Random Science Facts Thread!

[Green Baron]

Catastrophes have sort of an appeal, don't they :-)

A landslide triggered a 193m tsunami 2015 in Alaska. It was caused by the rapid retreat of a glacier that in the time of its existence had stabilized the landmass with its weight. A study says that the landslide was a direct effect of glacier retreat due to climate change, the resulting tsunami an indirect. Threats to human property in similar situations (glacier retreat, forming of water bodies, mobilization of land and water ...) should be taken into account.

 

Edited September 8, 2018 by Green Baron

[MinimumSky5]

Life is already present, in a highly diverse community, below floating ice shelves. This will cause a local mass extinction, not a sudden flowering of life. 

[Green Baron]

You're right, there is something, though not much due to the lack of sunlight (no photosynthesis), maybe like in the deep ocean. Mass extinction feels somehow reserved for larger scale things, like "the big five" (without the human caused one, that is the big sixth).

Maybe i should better have said "how the ecosystem responds to the changing environment". :-)

https://www.nature.com/news/giant-iceberg-s-split-exposes-hidden-ecosystem-1.22670

In other exposed areas of the ice shelf deep sea species were discovered. The problem apparently is to be fast enough because exploration vessels are booked years in advance.

Edited September 8, 2018 by Green Baron

[Green Baron]

Reviving this thread :-)

An attempt to find the oldest animals (apart from Ediacaran bio which still lacks undisputed classification).

Article, but pay-walled ...

tl, dr: Earliest animals (sponges) may date back to 660Ma, into the Cryogenian and pre-Ediacaran, derived indirectly from biomarkers (sterane lipids) whose origin can be connected to demosponges.

critique: There is no undisputed pre-Cambrian fossil record of sponges, despite them having silica based skeletons. Also, it is not clear if sponges really are the only explanation of the finding.

 

Edited October 18, 2018 by Green Baron

[Green Baron]

Microbial life on earth is probably 3.5by old (e. g. Pilbara Craton), though arguments wave back and forth. In discussion are furthermore 3.7by, 3,9by and questionably even 4.1 to 4.3by with the first open water.

One of these interpretations for very early life, structures resembling stromatolites in the Isua belt of Greenland being 3.7-3.8by old, has now been re-assessed as being of geological, not biological origin. Study.

Because all of the very early interpretations are based on indirect markers, this is probably not the last word, but very interesting.

Edited October 20, 2018 by Green Baron

[Porucznik inżynieracy]

if you would use saturn V rocket first stage to deorbit the Moon, your deceleration rate would be 4,77702260×10^−19m/s^2, and it would take you 2,09335413×10^18 seconds to slow down by 1m/s, so about 66.379.824.010 years

[kerbiloid]

Just btw, some nice pages are here:
https://www.kosmonavtika.com
https://ciudad-futura.net

A webpage with detailed photos of Quantum-2 Mir Module.
https://www.kosmonavtika.com/vaisseaux/mir/tech/kvant2/kvant2.html

[Green Baron]

According to Ziolkovsky, assuming an exhaust velocity of 5200m/s, to accelerate a mass of 1 ton to 0.2c(*) takes 10²⁶⁰⁵⁷ tons of fuel. (From a book, exceeds double precision ;-))

This is ludicrously more mass than the entire observable universe contains (~10⁵¹ tons).

Assuming an ion thruster with 50km/s v exhaust still needs 10⁵²¹ tons of propellant, which still is ~470 magnitudes off the entire mass in the obs uni.

 

Corrections ?

(*) Calculation does not work for relativistic speeds !

Edited October 25, 2018 by Green Baron

[p1t1o]

1 hour ago, Green Baron said:

According to Ziolkovsky, assuming an exhaust velocity of 5200m/s, to accelerate a mass of 1 ton to 0.2c(*) takes 10²⁶⁰⁵⁷ tons of fuel. (From a book, exceeds double precision ;-))

This is ludicrously more mass than the entire observable universe contains (~10⁵¹ tons).

Assuming an ion thruster with 50km/s v exhaust still needs 10⁵²¹ tons of propellant, which still is ~470 magnitudes off the entire mass in the obs uni.

 

Corrections ?

(*) Calculation does not work for relativistic speeds !

What is the reduction if you, say, double exhaust velocity?

[kerbiloid]

M_start/M_final = ( (1+v/c) / (1-v/c) ) ^{(c/2v_exhaust)}

[Green Baron]

57 minutes ago, p1t1o said:

What is the reduction if you, say, double exhaust velocity?

I used the simple term Mstart = Mend * e^{(dV/v exhaust)} from the wikipedia article about the rocket equation.

