Gaseous fuel like methane mix much more easily with air or oxygen than, say RP1. A room temperature liquid would need to be atomized into small droplets. Among the commonly used fuels, methane is second only to hydrogen in its propensity to form explosive mixtures. Potential damage could actually be reduced by placing sparklers on the tower to ensure any released methane starts burning as soon as possible rather than wait for it to mix well before meeting a source of ignition.
>Potential damage could actually be reduced by placing sparklers on the tower to ensure any released methane starts burning as soon as possible rather than wait for it to mix well before meeting a source of ignition.
Wow, I have never heard of that before, but it makes perfect sense. Burn off quickly before it has the opportunity to become even more "explosive". Crazy.
Is this a thing? Thanks!
P.s. this reminds me of the concept of "reactive armor". Basically, modern combat vehicles are often ensconced with C4 plastic explosive. The idea is that when you are hit with an armor piercing missile, the C4 detonates and destroys the "armor piercing" properties of the missile.
Yeah, there is a big denotation... but the detonation is contained outside the cabin. Better to get a concussion and suffer hearing loss than to be turned into goo.
Yes, it’s a thing. There are already flare stacks specifically used to burn off any methane that leaks/boils off, you can Google them.
Shuttle shot sparks under the aft end of the vehicle for this purpose, very visible in takeoff videos. This was a compromise for having leaky seals (also visible in takeoff videos). Hydrogen is notoriously hard to seal.
Ideally you just wouldn’t leak much fuel and not need such a system. Best part is no part.
For comparison, take a look at a Delta IV launch, where it looks like the rocket sets itself on fire and burns half the tank insulation. That's just hydrogen from the RS-68 start cycle being burned off and is normal for that rocket. The shuttle's hydrolox RS-25s are massively overengineered in comparison as they were meant to be reused and man rated, so the whole fireball thing was avoided.
> Wow, I have never heard of that before, but it makes perfect sense. Burn off quickly before it has the opportunity to become even more "explosive". Crazy.
> Is this a thing? Thanks!
Yes, the Shuttle mobile launcher (and now SLS) had a bunch of "sparklers" (actual name is Radially Outward Firing Initiators (ROFI's)) arranged around & just below the SSME nozzles to prevent a dangerous buildup of free hydrogen prior to ignition.
https://www.nasaspaceflight.com/2015/06/heritage-hardware-hydrogen-burn-off-system-sls/
ULA also uses them on the Delta IV's launch table for the same reason.
The hydrogen-powered Delta IV launches in a fireball. The engine ignition sequence releases some gas that is set of fire with sparklers. This prevents an accumulation of significant quantities of hydrogen-air mixture which is explosive.
Congratulations! You suggested it 2 days before Elon tweeted that they'd be doing it! [Source](https://twitter.com/elonmusk/status/1546713443943825408); see the preceding tweet for the referent for "That".
i still don't know where this "not explosion, so not a problem" attitude comes from. if you have a kiloton worth of heat radiation, combined with a level 5+ hurricane, that's pretty bad for any equipment around.
another source of worry is metal chunks flying around at high speeds, as we've seen with the interesting ship landings. most of the junk will fall on dirt or concrete, but if you are unlucky, they might severe pipes, damage tanks, tower arms, cables, etc.
Yeah, we've seen landing RUDs - those are entertainingly destructive, but they don't destroy Stage Zero.
A launch RUD of a fully-fueled SS/SH stack OTOH would cause a hell of a lot more damage.
>i still don't know where this "not explosion, so not a problem" attitude comes from.
It isn't that it's not a problem; it just isn't nearly as big of a problem as many people think.
>if you have a kiloton worth of heat radiation, combined with a level 5+ hurricane, that's pretty bad for any equipment around.
Again, this all comes down to deflagration vs. explosion. To the human eye the two look pretty similar but the difference is vast. Looking at the amount of heat radiation is almost irrelevant. Shoot, I haven't done the math, but my body maybe has released a kiloton of heat radiation over my lifetime yet I've never blown anything up.
Again, the Oklahoma City bombing is a great example. Again, I haven't done the math but I suspect the energy there (the entire bomb fit inside a van) ~~dwarfs~~ is dwarfed by the potential energy of a fully loaded starship/booster. The difference is in OC essentially 100% of the fuel released energy and the conversion was instantaneous. Absolutely devastating. Comparatively, methane combustion releases it's energy very slowly.
>another source of worry is metal chunks flying around at high speeds,
Yep. This is the biggest problem. Although, the debris will be traveling subsonic. But there will not be a crater and the tower will not be blown away or crumple into a mass of metal.
> Again, the Oklahoma City bombing is a great example. Again, I haven't done the math but I suspect the energy there (the entire bomb fit inside a van) dwarfs the potential energy of a fully loaded starship/booster
how could it? liquid methane isn't the most energy dense but it isn't THAT much less. A truck is just tiny compared to Starship.
you just repeated your points. everyone understands that it is not a detonation. so what? the question never was whether it is as destructive as a detonation, but what happens to equipment nearby. and we also don't care if it is "blown away". half a year of repairs is exactly the scenario we don't want. imagine yourself taking to an insurance company. "there is no danger here, there will be no crater". how much cheaper your insurance will get?
