For Questions That Don't Merit Their Own Thread

[Green Baron]

Yeah, small explosions with local (decimeters or meters) effects. Newer mining techniques avoid explosives if possible, too dangerous and sideeffects.

 

Big bomb = bad idea, sorry. The local geology will become unstable, the rock shattered and cracked, depending on number and strength of the explosions and the rock composition of course. You'll provoke earthquakes and landslides that makes the whole mountain inaccessible and can even expose the cavities formed by the "megabombs", so if they were nuclear you'll have isotopes in the garden where your children are playing. Bad idea :-)

Edit: mining is more a question of how to separate the waste from the interesting stuff, which forbids the use of overkill methods.

Edited December 23, 2017 by Green Baron

[0111narwhalz]

On the subject of mining:

Many scifi space works feature "mining lasers." Is there any way within current or near-future technology to make a beamlike mining tool, especially for use in vacuum (and 0g)? Of course, lasers can ablate and fracture materials, so the real question is collection. Perhaps some kind of electrostatic device?

[Green Baron]

You said it, scifi spaceworks :-)

Mining is all about separating the good stuff from the bad. For that the material is blasted or cracked by pressure from steam, water, abraded or dissolved to transform it into transportable units, to be taken away by conveyor belts, trucks, trains, ships, etc. pp. to the respective processing facilities.

Lasers can be used for cutting or measuring and a few military schmucks want to use it to destroy things. If somebody (Industrial Light & Magic, Pixar, Bavaria Studios, etc.) can make them strong enough to vapourize rock on a large scale in space including the necessary energy production (which is where the scifi story about mining usually ends), then you will be left with the problem of catching the stuff you wanted to mine. How to transform the colourful cloud of minerals into transportable units ?

Edited December 24, 2017 by Green Baron

[winged]

On 19.12.2017 at 1:28 PM, K^2 said:

While sitting on the ground, a Cessna 150/152 will have about 15kN at effective I_SP of about 20,000s.

1,5 kN I think. With 15 kN of thrust and 900 kg of weight, the aircraft could start vertically.

[Green Baron]

Cessna 150 O-200 100hp static thrust +/-335pounds that is quite exactly 1.5kN :-)

State of atmosphere (temperature, humidity, pressure) has a big influence !

 

Question: how can we calculate the specific impulse of a propeller engine ?

Edited December 24, 2017 by Green Baron

[DDE]

11 hours ago, 0111narwhalz said:

On the subject of mining:

Many scifi space works feature "mining lasers." Is there any way within current or near-future technology to make a beamlike mining tool, especially for use in vacuum (and 0g)? Of course, lasers can ablate and fracture materials, so the real question is collection. Perhaps some kind of electrostatic device?

Only if you couple the laser with a very powerful magnetic field that can then somehow suck up what little of the matter is vapourized. Those sci-fi lasers either use a magic gravity field, or aren't actually bothering with collection.

[DerekL1963]

On 12/23/2017 at 12:48 AM, shynung said:

Is it possible to make a megaton-class nuclear bomb that doesn't leave radioactive fallout?

No.

7 hours ago, Green Baron said:

If somebody (Industrial Light & Magic, Pixar, Bavaria Studios, etc.) can make them strong enough to vapourize rock on a large scale in space including the necessary energy production (which is where the scifi story about mining usually ends), then you will be left with the problem of catching the stuff you wanted to mine.

Use pulse lasers, by vaporizing a few mm of material you create a shockwave the same as if you'd let off a couple of pounds of TNT on the rock face.  (This is the same damage mechanism that anti-missile lasers use.)   The problem is that untamped explosives on the surface aren't terribly efficient at breaking up rocks, there's a reason why they drill and emplace the explosives deep inside the rock.

[Green Baron]

Anti missile lasers aren't developed further. Too weak and too expensive, or, in one word, impractical. A pulse laser would be uselaser -less against a rock. The shock would just run dead in the relative soft rocky body. You'd rather need constant heat to cut something out. Apart from that, lasers for drilling in mining style don't exist and probably will never. Too much energy needed. Lasers are nice for precision jobs, cutting, measuring, drilling precision holes in sub- and millimeter range.

