Elon Musk: "It's game over for all the other heavy lift rockets"

Mark Friedenbach · 2020-03-10 16:43:45

Spaniard wrote:

I think that the active cooling has been discarted from the first version of the Rocket.

By first version do you mean the SNx orbital test vehicles, or the first commercial versions? The test vehicles are treated as expendable and I doubt they're targeting same-day reuse for them.

SpaceNut · 2020-03-10 18:10:52

I gave a time line in #21 post
GW Johnson post answers the post question a bit in #17
and finishes it in post #22
Long and short pressure builds under a tile that is hot will cause it to crack and or become no longer adhered to its location on the hull of the ship.

elderflower · 2020-03-11 04:41:28

It would be possible to make both tile and substrate with tiny holes for transpiration. These wouldn't be a part of the pressure hull.
My question was whether it had been tried. If it has, how was it done?

Quaoar · 2020-03-11 09:47:45

GW Johnson wrote:

And that's lateral skins, not nosetips and leading edges. Those are way worse.
GW

In an article about Project Exodus waverider for Venus atmosphere I read they planned to use leading edge of iridium coated reinforced carbon-carbon, actively cooled via lithium-tungsten heat-pipes.

https://ntrs.nasa.gov/search.jsp?R=19900016710

Do you think it may work?

Last edited by Quaoar (2020-03-11 09:48:06)

GW Johnson · 2020-03-11 12:25:48

This is an academic paper study. An idea. Most such do not turn out to be very practical.

The waverider is likely to lose as much delta-vee in drag, as gain any from from Venus's orbital speed. That's because Venus has a denser atmosphere. So, I don't see a lot of promise in the mission concept.

The nosetip for the waverider may have an iridium coating, and it may be cooled from the backside with heat pipes, but it is still carbon-carbon, and that means it's an ablative. Simple as that.

It changes shape as it ablates. That shape change affects vehicle aerodynamics. That effect, more than simple thickness loss, is very likely what limits its life. No different than with Space Shuttle nosetips and leading edges.

In point of fact, the iridium coating might be a bad idea. It lowers the thermal emissivity of the carbon-carbon, being a shiny metal. That greatly reduces the ability of the carbon-carbon to cool by radiation to the environment.

You have that, and you have backside cooling by conduction. Or maybe transpiration cooling if you add porosity and a sacrificial liquid to the design. That's about all the ways there are to cool the structure in any practical way. So why "kill" one of the best that you have with a shiny coating?

The heat pipe cooling is an alternate implementation of the graphite nose tip with imbedded tungsten rods that was proposed for the 1955-vintage X-20 Dynamic-Soaring ("Dyna-Soar") design. This was cancelled with the first three production articles on the assembly line in 1958.

Heat conducts down the metal rods, or a bit more efficiently down the heat pipes, cooling the graphite or carbon-carbon from the backside; there is very little actual difference.

For a space vehicle, you must deal with the heat conducted down the rods or heat pipes. You either heat sink it in some way, or find some way to dump it overboard. It just does not "disappear".

GW

PS:

This energy management stuff during entry is a small piece of an article I posted on "exrocketman" that covers the basics. Its title is "On High Speed Aerodynamics and Heat Transfer", dated 18 January 2020. It seems to have drawn a lot of readership in a very short time.

There are some other recent articles I posted there that might also be of interest to readers here. One is "Solid Rocket Analysis" dated 16 February 2020. Another is "One of Several Ramjets That I Worked On" dated 4 February 2020. And another is "Ramjet Flameholding" dated 3 March 2020. They all have lists of related articles on the site.

There's also my analyses of the performance potential of the various Spacex "Starship/Super Heavy" vehicles, before they started building prototypes to test. The latest one of those is "Reverse-Engineering the 2019 Version of the Spacex "Starship" / "Super Heavy" Design" dated 22 October 2019.

And I did some reverse-engineering of the Dragon capsules as well. That was "Reverse-Engineered Dragon Data" dated 6 March 2017, before Red Dragon was cancelled, and before Crew Dragon was relegated to only parachute recovery.

