SpaceX Texas launch site Discussion and Updates - Thread 12

[Herb Schaltegger]

When they first installed the launch mount, at some point Musk said that it was way over-built.  Yet they've been adding thousands of pounds of shielding and plating to it over the last few weeks, and more piping and tubing and electrical. 

That stray methane explosion in July really got their attention, and appears to have really led to a redesign in place for a lot of it.  They really, really don't want rocket exhaust or other explosion coming up through the center.

Who knows what this has meant for the crew building the one in Florida.  It should outwardly look similar, because it has to fit the same rocket footprint.  I hope we'll get to see what the innards look like.  Maybe Tim Dodd will get a tour.

Even so, as armored as it is, I'm not overly confident that it's going to be able to be rapidly reused.

There are abou 33GW coming off of the Booster for about 10 seconds or so (lighting engines to clearing the tower).  That's 330GJ of energy that has to be dispersed.

Enough to boil 127t of room temperature water.  Or melt 445t of steel.

I look at the steel covers for their plumbing and shake my head.

Setting aside your numbers (which I have not independently calculated), but do you know or can you estimate how much of that energy is being dissipated acoustically? How much is being dissipated by the kinetic energy of the exhaust gases? How much is being dissipated by IR? Etc.

Maybe you shouldn't shake your head very hard until you have a job as SpaceX with responsibility for the OLM and pad structures.

[Nomadd]

There are abou 33GW coming off of the Booster for about 10 seconds or so (lighting engines to clearing the tower).  That's 330GJ of energy that has to be dispersed.

Enough to boil 127t of room temperature water.  Or melt 445t of steel.

I look at the steel covers for their plumbing and shake my head.

You're saying that boiling room temperature water takes 3-1/2 times as much energy as melting steel?

[InterestedEngineer]

There are abou 33GW coming off of the Booster for about 10 seconds or so (lighting engines to clearing the tower).  That's 330GJ of energy that has to be dispersed.

Enough to boil 127t of room temperature water.  Or melt 445t of steel.

I look at the steel covers for their plumbing and shake my head.

You're saying that boiling room temperature water takes 3-1/2 times as much energy as melting steel?

Specific heat 304 stainless:   0.500 J/g-°C
Specific heat Water:  4.182 J/g-°C
Vaporizing Water: 2260 J/g
Heat of fusion (melting) 304 stainless: .27 J/g

water: 20 -> 100deg = 335 J/g
boiling water:  2260 J/g
Water total:  2595 J/g

304 stainless 20->1400:  690 J/g
304 stainless Melt:  0.27 J/g
304 total: 690 J/g

2595/690 = 3.76.

Boiling water requires 3.76 times the heat than melting 304 stainless starting at room temperature, gram for gram.

references:

https://www.azom.com/properties.aspx?ArticleID=965
https://letmegooglethat.com/?q=is+it+easier+to+heat+water+or+metal

[InterestedEngineer]

Setting aside your numbers (which I have not independently calculated), but do you know or can you estimate how much of that energy is being dissipated acoustically? How much is being dissipated by the kinetic energy of the exhaust gases? How much is being dissipated by IR? Etc.

Maybe you shouldn't shake your head very hard until you have a job as SpaceX with responsibility for the OLM and pad structures.

You work for SpaceX?

If not, you can and should show your work as well.  Just where does all that energy go?  Help do the calculations.

I need to fix something:   Each engine is 6.7GW thermal plus kinetic:   https://forum.nasaspaceflight.com/index.php?topic=53555.660

so it's really 222GW, of which 125GW is kinetic and 97GW is thermal.  The problem is 6.7 times worse than I stated.

I see pipes, thin panels, and other such things exposed to 97GW of thermal energy.  Even if 1/100 of that thermal blast goes into heating metal, it's still going to melt a lot of stuff, there will be hot spots.

The blast is also moving at ~3.2km/sec, 3 times faster than a NATO 5.56 round.  And the round doesn't mass 3.6 grams, it masses 23Mg per second (23 tons per second).   IOTW, 125GW of kinetic energy.   Yes, a lot of that kinetic energy will be turned into sound waves.  But not all of it.

