How To Play Asteroids....For Real

[KerikBalm]

On 11/26/2020 at 7:24 PM, KSK said:

Yeah, blasting a rock into chunks with a laser is probably a tall order, but cutting rock with a laser should be feasible. It may take a while though, so as @mikegarrison said, space sims go for rule of cool instead.

Some very simplified notes on lasers based on conversations with a colleague a couple of years back:

You've got two main modes of interaction between a laser beam and a surface. Photothermal - where the material under the laser evaporates or sublimes away (think of the laser as a fancy blowtorch), and photoablative, where the material turns to plasma and dissipates. Which one you get depends critically on the power density of the beam at the surface. Typically,  a continuous wave laser will operate in a photothermal regime because its difficult to build a continuous wave laser capable of reaching the required power density. Pulsed lasers on the other hand can get around that problem by shortening the pulse width. The actual energy per pulse can be relatively low but because its delivered over picoseconds or even femtoseconds, the power densities involved can get quite extreme. When you're dividing by 10^-12 or 10^-15, the numbers can get pretty big pretty fast.

Whilst photoablation sounds pretty violent, in practice everything happens so quickly that very little thermal energy is transferred to the material that isn't directly under the laser beam, so it's a very precise technique with a whole bunch of applications, including dental or medical applications. 

I should also point out that if your goal is to blow the rock apart, a pulse laser could do what you want. While a continuous laser may cut by melting through, and a rapidly pulsed laser can "drill" through, a massive petawatt pulse laser will essentially make the rock explode at the surface, and will act very much like a chemical explosive detonating right on the surface. If you drill with a few small pulses, then set off a big pulse into the hole, its very much as if you just drilled a hole and detonated an explosive.

As far as energy efficiency, a free electron laser might get 50%. A railgun... that depends on the material property. If the round goes clean through a rubble pile, with the shockwave scattering the rubble, you basically need to compare the KE of the railgun slug, to the KE imparted to the rubble.

If its a more solid metal, and you fracture it, then well done.

Anyway, as far as weaponized space lasers, I think people often underestimate the potential effects on the target. Vaporizing a significant amount of material right on the surface is literally like detonating an explosive on the surface... granted, against a tank, high explosive shells are ineffective, and you're not going to get the effect of a shaped charge /explosively formed penetrator - but it would still shred lightly built spacecraft, and the effect would primarily be kinetic, not thermal

[kerbiloid]

I don't see any purpose for the orbital bombardment at all.

They don't need a clouds of debris. They need the debris to be gathered.

So, they would more likely put a plastic patch on top of the mining spot, use underground explosions to crush the rock and catch with the patch, then collect and process.

Edited December 4, 2020 by kerbiloid

[StrandedonEarth]

4 minutes ago, kerbiloid said:

I don't see any purpose for the orbital bombardment at all.

They don't need a clouds of debris. They need debris to de gathered.

So, they would more likely put a plastic patch on top of the mining spot, use underground explosions to crush the rock and catch with the patch, then collect and process.

Tag it and bag it, then disassemble the roid at your leisure without letting any of those valuable volatiles (or other debris) escape

Edited December 4, 2020 by StrandedonEarth

[Spacescifi]

On 12/4/2020 at 6:02 AM, KerikBalm said:

I should also point out that if your goal is to blow the rock apart, a pulse laser could do what you want. While a continuous laser may cut by melting through, and a rapidly pulsed laser can "drill" through, a massive petawatt pulse laser will essentially make the rock explode at the surface, and will act very much like a chemical explosive detonating right on the surface. If you drill with a few small pulses, then set off a big pulse into the hole, its very much as if you just drilled a hole and detonated an explosive.

As far as energy efficiency, a free electron laser might get 50%. A railgun... that depends on the material property. If the round goes clean through a rubble pile, with the shockwave scattering the rubble, you basically need to compare the KE of the railgun slug, to the KE imparted to the rubble.

If its a more solid metal, and you fracture it, then well done.

Anyway, as far as weaponized space lasers, I think people often underestimate the potential effects on the target. Vaporizing a significant amount of material right on the surface is literally like detonating an explosive on the surface... granted, against a tank, high explosive shells are ineffective, and you're not going to get the effect of a shaped charge /explosively formed penetrator - but it would still shred lightly built spacecraft, and the effect would primarily be kinetic, not thermal

 

Lasers run into the same problem as fusion torchships.

The amount of mass equipment to reject the heat of pulse lasers with blast ability will be so much that any ship carrying it will have poor thrust.