With a v exhaust of 100km/s, to accelerate Mend of 1t to 0.2c, we need ~3.8 * 10²⁶⁰ tons.

What i am up to is that dreaming of interstellar travel is totally in vain if reaction mass must be taken along. Which leaves us with our imagination about wormholes and vacuum energy or whatever.

Edited October 25, 2018 by Green Baron

[p1t1o]

<tappity tappity tap tap on a calculator>

So....to accelerate 1t to 0.2c with a much more manageable, mere 1billion tons of reaction mass, the exhaust velocity needs to be around 3000km/s or 0.1c 0.01c (god-DAMNit!)

 

So in order to make an object reach relativistic speeds, we need to be able to make matter reach...relativistic speeds.

Who doesnt love a bit of circular logic

 

******

edit: 0.01c not 0.1c, so the "relativistic" exhaust velocity is somewhat more underwhelming now, but you only need to tweak the numbers slightly to reveal the point I was getting at.

Edited November 1, 2018 by p1t1o

[Green Baron]

I am still waiting for corrections ... but so it seems. But once you get to relativistic speeds you must mess with the Lorentz factor .... may be one of out physicists shows up and clarifies. It seems to me that the first 0.2c dV are the easier impossibility of all the impossibilities of interstellar travel.

but 3000km/s are .01c. :-)

Edited October 25, 2018 by Green Baron

[p1t1o]

12 minutes ago, Green Baron said:

I am still waiting for corrections ... but so it seems. But once you get to relativistic speeds you must mess with the Lorentz factor .... may be one of out physicists shows up and clarifies. It seems to me that the first 0.2c dV are the easier impossibility of all the impossibilities of interstellar travel.

but 3000km/s are .01c. :-)

Lorentz factor at 0.2c is almost negligible (about 1.02), the figures should be ok?

Lorentz factor doesnt even hit 1.1 until you get to 0.4c but starts to rise rapidly soon after that.

 

Ref: 

https://www.fxsolver.com/solve/

https://www.fxsolver.com/browse/formulas/Lorentz+Factor

 

[Green Baron]

Brain mass shrinks in long term spaceflight missions

Long term spaceflight lets brain mass shrink . Some of the effects, but not all are reversed after several months on earth. Visual abilities suffer from a long stay in weightlessness. Moar investigations.

Edited October 25, 2018 by Green Baron

[kerbiloid]

Spoiler

>> hardcore mode on
>> no fasttravel

 

[Green Baron]

A mass could be orbiting our galaxy's central black hole Sagittarius A* with 30% light speed. This is assumed to be the lowest possible stable orbit, at an orbital height of around 6-10 times the diameter of a 4 million solar masses black hole.

Article

The mass (probably a compact gas cloud) orbits prograde, almost face on and changes polarization together with its from centroid(*) calculation inferred orbit. Orbital period is around 45 min.

 

(*) a technique to calculate sub pixel resolution from small changes of exposure in neighboring pixels.

Edited November 1, 2018 by Green Baron

[p1t1o]

On 10/25/2018 at 2:54 PM, p1t1o said:

<tappity tappity tap tap on a calculator>

So....to accelerate 1t to 0.2c with a much more manageable, mere 1billion tons of reaction mass, the exhaust velocity needs to be around 3000km/s or 0.1c

 

So in order to make an object reach relativistic speeds, we need to be able to make matter reach...relativistic speeds.

Who doesnt love a bit of circular logic

 

I've just noticed that - though it seems like an obvious thing, you dont often see the numbers: if we "merely" double the above exhaust velocity from 0.1c to 0.2c, we can reduce the required reaction mass (to accelerate 1t to 0.2c) from 1billion tons...to 1ton.

Edited November 1, 2018 by p1t1o

[Bill Phil]

25 minutes ago, p1t1o said:

I've just noticed that - though it seems like an obvious thing, you dont often see the numbers: if we "merely" double the above exhaust velocity from 0.1c to 0.2c, we can reduce the required reaction mass (to accelerate 1t to 0.2c) from 1billion tons...to 1ton.

If exhaust velocity is 0.1c and we have 1 ton dry mass you should only need 6.4 tons of propellant. Of course, not taking into account relativity. 

Dv = Ve * ln|R| where R is the mass ratio.

The great thing about this is that ln|R| is unitless (dimensionless?). So we can just slap in 0.2 for Dv and 0.1 for Ve. Then we see that Dv/Ve is 2, meaning that R is e^2, or ~7.4. Take out 1 ton of dry mass and we get 6.4 tons of propellant per ton of dry mass. Actually, 6.4 of anything per 1 of anything, so long as the units are the same. Grams, kilograms, slugs, pound masses, anything. So with Ve of 0.2, Dv/Ve is 1, making R e^1, essentially about 1.7 tons of propellant for every ton of dry mass. 

