Planetary Defense: Shielding Earth from Asteroids

[mistermack]

13 minutes ago, swansont said:

Yes. Perhaps you need to refresh your memory of it. You can’t stay in the shade, and even mirrors heat up. You have to get away from earth to leverage the cold of space. In LEO, where it’s relatively accessible, it’s difficult to maintain something cold. Out where you have the Webb telescope, you can. What’s the point of storing it where you can’t get it?

Yes, it was the Webb telescope that I looked up previously, specifically, the temperature difference between the sunny side, and dark side of the sunshield was phenomenal considering the small thickness. 

But on the Moon, there are super cold temperatures available in naturally shaded places. Like down to minus 246C in permanent shadow at the poles. 

It would be fairly easy to build some permanent shade anyway, even if away from the poles, using some insulation and reflection to disperse the heat of the day. This is from NASA : 

" The lunar exosphere is too skimpy to trap or spread the Sun’s energy, so differences between sunlit and shadowed areas on the Moon are extreme. Temperatures near the Moon’s equator can spike to 250°F (121°C) in daylight, then plummet after nightfall to -208°F (-133°C). In deep craters near the Moon’s poles, permanent shadows keep the surface even colder — NASA’s Lunar Reconnaissance Orbiter has measured temperatures lower than -410°F (-246°C). These forever-dark places harbor ice deposits that may be billions of years old."   

Weather on the Moon | Dynamic Moon – Moon: NASA Science  

[swansont]

2 hours ago, mistermack said:

But on the Moon, there are super cold temperatures available in naturally shaded places. Like down to minus 246C in permanent shadow at the poles. 

And how accessible is the moon?

[mistermack]

46 minutes ago, swansont said:

And how accessible is the moon?

Getting more accessible all the time. The latest mission, Chandrayaan-3 by India to the South Pole of the Moon, cost 90 million US dollars equiv. I believe it was a soft landing with a rover. 

And of course, a mission can have more than one purpose. People are doing it now, that makes it accessible, to me. Dna storage could be just a small side show in the future. 

There isn't really an alternative on Earth that would withstand a major asteroid impact, so if you want that insurance, the Moon is first choice. 

Having said that, I'm not convinced that low Earth orbit would be out of the question. 

You said "You have to get away from earth to leverage the cold of space. In LEO, where it’s relatively accessible, it’s difficult to maintain something cold." 

How difficult, and how cold? 

[swansont]

1 hour ago, mistermack said:

Getting more accessible all the time. The latest mission, Chandrayaan-3 by India to the South Pole of the Moon, cost 90 million US dollars equiv. I believe it was a soft landing with a rover. 

And of course, a mission can have more than one purpose. People are doing it now, that makes it accessible, to me. Dna storage could be just a small side show in the future. 

There isn't really an alternative on Earth that would withstand a major asteroid impact, so if you want that insurance, the Moon is first choice. 

That's not accessible now, though. That's a lander that's not returning.

 

1 hour ago, mistermack said:

Having said that, I'm not convinced that low Earth orbit would be out of the question. 

You said "You have to get away from earth to leverage the cold of space. In LEO, where it’s relatively accessible, it’s difficult to maintain something cold." 

How difficult, and how cold? 

I've seen a study where DNA was stored at temperatures below -20ºC and was stable for 24 months.

The units that have only recently been available to the ISS don't get that cold.

Once the temperature issue gets solved for LEO, the next issue is radiation. 

 

[mistermack]

2 hours ago, swansont said:

The units that have only recently been available to the ISS don't get that cold.

Once the temperature issue gets solved for LEO, the next issue is radiation. 

No, because they don't want them to get cold. The temperature in the shade in low earth orbit is what's relevant. There's not going to be much difference between the shade in LEO and the shade on the Moon. The only substantial difference is the warmth coming off the Earth, which would be a lot less than direct sunlight, but might still justify shading and reflecting. But as there is no atmosphere to warm you in the shade, you will be radiating heat to space, and only receive the tiny bit of heat that penetrates the shade, and a tiny bit conducted through the stays that hold the shields. 

Low Earth orbit would also benefit from periods of darkness, when the Earth is blocking the sunlight. 

As far as radiation goes, that's a different matter, although LEO can be inside the shielding of the Earth's magnetic field, compared to the Moon. But all in all, the Moon would be the better bet, and if you want to return stuff to Earth, it doesn't take a whole lot of energy to lift off from the Moon and return to Earth, going by the size of the Apollo vehicles. It's getting up there that takes the huge amounts of energy, not getting back. A stripped down remotely operated craft could be a lot smaller than what the Apollo mission used. 

[TheVat]

53 minutes ago, mistermack said:

No, because they don't want them to get cold. The temperature in the shade in low earth orbit is what's relevant. There's not going to be much difference between the shade in LEO and the shade on the Moon. The only substantial difference is the warmth coming off the Earth, which would be a lot less than direct sunlight, but might still justify shading and reflecting. But as there is no atmosphere to warm you in the shade, you will be radiating heat to space, and only receive the tiny bit of heat that penetrates the shade, and a tiny bit conducted through the stays that hold the shields. 