Actually one does not place explosives deep in the rock but arrange a series of small explosions (several dozens or even more) in a shield area in a depth of a few meters, just so much that you can get rid of the stuff before it blocks the way. The timing of the explosions is extremely important, so that the material from the first explosions leave the shield already when the following ones go up. For example from the center out it spirals. It depends on the situation, you'll always have a geologist there. I am sure you can find high speed videos from the process. This technique would be ... impractical in space.

Btw., it is not the shock wave from the atmosphere but the expanding gases from the explosives that shatter the rock, so this technique could in principle work inside an asteroid, were it not so impractical to get stuff there.

But we aren't that far yet as to think about this in detail beyond scifi (including Nasa) ;-)

Edited December 24, 2017 by Green Baron

[Terwin]

If you had a reactionless lift system that could provide ~12m/s/s (or 1.2g if the math is easier) continuous thrust, how long would it need to run to get to orbit?

How much would these numbers change if the constant thrust was 2g or 1.1g instead of 1.2 g?

(hmm, 1 hour of 1.2g thrust at each end gets you to mars in ~ 15 days from LEO...)

[Green Baron]

Let's say you want to achieve 8,000m/s with a constant acceleration of 12m/s² that'll take you .... crunchcrunch 666and2/3 seconds or 11.1 minutes.

Not regarding atmospheric drag and gravity loss, add another 2km/s for that. Much time to enjoy the flight :-)

Hope that wasn't too simple ?

Nonsense. The acceleration is only ~2m/s² since you're fighting 1g. Gravity losses are much higher. idk and withdraw :-)

Edited December 27, 2017 by Green Baron

[K^2]

On 12/24/2017 at 3:49 AM, Green Baron said:

Question: how can we calculate the specific impulse of a propeller engine ?

I_SP = F / (m' g), where F is thrust, g is standard gravity, and m' is the fuel mass flow rate in kg/s. If you know gph or Lph fuel consumption of your engine and density of fuel, you can compute m'.

And yeah, that's definitely 1.5kN. Sorry about the mis-placed decimal place. Good catch, @winged

[wumpus]

On 12/23/2017 at 7:50 PM, 0111narwhalz said:

On the subject of mining:

Many scifi space works feature "mining lasers." Is there any way within current or near-future technology to make a beamlike mining tool, especially for use in vacuum (and 0g)? Of course, lasers can ablate and fracture materials, so the real question is collection. Perhaps some kind of electrostatic device?

There are two things you could use lasers for in mining.  As mentioned, using a laser to smelt the rocks would be pretty extreme.  I'd recommend a solar oven for any high power melting.  All the "solar oven" would be is a huge array of sheet of mylar reflecting solar light into an asteroid-sized focal area.  You might have to spin the asteroid before heating: smelting typically relies on the buoyancy of slag vs. metal (which won't exist in zero-g).

The second is to remove the ore from non-ore.  I'd assume any near-future space mining would involve asteroids that would simply process the entire asteroid at once (assume all the asteroid is ore, and expose it to the solar oven).

[Terwin]

On 12/27/2017 at 12:16 PM, Green Baron said:

Let's say you want to achieve 8,000m/s with a constant acceleration of 12m/s² that'll take you .... crunchcrunch 666and2/3 seconds or 11.1 minutes.

Not regarding atmospheric drag and gravity loss, add another 2km/s for that. Much time to enjoy the flight :-)

Hope that wasn't too simple ?

Nonsense. The acceleration is only ~2m/s² since you're fighting 1g. Gravity losses are much higher. idk and withdraw :-)

Yea, probably less atmospheric drag and more gravity losses.  Both horizontal velocity and altitude would reduce gravity losses, but I am not sure how to calculate that.

Would you even want to have the same launch trajectory with a constant acceleration vehicle?

[K^2]

No, ascent trajectories are different depending on available thrust. Whether you have insufficient power, or you can't throttle back, you'll have to adjust to cut the losses. In both cases, you are likely to start pitching over later than you would at optimal thrust, but the gravity turn will be much more abrupt if you have too much thrust than in the case with insufficient thrust.

[KG3]

On ‎12‎/‎23‎/‎2017 at 7:50 PM, 0111narwhalz said:

On the subject of mining:

Many scifi space works feature "mining lasers." Is there any way within current or near-future technology to make a beamlike mining tool, especially for use in vacuum (and 0g)? Of course, lasers can ablate and fracture materials, so the real question is collection. Perhaps some kind of electrostatic device?