10 seconds of this is equivalent to 500T of TNT, or "suitcase nuke" range.

I'm mostly shaking my head at the scale of it.  We'll find out how much margin SpaceX engineers put into it, hopefully sooner than later.

[su27k]

Even so, as armored as it is, I'm not overly confident that it's going to be able to be rapidly reused.

Nothing will be rapidly reused out of the gate, it would take a few iterations for them to achieve that. I wouldn't be surprised if they'll build a 2nd launch mount at Boca Chica not to increase flight rate, but simply because the current mount is so outdated and jerry rigged it's just easier to start from fresh to implement all the future enhancements.

[InterestedEngineer]

but do you know or can you estimate how much of that energy is being dissipated acoustically?

I can guess at an outer limit.  About 100GW out of the 125GW of kinetic energy, leaving 25GW of kinetic energy flow against the base and partially the top of the OLM, as well as 97GW of thermal energy flow.

Here's how I get that, using: http://www.sengpielaudio.com/calculator-soundpower.htm

Q=2 (hemisphere)

South Padre has civilian buildings 8km away.   I put a limit at ~133dB SPL, at which point windows will start to break depending on frequency components of the exhaust note.   This level will also damage hearing

That corresponds to 220dB SWL at the source, or 100GW.  So if window breaking is taken as the limit, there's still 25GW of kinetic and 97GW of thermal energy that have to be dissipated.

If we take 114dB as the safe-for-humans-on-south-padre level, we're at 100MW going into the acoustics (SPL 200), which is rounding error.

It would appear that the atmosphere can't transmit more than 194dB, so it's less than 100MW of energy being dumped into acoustics.   Which is rounding error on 125GW.

sources:  https://www.cdc.gov/nceh/hearing_loss/what_noises_cause_hearing_loss.html#:~:text=A%20whisper%20is%20about%2030,immediate%20harm%20to%20your%20ears.

http://www.sengpielaudio.com/calculator-soundpower.htm

https://www.quora.com/How-many-decibels-did-the-space-shuttle-generate-during-lift-offs

[InterestedEngineer]

How much is being dissipated by the kinetic energy of the exhaust gases?

the 125GW of kinetic energy in the exhaust gases has to go somewhere, and it lasts in the area of the OLM about 10 seconds.

125GJ/sec * 10sec = 1.25 teraJ (kinetic)

with 970GJ of thermal (97GW for 10 seconds)

That's enough to heat up the sphere of air 120m radius around the starship+booster (its height), which masses 6.6kt to about 170degC (+147) while accelerating it to a velocity of 615m/sec, or almost 2x faster than the speed of sound.

It takes a half a kilometer radius hemisphere of air to be able to dissipate that kind of energy down to 100m/sec velocity and heated by 4degC.   Mind you that's 236,000kt of air moving at 100m/sec.   (though I suspect some of the kinetic energy of the exhaust gets turned into thermal).  Forget fires near the OLM, the brush will be ripped out of the ground down to bare earth.

I've done a similar level of detail of thermal calcs for the heatshield, I can back of the envelope it and it looks completely reasonable from LEO velocities even with lost tiles.   Which I've found is true for nearly all aspects of the vehicle engineering, probably because that's what Elon does as well (spreadsheets).

I can't make the energy dissipation of the OLM in the 10 seconds around launch work out.  The density of energy is insane.  nuclear bomb levels insane.

[Hamish.Student]

How long do people think it will be until Chopstick operations are "routine" enough to no longer require pad clear for lifts?

[edzieba]

Exhaust energy is not perfectly transferred solely to the launch mount. Or else launch mounts would not routinely survive rocket launches.
You have radiation to free space (surrounding ground and air), huge amounts being carried away by hot gas flowing away from the mount (with little being transferred to the mount, as gas is pretty poor at that), energy being removed acoustically, etc.

