For Questions That Don't Merit Their Own Thread

[kerbiloid]

4 hours ago, DDE said:

Using a clock wasn't proposed until 1530, major efforts began in the 1700s

Got it. The original ones were using gravitational pendulum, useless in sea. The spring-based clock, independent to tilting, appeared later, and became useful for navigation since 1700s.

[darthgently]

6 hours ago, kerbiloid said:

n the Mediterranean pool and along the European coastline. Not in the ocean

No, not really.  For a very, very long time, sailing craft bound for the Americas would catch the trade winds, maintain their latitude, and wait to make landfall.  In between crews would sometimes mutiny because not making landfall on a predictable schedule would convince them the captain was lost.  And honestly, he was lost for awhile longitudinally

Latitude is far simpler as the angle of Polaris above the horizon is your latitude for all practical purposes

[JoeSchmuckatelli]

Stupid question time 

H2 is notorious for its ability to escape containment.  Would it be possible to simply sleeve the liquid H2 tanks and pressurize the space between the outer sleeve and the tanks to keep the H2 where it's wanted? 

(presumes the containment gas cannot penetrate the H2 tank that the pesky H2 can leak from.) 

Why doesn't this simple thing work? 

[18Watt]

2 minutes ago, JoeSchmuckatelli said:

Would it be possible to simply sleeve the liquid H2 tanks and pressurize the space between the outer sleeve and the tanks to keep the H2 where it's wanted? 

Seems like a workable solution.  However, for starters you now have two high-pressure vessels instead of one- so twice the weight.  The outer pressure vessel would make it difficult to inspect the inner pressure vessel.

Biggest problem is that it would not stop H2 migration.  Say you fill the outer vessel with N2 (picked at random because it's readily available, but choose whatever gas you want.).  The partial pressure of H2 in the outer tank is zero, so you will still have H2 migration to the outer tank.  Eventually that H2 will also find it's way out of the outer tank.

I could be wrong, but I suspect that more of the losses would come from fittings and valves, not the tank itself anyway.  

[kerbiloid]

Also the cryogenic gas tank is situated in the medium which is hotter than the liquid gas (~273 K at this distance from the Sun > 10..100 K for liquid gases), so the energy is flowing into the tank, and is warming the liquid gas, partially vaporizing it.

The gas pressure of the vaporized part is growing, and especially quickly this happens to the lightweight gases like the hydrogen.

To prevent the tank from destruction, you must unstoppably drain out the evaporated gas from the tank, regardless of its structure.

On the Earth you can be actively cooling the tank by spending energy on that, which energy you should produce and thus warm the ocean and pollute the air (Greta is looking at you!), just to slow the hydrogen loss, which in turn makes the hydrogen energetics more funny.

In space you should have a reactor and a huge radiator for the active cooling, so you can just hold some amount of hydrogen for a while, but for a particular serious reason.

Protons are born to be wild!

[SOXBLOX]

On 12/30/2023 at 9:49 PM, JoeSchmuckatelli said:

Here's a crazy one - at dinner the other night, a friend of mine who sails comes out with the proposition that before the use of clocks to determine longitude, people were using observations of Jupiter's moons. 

I'm on vacation with crappy internet so I can't look this up - but my gut reaction is to call BS (because I cannot figure out how this could work. 

Anyone else heard this? 

Ooh, I know that one! It was proposed as a solution to the competitions the Great Powers at the time were holding, but Harrison's chronometer made the method obsolete.

Dana Sobel's Longitude was a fantastic read, and short, too. You should absolutely pick it up at the library or HPB.

[DDE]

Is/should lunar be deuterium-enriched?

Basically I'm thinking how Anno 2205 doesn't make sense on so many levels. The plot is about achieving He3 fusion on the Moon to then beam power back to Earth. But, because it's a game about production chains, the Lunar ice only gets used for oxygen and water, and the deuterium can only be produced exclusively in the Arctic and is then shipped to the Moon (unless you waste considerable resources on a late-game, DLC-only tech).

[magnemoe]

1 hour ago, DDE said:

Is/should lunar be deuterium-enriched?

