcom.com>,
Scott Lowther <lexcorp@ix.netcom.com> wrote:
>>....And the idea that
>>Dyna-Soar would automatically have a quick turnaround just because it
>>landed on a runway is quite adequately disproven by a look at the
>>shuttle turnaround process...
>
>I'm not sure that's true... the Shuttle has all of those goofy tiles
>(Dyna-Soar had a few large metal skin panels) ...

The problem with refractory-metal thermal protection is that refractory
metals are so damned heavy that you have to make them very thin to keep
mass under control... and that makes them very vulnerable to damage.
Think heavy-gauge foil rather than metal sheet.  Just because it's metal
doesn't mean it's durable.

The US military actually has some experience with very thin-skinned
aircraft.  The F4D Skyray, in particular, used an odd form of construction
with a very thin outer skin... and the results were not favorable, with
frequent damage and high maintenance loads.  The Skyray's successors went
back to conventional thick skins.

We'll soon find out just how durable metallic TPS systems are, because
X-33 is using them.

Note also that while the tiles are indeed a significant part of orbiter
turnaround, they do not dominate it.  Take them away by magic and it would
still be slow.

>AND those nightmarish SSME's...

Again, while the SSMEs are indeed bad, they don't dominate turnaround.
They're significant, yes, but getting rid of them wouldn't improve the
situation that much.  In particular, any significant SSME work is done by
simply swapping engines, to take them out of the processing flow.
--
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        | henry@zoo.toronto.edu

Newsgroups: sci.space.history,soc.history.what-if
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Dyna-Soar (was Re: What would it have taken to go...)
Date: Mon, 1 Dec 1997 17:01:27 GMT

In article <thomsonaEKHLG8.3Gr@netcom.com>,
Allen Thomson <thomsona@netcom.com> wrote:
>>Think heavy-gauge foil rather than metal sheet.  Just because it's metal
>>doesn't mean it's durable...
>>We'll soon find out just how durable metallic TPS systems are, because
>>X-33 is using them.
>
>An interesting point which I'd not known about. What kinds of damage
>might the X-33/VS TPS be vulnerable to? Ice on take-off? Rain? Hail?
>Birds? Runway rocks?

Basically, all the things that can damage the shuttle tiles.  Ice and
flying debris on takeoff (rocket takeoffs are violent events that do throw
things around a bit).  Rain etc. during climb and descent, more the latter
than the former because the climb will be near-vertical.  Hits from space
debris and micrometeorites while in orbit.  And bits of surface debris
kicked up during landing.  (Birdstrikes can be bad news even for military
aircraft, which are much more strongly built, so I think the X-33 had just
better not hit any.)  Finally, often the biggest mechanical hazard to a
spacecraft is not the flight environment but the ground handling before
and after; it helps immensely if the thing is robust enough to take a
certain amount of sloppy handling.

>What would it take to repair a ding?

If it's small enough, you can ignore it.  Bigger ones you might be able to
just flatten out, although the combination of a complex multi-layered
structure and metals with less than ideal mechanical properties (another
problem with refractory metals is that many of them are a bit brittle)
might turn this into an elaborate procedure involving panel removal,
disassembly, flattening, and perhaps heat-treatment.  Still larger ones
might start you worrying about cracking, and either that or an overt
puncture might well demand replacement of the panel.
--
If NT is the answer, you didn't                 |     Henry Spencer
understand the question.  -- Peter Blake        | henry@zoo.toronto.edu