Anything you find there you are welcome to use.

Last edited by GW Johnson (2020-03-11 15:30:01)

Quaoar · 2020-03-11 15:11:26

GW Johnson wrote:

This is an academic paper study. An idea. Most such do not turn out to be very practical.
The waverider is likely to lose as much delta-vee in drag, as gain any from from Venus's orbital speed. That's because Venus has a denser atmosphere. So, I don't see a lot of promise in the mission concept.
The nosetip for the waverider may have an iridium coating, and it may be cooled from the backside with heat pipes, but it is still carbon-carbon, and that means it's an ablative. Simple as that.
It changes shape as it ablates. That shape change affects vehicle aerodynamics. That effect, more than simple thickness loss, is very likely what limits its life. No different than with Space Shuttle nosetips and leading edges.
In point of fact, the iridium coating might be a bad idea. It lowers the thermal emissivity of the carbon-carbon, being a shiny metal. That greatly reduces the ability of the carbon-carbon to cool by radiation to the environment.
You have that, and you have backside cooling by conduction. Or maybe transpiration cooling if you add porosity and a sacrificial liquid to the design. That's about all the ways there are to cool the structure in any practical way. So why "kill" one of the best that you have with a shiny coating?
The heat pipe cooling is an alternate implementation of the graphite nose tip with imbedded tungsten rods that was proposed for the 1955-vintage X-20 Dynamic-Soaring ("Dyna-Soar") design. This was cancelled with the first three production articles on the assembly line in 1958.
Heat conducts down the metal rods, or a bit more efficiently down the heat pipes, cooling the graphite or carbon-carbon from the backside; there is very little actual difference.
For a space vehicle, you must deal with the heat conducted down the rods or heat pipes. You either heat sink it in some way, or find some way to dump it overboard. It just does not "disappear".
GW

Thanks GW,
Is it possible to cool the leading edge connecting the heat-pipes to radiators on the upper surface, or is it better to use something like a phase-change heat sink? Otherwise is it possible to waste some propellant to cool the leading edges?

P.S.
Here in Rome I'm under house arrest (as all Italians) and I'm writing my sf novels waiting for the end of the epidemic
I sincerely hope your country will never experience the hell in which we are living now

Last edited by Quaoar (2020-03-11 15:35:02)

GW Johnson · 2020-03-11 15:45:33

Hi Quaoar:

My answer about heat sinks is basically "I dunno, whatever you can cobble together to hold the most BTU's or watt-seconds". Latent heats help, but may or may not be the final answer. Every project is different in detail.

Over here in the US, the spread of this covid-19 crap is just starting. We are behind the curve in both stores of supplies, and in current isolation plans, despite the lies you hear from the White House. It is unlikely we will avoid anything. It just hasn't destroyed us yet.

GW

Quaoar · 2020-03-11 16:17:50

GW Johnson wrote:

Hi Quaoar:
My answer about heat sinks is basically "I dunno, whatever you can cobble together to hold the most BTU's or watt-seconds". Latent heats help, but may or may not be the final answer. Every project is different in detail.
Over here in the US, the spread of this covid-19 crap is just starting. We are behind the curve in both stores of supplies, and in current isolation plans, despite the lies you hear from the White House. It is unlikely we will avoid anything. It just hasn't destroyed us yet.
GW

What about radiators on the upper surface, or active cooling with propellant?
If the waverider has some cryogenic propellant in the tank, is it possible to do an aero-gravity assist?

I still hope you avoid it. Today we lost 197 people.

GW Johnson · 2020-03-11 16:58:18

197. Damn. Pandemics are hell, even at a low effective death rate. The Black Death 600 years ago was far worse. But still .....

Radiators on lee surfaces during entry are exposed to low wake-velocity scrubbing speeds, but the same really high driving temperatures for heat transfer, and similar plasma radiation, above 10 km/s. They are not as effective as you otherwise might think. But they are better than no such radiator at all. Once the plasma in the boundary layer goes opaque at really high speeds, they are totally ineffective.

