For Questions That Don't Merit Their Own Thread

[darthgently]

I would think ocean covered crust would cool more easily than continent covered crust creating a bias for continents having liquid plumes closer to the surface.  Add plate edges into the mix for another place where magma release would be easier and perhaps non-ocean-cooled plate edges are favored for higher plumes?  The more we know that we don't know much the more we will be open to learning I suppose

[JoeSchmuckatelli]

15 hours ago, DDE said:

According to the maps I see, the Greenland plume is minor/offshoot to the larger Iceland/mid-Atlantic plume.

The problem is, is there even a plume? I dug beyond surface-level publications, and it seems that there are two rival explanations, likely varying on a case-by-case basis, for intra-plate volcanism. Besides plumes, there's also plate tectonics, as in the crust simply tearing up enough to admit magma to the surface. And Iceland is a rather stark example of that in action, being a 24 mln years old mini-continent, so is there even a plume involved? Other plate-related factors include the slowly melting fragments of subducted plates, but there seems to be no consensus how deep they sink.

There's also a curious lack of (known) plumes beneath Eurasia (even though the African plate is AFAIK just as, if not more, thick and stable, as the Eurasian plate).

The asymmetry seems to correspond to the mysterious large low-shear-velocity provinces, which, depending on who you ask, are superplumes fueled by slabs of ancient (750+ MYO) oceanic crust, or the remnants of Theia.

I'm getting the distinct impression we know painfully little about deep geological processes.

The plumes (if that's what they are) in the rotating image don't look quite right - there's nothing near Yellowstone or Hawaii.  East Africa and Iceland are rift zones.  The Deccan Traps (@ the time of the last great mass extinction) were supposed to be hotspot plumes.

 

So I'd fear plumes rather than rift zones.

[K^2]

On 12/17/2023 at 4:57 PM, JoeSchmuckatelli said:

The plumes (if that's what they are) in the rotating image don't look quite right - there's nothing near Yellowstone or Hawaii.

The 3D image isn't meant to represent the plumes. It represents regions that have different wave-propagation properties than the rest of the mantle, which happen to correspond to some, but not necessarily all plumes.

On 12/17/2023 at 1:36 AM, DDE said:

I'm getting the distinct impression we know painfully little about deep geological processes.

That sums it up nicely.

[DDE]

How resistant is a GCNR against various lateral forces from maneuvering? I'm wondering whether it would even survive combat action without the fissioning vortex burning through the wall.

[kerbiloid]

The Generalized Constant-to-Noise Ratio is pretty invariant to the mechanical forces, but the Graduate Certificate in Natural Resources can be torn apart.

[SunlitZelkova]

7 hours ago, kerbiloid said:

The Generalized Constant-to-Noise Ratio is pretty invariant to the mechanical forces, but the Graduate Certificate in Natural Resources can be torn apart.

What about the Good Capybara Neutron Repository?

[darthgently]

3 hours ago, SunlitZelkova said:

What about the Good Capybara Neutron Repository?

And wouldn't the Gravitationally Crosslinked Neutron Radiator effectively be turbo-encabulated?

[SunlitZelkova]

27 minutes ago, darthgently said:

And wouldn't the Gravitationally Crosslinked Neutron Radiator effectively be turbo-encabulated?

I’m not sure, but the Geriatric Coffee Neutralizing Robot should maintain 78% levels of wumbo.

[JoeSchmuckatelli]

On 12/22/2023 at 9:14 PM, SunlitZelkova said:

I’m not sure, but the Geriatric Coffee Neutralizing Robot should maintain 78% levels of wumbo.

I hate that robot.  Waste of wumbo, if you ask me 

[ARS]

Is it more efficient to use cold gas thrusters for RCS purpose than using hypergolic rocket fuel? Since cold gas thruster has lower thrust than combustive rocket engines, they are not very good as main propulsion purpose, but could be useful for orienting/ maneuvering purpose

Using liquefied gases,  the gas pressure output will also remain relatively constant as the liquid gas volatilizes during use, on top of simplified fuel lines since instead of  using two tanks of hypergolic fuel, the space onboard the spacecraft can instead accomodate one large tank of liquified gas

Edited December 26, 2023 by ARS

[darthgently]

Using boiloff for RCS is a good way to do cold gas as you'd lose it anyway

[kerbiloid]

1 hour ago, ARS said:

Is it more efficient to use cold gas thrusters for RCS purpose than using hypergolic rocket fuel?

The cold gas ISP is extremely low, while the high-pressure tanks are extremely heavy.

So, it makes sense only in sense of effort minimization.

[ARS]

23 minutes ago, kerbiloid said:

The cold gas ISP is extremely low, while the high-pressure tanks are extremely heavy.

So, it makes sense only in sense of effort minimization.

So does that mean it's only good for low-mass spacecraft?

[kerbiloid]

33 minutes ago, ARS said:

So does that mean it's only good for low-mass spacecraft?

For low-mass and/or low-budget.

[AckSed]

What makes an RCS thruster good is closely correlated to what makes a rocket engine good, but the engineering requirements of simplicity, storability, fast start from cold and repeatability change that. Low specific impulse can be forgiven if the rest of the hardware is simple and lightweight.