[meekGee]

Exhaust energy is not perfectly transferred solely to the launch mount. Or else launch mounts would not routinely survive rocket launches.
You have radiation to free space (surrounding ground and air), huge amounts being carried away by hot gas flowing away from the mount (with little being transferred to the mount, as gas is pretty poor at that), energy being removed acoustically, etc.

I think a good question is how the Saturn V mount didn't melt down.

Sure it wasn't immediately reusable, but the inferno was comparable.

The governing numbers are exhaust temperature, density, and speed, not total energy.

I think most of the energy is carried away by hot gas and has little time to interact with the legs of the structure.

[Herb Schaltegger]

Exhaust energy is not perfectly transferred solely to the launch mount. Or else launch mounts would not routinely survive rocket launches.
You have radiation to free space (surrounding ground and air), huge amounts being carried away by hot gas flowing away from the mount (with little being transferred to the mount, as gas is pretty poor at that), energy being removed acoustically, etc.

Exactly. The amount of energy being carried away by the exhaust itself is the majority of the energy created by the engine in the first place - that’s how and why rocket (and jet) engines work at all. That energy is not dissipated instantly, or at any one point on the OLM, the pad surface or the surround facilities. It is dissipated by IR radiation, friction with surrounding air, acoustically, and by convection over time, by which time the vehicle will be kilometers up, down range, and accelerating ever-further away.

Engineering analysis of a dynamic system can’t ignore the dynamics OF the system.

[gsa]

You're saying that boiling room temperature water takes 3-1/2 times as much energy as melting steel?

Specific heat 304 stainless:   0.500 J/g-°C
Specific heat Water:  4.182 J/g-°C
Vaporizing Water: 2260 J/g
Heat of fusion (melting) 304 stainless: .27 J/g

water: 20 -> 100deg = 335 J/g
boiling water:  2260 J/g
Water total:  2595 J/g

304 stainless 20->1400:  690 J/g
304 stainless Melt:  0.27 J/g
304 total: 690 J/g

2595/690 = 3.76.

Boiling water requires 3.76 times the heat than melting 304 stainless starting at room temperature, gram for gram.

references:

https://www.azom.com/properties.aspx?ArticleID=965
https://letmegooglethat.com/?q=is+it+easier+to+heat+water+or+metal

From the first reference, Heat of fusion is not .27 J/g, but .27 kJ/g.
So the ratio should be:
2595/960 = 2.7.
Still impressive though.

[DanClemmensen]

You're saying that boiling room temperature water takes 3-1/2 times as much energy as melting steel?

Specific heat 304 stainless:   0.500 J/g-°C
Specific heat Water:  4.182 J/g-°C
Vaporizing Water: 2260 J/g
Heat of fusion (melting) 304 stainless: .27 J/g
water: 20 -> 100deg = 335 J/g
boiling water:  2260 J/g
Water total:  2595 J/g

304 stainless 20->1400:  690 J/g
304 stainless Melt:  0.27 J/g
304 total: 690 J/g

2595/690 = 3.76.

Boiling water requires 3.76 times the heat than melting 304 stainless starting at room temperature, gram for gram.

references:

https://www.azom.com/properties.aspx?ArticleID=965
https://letmegooglethat.com/?q=is+it+easier+to+heat+water+or+metal

From the first reference, Heat of fusion is not .27 J/g, but .27 kJ/g.
So the ratio should be:
2595/960 = 2.7.
Still impressive though.

127 tonne water = 127 m³ water, which is a circular pool 9 m in diameter and 2 m deep. No big deal in theory. Getting all the energy to go into boiling that pool would be a problem, and of course the resulting 216,000 m³ of steam needs to go somewhere.

[alugobi]

the current mount is so outdated and jerry rigged it's just easier to start from fresh to implement all the future enhancements.

This is what I see when looking at it.  It's like something out of Mad Max. 

Doesn't inspire confidence that they'll get two launches out of it.  I do trust in the competence overall of the pad engineers, but not knowing what you don't know and all that.  All this plating and rework they're doing right now suggests a big something that they didn't fully get the first time.  (Edit:  meaning, before they fired engines under it.)