I think you would need to get more specific about what you were mining for.  Are you trying to get water, iron and nickel, gold, iridium, carbon, Sulphur?  Some asteroids are somewhat solid and some are just piles of rubble that you could probably take apart with a spoon.  And then there is size, some asteroids are just meters across some are kilometers.

This looks interesting from Wikipedia: 

https://en.wikipedia.org/wiki/Asteroid_mining   

Extraction using the Mond process

The nickel and iron of an iron rich asteroid could be extracted by the Mond process. This involves passing carbon monoxide over the asteroid at a temperature between 50 and 60 °C, then nickel and iron can be removed from the gas again at higher temperatures, perhaps in an attached printer, and platinum, gold etc. left as a residue.

You might find that you will need to mine carbon monoxide from a comet to process material from an iron asteroid!   

[kerbiloid]

On 24.12.2017 at 3:50 AM, 0111narwhalz said:

Many scifi space works feature "mining lasers." Is there any way within current or near-future technology to make a beamlike mining tool, especially for use in vacuum (and 0g)? Of course, lasers can ablate and fracture materials, so the real question is collection. Perhaps some kind of electrostatic device?

My vision of this is something like a nuke-powered crawler looking like a snail or StarWars MTT or a hovercraft.

Spoiler

Snail

 

Spoiler

MTT

Spoiler

Hovercraft

 

The space beneath this harvester is its working area.
Powerful masers along the craft belly emit intense microwaves heating the ground from very close distance.
They don't vaporize the ground. But they modulate ultrasound frequency at particular resonant frequencies of this exact type of ground.
(This is self-adjusted. When a resonance appears, this can be easily detected by a EM receiver or so, so they just find the resonance frequency before mining running through the frequency spectre and then constantly adjust it while mining).

The ultrasound-frequent heating makes the ground to vibrate at a resonance frequency and crash into dust (i.e like any ultrasound crashing works).

UV-emitters placed between the masers ionize the dust particles (and gas atoms) making them charged.

Powerful magnetic field beneath the craft sucks the charged dust from below into the chamber.

I would not at all be surprised if the magnetic field and gas pressure below the craft would be enough high to keep the whole harvester levitating, though it's not necessary.

So, the craft crawls there and back like a crop harvester across a stadium-sized site.
After reaching the finish, it crawls back, still mining.
So, it shuttles many times across the same site while there is enough to mine.

The ground behind the harvester probably would not be melted (the temperature is relatively low, ultrasound makes all), would not be chemically transformed (pure mechanical effects) or so, but probably it would be polished like a glass. Where there were stones, there would be like random-shaped stone tiles , perfectly fitting each other.
The crawler has like smoothly shaved the stony site, taking off the upper centimeters-thick layer every pass.
So, where the wild rocks were, now you have a stony mosaic floor for a palace.

Of course, this requires a lot of energy, so the harvester should be equipped with a fusion or a gaseous fission reactor.
This in turn means, the harvester should be big. (Though, who needs a small mining harvester).

***

The dust in the chamber can be just delivered to the mining station for the further processing.
But:

1)
Earth. At least a half of the dust is oxygen. About a quarter is silicon. Here on Earth there's a lot of both. They are mostly heavy wastes.
Moon. Helium-3. It will be lost if not collect it right in situ. While it could be used at least to power the harvester and smelter themselves.
Mars. Don't know exactly what is waste from a Martian's pov, so let it be happy with the raw dust.

It would be nice to drop the wastes on the Earth and to collect Helium-3 on the Moon.
So, it would be nice to separate the dust elements right in the harvester, collect the useful ones, and drop wastes right aside the quarry.

2)
There is a powerful power plant inside the harvester, fusion or gaseous fission.
This means we already use technologies of not-so-hot plasma magnetic confinement in a closed chamber.

So, on the Earth:
After the mixture of the ionized dust and gases gets into the collecting chamber, the harvester heats it up to 10..20 kK with solenoids' magnetic field ionizing all atoms and disintegrating all molecules.
The hot cloud of ionized atoms of pure elements flows into a toroidal separation chamber.

