Author Topic: Astronomy/cosmology questions...  (Read 28814 times)

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Offline E_T

Re: Astronomy/cosmology questions...
« Reply #315 on: September 22, 2019, 06:07:51 PM »
oh kkkkk.....
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Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #316 on: September 23, 2019, 11:58:53 AM »
Look, if your error bars from observation are an order of magnitude greater than the error in your pi approximation, it doesn't really matter what number you use for pi. 3 is fiiiiine. 1 lets you pretend it's not even there, which lessens the odds you make some dumb math mistake.

Offline E_T

Re: Astronomy/cosmology questions...
« Reply #317 on: September 24, 2019, 02:11:40 AM »
Yeah, but Who ordered a Magnitude?
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Offline Geo

Re: Astronomy/cosmology questions...
« Reply #318 on: September 24, 2019, 11:12:18 PM »
Yeah, but Who ordered a Magnitude?

He did. :P





Offline ColdWizard

Re: Astronomy/cosmology questions...
« Reply #319 on: October 03, 2019, 12:32:13 AM »
So, with SN 2019bkc, it could be a stripped helium star with a companion neutron star (but they didn't detect helium in the spectral readings and it's odd to have massive stars in the intergalactic medium), or a merger between a white dwarf and a neutron star or stellar mass black hole if small amounts of calcium was ejected. Where the other possibilities of a double detonation or an intermediate mass black hole tidal disruption event don't quite fit as well. Am I reading any of this correctly?

Offline Lorizael

Re: Astronomy/cosmology questions...
« Reply #320 on: October 03, 2019, 07:01:46 PM »
How'd you come across this article? I haven't really seen any press about it.

This is pretty far outside my area of expertise (at least as far as astronomy goes), but I don't see anything blatantly wrong with your reading. It seems this whole class of events is pretty new and poorly understood at present.

Offline ColdWizard

Re: Astronomy/cosmology questions...
« Reply #321 on: October 03, 2019, 07:32:22 PM »
I don't subscribe but YouTube frequently recommends Anton Petrov's videos. I was interested enough in this one to read parts the linked paper, where I soon found myself hanging off the edge of the bed of my understanding and clinging on for dear life.

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Re: Astronomy/cosmology questions...
« Reply #322 on: October 24, 2020, 01:15:32 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...
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.
Y'know, it strikes me at this late date that there's a useful idea in there, if the engineering could be worked out - just, I was thinking about emergency power, when several orders of magnitude greater drag would be very valuable for leaving orbit w/o all that scary/dangerous reentry stuff, or at least less of it.

I suppose there's at least a half-decent science fiction idea there, supposing all the required gear weighs/bulks not-a-lot more than a heat shield would, and something useful to do with ~300 billion joules of energy in a tearin' hurry, or an impossibilium battery.  Either might have a significant impact on Elon Musk's cash flow...

Offline E_T

Re: Astronomy/cosmology questions...
« Reply #323 on: October 24, 2020, 03:45:00 PM »
As you slow down, you move inwards on the orbit.  BUT, you start to get to the altitude where the air density has more and more of an impact and heating from friction starts.  Which does start to slow down the thing faster than the tether would, but not fast enough to allow it to get to where the friction effect is negated by the airflow cooling effects (as well as lifting).  Slowing to Terminal velocity in sea level atmosphere (IIRC, somewhere near 200 MPH) from orbital speeds within the ranges of (relatively small when dealing with our atmosphere and gravity well) altitude differences and the speeds involved for orbital speeds.

Because, if you could speed up to orbital speed at sea level, your air resistance would burn you up too soon.  One reason that the Research on the Hyper Sonic Airplane is looking at dealing with airflows of something like Mach 25 (25 times speed of sound in 1 Atm) and altitudes of 100k feet to LEO.

And because the upper Atm is not consistent (weather, etc) the predictability for a tether slowing mechanism to touchdown time frame from LEO is not an easy task.  And don't forget all of the other space junk that is still in that area between the "stable" LEO altitudes and the beginning of the heating zone (where it starts to burn up)...  more than likely get chewed up on the way down.

BUT, this could be the beginning of an idea to use the slowing method with something large and robust enough to help clean up some of the trash in this zone...
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Re: Astronomy/cosmology questions...
« Reply #324 on: October 24, 2020, 11:04:01 PM »
I was sorta proceeding from a more optimistic set of assumptions, that it might be feasible to cancel out the orbital velocity before atmospheric friction became too significant; it might at least be more likely than a battery that wouldn't cook the vehicle or even explode.

Now, the idea about clearing the orbital debris, I thought of years ago, and it's a lot simpler/possible - two large balloons of aerogel -Uno suggested the aerogel- tethered a couple thousand feet apart would each move a little fast/slow for their respective orbits, gently catching junk until a modest maneuvering rocket at the center-point deorbit the whole mess.  Ought to be fairly cheap, though I can't imagine how many it would take to be effective.



Lori, what's going on with your space career these days?

Offline E_T

Re: Astronomy/cosmology questions...
« Reply #325 on: October 26, 2020, 03:54:12 AM »
Now, IIRC, you possibly could use the tether and reverse the current and possibly increase speed.  So, you could possibly have the tethered balloon gels up and down in LEO and the longer in orbit, the more trash removed...  Maybe, possibly...
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