totm nov 2023 SpaceX Discussion Thread

[Beccab]

Cryo shell on the move

[kerbiloid]

13 minutes ago, magnemoe said:

As I understand that was because liquid oxygen and the composite wrapped tanks inside the LOX tank.

Helium leakage caused unplanned rapid inflation.

https://spaceflightnow.com/2016/09/23/falcon-9-rocket-explosion-traced-to-upper-stage-helium-system/

Spoiler

_{And that sniper.}

 

Edited October 18, 2021 by kerbiloid

[AHHans]

31 minutes ago, JoeSchmuckatelli said:

Does Helium like to play fast and loose with its pipes like hydrogen - or is it considerably better behaved? 

AFAIK the latter. But that's mostly "I haven't heard anyone complaining about helium diffusing everywhere" and not "I know that helium is well behaved."

My main issue with these concepts is that helium as coolant usually means graphite as moderator, which then can lead to problems if oxygen reaches an overheating reactor.  [But if anyone wants to discuss that further then we should take that somewhere else.]

[sevenperforce]

On 10/17/2021 at 9:13 AM, Snark said:

Some rule-violating content has been removed, due to:

• trolling / flamebaiting
• personal remarks

Folks, please try to stay civil.  There's nothing wrong with expressing hearty disagreement, but it's possible to do so like an adult, without stooping to ridicule or name-calling.  Such tactics help no one, do not advance your argument, and make the forum less fun for everyone.

_{Clearly I missed some excitement.}

52 minutes ago, Jack White said:

"The use of helium significantly reduces the risks of corrosion, refrigerant boiling and contamination."

So I'm guessing we're looking at a persistently gaseous helium coolant loop? Heat transfer won't be as efficient without a liquid coolant BUT the regenerative heat capacity of helium will probably make up for it. I wonder how much helium it requires, though. Not exactly a renewable resource. I'm also curious as to what kind of local heat sink the generators need. They could be buried underground, I suppose, but a water-based heat sink would be much more efficient.

15 minutes ago, magnemoe said:

30 minutes ago, kerbiloid said:

  Reveal hidden contents

Helium.

 

Expand  

As I understand that was because liquid oxygen and the composite wrapped tanks inside the LOX tank.

There was a liquid oxygen incursion into the outer layers of the carbon overwrap. The superchilled helium caused the trapped LOX to freeze into solid oxygen crystals, warping the composite overwrap layers and causing a COPV failure. The energetic failure of the COPV provided ignition energy between the carbon composite and the LOX, and the rest was...toasty.

[JoeSchmuckatelli]

9 minutes ago, Beccab said:

Cryo shell on the move

We've talked at times about the accidental PR success /brilliance* of SX... And this kind of thing is one of the reasons. 

We are seeing 'spaceflight adjacent' stuff going on... And it's really a cool showcase of human ingenuity and our engineering success. 

Like - how often do you see something like those crawlers moving something huge? 

The public exposure (which SX initially resented) gives the public a fairly regular, free, unfiltered view that something is going on - even if it is not a flight or rocket test. 

 

 

*SX is notably better at their intentional PR than others - but the unintend, uncontrolled videos we get from neighbors is fantastic 

[sevenperforce]

7 minutes ago, kerbiloid said:

Helium leakage caused unplanned rapid inflation.

https://spaceflightnow.com/2016/09/23/falcon-9-rocket-explosion-traced-to-upper-stage-helium-system/

It was not initiated by a helium leak; it was initiated by LOX crystals freezing in the composite overwrap layers, resulting in COPV failure. Of course once the COPV failed then the helium certainly "leaked" in a very sudden and dramatic sense.

The first Falcon 9 failure was also a helium "leak" in the sense that a failed strut caused the COPV to break free and fall through the LOX and then fail on impact with the common bulkhead; the rupture of the COPV released the pressurized helium.