GW

Quaoar · 2020-03-11 17:27:14

GW Johnson wrote:

197. Damn. Pandemics are hell, even at a low effective death rate. The Black Death 600 years ago was far worse. But still .....
Radiators on lee surfaces during entry are exposed to low wake-velocity scrubbing speeds, but the same really high driving temperatures for heat transfer, and similar plasma radiation, above 10 km/s. They are not as effective as you otherwise might think. But they are better than no such radiator at all. Once the plasma in the boundary layer goes opaque at really high speeds, they are totally ineffective.
GW

197 people is only a one day toll. From the beginning of the epidemic we lost 827 people and still have 10590 infected people. It is not just like a flu is just like a war.

So can I waste some cryogenic propellant to cool the leading edge?
If not I fear I have to change the spaceship of my novel.

Last edited by Quaoar (2020-03-11 17:32:40)

SpaceNut · 2020-03-11 18:04:15

I trust that you will stay safe Quaoar, as you ride out this hell of a storm.
I think the issue for tile cooling is one that starts before we start getting them hot as a shock of cold once hot will tend to make them crack. It was said that a bag of ice if set in the hole of the shuttle would have been enough to allow for it to have made it down to earth. That said soaking those edges with the cold before entry seems to be the best option and keep it flowing as the temperature rises so as to keep up with the rise of temperature.

louis · 2020-03-11 20:02:49

You tend to be behind the curve...you didn't join WW2 till 1941 - lol - but when you do get involved, you tend to take it to the max! So it will be interesting to see how the USA copes with this.

GW Johnson wrote:

Hi Quaoar:
My answer about heat sinks is basically "I dunno, whatever you can cobble together to hold the most BTU's or watt-seconds". Latent heats help, but may or may not be the final answer. Every project is different in detail.
Over here in the US, the spread of this covid-19 crap is just starting. We are behind the curve in both stores of supplies, and in current isolation plans, despite the lies you hear from the White House. It is unlikely we will avoid anything. It just hasn't destroyed us yet.
GW

Quaoar · 2020-03-12 11:05:33

SpaceNut wrote:

I trust that you will stay safe Quaoar, as you ride out this hell of a storm.
I think the issue for tile cooling is one that starts before we start getting them hot as a shock of cold once hot will tend to make them crack. It was said that a bag of ice if set in the hole of the shuttle would have been enough to allow for it to have made it down to earth. That said soaking those edges with the cold before entry seems to be the best option and keep it flowing as the temperature rises so as to keep up with the rise of temperature.

Thanks
Safe is a big word: we are locked at home, but we still have to go out to buy food, which means hours lined-up in front of supermarkets with many people, not wearing masks because finding a mask is almost like finding gold. This reminds me my mother's tales of Rome during WW2.

Last edited by Quaoar (2020-03-12 11:11:58)

SpaceNut · 2020-03-12 18:58:43

The US is starting with cancelled large venue events of all types and while some sports will continue they will be televised without any crowd.
We have already seen store shelves empty of toilet paper, cleaning disenfecting products of all types, rubbing alcohol, hydrogen peroxide ect.. some stores are getting in product but they are going just as fast as they come in.

GW Johnson · 2020-03-13 15:58:04

Well, it's starting to "hit" here in the US. My best guess is that this virus has an oddity or two about it. One seems to be infectiousness for perhaps a week before any detectable symptoms kick in. The other seems to be that this is about like a cold or a mild flu for most folks, but potentially very deadly for oldsters (like myself), especially those with underlying heart of breathing problems.

That first oddity is why the field tests taking temperature proved to be so ineffective at containing this outbreak. I might be wrong because the real data are not yet in, but that's what the available experiences to date very strongly suggest.

All I can say is stay away from crowds, Quaoar. I will do the same.

Meanwhile, here is a quote from from AIAA's "Daily Launch" newsletter regarding why Spacex is using stainless steel for "Starship". It aligns very closely with what I have been saying for some time now.

It doesn't name the alloy, but I suspect 316L or maybe 347. 316L is cheaper than 347; otherwise they have similar properties, and both are good past 1200 F, unlike 301. Or 304L.

