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[Wij]

Thread:


View: https://twitter.com/RobDenBleyker/status/1605268924450349094

 

[Scouse]

Happy winter solstice everybody

 

[Tom]

Bloody hell @Bodhi now I see why you vote Tory, that level up thing really has helped you lot out!


View: https://www.youtube.com/watch?v=VzqhZLgpiv0

Interesting one that because they're only recovering the second stage, not the first. Difficult to see how they'd compete with SpaceX, unless they're just going to sell it to them.

 

[caLLous]

You can tell they're not actually from Stoke because he was so rude about pottery.

 

[DaGaffer]

How does a metal heatshield not just transfer heat to the inside?

Orthogonal heat transfer; you make the heat that's arriving at right angles to the shield transfer heat outwards to the edges of the shield and around the lip. It's all in the alloy structure of the metal innit? Easy peasy. Actually historically incredibly, impossibly difficult to manufacture over a surface the size of a heatshield but kind of well understood metallurgy (turbine blades shed heat in a directed way to cool the tips for example); I assume modern modelling techniques make it doable (my knowledge of metallurgy is 30 years out of date).

 

[Scouse]

Orthogonal heat transfer; you make the heat that's arriving at right angles to the shield transfer heat outwards to the edges of the shield and around the lip.

Cool. But where does it go then?

It's got to transfer out to the atmosphere, right? Or does the whole thing turn into a massive hot potato? Google says reentry speed is on average 7km/sec or 17,500 mph. That metal heatshield hitting the atmosphere is going to get hella hot. The space shuttle got to 1500 Celsius.

Surely atmos is too thin at that height to dissipate it - maybe lower down when it's slowed down and there's higher pressure? On the shuttle I understood the material was non-conductive - the stuff heated up really hot, some layers ablated by the sheer force of the air scraping material away - but I'm assuming that the ceramics get hot then rapidly radiate out the energy as black-body/infra-red. Metal isn't going to achieve that in the same way?

 

[Ormorof]

Cool. But where does it go then?

It's got to transfer out to the atmosphere, right? Or does the whole thing turn into a massive hot potato? Google says reentry speed is on average 7km/sec or 17,500 mph. That metal heatshield hitting the atmosphere is going to get hella hot. The space shuttle got to 1500 Celsius.

Surely atmos is too thin at that height to dissipate it - maybe lower down when it's slowed down and there's higher pressure? On the shuttle I understood the material was non-conductive - the stuff heated up really hot, some layers ablated by the sheer force of the air scraping material away - but I'm assuming that the ceramics get hot then rapidly radiate out the energy as black-body/infra-red. Metal isn't going to achieve that in the same way?

Heat shield - Wikipedia

en.m.wikipedia.org

Apparently some sort of resin that melts away to take heat with it or ceramics

 

[Scouse]

To achieve good functionality the three attributes required of a heat shield are low thermal conductivity (high thermal resistance), high emissivity and good thermal stability (refractoriness)

So, how does a metal heat shield have low thermal conductivity. It's not offering the thermal insulation (although radiative cooling should be higher).

Hence the questions

 

[Ormorof]

If melting temp is high enough that it doesn't get reached maybe they just get hot 😂

 

[Raven]

I always understood that it was the atmosphere that heats as the shield passes through it (which in turn heats the shield) so it's about a combination of travelling at a certain speed through the atmosphere and dissipating the heat, behind the object.

 

[DaGaffer]

Cool. But where does it go then?

It's got to transfer out to the atmosphere, right? Or does the whole thing turn into a massive hot potato? Google says reentry speed is on average 7km/sec or 17,500 mph. That metal heatshield hitting the atmosphere is going to get hella hot. The space shuttle got to 1500 Celsius.

Surely atmos is too thin at that height to dissipate it - maybe lower down when it's slowed down and there's higher pressure? On the shuttle I understood the material was non-conductive - the stuff heated up really hot, some layers ablated by the sheer force of the air scraping material away - but I'm assuming that the ceramics get hot then rapidly radiate out the energy as black-body/infra-red. Metal isn't going to achieve that in the same way?

The heat is pushed out to the edge of the shield circumference and then behind the body of the capsule, which is actually extremely cold.

 

[caLLous]

@Lamp, get in here, they're talking about science stuff.

 

[Tom]

They also form a shockwave ahead of them which diverts gases beyond the edge of the spacecraft.

How does a metal heatshield not just transfer heat to the inside?

It's probably cooled by pumped fluids. That sounds clever, but the truth is that it just leads to reduced payload capacity.

 

[Scouse]

The heat is pushed out to the edge of the shield circumference and then behind the body of the capsule, which is actually extremely cold.

Yep, but at higher altitudes extremely devoid of material to efficiently transfer heat to.