9 minutes ago, AHHans said:

46 minutes ago, JoeSchmuckatelli said:

Does Helium like to play fast and loose with its pipes like hydrogen - or is it considerably better behaved? 

AFAIK the latter. But that's mostly "I haven't heard anyone complaining about helium diffusing everywhere" and not "I know that helium is well behaved."

Helium diffuses through solids just like hydrogen does -- in fact, I believe it may diffuse a little better. However, diffusion is not what makes hydrogen so nasty. Hydrogen embrittlement happens because individually-migrating hydrogen atoms meet up inside the tank/pipe wall and decide to bond with each other, essentially producing nanoscale bubbles inside the metal, rapidly degrading its material strength.

It's like when Vision phases his hand into someone's chest and then unphases his hand while it's still inside.

[AHHans]

3 minutes ago, sevenperforce said:

Helium diffuses through solids just like hydrogen does -- in fact, I believe it may diffuse a little better. However, diffusion is not what makes hydrogen so nasty. Hydrogen embrittlement happens because individually-migrating hydrogen atoms meet up inside the tank/pipe wall and decide to bond with each other, essentially producing nanoscale bubbles inside the metal, rapidly degrading its material strength.

Thanks!

And maybe back to @JoeSchmuckatelli's unspoken original question: Helium diffusion out of a coolant loop of a nuclear reactor isn't going to be a contamination problem: that helium won't be radioactive because, well, helium isn't!

[sevenperforce]

19 minutes ago, AHHans said:

And maybe back to @JoeSchmuckatelli's unspoken original question: Helium diffusion out of a coolant loop of a nuclear reactor isn't going to be a contamination problem: that helium won't be radioactive because, well, helium isn't!

Aye. There are radioactive isotopes of helium, but the only one that could be created in a reactor by neutron capture would be ⁵He, which decays back into ⁴He by neutron emission in about 6e-22 seconds. 

[JoeSchmuckatelli]

1 hour ago, AHHans said:

Thanks!

And maybe back to @JoeSchmuckatelli's unspoken original question: Helium diffusion out of a coolant loop of a nuclear reactor isn't going to be a contamination problem: that helium won't be radioactive because, well, helium isn't!

I hadn't thought about contamination - and I knew escaped Helium wasn't a combustion /explosion risk; rather my concern was the slow loss of coolant in a proliferation of small reactors (increased likelihood of negligent maintenance) - where one placed in a populated area could overheat and... Well, you know. 

 

Thanks for the informed responses! 

[Rakaydos]

1 hour ago, JoeSchmuckatelli said:

I hadn't thought about contamination - and I knew escaped Helium wasn't a combustion /explosion risk; rather my concern was the slow loss of coolant in a proliferation of small reactors (increased likelihood of negligent maintenance) - where one placed in a populated area could overheat and... Well, you know. 

 

Thanks for the informed responses! 

Modern reactor design loves to play with thermal expansion as an emergency control- because nuclear material has to be  densely packed to generate a self sustaining reaction, which heats up the material, which lowers the density of the material. So it's possible to design a reactor that's just barely critical, as long as the coolant loop is functional at removing heat from the reactor- while at the same time making super-criticality a physical impossibility, as the reactor stops working well before the temperatures get high enough to be a problem for containment.

[JoeSchmuckatelli]

10 minutes ago, Rakaydos said:

thermal expansion as an emergency control

That's interesting - will have to look into that 

[KSK]

The old TRIGA design is interesting too - the hotter it gets, the slower it goes. So much so that I don't think it physically can melt down.

Public safety announcement - I recommend searching for "TRIGA reactor" if you want to know more, and not "TRIGA",  which is distinctly not safe for work.

[tater]

 

 

[sevenperforce]

Here's the typical schematic for a helium-cooled reactor.

Cool, pressurized helium is pumped around the reactor and through the reactor core, gaining thermal energy. It is then expanded through a turbine, which operates a series of compressors. The helium is cooled via heat sink and passed through the compressors in cycles to return it to its compressed, cool state. The turbine also operates the generator.

