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Steel for Shuttle



 
 
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  #1  
Old November 17th 19, 04:00 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,008
Default Steel for Shuttle

In article ,
says...

On 2019-11-14 19:54, Alain Fournier wrote:

Steel has much lower conductivity than aluminium. So this isn't as much
a problem as it would be if aluminium was used.


As I recall, no aluminium was bare on the shuttle, was all protected by
tiles/blankets. And the tiles were thick and heavy to ensure the
aluminium remain nice and comfy cool.


This is not at all true. The space shuttle's aluminum skin actually got
*hotter* after landing due to "heat soak". The heat that was still
inside the thermal protection had to go *somewhere*. Roughly half of it
radiated outward and the other half went into the aluminum skin.

https://www.nasa.gov/centers/johnson...s-ch4b-pgs182-
199.pdf

From above:

Thermal Protection System materials
protected the Orbiter?s outer skin from
exceeding temperatures of 176C
(350F).

So, the skin got pretty warm if the limit was 350 degrees F (literally
the default temperature of both of my ovens in the kitchen). I would
not call that "comfy cool" at all.

Starship will have portions of its skin as Shiny exposed steel and the
tiled portions will will still allow the steel under the tiles to heat
up to high temperatures (since it can support such, allowing for
thinner/lighter tiles).


Yes, but it won't conduct heat to the inside as well as aluminum would
because steel has lower thermal conductivity compared to aluminum.
That's why the bases of my stainless steel cookware all have copper
inside the base. Copper has a very high thermal conductivity, so it's
put there to more quickly move the heat from the stove to the food being
cooked (copper is also more expensive than stainless steel, so these
sorts of pans aren't cheap, but they'll last a lifetime if taken care
of).

6 Best Stainless Steel Cookware with Copper Core (Induction Ready)
https://www.magneticcooky.com/stainl...e-copper-core-
induction-ready/

If some of that shiny steel reaches 1000C, there is both conductive and
radiative heating of components inside the skin.


Yes, but I would think that there would be a healthy safety margin since
300 series stainless steel loses its strength at about 1000 degrees F.
Also, you can put interior insulation around sensitive components. You
don't have to turn the entire interior into an oven.

We know of mechanisms to control the "winglets" and landing gear which
would have to be fairly close to the skin. Not sure what sort of sensors
it will need to deploy for re-entry. For Earth, they can use good GPS
antennas to and innertial sensors well inside the ship to control
re-entry, but on Mars, wouldn't they need to deploy air probes, and air
pressure sensors and possibly radar to execute landing? Those would be
stowed inder the steel skin for re-entry and doors open to deploy them
once at safe altitude, but that still needs those sensors be near that
steel skin.


Sure. All of such "sensitive" equipment would likely have additional
insulation and possibly even active cooling.

This type of stuff is the bread and butter of structural and materials
engineers in aerospace engineering. Designing such things is literally
their day job.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
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  #2  
Old November 18th 19, 01:24 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,008
Default Steel for Shuttle

In article ,
says...

On 2019-11-17 10:00, Jeff Findley wrote:

Sure. All of such "sensitive" equipment would likely have additional
insulation and possibly even active cooling.


Active oooling becomes more problematic/costly on a cargo ship whose
volume is in vacuum.


This statement makes no sense. Starship is an upper stage whose
propellant tanks contain both cryogenic methane and cryogenic LOX.
There is your potential source of active cooling of things like
"sensitive equipment" during reentry. But, my guess is they don't need
even that. Reentry and landing is intense, but relatively brief so
active cooling using cryogenics isn't likely needed, IMHO.

If you need to run pipes carrying
ammonia/water/whateer to every noon and cranny to keep equipment within
limits, the weight of your vehicles starts to matter.


You didn't even click on the links I provided to high temperature
aerospace wiring, did you? You keep acting like Starship is the first
aerospace vehicle to experience atmospheric heating. SpaceX has
designed not one, but two reentry vehicles so far (Dragon and Dragon 2).
Both have flown successfully. There is zero evidence that any Dragon
has experienced any heat related issues during reentry.

That experience will transfer to the design of Starship.

Renmember that the initial justification for going to steel was that
while steel was heavier, it allows a reduction of heat tile weight that
is greater that weight ibcrease of going from aluminium/carbon to steel.


And you keep ignoring that steel has a lower thermal conductivity than
aluminum.

But if, once they factor in all the issues, the addition of inside
insulation, active cooling, and mreo tiles ends up adding more weight
than originally anticipated, the performance advantages of going to
steel may be lost.


For the umpteenth time, they've done the thermal analyses on this! CAE
is a thing. NASA has been doing CAE since the 1960s. NASA *literally*
created the CAE industry. Cites:

https://en.wikipedia.org/wiki/Nastran

https://ntrs.nasa.gov/search.jsp?R=19740006499

But as a business, it is possible that having a super heavy dump truck
may turn out to be a better business than having a lightweight ferrari
to deliver the same payloads.


The above is word salad. Starship is no "lightweight Ferrari". The
prototypes mass 200 tons *dry*.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #4  
Old November 19th 19, 01:25 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 2,008
Default Steel for Shuttle

In article ,
says...

On 2019-11-18 07:24, Jeff Findley wrote:

This statement makes no sense. Starship is an upper stage whose
propellant tanks contain both cryogenic methane and cryogenic LOX.


Active cooling of some sensor near the skin would require piping and
valves to bring the cryo to that point when needed. Valves also need
elextrical wiring to control them. This means extra weight and conplexity.

You didn't even click on the links I provided to high temperature
aerospace wiring, did you?

I don't doubt that wiring that resists heat is readily available. I have
some in the stove at home. But sensors are different. Consider the
Shuttle would pop out an pitot for air speed during the "gliding" phase
before landing. Whatever Starship uses will liekly need something near
to the skin (and antennas likely need to be under a non-steel portion of
skin).

Yep, things can be solved. But the issue is at what cost in weight.
Remember that this is a decision to allow for much higher tempoeratiure
of structure to save some weight in the heat shield.


When your spacecraft has a dry mass greater than 100 tons, you've got
quite a bit of mass margin to work with. SpaceX isn't designing this
using the "performance uber alles" philosophy of traditional aerospace
engineers. And if it's a ton or two overweight, so what? Is 148 tons
to LEO significantly different than 150 tons to LEO (especially when
compared to the competition)?

SpaceX has
designed not one, but two reentry vehicles so far (Dragon and Dragon 2).


Both of which are traditional in structure with a covering of the skin
to protect against heat. And much smaller in scale. So the SPaceX are
not merely applying same experienced onto StarShip, they need to develop
new way of protecting Starship that will have some exposed/naked Steel.


And that problem is actually easier due to the fact that Starship will
be mostly empty tankage on reentry. That means it's more "fluffy" which
means far lower total heat to deal with during reentry.

But as a business, it is possible that having a super heavy dump

truck
may turn out to be a better business than having a lightweight ferrari
to deliver the same payloads.


The above is word salad. Starship is no "lightweight Ferrari". The
prototypes mass 200 tons *dry*.


Exactly. I said that it might be possible the super heavy thing may have
terrible performance due to being overweight but still be a better at
generating profits.


On what planet is 150 tons payload to LEO "terrible performance"?

The problem with being an overweight dump truck is that when you are
pushing limits such as going to Mars, you might actually require the
perfornmance of a Ferrari.


More word salad.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
 




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