It's probably cooled by pumped fluids. That sounds clever, but the truth is that it just leads to reduced payload capacity.

This is what I'm thinking tbh.

I mean, NASA would have been using metal over ceramics if that was more advantageous. But maybe the question just needed to be asked again in 2020 with modern materials and engineering?

 

[Embattle]

On the same sort of subject:


View: https://www.youtube.com/watch?v=-Lsbi-bVfk0


He does a number of science videos.

 

[DaGaffer]

Yep, but at higher altitudes extremely devoid of material to efficiently transfer heat to.


This is what I'm thinking tbh.

I mean, NASA would have been using metal over ceramics if that was more advantageous. But maybe the question just needed to be asked again in 2020 with modern materials and engineering?

The original move to ceramics was because of the big complex surface of the space shuttle; they went for tiles so they would only have to replace small areas of the surface after each flight, and ceramics, unlike metal tiles, didn't suffer from expansion problems (which is of course a big deal if you have tiles butting up to each other). In reality they pretty much replaced all the tiles after each shuttle flight anyway, and NASA had created a whole new cottage industry in ceramic heat tiles; but it doesn't follow it's the best tool for the job; they designed that shit fifty years ago.

 

[Bodhi]

Cool. But where does it go then?

It's got to transfer out to the atmosphere, right? Or does the whole thing turn into a massive hot potato? Google says reentry speed is on average 7km/sec or 17,500 mph. That metal heatshield hitting the atmosphere is going to get hella hot. The space shuttle got to 1500 Celsius.

Surely atmos is too thin at that height to dissipate it - maybe lower down when it's slowed down and there's higher pressure? On the shuttle I understood the material was non-conductive - the stuff heated up really hot, some layers ablated by the sheer force of the air scraping material away - but I'm assuming that the ceramics get hot then rapidly radiate out the energy as black-body/infra-red. Metal isn't going to achieve that in the same way?

Not a massive hot potato no - more of a massive Staffordshire Oatcake. Hopefully with cheese and bacon.

 

[Scouse]

Question:

Anyone know of a service on the internet where you can hire someone to photoshop some stuff together cheaply?

Want to mock-up some solar panels against pics of my land from various angles.

 

[Gwadien]

Question:

Anyone know of a service on the internet where you can hire someone to photoshop some stuff together cheaply?

Want to mock-up some solar panels against pics of my land from various angles.

Fiverr?

Direct links to the nu-sweat shops.

 

[old.Osy]

View: https://twitter.com/fguzmanon7/status/1605410629149282304

 

[Raven]

View: https://www.youtube.com/watch?v=46flaThCYhE

 

[BloodOmen]

View: https://youtu.be/ATKir2UKVLg

 

[Lamp]

Not all Tesco own brand products suck
I braved a food shop today (no way am I going to a supermarket on Xmas Eve again)
One of the things I wanted to get (for me) was Lindt dark mint chocolate
They had sold out
So I thought sod it, I'll try the Tesco own brand equivalent
It was almost half price, thicker, and you could actually taste the mint. The dark chocolate tasted exactly the same

 

[Lamp]

And why do all those Lindt adverts have someone in a chefs hat carefully spooning out a tiny amount of chocolate ?
The Lindt factories churn out 10,000 bars of chocolate a minute
Does anyone actually think there's just one bloke in a hat spending 4 hours making one chocolate bar ?

 

[Gwadien]

Merry Christmas.

Maybe this year we can put Bezos back on the throne.
View attachment Snapsave_5a47fd9d3a1b8038c84874f666efc822_270p.mp4

 

[Wij]

Not all Tesco own brand products suck
I braved a food shop today (no way am I going to a supermarket on Xmas Eve again)
One of the things I wanted to get (for me) was Lindt dark mint chocolate
They had sold out
So I thought sod it, I'll try the Tesco own brand equivalent
It was almost half price, thicker, and you could actually taste the mint. The dark chocolate tasted exactly the same

Most own brand stuff is better than branded. Quality-wise in retail we usually rank Finest own brand > normal own brand > branded > value own brand.

 

[Scouse]

Most own brand stuff is better than branded. Quality-wise in retail we usually rank Finest own brand > normal own brand > branded > value own brand.

That go for butchery? And if so, what are the things that separate the quality out?

Not expecting you to actually know, being IT rather than business, but I'm interested

 

[Wij]

No idea about butchery tbh. I know it is a pain in the arse for replenishment algorithms to deal with. You can’t infer primals from the sales of cuts with any reliability.

 

[BloodOmen]

View attachment a8q3gwQ_460svvp9.webm

 

[Tom]

Chocolate choices in UK supermarkets are shockingly bad. You go to a French supermarket, they have half an aisle of the stuff. Tonnes of it.

The only bad thing is, no European supermarket has salt and vinegar crisps, the mentalists.