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2 minutes ago, kerbiloid said:
4 minutes ago, sevenperforce said:

A niobium heat shield for Starship would be vastly heavier than the tiles.

Indeed.

But if the constructors of 1960s could use bare steel without asking for the overexpensive niobium, they would definitely do this.

Since then, the steel unlikely has changed so much.

If the designers in the 1960s were creating a vehicle which never had to undergo re-entry, they certainly would never have bothered with niobium.

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10 minutes ago, sevenperforce said:

If the designers in the 1960s were creating a vehicle which never had to undergo re-entry, they certainly would never have bothered with niobium.

Starship is going to undergo, iirc.

10 minutes ago, magnemoe said:

Again steel can handle much higher temperatures than aluminium or composites. 

Enthalpy of vaporization: steel ~6 vs Aluminium ~10 MJ/kg.
Enthalpy of melting: steel ~250 vs Aluminium ~390 kJ/kg.

You need 1.5 times more energy to destroy an aluminium hull of same mass.
And the mass is why they choose aluminium. So, no difference.

Edited by kerbiloid
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4 minutes ago, magnemoe said:

It was expensive back in the 60's, having problem like not working in in air, falcon 9 vacuum engine nozzle is made from it. 
https://en.wikipedia.org/wiki/Niobium#Superalloys

Again steel can handle much higher temperatures than aluminium or composites. 

IIRC they upgraded from niobium to RCC at some point in the last few years but I could be wrong.

And yes, steel can handle higher temps than Al or AlLi or composites, which means we need less of a heat shield. But that's relevant to re-entry, not multi-pass aerobraking.

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7 minutes ago, kerbiloid said:

Starship is going to undergo, iirc.

We are talking about multi-pass aerobrake circularization by lunar Starship. Lunar Starship is never going to undergo re-entry. Why on earth would you think it would? 

7 minutes ago, kerbiloid said:

Enthalpy of vaporization: steel ~6 vs Aluminium ~10 MJ/kg.
Enthalpy of melting: steel ~250 vs Aluminium ~390 kJ/kg.

You need 1.5 times more energy to destroy an aluminium hull of same mass.
And the mass is why they choose aluminium. So, no difference.

Neither the enthalpy of formation nor the enthalpy of vaporization are relevant to structural weakening of a spacecraft skin due to heating.

Ductile failure takes place long before you reach melting point.

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7 minutes ago, kerbiloid said:

Enthalpy of vaporization: steel ~6 vs Aluminium ~10 MJ/kg.
Enthalpy of melting: steel ~250 vs Aluminium ~390 kJ/kg.

You need 1.5 times more energy to destroy an aluminium hull of same mass.
And the mass is why they choose aluminium. So, no difference.

Think that steel can take more heal before becoming soft, but yes the real benefit of steel for starship is cryogenic strength and that its much faster to do changes on than than composites. 

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3 minutes ago, sevenperforce said:

We are talking about multi-pass aerobrake circularization by lunar Starship. Lunar Starship is never going to undergo re-entry. Why on earth would you think it would? 

It should be another Starship or another purpose of Starship?

If the latter, then no difference.
If the former - why do you call it Starship? It's a lunar zeppelin.

3 minutes ago, magnemoe said:

real benefit of steel for starship is cryogenic strength

Cryogenic strength - in what sense?

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22 minutes ago, sevenperforce said:

And exactly zero of those projects (none of which were ever constructed, mind you) were intended to perform aerobrake circularization. The heat shields were for re-entry.

This is, to date, the only vehicle to have ever performed multi-pass aerobrake circularization:

NASA-MRO-Mars-640x353.jpg

You will note the conspicuous lack of a niobium heat shield anywhere.

They did this by just nipping the atmosphere, not much heating, downside is that it take an long time as you has to do loads of passes.
You also need to be in orbit. 
 

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6 minutes ago, kerbiloid said:

It should be another Starship or another purpose of Starship?

If the latter, then no difference.
If the former - why do you call it Starship? It's a lunar zeppelin.

Cryogenic strength - in what sense?

Please make yourself aware of the Artemis plan of record regarding Lunar Starship, Tanker Starships, and Depot Starships before continuing this line of questioning.

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7 minutes ago, Rakaydos said:

Please make yourself aware of the Artemis plan of record regarding Lunar Starship, Tanker Starships, and Depot Starships before continuing this line of questioning.

I mean its Starship version.
The Starships should be unified, shouldn't them? A base model for various purposes.

2 minutes ago, magnemoe said:

Quoting Musk here, he said the steel used for starship tanks retained most of it strength at cryogenic temperatures. Most steel become very brittle then cold. 