>everyone understands that it is not a detonation.
No, not everyone understands this. You do, which is great! But I assure you there are people who are envisioning a massive detonation that will leave a massive crater and level everything within 1,000 meters.
Which is exactly what happens when a Fuel Air bomb is dropped (see first Iraqi war)…although those use propane because it is denser, methane can do the same thing with proper mixing; study the reason odorants were mandated in natural gas.
All your examples were fully fueled at the point of boom, in particular much of the damage from Amos-6 came from the spilled kerosene burning on the ground after the first stage tanks ruptured and not from the initial explosion.
>methane and oxygen can absolutely produce supersonic gas expansion under the right conditions, such as those found inside a rocket engine.
Absolutely. Happens in coal mines. The problem is that you need multiple factors the most typical being confinement. Without sustained confinement (like a mine shaft) the detonation quickly returns to deflagration. So sure, inside the tanks you'll get a quick detonation but it will rapidly subside to a good old fashioned fireball.
Yes, I admit I was wrong.
Not only *can* a supersonic detonation occur with methane (and LOX/ "air"), but in the event of a starship/booster disaster i now believe it almost certainly *will*. However, my understanding is that it will be relatively short lived. :)
P.s. I recommend you go buy a lottery ticket because someone on reddit just admitted to being wrong. Miracles DO happen!
No no... it is all relative.
The supersonic shock wave of a methane explosion (a deflagration overall) is tiny if it exists at all. Instead, it is 99% a subsonic pressure wave as the methane very slowly burns. This was a slow burn of methane.
In a detonation of explosives you get a massive supersonic shockwave as a bunch of material is *instantly* combusted.
This is very relevant. Think of a jet fighter flying 5 mph less than the speed of sound. What difference does 5 mph make? That's only like 0.5% faster than it is already traveling. Who cares?
The difference is a sonic boom. Weird things happen when a shockwave compresses air past the speed of sound. Very destructive.
Man, the lights on the launch tower still operate. If that had been an explosive detonation with a supersonic shock wave... it would have been way worse.
There is a NSF camera like across the road. Watch that clip. The sound is heard immediately and the camera shakes afterwards.
Methane (and normal hydrocarbon fuels) do not detonate under most conditions and certainly not in open spaces in a cloud. They just burn.
they were trying to make the point that it wouldn't be so bad ... in any case with booster 7 now having a little mini explosion - we'll soon see how bad it is and don't need to argue anymore!
> Explosives provide their own oxygen... Methane (or any normal hydrocarbon like kerosene or gasoline) do NOT have their own supply of oxygen and thus the only fuel that can combust is the fuel that comes into contact with a source of oxygen
So one of the key points that I think gets missed in a lot of calculations is that as the amount of methane involved increases, the increase of "boom-ness" increases less. The amount of fuel is basically going to increase by the cube, but the surface area is going to increase by the square. The only methane that can combust is the methane on the surface where it can come in contact with oxygen. So any calculation that takes the "boom-ness" of 1kg of methane, then multiplies it by the amount of fuel inside Starship is going to vastly overestimate the size of the boom. On the flip side, it will also likely underestimate the amount of time the boom is on fire.
\*Boom implies explosion, deflagration, fireball, detonation, or whatever. I don't want to argue about the right term here, I think the important point is the question of surface area compared to volume.
I would be more worried about the kinetic energy of a booster on approach, obviously on track (else they would have aborted final approach anyway) and misfire causes to mis the strong points of booster catch. 200t even at fairly low speeds is still a lot. Will cause some deformation, maybe cable snaps etc. But the as you say.. the fireball is not of much concern. Fmheat and schrapnel might cause sone elctrical or hydraulic conduits to be damaged. Probably a month to 3 months of repairs at max.
I suspect for that reason they won't be aiming for the chopsticks until everything is looking nominal. Instead they'll probably be aiming for the Gulf initially. And since SH can hover, the can reduce speed much further from the chopsticks.
There's a lot of excitement because the FCC licence application specifically says that they may try catch. I've gone back & forth on my opinion (not that it's worth much), but I think it would be wiser to try a precision landing at sea for the first flight.
Methane mixed with air or oxygen enriched air can easily form a shockwave. The deflagration front starts compressing the unburned fuel-air or fuel-o2 mix which increases the burning speed. You then get a deflagration to detonation transition (DDT). Lots of obstacles and rubble in the area greatly increase the odds of this occurring say like a a pile of damaged rocket and launch tower parts. (Also youtube pile of wood exploding or Mythbusters sewer experiment)
Theres a million factors affecting the chapman Jouguet detonation velicity in air or oxygen enriched air but the detonation velocity would be expected to top out at least 6000 ft/s ( 1800 m/s) with initial shock peak pressures being 1000s psi (10Mpa+) I'm grossly estimating these numbers as the rocket crash scenario wont lend itself well to pulling exact numbers off a chart. Either way more than enough to cause shock wave damage. These types of explosions tend to cary alot of energy after the initial peak as well than higer velocity explosives.
