Re: NASA Administrator Agrees With What Many Critics Have Been Saying for Years
- From: "Jorge R. Frank" <jrfrank@xxxxxxxxxxx>
- Date: 04 Oct 2005 01:01:11 GMT
"tomcat" <jlavine@xxxxxxxxxxxxx> wrote in news:1128379679.087153.206400
@o13g2000cwo.googlegroups.com:
> The only major structural flaw in the Shuttle is the silica tiles on
> aluminum technology.
>
> Silica tiles are used in blast furnaces where their soft and brittle
> properties are not prohibitative. In a shockwave, however, even ice
> can break them. A major flaw for a hypersonic waverider.
>
> Aluminum has a melt point close to 1000 deg. F. Not anywhere near the
> possible 7000 deg. F. of reentry! Another major flaw connected to the
> silica tile flaw. If the tiles break, even a small bare patch, the
> aluminum underneath cannot last more than a few seconds.
>
> Today, titanium could be used with a melt point of about 2000 deg. F.
> Or, a titanium alloy might get the melt point to 3 or 4 thousand
> degrees.
Titanium would not have helped the survivability of the orbiter in a
Columbia-type debris impact. The superheated air that entered Columbia's
wing was probably over 5000 deg F and may have been as hot as 8000 deg F
near the breach. This has been discussed at length in sci.space.* in the
past. One of the better explanations was this one by Henry Spencer:
<http://groups.google.com/group/sci.space.tech/msg/39813114cef4544a?
hl=en&>
(Henry's post also contains some corrections to your misconceptions about
the maximum useful temperature of titanium alloys.)
Also, among several analyses not included in the final report, the CAIB
commissioned a "what-if" analysis of how much longer Columbia's wing
would have survived were it made of titanium. The answer: 13 seconds.
(Hopefully this report will see the light of day in the fourth edition of
Jenkins.) As Henry wrote, this isn't a case of aluminum being "almost"
good enough; there is a huge gap between the highest usable temperature
for a titanium alloy, and the temperatures Columbia experienced inside
the left wing.
> All in all, the Shuttle is a fine waverider with a hull design flaw.
> One that could easily be designed out of any new model.
You need to stop misusing terminology. The space shuttle is not a
waverider. Waveriders, by definition, have the shock wave *attached* to
the leading edge. The shuttle design goes to considerable trouble to
*avoid* allowing the shock to touch the vehicle at all.
If there's a design flaw in this area of the shuttle, it's not the
aluminum structure or the silica tiles. It's the fragile RCC leading
edges (and the fact that NASA failed to do enough impact tests to
understand just *how* fragile the RCC is) placed in proximity to a
debris-shedding external tank.
--
JRF
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