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#26 2018-12-26 17:59:57

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,571

Re: Starship is Go...

Kbd512 thanks for the links as they relate to my post #10 of topics that had the word Transpiring with in them.

Void as I indicated use the radiation shield water as its not of any use on re-entry and would add to the mass profile to which if we start the inbound trek means less heating to the shield materials.
All that is needed is to pump the water from the radiation storage tanks to the transpiring tanks before use.

The mock up prototype is not working on any of these things as it looks to be only for Raptor engines, a new fuel type, and some aeroshaping....

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#27 2018-12-26 18:31:14

louis
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From: UK
Registered: 2008-03-24
Posts: 4,632

Re: Starship is Go...

I don't know why you put so little store by tweets. Most of Musk's tweets do prove to be accurate or at least reasonably accurate pointers to what is coming down the line.   

You seem to be saying the "stainless steel starship" will fly and that it will be the subject of the hop test (slated for the first quarter of 2019).  If that ain't impressive progress, I don't know what is!

GW Johnson wrote:

Myself,  I put little stock in tweets.  Believe it only when hardware flies. 

The stainless steel vehicle under construction is not a prototype BFS,  despite all the sincere beliefs and wishes otherwise.  It is a full diameter,  short-length,  heavy-construction-but-right-takeoff-mass test vehicle for proving-out the controls of a BFS with a full complement of Raptor engines.  It will never fly fast or far,  and never experience re-entry conditions.  But it is a very necessary step along the way to a flying BFS.

Stainless steel exposed to re-entry aeroheating would only survive with massive amounts of liquid cooling.  SS covered in some PICA-X would require only minimal liquid cooling,  even steady state.  If too thin to be a heat sink,  it might require that minimal liquid cooling during the short re-entry transient. 

GW


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#28 2018-12-26 18:58:40

SpaceNut
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From: New Hampshire
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Posts: 15,571

Re: Starship is Go...

You do realize that stainless steel is not what they are normally made of as you want to reduce mass by using aluminum alloy. This is being done as its not getting anything but repeat uses at none space velocities and nothing close to the heating that would be seen on re-entry...

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#29 2018-12-26 19:49:46

louis
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From: UK
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Posts: 4,632

Re: Starship is Go...

Not making any claims to technical expertise here. Others who comment here seem to think steel is not such a bad bet for a rocket material. The melting point of alumnium is much lower than steel. I just looked that up. Aluminium based alloys are chosen for lightness I think, not resistance to heat.

SpaceNut wrote:

You do realize that stainless steel is not what they are normally made of as you want to reduce mass by using aluminum alloy. This is being done as its not getting anything but repeat uses at none space velocities and nothing close to the heating that would be seen on re-entry...


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#30 2018-12-26 20:06:06

SpaceNut
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Re: Starship is Go...

The capsule that are made by Space x are Aluminum alloy ISO grid pattern...the use of stainless is for the extra mass also and for its ability for repeat temperature cycles or robustness to thermal stresses...When doing the thrust calculations using the lighter materials will be like getting a boost from the engines for a greater payload mass.

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#31 2018-12-26 20:33:10

louis
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From: UK
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Re: Starship is Go...

I really don't think anyone knows yet...unless you can point to something really authoritative from Space X or Musk.

SpaceNut wrote:

The capsule that are made by Space x are Aluminum alloy ISO grid pattern...the use of stainless is for the extra mass also and for its ability for repeat temperature cycles or robustness to thermal stresses...When doing the thrust calculations using the lighter materials will be like getting a boost from the engines for a greater payload mass.


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#32 2018-12-26 20:42:48

Oldfart1939
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Registered: 2016-11-26
Posts: 1,598

Re: Starship is Go...

I happen to be a strong supporter of Mr. Musk, but even he cannot change the laws of physics. Then recall--Atlas I was built entirely of stainless steel so thin it had to be pressurized like a can of soda pop or beer. That's called a "monocoque construction," with no other members for support. Only the "skin" provided the entire pressurized structure.

Last edited by Oldfart1939 (2018-12-26 20:46:53)

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#33 2018-12-26 21:06:45

Oldfart1939
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Re: Starship is Go...

Just saw Musk's answer to the number of engines in this new "grasshopper." It will be 3 engines. That's enough to get sufficient flight time as a test bed, and finalize the design.