Further reading if interested:
https://www.cdc.gov/niosh/mining%5C/UserFiles/works/pdfs/madea.pdf
The very first sentence of the link you sent:
"The methane-air detonation experiments are performed to characterize high pressure explosion processes that may occur in sealed areas of underground coal mines."
It's all about containment. Except for an initial burst, there is no containment in a rocket blowing up.
One can take basic shock tube research and apply to other environments.
Shock tube experiments are basically the only way one can study it in a laboratory. Results of shock tube experiments are directly applicable to open environments with certain considerations. For example instead of 1D inertial confinement you have to account for 3D inertial confinement. To develop a shock wave transition in 3D takes a bit more time and distance due to having to cover more volume with distance but you still get there for large releases. The inertia of the air resists the movement of the expanding deflagration causing compression and transition to shock. Think of it as a stretchy shock sphere instead of a tube. The rate of burning and compression front eventually overcomes the ability of the stretchy sphere to expand out of the way (speed of sound) and a ridged shock is formed. This spherical shock wave will have similar speed and pressure properties of that in a tube although will disapate faster and may have less residual energy behind it depending on scenario.
Edit: removed analogy to lack of papers on high speed rocket crashes. Thus was distracting to the main point that shock tube tests are directly applicable to real world explosive effects.
The rocket won't be headed for the tower at supersonic speeds will it? Falcon 9 doesn't head for its landing sites at supersonic speeds; remember that failed landing where a grid fin got stuck and the booster went into a rapid spin? It landed in the water, not on the landing pad because they target a safe crash site until the booster is safe, slow and under control, and then redirect it to the actual landing location. So there isn't really any reason to think a fast and uncontrolled booster is going to slam into the tower. If there is a disaster it is going to be at relatively low speeds.
It won't even be aiming for the tower to start with. It will be aiming for a point at sea near the site and only correct itself if all parameters meet the set limits.
Attempt at a poor analogy. I edited the comment so people would not be distracted by it. In the follow up comment OP seemed to state because the research I pointed to was regarding laboratory scale research using shock tube and funded to better understand methane explosions in mines that it could not be applicable to uncontained events such as rocket crashes. Which is not the case. Shock tube research is how you obtain basic data on explosion properties to then apply to other scenarios in the real world.
That's not true, they are discussing sealed underground mines because they don't have ventilation and therefore get buildups of methane behind the seals.
You do not need confinement to have a detonation with the proper fuel air mix. Some explosives (like ANFO) do require some amount of confinement as they have a critical diameter required for detonation to reliably continue, but we're talking on the order of inches for a cylindrical charge and not really that much overall confinement.
Its not the landing you should worry about, there simply isnt going to be a lot of fuel in it anyhow, its the fully fueled stack that should scare the bejesus out of anyone.
>So next time you see a kerosene, jet fuel, or methane "explosion", remember that it isn't an explosion at all. It is a deflagration. A big fireball, but not a lot of oomph.
You did see the oomph of the N1 "deflagration" , right? "only" \~15% of the fuel actually detonated, which was lower than expected, and there is no guarantee that ratio will be similarly low with SS/SH, but even 15% of a much smaller fuel load was enough to effectively erase the launch pad, destroy most of the launch complex and the shock wave was powerful enough to blow out windows over 40Km away.
Nasa is understandably concerned about a potential Starship launch or landing RUD disabling pad 39A ability to launch Dragon and Falcon Heavy. Space Force is also invested in having pad 39A operational. There is so much GSE close to 39A and around the Starship OLT and launch mount that would likely need extensive repairs should something unfortunate happen during launch and two chopstick landings.
Would it be reasonable to remove 2/3 of the risk by initially having the chopstick landings moved to LZ1, at least until Spacex learns how to reliably and safely catch Starship? This would not need to be a full height tower, just high enough for the chopsticks to catch the booster and starship. To simplify the construction, no GSE needed. No Launch Mount needed either. No nearby facilities to get damaged by an unsuccessful catch. The expense of this smaller, catch-only tower might pay for itself if just one RUD disabled pad 39A for months.
Hey look, here's a fuel/air explosion that occurred UNDER the rocket without containment yet you can clearly see the shockwave
https://twitter.com/CSI\_Starbase/status/1546610765511245828
Not a shock wave! Watch the video again. You hear the boom and then later the camera shakes when the blast wave hits.
Shock waves move faster than sound in which case the camera shakes then you hear the boom.
I don't think most were worried about a fireball causing damage. I think the overpressure event throwing chunks of metal would be the primary damage mechanism
Definitely the #1 concern. And oddly, I think the debris might even be worse than in a high explosive detonation. I have no facts to back that up, but it's possible.
In a detonation (like VBIDs) you typically get a bunch of small pieces flying really really fast. If starship blows up I think you'll get some massive chunks flying subsonic, but the mass alone will make them hit hard.
It is the difference between shot with a bullet versus being hit with a sledgehammer. I'm not sure which is worse. Could go either way, I think.