Cold-gas is used, even though it's not that powerful or efficient, because it fulfils all those requirements.

If we talk about solid propellant, monopropellant, bipropellant, arcjets and resistojets, we'll be here all day. Instead, if you want to dive deep into about 5,000 different substances used on one satellite or another: On the selection of propellants for cold/warm gas propulsion systems

[kerbiloid]

3 hours ago, AckSed said:

the engineering requirements of simplicity, storability, fast start from cold and repeatability change that

Hypergolic RCS engines.

Monopropellant (hydrogen peroxide or monomethylhydrazine) or bipropellant (UDMH + NTO).

Ignited in a millisecond, doesn't need an ignition system (burns on component contact, or on contact with the catalyst plate), dosed accurately, reusable for many thousand times (say, the Almaz RCS had 1 000 ignitions planned, 10 000 ignitions tested).

[DDE]

17 hours ago, ARS said:

Is it more efficient to use cold gas thrusters for RCS purpose than using hypergolic rocket fuel?

Efficiency-wise, both lose to boil-off-powered non-hypergolic bipropellant ones. Buran burnt syntin with vaporized oxygen (although it generally deliberately heated the oxidizer) and ACES was designed to run on hydrolox boiloff.

And that the thing worked at all means even an ignition system isn't too complex for RCS. Let alone two valves for a hypergol instead of one higher-pressure one for a cold gas thruster.

Edited December 26, 2023 by DDE

[JoeSchmuckatelli]

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? 

[kerbiloid]

1 hour ago, JoeSchmuckatelli said:

before the use of clocks to determine longitude, people were using observations of Jupiter's moons. 

Jool moons were discovered in 1610.

Mechanical clock in 1300s.

[darthgently]

16 minutes ago, kerbiloid said:

Jool moons were discovered in 1610.

Mechanical clock in 1300s.

But clocks weren't small or accurate enough on rocking boats for longitude purposes until much later

[kerbiloid]

23 minutes ago, darthgently said:

But clocks weren't small or accurate enough on rocking boats for longitude purposes until much later

Columbus discovered America in 1492.

[darthgently]

58 minutes ago, kerbiloid said:

Columbus discovered America in 1492.

He thought he was in India.  That is fairly big error bars on the longitude calculation

2 hours ago, 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? 

There is a method that does this but it was never widely used from what I've read.   Basically, an ephemeris of the moon positions could tell you what time it was by looking at them.  Once you know the time and the position of a known celestial body one could narrow down one's longitude.  I can't imagine the Jupiter moon method being accurate within 100 miles, if that, but maybe it was.  Mostly it relied on tedious observations under a clear sky.  Hard to do at sea much of time.

Pocket watches a with mainsprings tiny enough to not be significantly affected by boat motion is what made longitude calculations practical, accurate, and more weather independent (one can usually get a noonish siting on most days, or a known star at night, but seeing the moons of Jupiter involves more luck)

Edited December 31, 2023 by darthgently

[DDE]

3 hours ago, kerbiloid said:

Columbus discovered America in 1492.

Yes, but at the time - and for a long while afterwards - maritime travel across open sea was based on latitude alone. You'd simply sail north or south and then adopt a course east or west and pray you don't deviate or run out of provisions until you find land again. Using a clock wasn't proposed until 1530, major efforts began in the 1700s, with Britain's Longitude Act establishing the Board of Longitude and a bunch of prizes, and John Harrison began to put forward practical deisgns in the 1730s, which were initially treated as a military secret.

No, it was a really, really big deal.

5 hours ago, 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. 

Apparently the method was used in land surveys, but like the also proposed lunar observation method, shipborne astronomy of this sophistication was deemed impossible.

For thise who like their longitude long-form:

Spoiler

 

 

[kerbiloid]

1 hour ago, DDE said:

Yes, but at the time - and for a long while afterwards - maritime travel across open sea was based on latitude alone. You'd simply sail north or south and then adopt a course east or west and pray you don't deviate or run out of provisions until you find land again.

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

The longitude is needed in a stormy open space.

1 hour ago, DDE said:

Using a clock wasn't proposed until 1530, major efforts began in the 1700s, with Britain's Longitude Act establishing the Board of Longitude and a bunch of prizes, and John Harrison began to put forward practical deisgns in the 1730s, which were initially treated as a military secret.

https://en.wikipedia.org/wiki/Lunar_distance_(navigation)

Was proposed a century before the Jool moons were discovered, in 1524.

(And like any military significant technologies, was probably in use several decades before, before some nerd made it public).

3 hours ago, darthgently said:

He thought he was in India.

They called India everything which is not Europe  and MidEast.

Like till early XX in Russian literature they were calling any Asian peoples "Tatars".

Also, the fact that he called it India doesn't mean that he actually didn't know that it isn't. It was wise to keep in secret a new land, to make others think, that there is nothing interesting.
 Even if Columbus didn't know, Vatican in any case did, because they were sending missionaires to both.

*) Arzamas-16 and Chelyabinsk-70, and Moscow-400 were called so, being situated far away from these cities.

So, India-1492 doesn't have to be in India.

[DDE]

1 hour ago, kerbiloid said:

The longitude is needed in a stormy open space.

Indeed. But it wasn't available.

That's why they called it a "perilous adventure".