By poor I mean so poor it should be a station in orbit, not a spaceship.

And definitely not flying around looking for asteroids.

The one type of laser that I think is portable and can pulse blast...but only once, is the bomb pumped laser.

The kind you stand away from. Which either requires using rocket fuel or waiting patiently or jyst firing the BPL through mag rails, albeit not real fast as you don't need a lot of speed.

[KerikBalm]

1 hour ago, Spacescifi said:

 

Lasers run into the same problem as fusion torchships.

The amount of mass equipment to reject the heat of pulse lasers with blast ability will be so much that any ship carrying it will have poor thrust.

Im talking about weaponry, not as an engine.

Lasers for thrust are best used for beamed power, where the laser isn't on the ship being accelerated. Also FELs can have decent efficiency (50%). Vaporizing a solid fuel block (ablating) can get decent thrust and isp, but not really comparable to a gas core ntr.

Still, nuclear power + laser will do better than solar and ion.

Also, isru options around the asteroid belt are great

 

[Spacescifi]

18 minutes ago, KerikBalm said:

Im talking about weaponry, not as an engine.

Lasers for thrust are best used for beamed power, where the laser isn't on the ship being accelerated. Also FELs can have decent efficiency (50%). Vaporizing a solid fuel block (ablating) can get decent thrust and isp, but not really comparable to a gas core ntr.

Still, nuclear power + laser will do better than solar and ion.

Also, isru options around the asteroid belt are great

 

 

As was I.

Lasers are poor at blasting stuff unless you have lots of cooling equipment.

 

My point is simply that it is very ineficient to use lasers for blast mining at all.

At best they are not bad for burning, but blasting?

Too much mass required. Low thrust.

I don't care what your ship's drive is, if it is a rocket with known propellant and engines, even nuclear, thrust will suffer.

A lot.

 

That's my whole reason for this thread.

[kerbiloid]

It would be very interesting to get at least one exact example of an asteroid deserving any type of mining.

Total mass of the whole asteroid belt is 0.04 lunar mass.
The Moon surface total area is almost equal to Africa.

Most of the asteroids are just stones.

Largest asteroids (owning almost all asteroid belt mass) are hundreds of kilometers large, so almost all asteroid belt mass is hidden at tens of kilometers depth and will stay unavailable.

Small asteroids unlikely can contain enough treasures to pay for the expedition,

At least one known Eldorado?

[Spacescifi]

3 hours ago, kerbiloid said:

It would be very interesting to get at least one exact example of an asteroid deserving any type of mining.

Total mass of the whole asteroid belt is 0.04 lunar mass.
The Moon surface total area is almost equal to Africa.

Most of the asteroids are just stones.

Largest asteroids (owning almost all asteroid belt mass) are hundreds of kilometers large, so almost all asteroid belt mass is hidden at tens of kilometers depth and will stay unavailable.

Small asteroids unlikely can contain enough treasures to pay for the expedition,

At least one known Eldorado?

Asteroid mining never pays for the expenses unless the expenses are ALREADY paid.

QED: people already living in massive rotating space habitats with constant 1g acceleration scifi spaceships that either do not use propellant or are ridiculously efficient with it.

Edited December 6, 2020 by Spacescifi

[kerbiloid]

3 hours ago, Spacescifi said:

Asteroid mining never pays for the expenses unless the expenses are ALREADY paid.

Why pay for that what will never pay for it?

[KerikBalm]

On 12/5/2020 at 2:01 PM, Spacescifi said:

My point is simply that it is very ineficient to use lasers for blast mining at all.

As mentioned, why would you blast mine at all?

Quote

At best they are not bad for burning, but blasting?

By burning, I assume you mean melting, and that will take the most heat.

For effect on target, you get the best damage per unit energy if you cause kinetic effects on your target.

Quote

I don't care what your ship's drive is, if it is a rocket with known propellant and engines, even nuclear, thrust will suffer.

Nuclear thermal can have great thrust.

You make a lot of sweeping statements with no facts or math behind them.

[snip]

Edited December 7, 2020 by Vanamonde

[Spacescifi]

On 12/5/2020 at 10:40 PM, KerikBalm said:

As mentioned, why would you blast mine at all?

By burning, I assume you mean melting, and that will take the most heat.

For effect on target, you get the best damage per unit energy if you cause kinetic effects on your target.

Nuclear thermal can have great thrust.

You make a lot of sweeping statements with no facts or math behind them.