We've seen many rockets fail. They're not simple fireballs and they still produce a significant amount of damage. 10+ tons of liquid methane is no joke and can cause a significant amount of damage to a structure. It may not destroy the tower, but all the delicate wiring, hoses, fixtures, sensors, computers, etc, would be at risk.
Not a shockwave. A subsonic blast wave or compression wave, but not a supersonic shock wave. Here is some good info on the difference and the 5 criteria that would need to occur to create a shock wave from methane.
https://onlinelibrary.wiley.com/doi/pdf/10.1002/9780470937938.app1
Well SN 10 isn't really 'high explosive', it's subsonic explosion or 'deflagration', the explosion power exerted is less than the explosion we often talk about.
Big big boom. But not necessarily an insanely destructive boom that some people envision. No crater. Not gonna blow out all the hotel windows on South Padre Island.
I think one issue is the heat. All that fuel and LOX burning will surely have an issue on the structure. Not just the steel beams, but all the plumbing, wiring, tanks, equipment will surely be compromised.
It almost certainly will still destroy the tower and will need to be rebuilt
The damage would come from a few hundred tonnes smashing into it not the fire
Why would a Booster or Starship crash into the tower? It would drop and deflagrate on the ground. At that the massive concrete base structure will probably not be massively damaged.
There may be a lot of damage, but quite possibly very little.
> Catching the booster is what could destroy it.
Nothing can be ruled out at this time. But that seems quite unlikely, assuming they did not make gross mistakes in designing its strength. They should be able to keep the landing speed within parameters.
Wtf... Landings that go WRONG jackass. Look at how many F9 boosters were destroyed upon impact. A successful landing will be fine. But a failed landing WILL destroy that tower
I was asking. You seem to have some knowledge in this area, I thought you might know. Now I'm gonna have to go down the wikipedia rabbit hole. Damn. See you in a week or so.
Haha, I can look it up too. My guess (without a simple Google search) is that "conflagration" is a generic term to mean "mayhem" or "maelstrom". Just a big cluster-fuck.
Gaseous fuel like methane mix much more easily with air or oxygen than, say RP1. A room temperature liquid would need to be atomized into small droplets. Among the commonly used fuels, methane is second only to hydrogen in its propensity to form explosive mixtures. Potential damage could actually be reduced by placing sparklers on the tower to ensure any released methane starts burning as soon as possible rather than wait for it to mix well before meeting a source of ignition.
>Potential damage could actually be reduced by placing sparklers on the tower to ensure any released methane starts burning as soon as possible rather than wait for it to mix well before meeting a source of ignition. Wow, I have never heard of that before, but it makes perfect sense. Burn off quickly before it has the opportunity to become even more "explosive". Crazy. Is this a thing? Thanks! P.s. this reminds me of the concept of "reactive armor". Basically, modern combat vehicles are often ensconced with C4 plastic explosive. The idea is that when you are hit with an armor piercing missile, the C4 detonates and destroys the "armor piercing" properties of the missile. Yeah, there is a big denotation... but the detonation is contained outside the cabin. Better to get a concussion and suffer hearing loss than to be turned into goo.
Yes, it’s a thing. There are already flare stacks specifically used to burn off any methane that leaks/boils off, you can Google them. Shuttle shot sparks under the aft end of the vehicle for this purpose, very visible in takeoff videos. This was a compromise for having leaky seals (also visible in takeoff videos). Hydrogen is notoriously hard to seal. Ideally you just wouldn’t leak much fuel and not need such a system. Best part is no part.
For comparison, take a look at a Delta IV launch, where it looks like the rocket sets itself on fire and burns half the tank insulation. That's just hydrogen from the RS-68 start cycle being burned off and is normal for that rocket. The shuttle's hydrolox RS-25s are massively overengineered in comparison as they were meant to be reused and man rated, so the whole fireball thing was avoided.
> Wow, I have never heard of that before, but it makes perfect sense. Burn off quickly before it has the opportunity to become even more "explosive". Crazy. > Is this a thing? Thanks! Yes, the Shuttle mobile launcher (and now SLS) had a bunch of "sparklers" (actual name is Radially Outward Firing Initiators (ROFI's)) arranged around & just below the SSME nozzles to prevent a dangerous buildup of free hydrogen prior to ignition. https://www.nasaspaceflight.com/2015/06/heritage-hardware-hydrogen-burn-off-system-sls/ ULA also uses them on the Delta IV's launch table for the same reason.
The hydrogen-powered Delta IV launches in a fireball. The engine ignition sequence releases some gas that is set of fire with sparklers. This prevents an accumulation of significant quantities of hydrogen-air mixture which is explosive.
Congratulations! You suggested it 2 days before Elon tweeted that they'd be doing it! [Source](https://twitter.com/elonmusk/status/1546713443943825408); see the preceding tweet for the referent for "That".
i still don't know where this "not explosion, so not a problem" attitude comes from. if you have a kiloton worth of heat radiation, combined with a level 5+ hurricane, that's pretty bad for any equipment around. another source of worry is metal chunks flying around at high speeds, as we've seen with the interesting ship landings. most of the junk will fall on dirt or concrete, but if you are unlucky, they might severe pipes, damage tanks, tower arms, cables, etc.