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#34 2018-12-26 21:16:59

SpaceNut
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Posts: 15,571

Re: Starship is Go...

I had seen that as well from the several pages that I posted links for...

The company has been working on a Starship test article for low-altitude flight tests at the company's South Texas launch site under development. That test article, dubbed a "hopper," would have the same nine-meter diameter as the full-scale vehicle of the vehicle, but would not be as tall.

SpaceX had shifted to a "fairly heavy metal" for use in the vehicle and not using carbon composite materials, which are lightweight but have high strength but have a much lower temperature of operation.

SpaceX had developed a "superalloy" for Raptor, called SX500, designed to handle hot oxygen-rich gas at pressures of up to 12,000 pounds per square inch. "Almost any metal turns into a flare in those conditions,"

aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzA4MS85MDAvb3JpZ2luYWwvc3BhY2V4LXN0YXJzaGlwLWVsb24tbXVzay1kZWNlbWJlci0yMDE4LmpwZw==

Looking at the size and engine count this looks like it what would be used for lunar flyby and for possible lunar landing.for cargo or crews to begin working and to stay on the moon.

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#36 2018-12-27 05:03:58

Void
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Re: Starship is Go...

It seems that it is steel, and active cooling with Methane.  The leeward side only needs steel, the windward side will need steel and regenerative cooling as well.
https://www.teslarati.com/spacex-elon-m … g-rapidly/
Quote:

Replying to @Erdayastronaut @13ericralph31 and 2 others
Leeward side needs nothing, windward side will be activity cooled with residual (cryo) liquid methane, so will appear liquid silver even on hot side
4:01 PM - 24 Dec 2018

So, I don't know it to be fact, but I am presuming that that would be the supercooled liquid Methane, and that it will be somewhat heated in the process and expand a bit, and then be burned in the landing burn.   In that case it is possible that indeed per my speculation of post #25, some of the inertia of the "Starship" is recaptured into faster molecular motion in the Methane.


The article indicates that the move to stainless steel was made because they wanted to hurry the program up.  However then they indicate that they realized that it had

Quote:

Combined with a decision – made public at a September 2018 media event – to delay the debut of a vacuum-optimized upper stage Raptor (RVac) and stick with its mature sea level variant, Musk apparently is quite confident that these dramatic shifts in strategy will allow SpaceX to aggressively slash the development schedules of its next-gen launch vehicle. Intriguingly, Musk noted that while these “radical” design changes were almost entirely motivated by his desire to expedite the fully-reusable rocket’s operational debut, it apparently became clear that the cheaper, faster, and easier iteration could actually end up being (in Musk’s own words) “dramatically better” than its exotic carbon-composite progenitor.

……

I will wonder if the engines will have a better performance with the redesign.  Better for power?  Better for cost?

Last edited by Void (2018-12-27 05:29:30)


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#37 2018-12-27 09:07:38

SpaceNut
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Re: Starship is Go...

The temperature of the triple point of methane was determined as 90.6861 K ± 0.2 mK at 11.7 kPa (0.115 atm) using the triple point of argon (83.798 K) as the reference. The reproducibility of this fixed point is at least as good as that of argon.

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

https://en.wikipedia.org/wiki/Methane
https://en.wikipedia.org/wiki/Methane_(data_page)

https://mychemengmusings.wordpress.com/ … e-methane/

https://www.engineeringtoolbox.com/gas- … d_161.html

Since the engines run on liquid methane and not gasseous that will mean that its vented overboard as a function of the cooling through the tiny pin holes in the leaward side or what is the heatshield side of the ship. It would be less of an explosive oportunity to use water for the cooling fluid.

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#38 2018-12-27 09:17:43

SpaceNut
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From: New Hampshire
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Re: Starship is Go...

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

So the temperature of the heatshield on reentry...

https://space.stackexchange.com/questio … ng-reentry

The Stardust sample return probe had an interesting re-entry to Earth's atmosphere. Returning from a solar orbit the maximum deceleration has been reported as 34g. Maximum temperatures are estimated at around 3,200 Kelvin or 2900 degrees C at the surface.

The Space Shuttle thermal protection system is rated for temperatures of up to 1510 °C. There's a boundary layer of air just above the TPS, outside that temperatures can reach 5500 °C. NASA used HYTHIRM to make thermal images of the orbiter during reentry:

hWx86.png

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#39 2018-12-27 11:33:24

louis
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From: UK
Registered: 2008-03-24
Posts: 4,632

Re: Starship is Go...

