Titanium in the Shuttle

I understand that the basic structure of the Shuttle is aluminum,
rather like a Boeing 747. A titanium structure would weigh less.
Further a titanium structured craft could have a less
massive thermal protection system, since things like the wings and tail
could be allowed more heat.

NASA did study this option. Why did they pick aluminum? Was it just
the cost of titanium fabrication. It would seem to me that the cost of
fabricating the basic structure is a vanishingly small cost of the
total space shuttle system, especially when you plan on 50 launches per
year. It would also seem to me that the reduction in weight would be
nice, and help with either added payload, higher orbits, larger return
payload, and safer aborts.

Anyone know .. is it some exotic alloy of aluminum, or just standard
aircraft grade aluminum?


-Thanks

wrote in
ups.com:

I understand that the basic structure of the Shuttle is aluminum,
rather like a Boeing 747. A titanium structure would weigh less.
Further a titanium structured craft could have a less
massive thermal protection system, since things like the wings and tail
could be allowed more heat.

NASA did study this option. Why did they pick aluminum? Was it just
the cost of titanium fabrication. It would seem to me that the cost of
fabricating the basic structure is a vanishingly small cost of the
total space shuttle system, especially when you plan on 50 launches per
year. It would also seem to me that the reduction in weight would be
nice, and help with either added payload, higher orbits, larger return
payload, and safer aborts.

Anyone know .. is it some exotic alloy of aluminum, or just standard
aircraft grade aluminum?

This topic has been discussed at length recently in sci.space.tech - I
recommend Googling there.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

writes:

I understand that the basic structure of the Shuttle is aluminum,
rather like a Boeing 747. A titanium structure would weigh less.

Not that much less. Titanium alloys have only 30-40% better strength
to weight than aluminum alloys, and slightly *less* stiffness to weight.
Also higher density and more difficult fabrication, which complicate
structural design.


Further a titanium structured craft could have a less massive thermal
protection system, since things like the wings and tail could be allowed
more heat.

The temperature behind the bow shock of a space shuttle on re-entry is
vastly higher than either aluminum *or* titanium can handle. You're
still going to need the tiles, and you're not really going to be able
to shave that much weight off them. It's like suggesting that you
could make it easier for people to walk through a blast furnace if you
were able to tweak the natural body temperature up to 180 F.

Aluminum also has an edge in this respect in that, A: it has a very
high heat conductivity, and B: it has a moderately high heat capacity.
So any local overheating will be diffused throughout the structure and
absorbed, and you mostly just have to worry about the average. With
titanium, local overheating leads to local failure, and you have to get
your thermal protection system right *everywhere*.


NASA did study this option. Why did they pick aluminum?

Because it was almost as good, and a lot cheaper and easier to deal
with.


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*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
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wrote:
A titanium structure would weigh less.

I'm not sure that's correct. The aircraft grade aluminum alloys
available when the shuttle were built had comparable strength (on a
weight basis) to the available titanium alloys.

Further a titanium structured craft could have a less
massive thermal protection system, since things like the wings and
tail
could be allowed more heat.

Somewhat more heat, yes, but titanium is not a cure-all in that regard.

Anyone know .. is it some exotic alloy of aluminum, or just standard
aircraft grade aluminum?

I think it's "standard aircraft grade aluminum," though some of the
shuttle structures are composites of aluminum reinforced with boron
fibers.

Mike Miller, Materials Engineer

wrote:
I understand that the basic structure of the Shuttle is aluminum,
rather like a Boeing 747. A titanium structure would weigh less.
Further a titanium structured craft could have a less
massive thermal protection system, since things like the wings and
tail
could be allowed more heat.

NASA did study this option. Why did they pick aluminum? Was it just
the cost of titanium fabrication. It would seem to me that the cost
of
fabricating the basic structure is a vanishingly small cost of the
total space shuttle system, especially when you plan on 50 launches
per
year. It would also seem to me that the reduction in weight would be
nice, and help with either added payload, higher orbits, larger
return
payload, and safer aborts.