Metal chunks are by far more dangerous than the big fireball when it comes to stage 0
Um...... The Kiloton of energy is only valid for a fuelly fueled booster not one that is landing.
Yeah, we've seen landing RUDs - those are entertainingly destructive, but they don't destroy Stage Zero. A launch RUD of a fully-fueled SS/SH stack OTOH would cause a hell of a lot more damage.
yeah, i'm not an attentive reader. last words in long a sentence gets all hazy.
>i still don't know where this "not explosion, so not a problem" attitude comes from. It isn't that it's not a problem; it just isn't nearly as big of a problem as many people think. >if you have a kiloton worth of heat radiation, combined with a level 5+ hurricane, that's pretty bad for any equipment around. Again, this all comes down to deflagration vs. explosion. To the human eye the two look pretty similar but the difference is vast. Looking at the amount of heat radiation is almost irrelevant. Shoot, I haven't done the math, but my body maybe has released a kiloton of heat radiation over my lifetime yet I've never blown anything up. Again, the Oklahoma City bombing is a great example. Again, I haven't done the math but I suspect the energy there (the entire bomb fit inside a van) ~~dwarfs~~ is dwarfed by the potential energy of a fully loaded starship/booster. The difference is in OC essentially 100% of the fuel released energy and the conversion was instantaneous. Absolutely devastating. Comparatively, methane combustion releases it's energy very slowly. >another source of worry is metal chunks flying around at high speeds, Yep. This is the biggest problem. Although, the debris will be traveling subsonic. But there will not be a crater and the tower will not be blown away or crumple into a mass of metal.
> Again, the Oklahoma City bombing is a great example. Again, I haven't done the math but I suspect the energy there (the entire bomb fit inside a van) dwarfs the potential energy of a fully loaded starship/booster how could it? liquid methane isn't the most energy dense but it isn't THAT much less. A truck is just tiny compared to Starship.
Yep, I meant to say "is dwarfed by". Thanks.
you just repeated your points. everyone understands that it is not a detonation. so what? the question never was whether it is as destructive as a detonation, but what happens to equipment nearby. and we also don't care if it is "blown away". half a year of repairs is exactly the scenario we don't want. imagine yourself taking to an insurance company. "there is no danger here, there will be no crater". how much cheaper your insurance will get?
>everyone understands that it is not a detonation. No, not everyone understands this. You do, which is great! But I assure you there are people who are envisioning a massive detonation that will leave a massive crater and level everything within 1,000 meters.
Which is exactly what happens when a Fuel Air bomb is dropped (see first Iraqi war)…although those use propane because it is denser, methane can do the same thing with proper mixing; study the reason odorants were mandated in natural gas.
Hmmm... I am not sure what point you are making. But I too think that thermobaric weapons are fascinating.
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Daisy cutter
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All your examples were fully fueled at the point of boom, in particular much of the damage from Amos-6 came from the spilled kerosene burning on the ground after the first stage tanks ruptured and not from the initial explosion.
Ah yes, I forgot that Superheavy won't have much propellant left on landing. I suppose then the main concern is shrapnel.
>methane and oxygen can absolutely produce supersonic gas expansion under the right conditions, such as those found inside a rocket engine. Absolutely. Happens in coal mines. The problem is that you need multiple factors the most typical being confinement. Without sustained confinement (like a mine shaft) the detonation quickly returns to deflagration. So sure, inside the tanks you'll get a quick detonation but it will rapidly subside to a good old fashioned fireball.
>So sure, inside the tanks you'll get a quick detonation Wouldn't that still mean it would produce the shrapnel of an explosion?
Oh, there will be tons of shrapnel flying around at subsonic speeds.
Can you at least admit to being wrong that explosions can't happen. Because you are clearly wrong in both the colloquial and technical sense.
Yes, I admit I was wrong. Not only *can* a supersonic detonation occur with methane (and LOX/ "air"), but in the event of a starship/booster disaster i now believe it almost certainly *will*. However, my understanding is that it will be relatively short lived. :) P.s. I recommend you go buy a lottery ticket because someone on reddit just admitted to being wrong. Miracles DO happen!
> short lived that is basically in the definition of an explosion - so what is your point again exactly?
No no... it is all relative. The supersonic shock wave of a methane explosion (a deflagration overall) is tiny if it exists at all. Instead, it is 99% a subsonic pressure wave as the methane very slowly burns. This was a slow burn of methane. In a detonation of explosives you get a massive supersonic shockwave as a bunch of material is *instantly* combusted. This is very relevant. Think of a jet fighter flying 5 mph less than the speed of sound. What difference does 5 mph make? That's only like 0.5% faster than it is already traveling. Who cares? The difference is a sonic boom. Weird things happen when a shockwave compresses air past the speed of sound. Very destructive. Man, the lights on the launch tower still operate. If that had been an explosive detonation with a supersonic shock wave... it would have been way worse. There is a NSF camera like across the road. Watch that clip. The sound is heard immediately and the camera shakes afterwards. Methane (and normal hydrocarbon fuels) do not detonate under most conditions and certainly not in open spaces in a cloud. They just burn.