This video would seem to give a good summary of where we are now with the BFR Starship project...and it looks much promising than a few months ago.

https://www.youtube.com/watch?v=mEZhIpXOEgY

Last edited by louis (2018-12-27 11:33:41)


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#40 2018-12-27 13:16:43

Void
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Posts: 3,011

Re: Starship is Go...

Louis,

I enjoyed the video.

Spacenut.  Yes, triple point of Methane.  But the fluid in the ship may be near the freezing point at under pressurization, and not at it's boiling point.  At least at launch.  Superchilled is what they call it I think.

I too had a video, where they said that in part the stainless steel is expected to reflect a lot of energy, but not enough on the windward side.
Something else is needed.  Your shown method, which they very well may use in my opinion, is one such possibility.  However by the video I was watching the presenter said that in some cases you can heat sink the extra heat into the interior of the ship. 

So, I had a curiosity as to if that if that were practical, would it provide a benefit in the recovery of a small amount of the ships energy of it's inertia.  The Methane fluid under these circumstance may then rise in temperature from near freezing to near boiling.  I do believe that the tanks are pressurized, so those two may not be so near in temperature.

Autogenous  (Auto Geno Us) smile  Pressurization.  (I trouble even saying it).

While I did say the above, and can be given reflections of corrections, I don't feel that it was a shameful thing to ask about it.
https://space.stackexchange.com/questio … propellant
The information is ambiguous.  I do see that Elon Musk prefers supercooled as it reduces cavitation.  And in the vacuum of space the supercooled condition is favored.  However to then sink heat into the propellant tanks and reduce their supercooled nature would perhaps allow for greater cavitation.  So, honestly I am not educated enough in this situation to be even dangerous.

Still things to learn.

Remember once I suggested a rocket with wings, and you gave me a real work over for that as well.  And then (I think) Starship will have "Wings".  They are for guidance not lift.

Heat shields?  Well I guess in the worst cases Ablation and what you indicated are needed (Fluids boiled and vented through pores).

No anger, just not quite willing to play doormat.

Last edited by Void (2018-12-27 13:32:04)


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#41 2018-12-27 14:31:26

Oldfart1939
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Registered: 2016-11-26
Posts: 1,598

Re: Starship is Go...

Before everyone gets too excited: this is a prototype constructed specifically as a "hopper," in order to test 3 of the new Raptor engines, and associated software for landing/hovering control. I suspect the structure will be much different for a craft reentering for LEO. This is a test bed airframe, and not the final iteration. "There's many a slip twixt the cup and the lip." This is a vehicle to find the  "slips."

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#42 2018-12-27 15:19:47

SpaceNut
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Posts: 15,571

Re: Starship is Go...

The temperature and pressure goes up together from the triple point of -187 c and 11.7 kpa with the temperature rise from heating means the pressure will go up as a function of temperature rise which means it will burst the walls that hold it and with no way to cool it back down its going to go gaseous which causes the cavitation due to the bubbles that form which means baffles will be put inside the area to keep the banging effect to a minimum. So we then have a choice to circulate or vent the pressure to remove heat keeping in mind that warm fuel going back into the fuel tank will cause a fuel pressure rise even when pumping the cold fuel out to the shield. There is only just so much heat we can obsorb for the small quantity of fuel that we will have to land the ship with. So I do not think the fuel tank will be an issue for either method as there is exspansion area for the warm fuel to go in the partially filled tank at that point. Closed loop no venting this will work as a heat exchanger obsorbing the heat to the working fluid which is under pressure. For a transpiring heatshield its not to obsorb and retain but to obsorb and remove via the working fluid being dumped.

While shiny does reflect heat its the air friction that is coming in contact with the metal that will make it hot.

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#43 2018-12-27 15:37:03

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 15,571

Re: Starship is Go...

The wings or winglets and number count as well as placement keeps changing and that changes there function. The size also changes the function as to whether they are lift or guidance and since the have no evalones to change rise or fall, or turning they are orientation wings to aid in the brick sliding effects of the air it is plowing through, just the same as the shuttle and serve no purpose other than for in transition of landing entry into an atmospher. The current plan for the small none function wings is to hide the landing feet at the rear of the ship. The false winglet along the near centerline from nose to part way back acts as a glide indicator for heat flow. As these are not the grid fins on the first stage booster of the falcon 9.