Basically I'm thinking how Anno 2205 doesn't make sense on so many levels. The plot is about achieving He3 fusion on the Moon to then beam power back to Earth. But, because it's a game about production chains, the Lunar ice only gets used for oxygen and water, and the deuterium can only be produced exclusively in the Arctic and is then shipped to the Moon (unless you waste considerable resources on a late-game, DLC-only tech).

I assume the moon has as much deuterium as earth. Now you separate deuterium out of normal hydrogen anywhere you have decent hydrogen production either from hydrocarbons or splitting water. 
Separation system is not very large, an hydrogen-deuterium molecule is 50% heavier so you might trap it trying to clean hydrogen from heavier stuff in the gas. 

[ARS]

12 hours ago, DDE said:

Is/should lunar be deuterium-enriched?

Basically I'm thinking how Anno 2205 doesn't make sense on so many levels. The plot is about achieving He3 fusion on the Moon to then beam power back to Earth. But, because it's a game about production chains, the Lunar ice only gets used for oxygen and water, and the deuterium can only be produced exclusively in the Arctic and is then shipped to the Moon (unless you waste considerable resources on a late-game, DLC-only tech).

There is very few hydrogen on the Moon, mainly under the form of some frozen ice in some cold places. There is a natural proportion of deuterium in hydrogen, probably different than Earth’s hydrogen. But the overal quantities are very small

Tritium is an unstable isotope of hydrogen, with a short half-life. So that it can exist in nature only when there is an active production process. Save cosmic rays, there is no such process on the Moon, so that the tritium quantities may be counted in atoms.

Helium3 was formed in the Big Bang, and it appears from the decay of tritium. It represents a small fraction of natural helium, itself considerably enriched in Helium4 from the radioactivity of rocks. So to start with, Helium in general is very rare on the Moon, and much rarer on the surface. There may be underground pockets of it. But this would require us to find them, and dig hundreds of kilometres down the moon's crust, only for small quantities, and much smaller quantities of Helium3

So I guess catching the solar wind with huge electrostatic traps on orbital satellite platform would be more feasible  economically that crushing billions tons of Lunar soil just to get trace amount of it

[kerbiloid]

Helium-3 is the main product of D-D fusion (both of its branches), so it's slowly being produced in the Sun, where hit comes from to the Moon regolith.

The lunar ice, I guess, should be slightly enriched with D, because the Earth wasn't ever melted like the Moon, so it keeps more light hydrogen.

Powering the Earth from the Moon sounds silly, as the terrestrial ocean is full of deuterium, and any hydrogen-rich planet as well, so the D-D reactors are the future, while the He3 ones have a local application in cramped conditions like a lunar base, where the reactor shoul be compact, while on the Earth the ocean is both a fuel source and a neutron protection.

[DDE]

5 hours ago, kerbiloid said:

Powering the Earth from the Moon sounds silly

IKR?

5 hours ago, kerbiloid said:

The lunar ice, I guess, should be slightly enriched with D, because the Earth wasn't ever melted like the Moon, so it keeps more light hydrogen.

My thought process was, everywhere we look, the deuterium ratio is greater than on Earth because high temperatures and lack of strong magnetic fields "bake out" the protium. Venus, cometary ice, et cetera...

9 hours ago, ARS said:

So to start with, Helium in general is very rare on the Moon, and much rarer on the surface. There may be underground pockets of it.

Oh, don't worry, the game merely buys into the standard marketing jazz of lunar He3.

Spoiler

That group of three truck-sized harvesters in the bottom left is their idea of a He3 mining operarion.

 

[kerbiloid]

2 hours ago, DDE said:

My thought process was, everywhere we look, the deuterium ratio is greater than on Earth because high temperatures and lack of strong magnetic fields "bake out" the protium

The Moon was hotter than the Earth on creation, because it was melted completely.

So, it was a hotter place than the Earth.

2 hours ago, DDE said:

That group of three truck-sized harvesters in the bottom left is their idea of a He3 mining operarion.

That's great! So, they can harvest He-3 between the potato rows.