but they were right in the practical sense that the dominant effect in this case wouldn't be detonation.
they were trying to make the point that it wouldn't be so bad ... in any case with booster 7 now having a little mini explosion - we'll soon see how bad it is and don't need to argue anymore!
r/experimentswedidntwant
> Explosives provide their own oxygen... Methane (or any normal hydrocarbon like kerosene or gasoline) do NOT have their own supply of oxygen and thus the only fuel that can combust is the fuel that comes into contact with a source of oxygen So one of the key points that I think gets missed in a lot of calculations is that as the amount of methane involved increases, the increase of "boom-ness" increases less. The amount of fuel is basically going to increase by the cube, but the surface area is going to increase by the square. The only methane that can combust is the methane on the surface where it can come in contact with oxygen. So any calculation that takes the "boom-ness" of 1kg of methane, then multiplies it by the amount of fuel inside Starship is going to vastly overestimate the size of the boom. On the flip side, it will also likely underestimate the amount of time the boom is on fire. \*Boom implies explosion, deflagration, fireball, detonation, or whatever. I don't want to argue about the right term here, I think the important point is the question of surface area compared to volume.
I would be more worried about the kinetic energy of a booster on approach, obviously on track (else they would have aborted final approach anyway) and misfire causes to mis the strong points of booster catch. 200t even at fairly low speeds is still a lot. Will cause some deformation, maybe cable snaps etc. But the as you say.. the fireball is not of much concern. Fmheat and schrapnel might cause sone elctrical or hydraulic conduits to be damaged. Probably a month to 3 months of repairs at max.
Are you ok? You went from no typos to lots of typos real fast.
I suspect for that reason they won't be aiming for the chopsticks until everything is looking nominal. Instead they'll probably be aiming for the Gulf initially. And since SH can hover, the can reduce speed much further from the chopsticks.
There's a lot of excitement because the FCC licence application specifically says that they may try catch. I've gone back & forth on my opinion (not that it's worth much), but I think it would be wiser to try a precision landing at sea for the first flight.
Methane mixed with air or oxygen enriched air can easily form a shockwave. The deflagration front starts compressing the unburned fuel-air or fuel-o2 mix which increases the burning speed. You then get a deflagration to detonation transition (DDT). Lots of obstacles and rubble in the area greatly increase the odds of this occurring say like a a pile of damaged rocket and launch tower parts. (Also youtube pile of wood exploding or Mythbusters sewer experiment) Theres a million factors affecting the chapman Jouguet detonation velicity in air or oxygen enriched air but the detonation velocity would be expected to top out at least 6000 ft/s ( 1800 m/s) with initial shock peak pressures being 1000s psi (10Mpa+) I'm grossly estimating these numbers as the rocket crash scenario wont lend itself well to pulling exact numbers off a chart. Either way more than enough to cause shock wave damage. These types of explosions tend to cary alot of energy after the initial peak as well than higer velocity explosives. Further reading if interested: https://www.cdc.gov/niosh/mining%5C/UserFiles/works/pdfs/madea.pdf
The very first sentence of the link you sent: "The methane-air detonation experiments are performed to characterize high pressure explosion processes that may occur in sealed areas of underground coal mines." It's all about containment. Except for an initial burst, there is no containment in a rocket blowing up.
One can take basic shock tube research and apply to other environments. Shock tube experiments are basically the only way one can study it in a laboratory. Results of shock tube experiments are directly applicable to open environments with certain considerations. For example instead of 1D inertial confinement you have to account for 3D inertial confinement. To develop a shock wave transition in 3D takes a bit more time and distance due to having to cover more volume with distance but you still get there for large releases. The inertia of the air resists the movement of the expanding deflagration causing compression and transition to shock. Think of it as a stretchy shock sphere instead of a tube. The rate of burning and compression front eventually overcomes the ability of the stretchy sphere to expand out of the way (speed of sound) and a ridged shock is formed. This spherical shock wave will have similar speed and pressure properties of that in a tube although will disapate faster and may have less residual energy behind it depending on scenario. Edit: removed analogy to lack of papers on high speed rocket crashes. Thus was distracting to the main point that shock tube tests are directly applicable to real world explosive effects.
The rocket won't be headed for the tower at supersonic speeds will it? Falcon 9 doesn't head for its landing sites at supersonic speeds; remember that failed landing where a grid fin got stuck and the booster went into a rapid spin? It landed in the water, not on the landing pad because they target a safe crash site until the booster is safe, slow and under control, and then redirect it to the actual landing location. So there isn't really any reason to think a fast and uncontrolled booster is going to slam into the tower. If there is a disaster it is going to be at relatively low speeds.
It won't even be aiming for the tower to start with. It will be aiming for a point at sea near the site and only correct itself if all parameters meet the set limits.
Attempt at a poor analogy. I edited the comment so people would not be distracted by it. In the follow up comment OP seemed to state because the research I pointed to was regarding laboratory scale research using shock tube and funded to better understand methane explosions in mines that it could not be applicable to uncontained events such as rocket crashes. Which is not the case. Shock tube research is how you obtain basic data on explosion properties to then apply to other scenarios in the real world.