With 3000 km/s, the Ve is 0.01, so Dv/Ve is 20, making R e^20, about 485 million. Doubling exhaust velocity in this case makes Dv/Ve 10, so R is e^10. About 22 thousand.

1 billion tons and 3000 km/s gets you to 0.207c.

[Green Baron]

I get 2.72 ?

But which energy source delivers the energy to accelerate stuff to 60,000km/s ? We are between the stars. Lots of nothing all around ...

Edit: Even the sparse info i get on fantastic fusion rockets from wikipedia is 2 magnitudes off. Which leaves us with more mass than the universe contains ...

Edited November 1, 2018 by Green Baron

[Bill Phil]

3 minutes ago, Green Baron said:

I get 2.72 ?

But which energy source delivers the energy to accelerate stuff to 60,000km/s ? We are between the stars. Lots of nothing all around ...

That's e. Subtract 1 and you get the propellant. Remember that R is wet mass over dry mass, wet mass includes dry mass. So 1.7 tons of propellant per ton of dry mass, with a little rounding.

As for energy sources... pre accelerated fuel pellets? Maybe lasers from our solar system. Antimatter? Fusion can theoretically get Ve above 0.1c...

[Green Baron]

47 minutes ago, Bill Phil said:

That's e.

 

Yes. Because 1ton * e¹ ;-)

47 minutes ago, Bill Phil said:

Antimatter? Fusion can theoretically get Ve above 0.1c...

Antimatter is fantastic. Impossible to generate in quantities with our available energy sources and near impassible to keep stable. Even in a high vacuum there are always a handful of molecules around to spoil the day.

Can you give a sauce for the 0.1c ? I get 100-1000km/s from wikipedia ?

What are "pre accelerated fuel pellets" ? They come pretty fast ?

Forget lasers. We (not me) want to travel to another star. Even for the starshot gram size leafs they need 100 Gigawatts of laser. These are 100 millions of 1kW lasers !

Edit: anyway, in 50 or so years we may know more about fusion stuff. And if it can be scaled to something movable.

Edited November 1, 2018 by Green Baron

[Bill Phil]

7 minutes ago, Green Baron said:

Yes. Because 1ton * e¹ ;-)

Antimatter is fantastic. Impossible to generate in quantities with our available energy sources and near impassible to keep stable. Even in a high vacuum there are always a handful of molecules around to spoil the day.

Can you give a sauce for the 0.1c ? I get 100-1000km/s from wikipedia ?

Edit: anyway, in 50 or so years we may know more about fusion stuff. And if it can be scaled to something movable.

1 ton * e^1 and then subtract 1 ton.

R = (prop mass + dry mass)/dry mass

(dry mass * R) - dry mass = prop mass

Or

dry mass * (R - 1) = prop mass

Dry mass is 1 ton, so dry mass * R is just R. Subtract dry mass, and prop mass is R - 1. 

http://www.projectrho.com/public_html/rocket/fusionfuel.php#id--Fusion_Reactions

It's the theoretical maximum.

Antimatter isn't possible to acquire in large amounts now, of course. This situation is likely to persist for a long time, but if our energy use continues to grow we could generate significant quantities in the (likely very far) future.

[Green Baron]

19 minutes ago, Bill Phil said:

http://www.projectrho.com/public_html/rocket/fusionfuel.php#id--Fusion_Reactions

 

Very theoretical/fantastical and impractical for a heavy spaceship; laughably low thrust.

Yeah, i got the math. I proposed it upthread ;-) The start mass to accelerate 1ton with an exhaust-v of 0.2c to 0,2c is 2,7 tons, the fuel mass 1.7 tons. I didn't make that clear, but we totally agree here :-)

But there is no energy source to accelerate any mass to 0.2c, not fusion nor antimatter, not even theoretically. So we must live, even under the assumption of the best imaginable fusion drive (which we can imagine to have around 1.000km/s according to the link above and wikipedia), with around a billion tons of reaction mass per ton to accelerate to 0.2c. And the same to slow down. Sometime in a future. Is that correct ?

Which brings us back to the initial point i proposed: imo, without shortcuts and a yet to discover energy source there is no imaginable way for humans to travel to other planets bs stars.

Edited November 1, 2018 by Green Baron

[StrandedonEarth]

Particle accelerators routinely accelerate protons to 0.99c, but I have no idea how much energy it would take to make more thrust than a photon drive...