You want the L suffix if you intend to weld. If you don't select for that, your welds crack. Surprise, surprise!

GW

Quote from "Daily Launch":

SpaceX To Change Starship Stainless Steel Alloy

SPACE (3/12) reports that thus far, SpaceX has constructed its Starship prototypes out of a stainless-steel alloy named 301. But “aerospace engineers have been using that particular metallic blend since the middle of the last century, and it’s time for SpaceX to make a change, Elon Musk said.” Musk said during the Satellite 2020 conference, “We should be able to do better in the 2020s than they did in, like, the ‘50s, you know? So, I think we’ll start switching away from 301 maybe in the next month or two.” SpaceX still plans to use stainless steel for both the Starship and Super Heavy rocket, but the company will “migrate to a different alloy, whose constituents SpaceX will tweak over time, Musk said.” SpaceX is using stainless steel because it is cheaper than carbon fiber and handles heating better than carbon composites, among other reasons.

SpaceNut · 2020-03-14 17:35:53

I think we should discontinue the virus discusion in this topic as the other contains all of these posts.

2019 NCOV a.k.a. Wuhan's Diseases

Quaoar · 2020-03-15 05:25:48

GW Johnson wrote:

Well, it's starting to "hit" here in the US. My best guess is that this virus has an oddity or two about it. One seems to be infectiousness for perhaps a week before any detectable symptoms kick in. The other seems to be that this is about like a cold or a mild flu for most folks, but potentially very deadly for oldsters (like myself), especially those with underlying heart of breathing problems.
That first oddity is why the field tests taking temperature proved to be so ineffective at containing this outbreak. I might be wrong because the real data are not yet in, but that's what the available experiences to date very strongly suggest.
All I can say is stay away from crowds, Quaoar. I will do the same.
Meanwhile, here is a quote from from AIAA's "Daily Launch" newsletter regarding why Spacex is using stainless steel for "Starship". It aligns very closely with what I have been saying for some time now.
It doesn't name the alloy, but I suspect 316L or maybe 347. 316L is cheaper than 347; otherwise they have similar properties, and both are good past 1200 F, unlike 301. Or 304L.
You want the L suffix if you intend to weld. If you don't select for that, your welds crack. Surprise, surprise!
GW
Quote from "Daily Launch":
SpaceX To Change Starship Stainless Steel Alloy
SPACE (3/12) reports that thus far, SpaceX has constructed its Starship prototypes out of a stainless-steel alloy named 301. But “aerospace engineers have been using that particular metallic blend since the middle of the last century, and it’s time for SpaceX to make a change, Elon Musk said.” Musk said during the Satellite 2020 conference, “We should be able to do better in the 2020s than they did in, like, the ‘50s, you know? So, I think we’ll start switching away from 301 maybe in the next month or two.” SpaceX still plans to use stainless steel for both the Starship and Super Heavy rocket, but the company will “migrate to a different alloy, whose constituents SpaceX will tweak over time, Musk said.” SpaceX is using stainless steel because it is cheaper than carbon fiber and handles heating better than carbon composites, among other reasons.

Hi, to all
What will happen to the cryogenic propellant for landing, still inside the tank, when the SpaceX Spaceship make a direct entry from orbit?

P.S. I will pass to the aforementioned topic for covid19 adjournment from Italy

Last edited by Quaoar (2020-03-15 05:41:49)

SpaceNut · 2020-03-15 07:14:45

Venting hydrogen could be done, I would hope slowly when we are on the ground but one would hope that they can couple up to a pumping system that would draw it down for reuse to the filling ports.

Thanks Quaoar and be well.

GW Johnson · 2020-03-15 10:21:11

It was my understanding from the various Musk presentations that the Starship tank design featured a set of "header tanks" nested within the main tanks. The main tanks would be essentially emptied by the launch burn or the Earth orbit departure burn. The much smaller volume inside the "header tanks" would be the landing burn allowance. There was no other propellant volume stored.