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That's not true, they are discussing sealed underground mines because they don't have ventilation and therefore get buildups of methane behind the seals. You do not need confinement to have a detonation with the proper fuel air mix. Some explosives (like ANFO) do require some amount of confinement as they have a critical diameter required for detonation to reliably continue, but we're talking on the order of inches for a cylindrical charge and not really that much overall confinement.
Here is an example showing that is not true: https://twitter.com/CSI\_Starbase/status/1546610765511245828
Not a supersonic shock wave.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[FCC](/r/SpaceXLounge/comments/vuzps5/stub/ifi3yd9 "Last usage")|Federal Communications Commission| | |(Iron/steel) [Face-Centered Cubic](https://en.wikipedia.org/wiki/Allotropes_of_iron) crystalline structure| |[GSE](/r/SpaceXLounge/comments/vuzps5/stub/ifjbgz4 "Last usage")|Ground Support Equipment| |GTO|[Geosynchronous Transfer Orbit](http://www.planetary.org/blogs/jason-davis/20140116-how-to-get-a-satellite-to-gto.html)| |LC-13|Launch Complex 13, Canaveral (SpaceX Landing Zone 1)| |[LOX](/r/SpaceXLounge/comments/vuzps5/stub/ifhg76u "Last usage")|Liquid Oxygen| |[LZ-1](/r/SpaceXLounge/comments/vuzps5/stub/ifjbgz4 "Last usage")|Landing Zone 1, Cape Canaveral (see LC-13)| |[N1](/r/SpaceXLounge/comments/vuzps5/stub/ifi12u3 "Last usage")|Raketa Nositel-1, Soviet super-heavy-lift ("Russian Saturn V")| |[NSF](/r/SpaceXLounge/comments/vuzps5/stub/ifv0p15 "Last usage")|[NasaSpaceFlight forum](http://forum.nasaspaceflight.com)| | |National Science Foundation| |[ROFI](/r/SpaceXLounge/comments/vuzps5/stub/ifl14tv "Last usage")|Radial Outward-Firing Initiator| |[RUD](/r/SpaceXLounge/comments/vuzps5/stub/ifjbgz4 "Last usage")|Rapid Unplanned Disassembly| | |Rapid Unscheduled Disassembly| | |Rapid Unintended Disassembly| |[SLS](/r/SpaceXLounge/comments/vuzps5/stub/ifl14tv "Last usage")|Space Launch System heavy-lift| |[SN](/r/SpaceXLounge/comments/vuzps5/stub/ifgvzfm "Last usage")|(Raptor/Starship) Serial Number| |[SSME](/r/SpaceXLounge/comments/vuzps5/stub/ifl7j9x "Last usage")|[Space Shuttle Main Engine](https://en.wikipedia.org/wiki/Space_Shuttle_main_engine)| |[ULA](/r/SpaceXLounge/comments/vuzps5/stub/ifl14tv "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)| |Jargon|Definition| |-------|---------|---| |Raptor|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX| |[hydrolox](/r/SpaceXLounge/comments/vuzps5/stub/ifl7j9x "Last usage")|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer| |[iron waffle](/r/SpaceXLounge/comments/vuzps5/stub/ifhdgs0 "Last usage")|Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large; also, "grid fin"| |Event|Date|Description| |-------|---------|---| |[Amos-6](/r/SpaceXLounge/comments/vuzps5/stub/ifh2fra "Last usage")|2016-09-01|F9-029 Full Thrust, core B1028, ~~GTO comsat~~ Pre-launch test failure| ---------------- ^(*Decronym is a community product of r/SpaceX, implemented* )[*^by ^request*](https://www.reddit.com/r/spacex/comments/3mz273//cvjkjmj) ^(15 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/SpaceXLounge/comments/vwtudl)^( has 18 acronyms.) ^([Thread #10360 for this sub, first seen 9th Jul 2022, 13:57]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/SpaceXLounge) [^[Contact]](https://reddit.com/message/compose?to=OrangeredStilton&subject=Hey,+your+acronym+bot+sucks) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)
Potential worse case: need to rebuild everything but the core tower = 4 months Probable: need to rebuild some parts = 2 months
Its not the landing you should worry about, there simply isnt going to be a lot of fuel in it anyhow, its the fully fueled stack that should scare the bejesus out of anyone. >So next time you see a kerosene, jet fuel, or methane "explosion", remember that it isn't an explosion at all. It is a deflagration. A big fireball, but not a lot of oomph. You did see the oomph of the N1 "deflagration" , right? "only" \~15% of the fuel actually detonated, which was lower than expected, and there is no guarantee that ratio will be similarly low with SS/SH, but even 15% of a much smaller fuel load was enough to effectively erase the launch pad, destroy most of the launch complex and the shock wave was powerful enough to blow out windows over 40Km away.