 

This sounds not quite correct.  Space has no temperature, it's a vacuum, only objects in space have temps.  And any shade would be (as a practical matter) an object that is thin and radiates IR from its backside, so it is not clear that only a tiny bit of heat penetrates.  Also, objects cool more slowly in space, because there is no conduction or convection, only radiation.  So that shade will be slowly radiating heat a lot of the time.  

I don't know enough about IR reflecting surfaces - are there materials that would affordably create your near-perfect shade? Otherwise you may need some fancy system circulating coolant theough the shade.

Edited August 26, 2023 by TheVat

[swansont]

34 minutes ago, mistermack said:

No, because they don't want them to get cold.

And your reference for this is...?

What's the point of discussing things if you're just going to make stuff up?

 

 

 

 

[mistermack]

1 hour ago, TheVat said:

And any shade would be (as a practical matter) an object that is thin and radiates IR from its backside, so it is not clear that only a tiny bit of heat penetrates. 

I've posted this before, but here we go again :

James Webb Space Telescope sunshield - Wikipedia  

 

 

57 minutes ago, swansont said:

And your reference for this is...?

If they wanted them to get cold, they could fit a sunshade, as above. You're asking me to explain the obvious here. 

[swansont]

The Webb isn’t in LEO

You have no reference for “they don't want them to get cold”

[mistermack]

1 hour ago, swansont said:

The Webb isn’t in LEO

And you haven't explained the point you are making.

 

2 hours ago, swansont said:

You have no reference for “they don't want them to get cold”

Since when did the bleedin obvious need a reference? The ISS has a human crew, and it's obvious that they will aim at a steady comfortable temperature for them. Not too hot or too cold, in the low 20s C. 

In the shade, according to several accounts on the web, at the ISS, the temperature drops to -157c. In the sunshine, it rises to +120c . You get those extremes several times a day as the orbit goes into the Earth's shade. Even in the Sunshine, the dark side of the station drops to about -157, so if they wanted it to be cold, they would obviously shade it. Is It Hot Or Cold At The International Space Station? » Science ABC  

[swansont]

49 minutes ago, mistermack said:

And you haven't explained the point you are making.

The conditions are not the same, so you won’t get that result.

 

49 minutes ago, mistermack said:

Since when did the bleedin obvious need a reference? The ISS has a human crew, and it's obvious that they will aim at a steady comfortable temperature for them. Not too hot or too cold, in the low 20s C. 

Are you being deliberately obtuse? We weren’t discussing the crew. 

49 minutes ago, mistermack said:

In the shade, according to several accounts on the web, at the ISS, the temperature drops to -157c. In the sunshine, it rises to +120c . You get those extremes several times a day as the orbit goes into the Earth's shade. Even in the Sunshine, the dark side of the station drops to about -157, so if they wanted it to be cold, they would obviously shade it. Is It Hot Or Cold At The International Space Station? » Science ABC  

No, that’s not what the article says. 

On the other hand, when it’s on the side when our planet completely blocks out the sun, the thermometers plummet to minus 250 degrees Fahrenheit (-157 degrees Celsius).

-157 is not in the dark side in sunshine

[Ken Fabian]

Surely storing DNA is the easy part; it is the rest of using that DNA as backup of Earth life that we are not capable of. ie turning frozen samples into live, independently capable organisms. I suppose it would have to be many species, sufficient for working ecosystems. Capable because some animals will fail to learn necessary survival skills without parental care within a working ecosystem. Or is it just homo sapiens and species we know we depend on that we would be seeking to preserve? I expect it to be a lot more complicated than just having the dna of humans and food species; the interdependencies get complex.

I keep coming back to the requirement for a comprehensively capable advanced economy independent of Earth for surviving beyond Earth; being able to support advanced biotechnology beyond what the most advanced nations are currently capable of is no small thing, on top of supplying more immediate needs. I  think just immediate needs will be so extremely challenging as to be prohibitive.

 

[Genady]

50 minutes ago, Ken Fabian said:

it would have to be many species, sufficient for working ecosystems.

It also would have to be all the bacteria and archaea which live within the larger organisms, and which are necessary for these organisms' functioning.

[falkor1995]

Please I’m confused on what you really are trying to get at op, I would like to try and understand but this is pretty jambled 

[MigL]

I thought this thread was about planetary defense against large asteroids on collision course with Earth.
I never worried much about it, but it might be time to have a back-up plan.

After all, Bruce Willis is retired with a form of dementia, and Ben Affleck is constantly drunk and in rehab.
And I don't think Steve Bushemi, Billy Bob Thornton, Owen Wilson, and Michael Clark Duncan can do it on their own; even if Liv Tyler lends a hand.

( yes, it's a reference to the movie Armageddon 😄 )

Edited April 15 by MigL