Doing this means the main tank wall need not be insulated for long term cryogenic storage, since the propellant need be stored only for a few hours (waiting to launch mostly). The outer main tank wall then does not have cold liquid in contact with it during the hot exposure of atmospheric entry. It does provide a solar shading effect that lowers evaporation rates from the insulated header tanks nested inside, which enhances storage life of the landing burn propellant.

OK, now the outer main tank wall (and the wall of the cargo and pressurized living spaces) must resist high angle-of-attack airloads during entry. Order of magnitude, the pressure that must be resisted by the curved surfaces is the vehicle weight times max gees divided by the exposed area. It has to resist those airload pressures while equilibriated hot enough for re-radiation to balance peak entry heating.

300 series stainless steels have ultimate tensile strengths in the neighborhood of only 5 ksi when soaked out to 1200 F. Hotter is far weaker. So about 1000-1200 F is all you can allow. 301 and 304L are going to form oxide scaling at 1200 F, 316L and 347 do not until about 1600 F. But all have about the same tensile strength, and it "falls off a cliff" hotter than 1200 F.

You have to coat or treat the surface to be dark if you expect to radiationally cool the structure. By that, I mean the emissivity (same as absorbtivity) must be high (above 0.80) at the wavelengths band associated with a material temperature in the 1000-1200 F range. This re-radiational heat flow is a large number at high emissivity, large enough that this method of cooling is much to be preferred over any other method.

What messes this up is plasma radiation from the boundary layer adjacent to the material. Once radiational heating is dominant above 10 km/s entry speeds, then the plasma layer gets more and more opaque to the thermal radiation coming from the skin. That opacity effectively "cuts off" the radiation cooling mode.

And THAT is why entry returning from the moon (10.9 km/s) or from deep space (12-17 km/s) is SO much more challenging than entry from low Earth orbit (8 km/s). Or from low Mars orbit (3.6 km/s).

You DO NOT want the "shiny metal space ship" for returning from Earth orbit. You want a dark or black surface, and you probably need a heat shield on your windward side. It'll last longer if its dark, because the heat input rate causing ablation will be lower.

Coming back from the moon or deep space, you do want the shiny metal skin to reflect plasma radiation away, but you have to cool it! And that's very heavy and energy-consumptive. Or else cover it with a whitish heat shield, like we did Apollo.

NO ONE is immune to these physics. They simply "are". Truth lies in the numbers, not the tweets, and not the press releases.

GW

Last edited by GW Johnson (2020-03-15 10:25:12)

Quaoar · 2020-03-15 13:13:02

GW Johnson wrote:

It was my understanding from the various Musk presentations that the Starship tank design featured a set of "header tanks" nested within the main tanks. The main tanks would be essentially emptied by the launch burn or the Earth orbit departure burn. The much smaller volume inside the "header tanks" would be the landing burn allowance. There was no other propellant volume stored.
Doing this means the main tank wall need not be insulated for long term cryogenic storage, since the propellant need be stored only for a few hours (waiting to launch mostly). The outer main tank wall then does not have cold liquid in contact with it during the hot exposure of atmospheric entry. It does provide a solar shading effect that lowers evaporation rates from the insulated header tanks nested inside, which enhances storage life of the landing burn propellant.
OK, now the outer main tank wall (and the wall of the cargo and pressurized living spaces) must resist high angle-of-attack airloads during entry. Order of magnitude, the pressure that must be resisted by the curved surfaces is the vehicle weight times max gees divided by the exposed area. It has to resist those airload pressures while equilibriated hot enough for re-radiation to balance peak entry heating.
300 series stainless steels have ultimate tensile strengths in the neighborhood of only 5 ksi when soaked out to 1200 F. Hotter is far weaker. So about 1000-1200 F is all you can allow. 301 and 304L are going to form oxide scaling at 1200 F, 316L and 347 do not until about 1600 F. But all have about the same tensile strength, and it "falls off a cliff" hotter than 1200 F.
You have to coat or treat the surface to be dark if you expect to radiationally cool the structure. By that, I mean the emissivity (same as absorbtivity) must be high (above 0.80) at the wavelengths band associated with a material temperature in the 1000-1200 F range. This re-radiational heat flow is a large number at high emissivity, large enough that this method of cooling is much to be preferred over any other method.
What messes this up is plasma radiation from the boundary layer adjacent to the material. Once radiational heating is dominant above 10 km/s entry speeds, then the plasma layer gets more and more opaque to the thermal radiation coming from the skin. That opacity effectively "cuts off" the radiation cooling mode.
And THAT is why entry returning from the moon (10.9 km/s) or from deep space (12-17 km/s) is SO much more challenging than entry from low Earth orbit (8 km/s). Or from low Mars orbit (3.6 km/s).
You DO NOT want the "shiny metal space ship" for returning from Earth orbit. You want a dark or black surface, and you probably need a heat shield on your windward side. It'll last longer if its dark, because the heat input rate causing ablation will be lower.
Coming back from the moon or deep space, you do want the shiny metal skin to reflect plasma radiation away, but you have to cool it! And that's very heavy and energy-consumptive. Or else cover it with a whitish heat shield, like we did Apollo.
NO ONE is immune to these physics. They simply "are". Truth lies in the numbers, not the tweets, and not the press releases.
GW