29906170001_5835936893001_5835925305001-vs.jpg?pubId=29906170001&quality=10

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#44 2018-12-27 16:38:27

Void
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Re: Starship is Go...

Reasonable.


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#45 2018-12-27 17:52:54

Oldfart1939
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Re: Starship is Go...

This is the essence of science and engineering: build it; test it; redesign it; repeat until it works.

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#46 2018-12-27 18:11:53

louis
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Re: Starship is Go...

So what are they really testing in the initial "bighopper" test? 

Is it the aerodynamics of the body shape?

Is it the electronic control systems within the craft?

Is it the radio coms with the craft?

Landing control accuracy?

I am presuming it can't possibly test resistance to heat on re-entry.


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#47 2018-12-27 18:20:30

Oldfart1939
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Re: Starship is Go...

Primarily testing the Raptor engines in throttleable mode. Guidance and control during landings. Software development.
I read somewhere that the FAA has assigned a 2,500 foot flight ceiling. Not certain this is "gospel."

Last edited by Oldfart1939 (2018-12-27 18:24:56)

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#48 2018-12-27 18:48:57

louis
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From: UK
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Posts: 4,632

Re: Starship is Go...

Noted, thanks.

So it's really testing the engines in a reaction chamber... while subject to aerodynamic, lift and other forces...?

Oldfart1939 wrote:

Primarily testing the Raptor engines in throttleable mode. Guidance and control during landings. Software development.
I read somewhere that the FAA has assigned a 2,500 foot flight ceiling. Not certain this is "gospel."


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#49 2018-12-27 19:16:08

louis
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From: UK
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Re: Starship is Go...

Some nice live, atmospheric video of the "Bighopper" construction site.

https://www.youtube.com/watch?v=UHGlw9H_OaI

Don't think this has been aired here before...


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#50 2018-12-27 19:21:50

kbd512
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Re: Starship is Go...

SpaceX has to decide whether or not they'd rather have a vehicle that's lightweight and thus high performance, durable, or cost effective to operate.  The way I see it, they can build a launch vehicle that has 2 of those 3 characteristics, but not all 3 at the same time.  All historical evidence says that's not possible.  If it were me, I'd choose durability and operational cost-effectiveness.  A vehicle that costs a bit less to construct using cheaper materials is virtually meaningless when you throw the entire vehicle away after its first use and I completely agree with SpaceX's thought process on that matter.  If the materials cost a bit more, but used to construct a durable and dependable vehicle, then I judge the trade in absolute payload performance to be worth it.

Stainless Steel retains adequate ductility and strength at the cryogenic temperatures of LOX and LCH4, making it the material of choice for cryogen transport here on Earth.  The additional benefits are that it's easy to bend and weld, has moderate cost thanks to the increasing variety of uses for the material, and retains strength at temperatures that turn all Aluminum alloys, even CMC's, into silly putty.  A high grade Stainless Steel will eventually fail, as all materials do, but Aluminum and Carbon Composites will fail much faster.  There will never be a time in the life of this vehicle when it's acceptable to have no propellants left in the tanks, and both are cryogens so autogenous pressurization is practical.  Every LOX/LH2 Centaur stage from about the late 1950's onwards proved that monocoque Stainless Steel construction works.

If some geniuses working for NASA or their contractors come up with a composite that can take the abuse, then great.  SpaceX can capitalize on that technology advancement after it's proven to work acceptably well with adequate flight heritage.  For those in doubt, that's what we really need NASA for.  The government can afford to take a loss on a high-risk / high-payoff technology that doesn't pan out.  A corporation could easily bankrupt itself trying to make something work that's just not ready for prime time.  That's how I feel about composite cryogen tanks.  There's no reason to stop working on the technology, but it needs to be done on Uncle Sam's dime as part of public-private partnerships so that the contractors who provide bread and butter launch services to the government can continue to butter the government's bread with functional and affordable launch services.

I think Sylramic and Super Sylramic could provide a durable surface insulation solution for most of Starship.  NASA has completed 9,000 hours of testing in jet engine combustion liners at 2,200F without fatigue failure and it's now a commercial material that SpaceX could simply purchase.  GE's plant in Huntsville could mass manufacture the stuff.  This material is more than 30+ years in the making and GE only started fabrication for commercial aircraft engines in 2018 after qualifying the materials and components.