Also, following the Mark Watney experience, they can just send hydrazine from the Earth to the Moon, and produce water out of it.

P.S.
The picture looks strangely familiar...

Spoiler

 

[ARS]

18 hours ago, DDE said:

Oh, don't worry, the game merely buys into the standard marketing jazz of lunar He3.

Yeah, I played Anno 2205 before, and the first time I saw how they gather He3 I'm like... what? seriously?

[kerbiloid]

Why not? Pieces of helium-3 are digged everywhere.

[totalitor]

In Spain Gran Canaria in village Carrizal I found a street: CALLE COSMONAUTA COLLINS.

Eh...astronauta Collins? What?

https://i.imgur.com/BAxfxdf.jpg

 

Edited January 18 by totalitor

[ARS]

Is there a formula to calculate reentry heating temperature based on object velocity? (assuming the object in question is Space Shuttle, nose-high 40 degree reentry angle and it entered from geostationary orbit)

Edited January 22 by ARS

[kerbiloid]

The Ancient Kerbals have written this on the tablets:

 

[PakledHostage]

36 minutes ago, kerbiloid said:

The Ancient Kerbals have written this on the tablets:

I'm ancient, but not yet pining for the fjords...

Also, I incorporated much of that into my rudimentary re-entry heat mod and it worked a lot more believably than the silly re-entry heat that Squad eventually added into the game about 2 years later. I never understood why their model was so bad when better was clearly possible.

 

[ARS]

44 minutes ago, PakledHostage said:

I'm ancient, but not yet pining for the fjords...
....

Interesting... Does this also applicable for a situation where there's a sudden tumbling of the object that causes  significantly increased drag? (for example, something breaks during reentry and causing the shuttle to tumble in such a way that there are now greater surface area being exposed to drag)

[PakledHostage]

8 hours ago, ARS said:

Interesting... Does this also applicable for a situation where there's a sudden tumbling of the object that causes  significantly increased drag?

I would say no. Surviving re-entry is all about managing the heat transfer rate and controlling where that heat is going. When a vehicle starts to tumble, you lose control of both those things. 

As a rough approximation, you could look at the rate of change of the re-entering body's kinetic and potential energy. Most of that is being disipated as heat. Doing that also illustrates why sub-orbital vehicles like Blue Origin's New Shephard and Virgin Galactic's Spaceship One don't experience significant re-entry heating: Their kinetic and potential energy are on the order of 2% of that of an orbital vehicle.

[SOXBLOX]

I haven't seen anyone post this: https://skyandtelescope.org/astronomy-news/asteroid-2024-bx1-from-a-dot-of-light-to-fireball-to-rocks-on-the-ground/

 

Basically an asteroid (~1m diameter, IIRC) was detected a few hours before breaking up over Germany. Great footage all around & fragments recovered!

[magnemoe]

On 1/24/2024 at 7:08 AM, ARS said:

Interesting... Does this also applicable for a situation where there's a sudden tumbling of the object that causes  significantly increased drag? (for example, something breaks during reentry and causing the shuttle to tumble in such a way that there are now greater surface area being exposed to drag)

I think this generates meteorite air bursts, it fragments and some fragments will be small this increase surface area by order of magnitudes who increases heating and drag so you get an chain reaction. 
You are unlikely to get this with space junk as it has more structural integrity than loosely packed dust. 

[DDE]

Dumb question: given that takeoff and landing are the most hazardous regimes, why were aircraft cockpits stubbornly placed on top instead of in the nose?

[darthgently]

41 minutes ago, DDE said:

Dumb question: given that takeoff and landing are the most hazardous regimes, why were aircraft cockpits stubbornly placed on top instead of in the nose?

I'm going to guess that part of it is to give a clean view for the radar that is often in the nose.   This is a low quality guess

[DDE]

4 hours ago, darthgently said:

I'm going to guess that part of it is to give a clean view for the radar that is often in the nose.   This is a low quality guess

The question was inspired by pre-WW2 bombers, where this wasn't an issue, and extensive nose glazing for the navigator and gunners was present.