So my interplanetary waverider heat shield, which ha to stand 17-18 km/s entries, has to be white, and even ablative. Which material do you suggest? May a reinforced carbon-carbon be white?

Thanks

Last edited by Quaoar (2020-03-15 13:13:44)

GW Johnson · 2020-03-15 14:41:00

Hi Quaoar:

You kinda have to take what you can get. Carbon-carbon is pretty much black. I'm not familiar with any coatings that might work which would change its effective color. But any such would have to survive at the ablation temperature, which for carbon, is very high indeed.

You would only need carbon-carbon the ablative at stagnation zones. That's nosetips and aerosurface leading edges. The rest of the heat shield can be something else, such as PICA-X ablative tiles, which actually can be anywhere from near white to pretty-much-black in color.

I don't know enough about PICA-X to know if it can be used at stagnation zone conditions, but I suspect that it can. It was developed from the earlier version PICA, in turn developed for Mars free-return capability at 12-17 km/s entry speeds. If it can serve at stagnation zones like I suspect, then you don't need the carbon-carbon. Your speeds look about like high-end Mars return speeds.

I already know PICA-X works for the entire Dragon capsule heat shield, including its stagnation zone. That's well-tested and flyable multiple times through Earth orbit entries at 8 km/s. The "voice of rumor control" says it'll survive perhaps twice coming back from the moon at nearly 11 km/s. Supposedly, it'll survive a Mars entry at 7.5 km/s and one Mars free return at 12-17 km/s.

You end up using thicker tiles on the more windward surfaces, thickest at the stagnation zones. I do not know what they use to bond them down to the substrate. The tile does have some thermal gradient through it, but not nearly what the low density ceramic tiles did on the Space Shuttle.

I suspect the PICA-X bondline is rather hot, and the substrate cannot be composite or aluminum, and probably not titanium. My guess is around 1000-1200 F, based on what Spacex has been uncovering in its work. Spacex developed PICA-X as an easier-to-make version of NASA's PICA.

The bondline temperature you have to tolerate depends very critically upon the surface ablation temperature, the thermal conductivity through the ablative, and the thermal resistance of the path or paths for the heat conduction on into the interior structure. Thermal conductivity is inherently density-related: higher density materials have inherently higher thermal conductivity, and therefore tend to be very nearly isothermal, even at very high thermal fluxes through them.

Myself, I am more familiar with materials like the fiber-reinforced phenolic plastic. The very early heat shields on Mercury and Gemini were made of such. I used them differently, though. As rocket and ramjet nozzle materials. That's a completely-different problem, even though ablation is involved.