I wonder what kind of heat sink is used for cooling the helium. I'm also curious to know how cool the helium is supposed to be when it enters the reactor. Helium obviously can remain gaseous at very low temperatures; is there an advantage to getting the largest temperature swing possible? Would the system efficiency be improved by a secondary refrigerant loop?

[mikegarrison]

2 hours ago, sevenperforce said:

I wonder what kind of heat sink is used for cooling the helium. 

Most nuclear power plants use rivers for their heat sink. Either that or the ocean or a large lake.

Edited October 19, 2021 by mikegarrison

[sevenperforce]

38 minutes ago, mikegarrison said:

Most nuclear power plants use rivers for their heat sink. Either that or the ocean or a large lake.

I suppose that would be necessary, yes.

“The company began to create a budget microreactor that could fit in a regular shipping container. The megawatt model will be capable of powering up to 1,000 homes and is expected to use helium for cooling instead of water. The main places of use are remote settlements, zones of natural or other disasters, and military bases.”

So presumably it would be limited to a locale with water access…not scaleable or suitable for residential solutions, for example. At least that’s what I would imagine. At 1 MW and a Braxton efficiency of ~65% (enabled by a high-temperature coolant), that’s 1.53 MW of thermal power that needs to be rejected.

I ran the numbers (after typing that) and it’s not as bad as I thought. If your water heat sink loop raises water temperature by 20 degrees Celsius, you only need a flow of 1100 liters per minute. 

[Beccab]

And, after 57 3-minutes comments (plus a 3+ minutes one from a starbase oppositor that refused to stop at the time limit and had to be muted):

A preburner test (like was done on SN8) was also completed tonight:

The pre ignition sequence of the SN starships has changed quite a lot for S20, the siren still remains our best indication of an imminent ignition

[CastleKSide]

Perhaps we should start another thread for nuclear reactor design. It is something I would greatly enjoy learning about in detail with all of you

[Beccab]

The final Cryo shell and the second (possibly last) giant horizontal tank are on their way to the launch site, completing the ground support equipment for Boca Chica.

It's also becoming increasingly likely the Mechazilla catching and lifting arms will be lifted today:

 

[CatastrophicFailure]

 

[tater]

 

[AtomicTech]

Stupid Idea: Is the U.S. Government delaying Starship on purpose so that the SLS can fly first?

[RealKerbal3x]

4 minutes ago, AtomicTech said:

Stupid Idea: Is the U.S. Government delaying Starship on purpose so that the SLS can fly first?

No.

The FAA is going through their normal process for approving launches from a new site, which has always been a long process with a lot of paperwork. They're working on it, but the government usually doesn't work three shifts 24/7 like SpaceX does.

Besides, Starship is in no way a competitor for SLS. Both vehicles will literally be working together to put humans back on the Moon as part of Artemis. A government conspiracy to slow Starship down so that SLS can 'win the race' wouldn't make any sense.

[cubinator]

11 minutes ago, AtomicTech said:

Stupid Idea: Is the U.S. Government delaying Starship on purpose so that the SLS can fly first?

No, I think SLS's sad state of affairs is it's own problem.

[AtomicTech]

34 minutes ago, RealKerbal3x said:

No.

The FAA is going through their normal process for approving launches from a new site, which has always been a long process with a lot of paperwork. They're working on it, but the government usually doesn't work three shifts 24/7 like SpaceX does.

Besides, Starship is in no way a competitor for SLS. Both vehicles will literally be working together to put humans back on the Moon as part of Artemis. A government conspiracy to slow Starship down so that SLS can 'win the race' wouldn't make any sense.

 

33 minutes ago, cubinator said:

No, I think SLS's sad state of affairs is it's own problem.

Thanks for stopping the Konspiracy Theorist in me 

Spoiler

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