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Some info on the B4 test campaign:
- In two weeks B4 should be mounted back on the OLM in preparation for static fires, depending on GSE and testing
- Booster thrust simulator to be likely skipped, it's possible it will be done on the B2.1 test tank instead before the proper B4 static fire series

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On 10/25/2021 at 1:35 PM, mikegarrison said:

On the other hand, the skin is also the fuel tank. So any heating (or worse, burn-through) is directly impacting the fuel and oxidizer.

I'd put the "skin is the fuel tank" design as one of the riskiest parts of the entire Starship design in general. All aspects of the mission essentially boil back down to this one risky design decision in terms of risk. 

At the same time, its the sort of decision that isn't really something worth dabbling over too much. As its not like adding another layer of something, or another surface would do much in most scenarios. If you have a burn through of your primary structure... having another layer probably wouldn't change the outcome much at the end of the day. The same is true for most things related to the integrity of the structure, and weight related to changing the structure overall. You could add more steel, but then weight becomes a problem. Either engineer through that weak point, or the entire concept probably wont work due to weight. 

 

 

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15 minutes ago, MKI said:

I'd put the "skin is the fuel tank" design as one of the riskiest parts of the entire Starship design in general. All aspects of the mission essentially boil back down to this one risky design decision in terms of risk. 

Isnt that a core design feature of any rocket with a significant mass ratio? Otherwise starship would possibly have a hard time reaching orbit or carry a payload. I cant remember any project other than skylon where fuel tanks arent the outer surface of the rocket.

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1 hour ago, MKI said:

  I'd put the "skin is the fuel tank" design as one of the riskiest parts of the entire Starship design in general. All aspects of the mission essentially boil back down to this one risky design decision in terms of risk. 

It's extremely common aerospace vehicle design. However, it's not so common for re-entry vehicle design, as far as I know.

Anyway, my intended point was just that I think way too many people in this forum simply shrug off all issues with the magic phrase, "it's made of steel", as if steel were indestructible and impermeable and in all senses a perfect material.

Nearly empty tanks are actually more dangerous than full tanks, generally. Because vapors tend to be more dangerous than liquids. I don't know how inert these tanks are. Do they inert them with nitrogen or helium?

Edited by mikegarrison
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1 hour ago, mikegarrison said:

Anyway, my intended point was just that I think way too many people in this forum simply shrug off all issues with the magic phrase, "it's made of steel", as if steel were indestructible and impermeable and in all senses a perfect material.

heh, I was just drilling holes in steel yesterday with a hand drill. For a rocket, too.

Edited by cubinator
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3 hours ago, MKI said:

  

I'd put the "skin is the fuel tank" design as one of the riskiest parts of the entire Starship design in general. All aspects of the mission essentially boil back down to this one risky design decision in terms of risk. 

At the same time, its the sort of decision that isn't really something worth dabbling over too much. As its not like adding another layer of something, or another surface would do much in most scenarios. If you have a burn through of your primary structure... having another layer probably wouldn't change the outcome much at the end of the day. The same is true for most things related to the integrity of the structure, and weight related to changing the structure overall. You could add more steel, but then weight becomes a problem. Either engineer through that weak point, or the entire concept probably wont work due to weight. 

 

 

To me, the tile/skin/tankspace arrangement isn't too concerning for the normal rocket operations of launch, re-entry, and landing, if one could consider the last two "normal" operations. For SpaceX it is, but re-entry from orbital speeds with a big (nearly) empty fuel tank on the other side of the heatshield is unprecedented, it is a known regime.

The real risk I see with the single skin is for vehicles that spend an extended time in space exposed to the probability of MMOD strikes, like depot tankers or deep space (HLS) missions. The capability to repair and repressurize will be mandatory, I think. How big of a strike can Starship resist? At least the tiles offer some protection to half the vehicle, and could be replaced. The radiator panels on the ISS and two shuttle orbiters were perforated by MMOD, fortunately not puncturing any coolant lines.

1 hour ago, mikegarrison said:

Nearly empty tanks are actually more dangerous than full tanks, generally. Because vapors tend to be more dangerous than liquids. I don't know how inert these tanks are. Do they inert them with nitrogen or helium?

Is a tank full of homogenous vapors (all fuel or all oxidizer) that much more dangerous? I thought vapors were only really dangerous (from a flammable standpoint) when the two were mixed? 

 

 

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5 hours ago, StrandedonEarth said:

Is a tank full of homogenous vapors (all fuel or all oxidizer) that much more dangerous? I thought vapors were only really dangerous (from a flammable standpoint) when the two were mixed? 

What tends to blow up tanks on Earth is when you have air+vapors. This is why, after TWA 800, all commercial airplanes now have nitrogen inerting for their center fuel tanks.

