Author Topic: Astronomy/cosmology questions...  (Read 22983 times)

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Offline Geo

Re: Astronomy/cosmology questions...
« Reply #300 on: March 05, 2019, 07:46:57 AM »
I'd say the ISS doesn't have power to spare for such a project?

Besides, isn't the ISS still within Earth's magnetic field? Its barely 500 clicks up...

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Re: Astronomy/cosmology questions...
« Reply #301 on: March 05, 2019, 07:45:01 PM »
Yes, it's inside the Van Allen belts.

Still...

Offline Elok

Re: Astronomy/cosmology questions...
« Reply #302 on: March 06, 2019, 03:26:05 AM »
So, probably question for Lori specifically: is the Seveneves scenario plausible, in the sense that if something fragged the moon, the pieces would stay in close proximity for a bit banging into each other, but gradually break into smaller and smaller pieces?  I always found that really hard to visualize.  Threw this question out to the Slate Star Codex hivemind, but didn't get a complete answer.

Offline Unorthodox

Re: Astronomy/cosmology questions...
« Reply #303 on: March 07, 2019, 12:27:45 PM »
If I understand the synopsis correctly: the moon breaks into several large chunks that stay where the moon was, I'd rate it as rather impractical but technically plausible. 

Anything that would destroy the moon would most likely severely impact it's orbit.  Given some theoretical internal break up, it's theoretically possible for larger chunks to stay together (The Armageddon movie wouldn't have worked, for instance, gravity would have held the two pieces together at least enough to strike earth) However, it's far more likely that smaller pieces would be drug into a different orbit by gravity, or even ejected from orbit by the larger chunks.

Assuming the pieces somehow stayed close, those pieces would likely interact rather violently, sending hunks in all directions when they eventually collided or tossing out their smaller counterparts.  Earth would most likely be struck by a civilization ending piece from this fairly quickly. The large pieces are at least just as likely to fuse back together during these impacts as they are playing bumper cars (I haven't studied impacts at all, so just really basic knowledge of this bit, but we have plenty of evidence of collision fusing out there, it might actually be more likely), but the debris would be massive. 

If any of the pieces drifted inside the Roche limit, it would be ground up by tidal forces, eventually forming equatorial rings and likely pelting the earth.   

Lord knows what the loss/changes of lunar gravity would do to the systems here on earth.

Offline E_T

Re: Astronomy/cosmology questions...
« Reply #304 on: March 07, 2019, 03:35:07 PM »
As well as the effects of Earth Tidal Forces on the Lunar Debris.
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Re: Astronomy/cosmology questions...
« Reply #305 on: July 10, 2019, 08:06:15 PM »
Could y'all edumacate me about why they don't wrap something like a Faraday cage -or maybe just a silvered mylar envelope- around the ISS -or one whole module, anyway- and run a current through it for a radiation shield?  Same for traveling crew capsules, though I see that's a considerably greater engineering challenge...

Like, the big short-term threat is solar flares, right?  And that's a particle radiation problem, right?  And a large/intense enough magnetic field will handle particle radiation -if not the x, gamma, etc., wave radiation- nicely.  So, this is an obvious enough thing that I figure, with fair confidence, that there were pretty definitive theoretical/engineering studies done by the time I was born in the mid-sixties, and either the power requirements are prohibitive to do that for three days or so, or there's too much wave radiation in a flare - or both.  Help me out here, if you can...
ANYone?

Especially Lori, maybe Uno?

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #306 on: July 11, 2019, 12:46:46 AM »
So part of the answer is that, for solar flares, the extra protection isn't really necessary. The ISS is in a low orbit that is still fairly well protected by Earth's magnetic field. You also get a day or two of warning, so the crew can move to more shielded areas of the station when necessary. That is, the aluminum hull of the space station does an alright job of deflecting particle radiation, and you can put more shielding in particular places.

The greater threat is from cosmic rays, and the current solution is to basically do nothing. Cosmic rays rain down constantly, so you'd need a constantly powered magnetic field over a large volume of space (because you're redirecting the rays rather than stopping them cold), which would take a lot of energy, and it turns out that being in the middle of a very powerful magnetic field could be dangerous, too, so there are engineering hurdles to overcome there.

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Re: Astronomy/cosmology questions...
« Reply #307 on: July 11, 2019, 02:21:30 AM »
Cosmic rays are wave radiation?

I'm asking for a friend in the Fantastic Four.

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #308 on: July 11, 2019, 02:42:42 AM »
Nope, they're particles, too, usually protons or naked atomic nuclei. But if they hit something they decay into a shower of secondary particles and some genuine gamma radiation.

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Re: Astronomy/cosmology questions...
« Reply #309 on: July 11, 2019, 03:11:24 AM »
When they did that power generation test with a conductive tether, the one that melted from all the juice it produced, any idea how much drag?  I never heard anything about that in the reporting...

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #310 on: July 16, 2019, 03:47:45 PM »
* Lorizael does some googling.
Wow, uh, I had never even heard of that experiment before! Interesting. I don't think drag would be much more of an issue than normal, but I can't find anything about that.

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Re: Astronomy/cosmology questions...
« Reply #311 on: July 16, 2019, 04:31:30 PM »
Well, it's passing through Earth's magnetic field to generate 'letricity.  Q.E.D, the energy has to come from SOMEwhere - there's got to be drag, since the power source seems to be kinetic energy.

-I was just thinking about an emergency power source...

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #312 on: July 16, 2019, 05:52:16 PM »
Yeah, on that end... they measured a voltage of 3500 V and a current of about half an amp, so that's ~1750 W (Joules/second) being generated, which is drained from the shuttle's kinetic energy. Shuttle's mass was 10,500 kg and moving at like 7-8 km/s, which gives it roughly 300 billion joules of energy. So I think it would take a long time to slow it down appreciably by this method, unless there's some other factor I'm missing.

Offline E_T

Re: Astronomy/cosmology questions...
« Reply #313 on: July 17, 2019, 01:28:43 PM »
IIRC, the tether was oriented to be above the station.  Part if the drag could be tidal effects from the total object weight, maybe?  Or does out help speed it up and In would slow it down (from tidal effects)?

But, if the tether is oriented inwards, would it produce less or more and would the "drag" be the same?

It did generate a lot more than they anticipated, so why not go with shorter ones, so that the ones they can make now will be able to take the reduced load?
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Re: Astronomy/cosmology questions...
« Reply #314 on: September 22, 2019, 03:29:32 PM »

 

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