Can't see any relation between the cryogenic and heated strength then.

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9 minutes ago, kerbiloid said:

I mean its Starship version.
The Starships should be unified, shouldn't them? A base model for various purposes.

 

The "base model" is much more flexible than you seem to understand. There's heat shields on all the ones that will return to earth, but depots will have cryogenic insulation instead, and Lunar Starship is a customized build for NASA's HLS program that's built on the same line as Starship, but has a bunch of one-off features and will never return to earth's surface.

Edited by Rakaydos
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5 minutes ago, kerbiloid said:

Can't see any relation between the cryogenic and heated strength then.

Explain?

Musk said they've developed a couple of unique alloys (vis the cryogenic strength quote).  Doing that shouldn't change the temperature at which the steel deforms when heated, should it?  Most need to be 800-1500 degrees F for that, IIRC.

Or - were you talking about something else, and I misinterpreted it?

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20 minutes ago, JoeSchmuckatelli said:

Explain?

Musk said they've developed a couple of unique alloys (vis the cryogenic strength quote).  Doing that shouldn't change the temperature at which the steel deforms when heated, should it?  Most need to be 800-1500 degrees F for that, IIRC.

Or - were you talking about something else, and I misinterpreted it?

I mean, how does the alloy strength at low temperatures relate to the strength at high temperatures?

Edited by kerbiloid
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6 minutes ago, kerbiloid said:

I mean, how does the alloy strength at low temperatures relate to the strength at high temperatures?

It doesnt. By coincidence, the right recipe of stainless has a good strength at low temperatures, and ALSO has a high melting temperature.

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5 minutes ago, kerbiloid said:

I mean, how does the alloy strength at low temperatures relate to the strength at high temperatures?

It doesn't. Steel was chosen because, among other properties, it becomes stronger at low temperatures. It has good thermal properties at high temperatures but structural properties are the important bit at low temperatures.

40 minutes ago, kerbiloid said:

I mean its Starship version.
The Starships should be unified, shouldn't them? A base model for various purposes.

There is one Starship base configuration. There are a number of different modifications and adaptations. Starships that will return to the surface of Earth get heat shields and flaps. Just like there is one base Soyuz configuration but some have boosters and others don't; some have third stages and others don't, etc.

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1 hour ago, Rakaydos said:

The "base model" is much more flexible than you seem to understand. There's heat shields on all the ones that will return to earth, but depots will have cryogenic insulation instead, and Lunar Starship is a customized build for NASA's HLS program that's built on the same line as Starship, but has a bunch of one-off features and will never return to earth's surface.

This, one favorite of mine is the shuttle starship.  Smaller crew cabin as you will have an say 4-8 crew for some weeks. Larger un-pressurized cargo bay. an heavy arm but 1-2 light
Typically one for holding the target the second holding an astronaut or various tools. or parts. 

Able to work from LEO to geo, Lunar orbit and L1 and 2. We all know we will need one of these fixing future space telescopes :o
 

 

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4 minutes ago, magnemoe said:

This, one favorite of mine is the shuttle starship.  Smaller crew cabin as you will have an say 4-8 crew for some weeks. Larger un-pressurized cargo bay. an heavy arm but 1-2 light
Typically one for holding the target the second holding an astronaut or various tools. or parts. 

Able to work from LEO to geo, Lunar orbit and L1 and 2. We all know we will need one of these fixing future space telescopes :o
 

 

Couldnt you just use a standard crew starship, with utility arms in the aft cargo?

I'm already assuming that the Depot has a fueling arm that mates with other vessels QD ports, tucked in the aft cargo.

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1 minute ago, Rakaydos said:

Couldnt you just use a standard crew starship, with utility arms in the aft cargo?

I'm already assuming that the Depot has a fueling arm that mates with other vessels QD ports, tucked in the aft cargo.

Standard crewed starship is supposed to have an around two story pressurized payload bay with an large hatch. It will be depressurized then unloading. Yes you could store the arms there but the second part of my idea was also to recover satellites to earth or an low orbit refurbish facility who would be size limited  with the standard crew version. 
Much more so then you have to add the arm systems. 

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29 minutes ago, magnemoe said:

Standard crewed starship is supposed to have an around two story pressurized payload bay with an large hatch. It will be depressurized then unloading. Yes you could store the arms there but the second part of my idea was also to recover satellites to earth or an low orbit refurbish facility who would be size limited  with the standard crew version. 
Much more so then you have to add the arm systems. 

Sounds like a job for a full cargo variant. The aft cargo pods (in the engine bay) are always open to space but protected on launch and entry, so in my mind they make a better place to have utility arms equipped.

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