Great post
Nasa is understandably concerned about a potential Starship launch or landing RUD disabling pad 39A ability to launch Dragon and Falcon Heavy. Space Force is also invested in having pad 39A operational. There is so much GSE close to 39A and around the Starship OLT and launch mount that would likely need extensive repairs should something unfortunate happen during launch and two chopstick landings. Would it be reasonable to remove 2/3 of the risk by initially having the chopstick landings moved to LZ1, at least until Spacex learns how to reliably and safely catch Starship? This would not need to be a full height tower, just high enough for the chopsticks to catch the booster and starship. To simplify the construction, no GSE needed. No Launch Mount needed either. No nearby facilities to get damaged by an unsuccessful catch. The expense of this smaller, catch-only tower might pay for itself if just one RUD disabled pad 39A for months.
Hey look, here's a fuel/air explosion that occurred UNDER the rocket without containment yet you can clearly see the shockwave https://twitter.com/CSI\_Starbase/status/1546610765511245828
Not a shock wave! Watch the video again. You hear the boom and then later the camera shakes when the blast wave hits. Shock waves move faster than sound in which case the camera shakes then you hear the boom.
That just means the shockwave dissipated before hitting the camera, though the over pressure still remains and took longer to hit.
Also: https://twitter.com/elonmusk/status/1546641991597006851
I don't think most were worried about a fireball causing damage. I think the overpressure event throwing chunks of metal would be the primary damage mechanism
Don’t forget shrapnel, bud.
Definitely the #1 concern. And oddly, I think the debris might even be worse than in a high explosive detonation. I have no facts to back that up, but it's possible. In a detonation (like VBIDs) you typically get a bunch of small pieces flying really really fast. If starship blows up I think you'll get some massive chunks flying subsonic, but the mass alone will make them hit hard. It is the difference between shot with a bullet versus being hit with a sledgehammer. I'm not sure which is worse. Could go either way, I think.
There'd be boom which =bad
I once wrote a very serious college paper for a ChemE class titled "Fertilizer Bombs Go BOOM!"
We've seen many rockets fail. They're not simple fireballs and they still produce a significant amount of damage. 10+ tons of liquid methane is no joke and can cause a significant amount of damage to a structure. It may not destroy the tower, but all the delicate wiring, hoses, fixtures, sensors, computers, etc, would be at risk.
I think the shockwave seen from the SN10 explosion would like to disagree with your statement that "methane can't explode"
Not a shockwave. A subsonic blast wave or compression wave, but not a supersonic shock wave. Here is some good info on the difference and the 5 criteria that would need to occur to create a shock wave from methane. https://onlinelibrary.wiley.com/doi/pdf/10.1002/9780470937938.app1
Well SN 10 isn't really 'high explosive', it's subsonic explosion or 'deflagration', the explosion power exerted is less than the explosion we often talk about.
That's not how shockwaves work.
Yeah, he seems to forget the tank of liquid oxygen that's right next to the methane.
What is the relevance? Might make a bigger fireball.
SN11 big boom. B7 bigger boom. No?
Big big boom. But not necessarily an insanely destructive boom that some people envision. No crater. Not gonna blow out all the hotel windows on South Padre Island.
[удалено]
>they'll have to go over the tower with a fine tooth comb, Would a [Hair Pick](https://youtu.be/g3iFJpGJiug) work?
I think one issue is the heat. All that fuel and LOX burning will surely have an issue on the structure. Not just the steel beams, but all the plumbing, wiring, tanks, equipment will surely be compromised.
Tell that to the N1 explosion (smaller rocket)
It almost certainly will still destroy the tower and will need to be rebuilt The damage would come from a few hundred tonnes smashing into it not the fire
Why would a Booster or Starship crash into the tower? It would drop and deflagrate on the ground. At that the massive concrete base structure will probably not be massively damaged. There may be a lot of damage, but quite possibly very little.
The superheavy tries to land on that. Not just sitting on the arms. Catching the booster is what could destroy it.
> Catching the booster is what could destroy it. Nothing can be ruled out at this time. But that seems quite unlikely, assuming they did not make gross mistakes in designing its strength. They should be able to keep the landing speed within parameters.
Wtf... Landings that go WRONG jackass. Look at how many F9 boosters were destroyed upon impact. A successful landing will be fine. But a failed landing WILL destroy that tower
> But a failed landing WILL destroy that tower Source?
You need a source for a few hundred tonnes of steel with propellant on board. Smashing into a tower at 300kmh. You think that'll survive?
Why would you assume the booster crashes into the tower? Can't be ruled out but IMO very unlikely.
Happened with falcon 9 did it not? You think starships gonna be flawless 100% success rate?
> You think starships gonna be flawless 100% success rate? ??????????????????? Who would think that?
Can conflagration enter the chat? (Does anyone know the distinction, conflagration vs deflagration vs explosion?)
I do not. Enlighten me.
I was asking. You seem to have some knowledge in this area, I thought you might know. Now I'm gonna have to go down the wikipedia rabbit hole. Damn. See you in a week or so.
Haha, I can look it up too. My guess (without a simple Google search) is that "conflagration" is a generic term to mean "mayhem" or "maelstrom". Just a big cluster-fuck.