Random Science Facts Thread!

[p1t1o]

1 hour ago, Bill Phil said:

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

Yes, thats the figure I showed as well.

However, I have made a mistake and a few times have said 0.1c instead of 0.01c (referring to 3000km/s), thats embarrassing , taints all my cool points!!

@Green Baron maybe thats where your factor of ten came from (with the 2.72 result)?

 

 

[Green Baron]

12 minutes ago, p1t1o said:

 

@Green Baron maybe thats where your factor of ten came from (with the 2.72 result)?

 

Oh, have i shifted a decimal ? I hope to my advantage :-)

Anyway, even a magnitude doesn't change things principally.

@StrandedonEarth, yep, the LHC can produce tiny amounts (100s of atoms) of e.g. Antihydrogen and store them for minutes. But a handful of particles aren't suitable for propulsion. This machine has the size of a proper landscape, weighs thousands or even tenthousands of tons, rests deep under the earth, draws a medium range power plant and need a lot of attention. And its the cutting edge right now. Until further notice :-)

Edited November 1, 2018 by Green Baron

[Bill Phil]

1 hour ago, Green Baron said:

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.

Photonic laster thrusters may be a potential solution. Still requires development work, of course. They've got 14 millinewtons with 500 watts. Basically a photon thruster that needs less power per newton.

[p1t1o]

26 minutes ago, Bill Phil said:

Photonic laster thrusters may be a potential solution. Still requires development work, of course. They've got 14 millinewtons with 500 watts. Basically a photon thruster that needs less power per newton.

Unfortunately the laws of physics means that you need 300MW per Newton, and no amount of fancy new materials or research can improve that due to conservation laws.

The equation boils down to a very simple form:

Power = Force * c

Watts = 1N * c = 300,000,000W/N

 

source: http://www.projectrho.com/public_html/rocket/enginelist.php#photon

 

Which is confusing because 14mN from 500W is only 35.7kW/N...  (and I think with that ratio, you could do a HECK of a lot already)

What am I missing?

But I just screwed up my decimal points in a previous calculation, so Im not really sure of anything anymore. 

Edited November 1, 2018 by p1t1o

[Green Baron]

31 minutes ago, p1t1o said:

What am I missing?

 

Maybe one should check the numbers and refer to a proper publication and the actual state of the technology ? Just proposing, not criticizing the poster. In the end it might come out that it is not as ready as it seems ...

Anyway, a micro- or millinewton here, an antiproton there, but wih today's tech we need energies and masses magnitudes beyond of what is in the obs. universe. It is easier to dust the Sahara alone over a weekend with a toothbrush :-)

E=mc². One either schlepps billions of tons, once someone has figured out how to accelerate them to 1000km/s, and/or one opens up a new energy source for use underway between the stars. And, of course, the travelers should somehow survive.

Edited November 1, 2018 by Green Baron

[Bill Phil]

42 minutes ago, p1t1o said:

Unfortunately the laws of physics means that you need 300MW per Newton, and no amount of fancy new materials or research can improve that due to conservation laws.

The equation boils down to a very simple form:

Power = Force * c

Watts = 1N * c = 300,000,000W/N

 

source: http://www.projectrho.com/public_html/rocket/enginelist.php#photon

 

Which is confusing because 14mN from 500W is only 35.7kW/N...  (and I think with that ratio, you could do a HECK of a lot already)

What am I missing?

But I just screwed up my decimal points in a previous calculation, so Im not really sure of anything anymore. 

Photonic laser thrusters are different in that they reflect the photons back to the source where they are again reflected back to the spacecraft, so each photon exchanges momentum to the spacecraft multiple times. It's weird, but from what I can find it's been successfully done in the lab. 

Essentially, you spend 300MW per Newton and then just let the photons do whatever. But the photons still have unused energy and momentum. So you could potentially reuse them. Add in the energy they lost when transferring momentum to the spacecraft, and you can keep it up.

13 minutes ago, Green Baron said:

Maybe one should check the numbers and refer to a proper publication and the actual state of the technology ? Just proposing, not criticizing the poster. In the end it might come out that it is not as ready as it seems ...

Anyway, a micro- or millinewton here, an antiproton there, but we need energies and masses magnitudes beyond of what is in the obs. universe. It is easier to dust the Sahara alone over a weekend with a toothbrush :-)

E=mc². One either schlepps billions of tons, once someone has figured out how to accelerate them to 1000km/s, or one opens up a new energy source for use underway between the stars. And, of course, the travelers should somehow survive.

Huh? Yeah, we don't have the propulsion tech at the moment and likely won't for some time. But it definitely does not take energies and masses exceeding what is in the observable universe. 

