Astronomy/cosmology questions...

[ColdWizard]

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.

[Buster's Uncle]

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...

[E_T]

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...

[Buster's Uncle]

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?

[E_T]

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...

[Buster's Uncle]

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

---

And you're familiar with the season ender of Doctor Who, I assume, when 12 Dr. was trapped in the Panopitcon and something something TARDIS destroyed all the stars in the visible universe in 1066 or something, avec little whirlpool spirals faintly showing...  And the next season began with child Amy Pond in the new timeline w/ a starless sky, and people didn't believe there used to be stars in the sky up to a thousand years ago, naturally.  (TARDIS in the Sun's position w/ some 'splody effect exactly replacing the Sun.)

SO - that's a LOT of rubber comic book "science" to unwrap.  I can neatly rationalize all visible stars in the sky going out simultaneously from earth POV by postulating an anti-time effect traveling back at lightspeed, ignoring the instant impossible whirlpools.  How it puts out the stars, fusion and glow/heat, no.  The whirlpools visible at a minimum of 4.something LYs, never.  -And that's even if we were shown the southern hemisphere view, which would account that much for one.-  Where the mass of the Sun went, no.  Maybe it was still there, lit by the Tardis, but why no whirlpool?  Something something origin point, never mind the Sun.

I've been idly trying to work out this into something that makes ANY sense for YEARS.  Yes, I know.

Lori, how much of the universe, we're assuming a minimum case for naked-eye visibility for people on Earth's surface, had to destruct to achieve the minimum?

-The rest is less brain-straining stuff about alternate history and sailing-ship navigation but I'll post this much now.  I really want your thoughts.  -And everyone's who wants to play, of course.

[Geo]

Since you didn't provide helpful links to last year's Dr. Who season, no comment.

[Buster's Uncle]

I didn't WATCH last season.  I'm not one of those misogynist/reactionary turds you could find all over the nets showing their butts not liking a girl Doctor, but I am cold to the idea and never heard anything that sounded very interesting - and I don't think my mood cycle lined up with going to any trouble to find/watch/post, probably first cause, there.


 

[Buster's Uncle]

Can anyone tell me anything about the very bright light that looks like an airplane running light that's currently, roughly, SSE almost 45 degrees up after sunset?  Two, three weeks ago, it was ESE, maybe 10 degrees above the horizon.  It's visible before anything but the moon, last week, and it more flashes than twinkles.

Before you say "Elon Musk disco ball" to me, no.   Those are in LEO, and have something like a half hour to cross the sky; I'd see motion.

[Geo]

For a moment I thought you were seeing Jupiter, but that's about 15-20° above the horizon now in the evening, right on the heals of the setting sun.
OTOH, if it isn't blinking, it might as well be this planet.


Another possibility is the star Sirius. It twinkles like a diamond, and you mentioning it in on the southeast and southwest fits with that description, as it moves throught the sky at night at different hours.
Normally, in even mediocre night conditions (streetlights and such), above and to the right of this star you can see the constellation Orion. Looks something like a big hourglass with a angled belt through the middle/center of it. But Sirius doesn't get much higher then 20° too.

[Unorthodox]

Can anyone tell me anything about the very bright light that looks like an airplane running light that's currently, roughly, SSE almost 45 degrees up after sunset?  Two, three weeks ago, it was ESE, maybe 10 degrees above the horizon.  It's visible before anything but the moon, last week, and it more flashes than twinkles.

Before you say "Elon Musk disco ball" to me, no.   Those are in LEO, and have something like a half hour to cross the sky; I'd see motion.

Have you tried an object tracker? 


This is the first one I see that has location and date time options:  https://theskylive.com/planetarium


I just got approval for more standing stones in the yard, so I'm going through such things to form more arrangements...

[Buster's Uncle]

It's hard to believe, but some sites I googled are trying to tell me it's just Sirius.

[Geo]

It's hard to believe, but some sites I googled are trying to tell me it's just Sirius.

 
Did my response pop us as well with your search?


Why don't you take a (night)pic of the object, with a bit of starscape around it, and post it here?

[Rusty Edge]

I thought that this was pretty cool, but perhaps NOT SO CAT PROOF.  Relocate this wherever, Buncle.

https://www.kickstarter.com/projects/quantumplanets/quantum-solar-system?utm_source=kickbooster-direct&utm_medium=kickbooster&utm_content=link&utm_campaign=f35ce992&ref=6kb4c7

[Buster's Uncle]

Here is fine.