Silicon Carbide (SiC) Fiber-Reinforced SiC Matrix Composites

Ultra High Temperature (UHT) SiC Fiber

Creep and Cyclic Fatigue Durability of 3D Woven SiC/SiC Composites with (CVI+PIP) Hybrid Matrix

COI Ceramics Inc - Sylramic SiC Fibers

The 600 and 700 series Inconels also do relatively well at cryogenic temperatures and better at higher temperatures than Stainless Steel, but they're a little heavier than the Stainless alloys I'm familiar with.  So...  Perhaps some of this new 3D woven fabric over Stainless or Inconel could get the job done, provided that the leading edges use ZrB2 or HfB2 with appropriate thermal sinks.  There are also developmental synergies between Sylramic fiber and ZrB2 since it can strengthen that particular UHTC by reducing grain size.

Critically, Snecma Propulsion Solide's SEPCARBINOX A500 SiC CMC's inhibit delimitation of the bound carbon fibers from oxidation through self-sealing of the matrix that prevents chemical vapor infiltration.  I believe the F414 turbofans' "turkey feathers" used by the US Navy's Super Hornets tested A500 in their exhaust nozzle divergent flaps and seals and some hot section components.  I think the F100 turbofans in the US Air Force's Falcons were some of the first technology testbeds, though.  I'm pretty sure some of this new tech has been incorporated into the F135 engines, too.

Ceramic Matrix Composites taking flight at GE Aviation

In case someone missed that concept, that means a small hole or imperfection in your heat shield fabric shouldn't create the dreaded "zipper effect" that Space Shuttle HRSI tiles were thought to be susceptible to.  That's kinda important for vehicle durability and survivability.  That said, few other materials top HRSI tiles for re-radiation of absorbed thermal flux.

Here's a nice little Science Direct article on Cobalt Super Alloys that kinda explains why CMC's are desirable where usable:

Cobalt-Based Superalloys

A very good article on CMC's from a book published in 1998 called "Ceramic Fibers and Coatings: Advanced Materials for the Twenty-First Century":

Current and Future Needs

There are also Aluminum fiber composites that can withstand LOX and LH2 that do not micro-crack after 100+ cycles from -450F to +250F.  These materials retain 85% of their strength to 700F.  They have half the CTE of conventional Aluminum alloy, less expansion than certain types of Titanium alloys in some cases, double the stiffness and strength of 7075-T6, are lighter than pure Aluminum, and are compatible with LOX / LH2 / LN2 / LHe2 (no idea about LCH4).  In terms of strength compared to a low alloy steel, the strength-to-weight ratio for two parts of identical mass would be approximately 5.3 times higher for this material.  If mass is a consideration, as it always is in aerospace applications, there are no steel alloys I'm aware of that have that kind of strength-to-weight.  The critical design figures of merit are thermal transfer rates and peak heating if using the structure as a cryogen tank the pulls double duty as a heat sink during reentry.

MetPreg Datasheet for Aluminum Matrix Composite

For good measure, here's another report from DLR that explains 3 different methods or approaches for carbon composite tank fabrication (from Boeing, Lockheed-Martin, and Northrop-Grumman):

Final Results of Advanced Cryo-Tanks Research Project CHATT

If someone here has a social media account, please ask Elon Musk if he's considered the use of SiC and thermal soaking the airframe to use the entirety of Starship's structures and propellant load for thermal control / protection.  It works in modern stealth fighters like the F-35 and it has a dramatic effect on thermal control as IR videos of hovering F-35B's have clearly demonstrated (the only way you get to a usable thermal signature to lock onto is if you're directly behind the F-135's exhaust nozzle), and it can also work for spacecraft made from appropriate materials designed to take the heat.  The only reason that the composites in the F-35 don't melt and delaminate is application of that design principle of using jet fuel to absorb the heat from aerodynamic heating and the engine and running it through a thermal exchanger to the atmosphere (won't work the exact same way for a reentry vehicle, but it still works).  There's just too much heat to use composites without aggressive active thermal control, but a combination of refractory alloys, CMC's, and cryogenic propellants should be able to get the job done.

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