With current photonic laser thruster kw/N values, 1g for 1 ton needs 350 megawatts. No exotic energy sources needed, just development of current technology. Will it take a lot of time to develop? Of course. But is it possible? Yes.

[Green Baron]

43 minutes ago, Bill Phil said:

Photonic laser thrusters are different in that they reflect the photons back to the source where they are again reflected back to the spacecraft, so each photon exchanges momentum to the spacecraft multiple times. It's weird, but from what I can find it's been successfully done in the lab. 

Essentially, you spend 300MW per Newton and then just let the photons do whatever. But the photons still have unused energy and momentum. So you could potentially reuse them. Add in the energy they lost when transferring momentum to the spacecraft, and you can keep it up.

Sounds fishy to me. How can it transfer a momentum several times ? Every time a tiny part ? And how does that help accelerating a craft away from a planet, as the beam opens up with distance ? Papers please :-)

Quote

Huh? Yeah, we don't have the propulsion tech at the moment and likely won't for some time. But it definitely does not take energies and masses exceeding what is in the observable universe. 

But it does. See the math above. In the case of an ion drive by 470 magnitudes, 10⁴⁷⁰. That is current tech and it is actually not my idea, i took it from an astronomical almanac.

Quote

With current photonic laser thruster kw/N values, 1g for 1 ton needs 350 megawatts. No exotic energy sources needed, just development of current technology. Will it take a lot of time to develop? Of course. But is it possible? Yes.

So how do you produce energy between the stars, for 100s of years ? Don't say nuclear. It is the toothbrush for the desert that lasts half an hour (the toothbrush, the desert laughs).

How do you accelerate a manned interstellar ship's mass of lets say 10,000 tons (if that is enough) with 1g/ton ? Or 350MW/ton ? The shiny laser (if it works as envisioned) has no power, if the manages to reach the outer solar system after decades of near 0 acceleration. It is not a computer game.

At home, the current comes out of the plug, but not in space.

A few photons, a hydrogen atom every now and then, neutrinos incognito, that's it. There is nothing there we can develop because there are no sources to use. Nothing comes from nothing. Either you take billions of tons with you, or you make them on the way. There is no other way.

Current tech projected into the future is by far not enough nothing is available in space. Current tech are ion drives and solar power, nuclear batteries for a few decades and a handful of Watts, and chemical engines.

 

Btw.: Laser propulsion often refers to using a laser to heat something and the ablation drives a vehicle. Or use a laser to shine into a tube and the expanding air accelerates something. But that plays no role here.

Apart from that, current serious proposals for laser thrusters are for station keeping and precise maneuvers in the inner solar system where there is energy available for conversion, not for interstellar travel.

Edited November 1, 2018 by Green Baron

[p1t1o]

15 hours ago, Bill Phil said:

Photonic laser thrusters are different in that they reflect the photons back to the source where they are again reflected back to the spacecraft, so each photon exchanges momentum to the spacecraft multiple times. It's weird, but from what I can find it's been successfully done in the lab. 

Copying in @Green Baron

Found it, its a sail. A"photonic thruster" is a photon sail concept, where the photons are reflected back and forth between stationary start point and the "thruster" itself.

Photon sails have their advantages, but also disadvantages.

[cubinator]

Bees navigate by the sun, and can do so even when it's cloudy because they can see polarization, making the sun visible through clouds.

[kerbiloid]

When your landscape generator suddenly glitches, and you must quickly explain to the kerbals that they don't live in a simulated world.

https://earthobservatory.nasa.gov/blogs/earthmatters/2018/11/05/famous-rectangular-icebergs-rough-journey/

Spoiler

 

[Green Baron]

"Oh, it is halfsun again. How time flies ..." :-)

Using the Gemini Planet Imager and the VLTI Sphere instrument, the shadows of a binary star system on a protoplanetary disk have been mapped in a system 73pc from here (V4046 Sgr), including phases.

paper

I only found an italian popscience article.

Here is a sketchy sketch of what i mean, but don't take it too serious. The differences are by far not as abrupt and symmetric as shown:

 

Edited November 27, 2018 by Green Baron

[p1t1o]

13 hours ago, Green Baron said:

"Oh, it is halfsun again. How time flies ..." :-)

Using the Gemini Planet Imager and the VLTI Sphere instrument, the shadows of a binary star system on a protoplanetary disk have been mapped in a system 73pc from here (V4046 Sgr), including phases.

paper

I only found an italian popscience article.

Here is a sketchy sketch of what i mean, but don't take it too serious. The differences are by far not as abrupt and symmetric as shown:

 

Thats so cool! You hardly would ever imagine a star casting a shadow!