However, remember that Apollo 13 managed to blow up one of their LOX tanks.

Edited by mikegarrison
Added "center" to be more accurate
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2 minutes ago, mikegarrison said:

However, remember that Apollo 13 managed to blow up one of their LOX tanks.

Yes, but that had oxygen and fuel (wiring/insulation) to burn, and it was probably reasonably full happening on the outbound leg. But I didn't know about inerting the tanks on commercial aircraft; that's sensible.

So yeah, rocket fuel tanks shouldn't have to worry about vapors igniting. Oxygen tanks, on the other hand, well, best not to have anything flammable in there. although pure oxygen will burn darn near anything if it gets hot enough...

On the gripping hand, that damaged tank should have never been cleared for flight...

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4 hours ago, StrandedonEarth said:

Yes, but that had oxygen and fuel (wiring/insulation) to burn, and it was probably reasonably full happening on the outbound leg. But I didn't know about inerting the tanks on commercial aircraft; that's sensible.

So yeah, rocket fuel tanks shouldn't have to worry about vapors igniting. Oxygen tanks, on the other hand, well, best not to have anything flammable in there. although pure oxygen will burn darn near anything if it gets hot enough...

On the gripping hand, that damaged tank should have never been cleared for flight...

Its worth noting that LOX can react explosively with titanium, but I don't think that would be an issue here. (The reaction also requires substantial impact to occur, so it's even less relevant. For example, the Titan I used titanium pressure vessels located inside the LOX tank to hold helium pressurant.)

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I'm curious, would it be possible to prevent an SN10-like failure? I.e. there's a multi engine failure while at the same time the last engine has a reduced output and the starship comes down too fast, ultimately rupturing a tank on landing. Is there anything the ground equipment could do to make the starship safe and prevent an explosion?

Edited by Beccab
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1 hour ago, Beccab said:

I'm curious, would it be possible to prevent an SN10-like failure? I.e. there's a multi engine failure while at the same time the last engine has a reduced output and the starship comes down too fast, ultimately rupturing a tank on landing. Is there anything the ground equipment could do to make the starship safe and prevent an explosion?

Crank up the damping on the chopsticks maybe? SS is smaller, that gives more distance to slow a fall… if they can really catch it…

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4 hours ago, Beccab said:

I'm curious, would it be possible to prevent an SN10-like failure? I.e. there's a multi engine failure while at the same time the last engine has a reduced output and the starship comes down too fast, ultimately rupturing a tank on landing. Is there anything the ground equipment could do to make the starship safe and prevent an explosion?

Firefighting foam would be the best option.

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36 minutes ago, JoeSchmuckatelli said:

Halon too? It's what we used for military applications.  Breaks the fire triangle.  Don't know how it would work with something that large and open air... But maybe? 

Is Halon heavier than air? Is there anything comparable that is heavier than air? If so (and money is no object :lol:). build a giant "bathtub", fill it with whatever, and land your rocket in the bathtub. 

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1 hour ago, Kerwood Floyd said:

Is Halon heavier than air? Is there anything comparable that is heavier than air? If so (and money is no object :lol:). build a giant "bathtub", fill it with whatever, and land your rocket in the bathtub. 

Cold nitrogen is also heavier than air. Doesn't really help if the rocket leaks both oxidiser and fuel. Also it would need to be filled after landing as the rocket exhaust would empty the berm.

I wonder if what is needed is an intermediate density gas. Methane's a lot lighter than oxygen at equivalent temperatures. Use something inert that Methane will float on and Oxygen will sink and that would keep the fuel and oxidiser apart!

Probably a lot of practical issues. Wind, for one. Momentum of leaking gasses is probably another.

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13 hours ago, Beccab said:

Is there anything the ground equipment could do to make the starship safe and prevent an explosion?

I don't think Starship is suppose to land with any ground equipment support? Or have I been out of it where Starship is also planning to be caught (!!!)

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4 minutes ago, MKI said:

I don't think Starship is suppose to land with any ground equipment support? Or have I been out of it where Starship is also planning to be caught (!!!)

My question was more general (i.e. foam as mikegarrison said) but on your question: currently it won't,  but it's a possible future addition that they are considering. There are two main ways in which starship could land, the best but unfeasible one being catching it horizontally without relighting the engines and the actually feasible/proven one being bellyflop and vertical landing. Catching the starship after the bellyflop would be the middle ground with some of the advantages and some of the disadvantages which requires some consideration: on one hand it needs more precision, but on the other hand it makes an SN10 like failure much harder if even just one engine relights since it gradually slows down starship smoothing out the landing and doesn't prevent landing on the ground if for some reason it can't be caught but bellyflops successfully

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