GW

Quaoar · 2020-03-15 15:04:59

GW Johnson wrote:

Hi Quaoar:
You kinda have to take what you can get. Carbon-carbon is pretty much black. I'm not familiar with any coatings that might work which would change its effective color. But any such would have to survive at the ablation temperature, which for carbon, is very high indeed.
You would only need carbon-carbon the ablative at stagnation zones. That's nosetips and aerosurface leading edges. The rest of the heat shield can be something else, such as PICA-X ablative tiles, which actually can be anywhere from near white to pretty-much-black in color.
I don't know enough about PICA-X to know if it can be used at stagnation zone conditions, but I suspect that it can. It was developed from the earlier version PICA, in turn developed for Mars free-return capability at 12-17 km/s entry speeds. If it can serve at stagnation zones like I suspect, then you don't need the carbon-carbon. Your speeds look about like high-end Mars return speeds.
I already know PICA-X works for the entire Dragon capsule heat shield, including its stagnation zone. That's well-tested and flyable multiple times through Earth orbit entries at 8 km/s. The "voice of rumor control" says it'll survive perhaps twice coming back from the moon at nearly 11 km/s. Supposedly, it'll survive a Mars entry at 7.5 km/s and one Mars free return at 12-17 km/s.
You end up using thicker tiles on the more windward surfaces, thickest at the stagnation zones. I do not know what they use to bond them down to the substrate. The tile does have some thermal gradient through it, but not nearly what the low density ceramic tiles did on the Space Shuttle.
I suspect the PICA-X bondline is rather hot, and the substrate cannot be composite or aluminum, and probably not titanium. My guess is around 1000-1200 F, based on what Spacex has been uncovering in its work. Spacex developed PICA-X as an easier-to-make version of NASA's PICA.
The bondline temperature you have to tolerate depends very critically upon the surface ablation temperature, the thermal conductivity through the ablative, and the thermal resistance of the path or paths for the heat conduction on into the interior structure. Thermal conductivity is inherently density-related: higher density materials have inherently higher thermal conductivity, and therefore tend to be very nearly isothermal, even at very high thermal fluxes through them.
Myself, I am more familiar with materials like the fiber-reinforced phenolic plastic. The very early heat shields on Mercury and Gemini were made of such. I used them differently, though. As rocket and ramjet nozzle materials. That's a completely-different problem, even though ablation is involved.
GW

Thank, GW

So I can use white PICA-X on a steel shell or on a 3D carbon-carbon shell.

GW Johnson · 2020-03-17 08:24:31

Well, the "right" answer to that is from a transient thermal-structural analysis. But probably "yes".

If the backside temperature of your PICA-X exceeds about 200 F, you can't use an organic-binder composite as your substrate. The limit is about 350 F with aluminum, 750 F with titanium, and 1200 F with stainless steel.

GW

Quaoar · 2020-03-17 11:13:30

GW Johnson wrote:

Well, the "right" answer to that is from a transient thermal-structural analysis. But probably "yes".
If the backside temperature of your PICA-X exceeds about 200 F, you can't use an organic-binder composite as your substrate. The limit is about 350 F with aluminum, 750 F with titanium, and 1200 F with stainless steel.
GW

Thanks GW,
Which is the temperature limit for reinforced carbon-carbon?
And how is fixed the PICA-X on the shell?

Last edited by Quaoar (2020-03-17 11:13:58)

SpaceNut · 2020-03-17 16:39:33

These should answer the questions...

https://spaceflight.nasa.gov/shuttle/re … arbon.html

https://ntrs.nasa.gov/archive/nasa/casi … 030739.pdf

https://science.ksc.nasa.gov/shuttle/te … s_sys.html

https://en.wikipedia.org/wiki/Space_Shu … ion_system

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Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#39 2020-03-12 18:58:43

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#40 2020-03-13 15:58:04

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#41 2020-03-14 17:35:53

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#42 2020-03-15 05:25:48

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#43 2020-03-15 07:14:45

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#44 2020-03-15 10:21:11

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#45 2020-03-15 13:13:02

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#46 2020-03-15 14:41:00

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#47 2020-03-15 15:04:59

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#48 2020-03-17 08:24:31

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#49 2020-03-17 11:13:30

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

#50 2020-03-17 16:39:33

Re: Elon Musk: "It's game over for all the other heavy lift rockets"

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