The ion cloud orbits along the torus. Magnetic traps deflect the atoms of different elements by charge/mass ratio into a tunnel, where they get slowed by the magnetic field and de-ionized by the electron flow from an electromagnetic electron emitter.

In such manner, one by one the dust gets splitted into pure element fractions.
The metal powders are mixed, as this is just a preliminary separation. But gaseous elements get separated.
The waste oxygen oxidize the waste silicon into SiO₂, which gets dropped aside the quarry just as sand (it is the sand).
Excessive oxygen gets thrown right into air.
The metal powders are delivered to the mining station.

On the Moon:
Just not so hot. As there are no wastes on the Moon, the dust in the chamber just gets warmed enough to release Helium-3. The Helium-3 gets collected into a balloon.
When the harvester is full, it delivers (itself or by shuttling trucks) the regolith dust and Helium balloons to the mining station.

In the mining station.
Exactly the same what was described in the harvester chapter.
Heats the delivered material once again and separates the ions into pure elements precisely, in a cascade of separation chambers.

Pure element powders get composed into technological mixtures and used for additive manufacturing (3d-printing) of things.
Some of the things are 3d-printed metal-ceramical construction blocks with reinforced structure and inner hollows, lightweight but strong. They use them to build the buildings.

Edited December 30, 2017 by kerbiloid

[wumpus]

Just ran across a job for somebody to integrate an electric propulsion system into a spacecraft (plenty of experience in both required).  $90-$100/hr [6 month contract].  Washington DC area.  Anybody do this for reals?  The job hasn't been filled for 30 days, so I'm guessing there isn't anybody in the area with the right skillset (or the contract hasn't been awarded and the job doesn't exist - a more likely story for this type of thing).

[magnemoe]

On 23.12.2017 at 10:34 AM, Green Baron said:

Yeah, small explosions with local (decimeters or meters) effects. Newer mining techniques avoid explosives if possible, too dangerous and sideeffects.

 

Big bomb = bad idea, sorry. The local geology will become unstable, the rock shattered and cracked, depending on number and strength of the explosions and the rock composition of course. You'll provoke earthquakes and landslides that makes the whole mountain inaccessible and can even expose the cavities formed by the "megabombs", so if they were nuclear you'll have isotopes in the garden where your children are playing. Bad idea :-)

Edit: mining is more a question of how to separate the waste from the interesting stuff, which forbids the use of overkill methods.

This you use explosives to break up rock, note that you sometimes use lots of explosives simply as you can drill holes and place explosives at your leisure but you have to evacuate the area to blast.
Explosives for each m^3 rock is pretty constant its just more efficient to do fewer and larger blast. 
An mining laser would probably work more like an jackhammer, you could probably do an say 100 kW beam over time to melt an hole follow by an 100 MW to blast rock at bottom of the 30 cm hole. 

[Exploro]

Returning to college that I am; and this term I'll be taking Calculus. Will I need to buy a graphing calculator or can I get by with decent scientific calculator?

[Steel]

10 hours ago, Exploro said:

Returning to college that I am; and this term I'll be taking Calculus. Will I need to buy a graphing calculator or can I get by with decent scientific calculator?

I never had a graphing calculator at university. It would certainly make some parts slightly quicker, but unless your college requires it, you can do everything you need on a scientific calculator.

[StrandedonEarth]

On 2018-01-12 at 3:24 PM, Exploro said:

Returning to college that I am; and this term I'll be taking Calculus. Will I need to buy a graphing calculator or can I get by with decent scientific calculator?

Graphing, no, but programmable could be useful 

[Green Baron]

Isn't there a recommendation from college as to what kind of calculator to use ?

 

 

Other question: The element Si, what is the correct English word: Silicon, Silicium, both ?

[Steel]

5 minutes ago, Green Baron said:

Other question: The element Si, what is the correct English word: Silicon, Silicium, both ?

Silicon, I've never heard it being referred to as Silicium. What language is that used in?

[Green Baron]

24 minutes ago, Steel said:

Silicon, I've never heard it being referred to as Silicium. What language is that used in?

French and German. Silicon in German means Silicone, which caused my confusion. Thanks for clarifying :-)

[Dfthu]

Is there a app for IOS that has notifications if there is a rocket launch happening soon?