So what else might there be?  Launch 1 will be revealing.

[gsa]

You're saying that boiling room temperature water takes 3-1/2 times as much energy as melting steel?

Heat of fusion (melting) 304 stainless: .27 J/g

Boiling water requires 3.76 times the heat than melting 304 stainless starting at room temperature, gram for gram.

references:

https://www.azom.com/properties.aspx?ArticleID=965
https://letmegooglethat.com/?q=is+it+easier+to+heat+water+or+metal

From the first reference, Heat of fusion is not .27 J/g, but .27 kJ/g.
So the ratio should be:
2595/960 = 2.7.
Still impressive though.

127 tonne water = 127 m³ water, which is a circular pool 9 m in diameter and 2 m deep. No big deal in theory. Getting all the energy to go into boiling that pool would be a problem, and of course the resulting 216,000 m³ of steam needs to go somewhere.

My remark was not about amount of water vaporized, but about amount of steel that water saves from melting.

[oldAtlas_Eguy]

Just from past large (Saturn 5 [7.5Mlbf) LVs. Which launched on top of a metal stricture without melting it. I think your exhaust temps of the thrust is way off and further once the thrust exhaust leaves the engine bells it continues to expand greatly also cause a much more thermal loss due to the first law of thermal dynamics. Metal is not going to melt. Get chared yes. Melt no. Plus just think of how an engine bell does not melt down into a puddle immediately. Much more energy is going into the gas velocity and pressure front than you think. I suggest you consult a thermodynamics modelling expert and a rocket engine designer.

[InterestedEngineer]

Exhaust energy is not perfectly transferred solely to the launch mount. Or else launch mounts would not routinely survive rocket launches.
You have radiation to free space (surrounding ground and air), huge amounts being carried away by hot gas flowing away from the mount (with little being transferred to the mount, as gas is pretty poor at that), energy being removed acoustically, etc.

Other launch mounts have much more extensive water deluge and don't have complicated tubing all over the place.

For example, the SLS launch system dumps 1,700 tons of water into its deluge, which is capable of absorbing 4 TeraJ of energy.   That's a number that makes sense on the back of the envelope.

[Herb Schaltegger]

Exhaust energy is not perfectly transferred solely to the launch mount. Or else launch mounts would not routinely survive rocket launches.
You have radiation to free space (surrounding ground and air), huge amounts being carried away by hot gas flowing away from the mount (with little being transferred to the mount, as gas is pretty poor at that), energy being removed acoustically, etc.

Other launch mounts have much more extensive water deluge and don't have complicated tubing all over the place.

For example, the SLS launch system dumps 1,700 tons of water into its deluge, which is capable of absorbing 4 TeraJ of energy.   That's a number that makes sense on the back of the envelope.

The water isn't there to "absorb" any energy as such - it's there to deaden acoustics enough to prevent damage to the vehicle during the first few seconds of ascent. The great majority of the energy goes into accelerating the vehicle itself. Only a small fraction of the net energy produced is mitigated by a deluge system.

[InterestedEngineer]

Just from past large (Saturn 5 [7.5Mlbf) LVs. Which launched on top of a metal stricture without melting it. I think your exhaust temps of the thrust is way off and further once the thrust exhaust leaves the engine bells it continues to expand greatly also cause a much more thermal loss due to the first law of thermal dynamics. Metal is not going to melt. Get chared yes. Melt no. Plus just think of how an engine bell does not melt down into a puddle immediately. Much more energy is going into the gas velocity and pressure front than you think. I suggest you consult a thermodynamics modelling expert and a rocket engine designer.

Saturn V's water deluge system was 300,000 gallons, which can dissipate 3TJ of energy, which is definitely in the ballpark

[InterestedEngineer]

You have radiation to free space (surrounding ground and air),

You should probably run Stefan Boltzmann on that assertion.   When I do, I'm in rounding error territory.

In the end, wherever you think the energy might go, conservation of energy rears its head.   You have to put those Joules somewhere.

I've tried to put those Joules all the places y'all have suggested, and the numbers don't add up.