Anyone know .. is it some exotic alloy of aluminum, or just standard
aircraft grade aluminum?


-Thanks


Aluminum has a much better heat sink than titanium.
With a thermally protected structure, aluminum can
be a better choice than titanium for minimizing
mass overall Beryllium/aluminum/magnesium is likely
to be a still better choice, but more expensive.
Beryllium/aluminum/magnesium also has a big advantage
with respect to stiffness.

For tankage, one must also consider compatibility
with LOX, etc.

The cost of the shuttle was management. Even with
aluminum structure, an additional orbiter would have
cost a couple of billion dollars. That works out
to about $15,000 per lbm of aluminum--which has nothing
to do with the cost of the material.

Best regards,
Len (Cormier)
PanAero, Inc.
(change x to len)
http://www.tour2space.com

In article . com,
wrote:
A titanium structure would weigh less...

No, substantially more -- NASA estimated an extra 2t -- although that
would be more than made up by lighter thermal protection.

NASA did study this option. Why did they pick aluminum? Was it just
the cost of titanium fabrication.

They balanced the extra costs of working with titanium against lighter and
lower-maintenance thermal protection, and decided that there was very
little overall difference. The decisive factor, in the end, was that the
USAF was worried about the limits of US titanium production and processing
facilities, especially with production starting on the F-15 (which used a
fair amount of it), and didn't want to see NASA using titanium in
quantity.

...It would also seem to me that the reduction in weight would be
nice, and help with either added payload, higher orbits, larger return
payload, and safer aborts.

At the point when this decision was being made, orbiter size was still
vague, so it wouldn't have made a difference in payload -- aluminum just
required a slightly larger orbiter.

Anyone know .. is it some exotic alloy of aluminum, or just standard
aircraft grade aluminum?

Pretty standard alloys -- mostly 2024, if I recall correctly. There's
some titanium, in particular in the engine thrust structure, and some
composites, notably the cargo-bay doors.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

wrote:
A titanium structure would weigh less...

No, substantially more -- NASA estimated an extra 2t -- although that
would be more than made up by lighter thermal protection.

NASA did study this option. Why did they pick aluminum? Was it just
the cost of titanium fabrication.

Why would a titanium structre weight 2 tons *more* than an aluminum
one?Titanium has a higher strength/weight ratio, and although aluminum
has a better stiffness/weight ration, that does not seem as relevent.
I would expect a titanium wing to weigh less, be stronger, but flex
more.

wrote:
Why would a titanium structre weight 2 tons *more* than an aluminum
one? Titanium has a higher strength/weight ratio,

That's a rather general statement for very broad groups of alloys. Some
titanium alloys are stronger (by weight) than some aluminum alloys. The
reverse is also true. Notably, the high end of aluminum alloys are
stronger (by weight) than a broad range of titanium alloys.

Mike Miller, Materials Engineer

In article .com,
wrote:
Why would a titanium structre weight 2 tons *more* than an aluminum
one?Titanium has a higher strength/weight ratio, and although aluminum
has a better stiffness/weight ration, that does not seem as relevent.

In real structures, surprisingly often, the structural design is driven by
stiffness requirements, not strength. For a wing in particular, excess
flexibility makes it prone to potentially-disastrous forms of aeroelastic
instability (wing flexes, airflow changes to match, aerodynamic forces on
wing therefore change, wing flexes farther...).
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

wrote:
wrote:
A titanium structure would weigh less...

No, substantially more -- NASA estimated an extra 2t -- although that
would be more than made up by lighter thermal protection.

NASA did study this option. Why did they pick aluminum? Was it
just
the cost of titanium fabrication.

Why would a titanium structre weight 2 tons *more* than an aluminum
one?Titanium has a higher strength/weight ratio, and although
aluminum
has a better stiffness/weight ration, that does not seem as relevent.
I would expect a titanium wing to weigh less, be stronger, but flex
more.


Flexing wing might be a bit of a bitch when it comes to the heat sheild
tiles..... load comes on, gaps open up, hot gases get in...... ???