[Green Baron]

Ir is never really night there, but there are phases when both suns shine on a spot or only one of them. Apparently one is a little bigger than the other, making for different phases and eclipsing angles depending on whether the smaller one eclipses the bigger one or vice versa.

The resolution of our instruments get ever better for detailed views around us.

Edited November 28, 2018 by Green Baron

[Green Baron]

Predictions from general relativity again proven to be correct, this time with four times higher accuracy than before.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.231102

Proven by repurposed satellites that were accidentally set out it a wrong orbit.

Well then, so be it :-)

Edited December 7, 2018 by Green Baron

[LaydeeDem]

On 11/27/2018 at 12:34 PM, Green Baron said:

"Oh, it is halfsun again. How time flies ..." :-)

Using the Gemini Planet Imager and the VLTI Sphere instrument, the shadows of a binary star system on a protoplanetary disk have been mapped in a system 73pc from here (V4046 Sgr), including phases.

paper

I only found an italian popscience article.

Here is a sketchy sketch of what i mean, but don't take it too serious. The differences are by far not as abrupt and symmetric as shown:

 

Link to the paper on a site that isn't blocked by a paywall: https://arxiv.org/pdf/1811.10621.pdf

 

Interesting stuff.

[Green Baron]

First observed on the 10th of November with the Subaru Telescope, in an Orbit ~120 AU away from the sun, orbital period >1000y, approx. 500km across (dwarf planet or not, we'll see) and of a pinkish color.

2018 VG 18

The most distant solar system object for now. Nicknamed "Farout". Until another object looks down on it from above, i presume :-)

 

[Green Baron]

Saturn's Rings might be gone in 100 to 300 million years. They are "raining down" on Saturn's equator.

link

It also has implications on their history, they must have formed long after the planet, maybe through a "dramatic" event or events, and they were much larger and brighter before our time.

Edited December 21, 2018 by Green Baron

[StrandedonEarth]

I thought that the rings were being replenished by cryovolcanoes on inner moons and moonlets 

[Green Baron]

Idk, maybe there is a contribution.

Apart from that, afaik, discussed sources are comets, asteroids, shattered moons, this sort of things.

Edit: the paper is open. Maybe you can find a reference that sheds light on the ring formation processes and make us clever :-)

https://www.sciencedirect.com/science/article/pii/S0019103518302999?via%3Dihub

Edited December 21, 2018 by Green Baron

[kerbiloid]

So, now the Martians can skating.

https://www.esa.int/Our_Activities/Space_Science/Mars_Express/Mars_Express_gets_festive_A_winter_wonderland_on_Mars

[Green Baron]

Yet another modelling of the Chicxulub impact, right in time for christmas.

link and link

tl, dr: big boom and splash.

I wouldn't take the play with numbers too serious until real world sediments are found for confirmation.

 

[YNM]

 

[Green Baron]

During the Krakatau eruption and landslide on the 22. that caused a tsunami in Indonesia with >400 hundred people dead, the Anak Krakatau lost approx 2km² of area and 200m of height, as observed by Japanese earth observation satellite Alos-2.

https://www.eorc.jaxa.jp/ALOS-2/en/img_up/dis_pal2_eruption_anak_krakatau_20181226.htm

 

Edited December 29, 2018 by Green Baron

[wumpus]

On 11/1/2018 at 12:05 PM, p1t1o said:

Yes, thats the figure I showed as well.

However, I have made a mistake and a few times have said 0.1c instead of 0.01c (referring to 3000km/s), thats embarrassing , taints all my cool points!!

@Green Baron maybe thats where your factor of ten came from (with the 2.72 result)?

Can anyone confirm just how many H-bombs it would take to get an Orion up to .1c?  That's the number that gets thrown around, but I can't imagine how a H-bomb is supposed to get an Isp in the millions or so.  Note that H-bombs emit most of their energy as photons, so that's a lot of momentum that doesn't otherwise require mass, but photons are typically an inefficient means of accelerating spacecraft.

Every time I plug the numbers into the rocket equation I suspect that Dyson was pulling a fast one.

[cubinator]

2 hours ago, wumpus said:

Can anyone confirm just how many H-bombs it would take to get an Orion up to .1c?  That's the number that gets thrown around, but I can't imagine how a H-bomb is supposed to get an Isp in the millions or so.  Note that H-bombs emit most of their energy as photons, so that's a lot of momentum that doesn't otherwise require mass, but photons are typically an inefficient means of accelerating spacecraft.

Every time I plug the numbers into the rocket equation I suspect that Dyson was pulling a fast one.

Hmmm, yeah, that's a problem. I wonder if you could use them similarly to a NTR, using the heat of the nukes to accelerate a more hefty reaction mass.