 

[snip]

You know (or should) I am discussing  blast lasers mounted on spaceships. The associated mass/weight of equipment for cooling and powering such a beast would lower  it's total thrust greatly. No matter the rocket engine used ro push it.

Thrust lowers automatically when mass pushed is high.

Why is it we have so we have such a high propellant to mass ratio with rockets?

[snip]

 

 

 

 

 

 

 

 

Edited December 7, 2020 by Vanamonde

[YNM]

What asteroid are we talking about ? As you know that we have both solid-body asteroids and rubble pile asteroids. Many asteroids fall on the latter than the former. Larger ones (from ten km above) are indeed monolithic (and by mass they'd stand out) but by the number of bodies most of them are going to be smaller, rubble-pile ones (largest suspected rubble pile is 253 Mathilde which measure about 50 km across). Some of the extremely small asteroids (only tens to hundred meter in size) are possibly whole rocks however.

[Spacescifi]

32 minutes ago, YNM said:

What asteroid are we talking about ? As you know that we have both solid-body asteroids and rubble pile asteroids. Many asteroids fall on the latter than the former. Larger ones (from ten km above) are indeed monolithic (and by mass they'd stand out) but by the number of bodies most of them are going to be smaller, rubble-pile ones (largest suspected rubble pile is 253 Mathilde which measure about 50 km across). Some of the extremely small asteroids (only tens to hundred meter in size) are possibly whole rocks however.

 

This is a profitable one if you already have the resources to get it and bring it around for processing 

https://www.google.com/amp/s/metro.co.uk/2019/06/27/gigantic-golden-asteroid-make-everyone-earth-billionaire-10075724/amp/

 

16 Psyche is a large asteroid discovered by the Italian astronomer Annibale de Gasparis on 17 March 1852 from Naples and named after the Greek mythological figure Psyche. It is one of the dozen most massive asteroids, containing about 1% of the mass of the asteroid belt, and is over 200 kilometres in diameter. 

 

NASA has no plans to bring the massive asteroid home and lacks the technology to mine it for its valuable metals. Researchers told CBS News in 2017 that they don't plan to take advantage of the value of the asteroid's composition. 

Edited December 6, 2020 by Spacescifi

[YNM]

1 hour ago, Spacescifi said:

This is a profitable one if you already have the resources to get it and bring itaround for processing 

So 16 Psyche, 200 km across, likely the solid bodies... We'll send a probe to it in ~2022, arriving at 2026. It will have a lot of imagers, but sadly no lander (and no sample return).
Our best imagery so far ?

We'll do a sample return of Phobos (~ 6 km diameter), likely a former asteroid, in 2028 (arrival on body 2025).

But just to be clear, the only unadulterated asteroid sample we have back at home are the rubble pile ones. Since we currently have exactly one of them (325 m diameter) and only micrometer-sized at that:

and the other one is just arriving (1 km diameter) :

Trying to determine what's best to try and mine a celestial body we haven't even sent a probe to is going to be harder than you think. Honestly given what asteroid you're proposing we'd most likely do it much like how it would hypothetically be done on a planet or major moons, namely with actual bases on the surface. But the smaller rubble piles might simply be scooped in to a processor.

Edited December 6, 2020 by YNM

[KerikBalm]

[snip]

Quote

You know (or should) I am discussing  blast lasers mounted on spaceships.

Ok... And this relates to what I said how?

Quote

The associated mass/weight of equipment for cooling and powering such a beast would lower  it's total thrust greatly.

Do you mean thrust to weight ratio? or more properly, acceleration?

You need to be precise when discussing technical subjects

Quote

Thrust lowers automatically when mass pushed is high.

No, it doesn't, TWR does

Quote

Why is it we have so we have such a high propellant to mass ratio with rockets?

[snip]

Edited December 7, 2020 by Vanamonde

[KerikBalm]

[snip]

Yet, if you meant dry mass, you make inaccurate statements (high dry mass just means a higher thrust engine is required, its not a case of "no matter the engine").  You mention cooling stuff and that thrust will suffer, so I thought that you meant that cooling limits power output of the laser, and thus the thrust of a laser engine. It doesn't make sense if you aren't talking about lasers as an engine. FWIW, if a laser if 50% efficient, and its powerful enough to achieve kinetic effects, then it just produces 2x as much heat for the same kinetic effect as a 100% efficient railgun, so its actually not that bad. If you are trying to achieve kinetic effects, a pulse laser's heat sink is most important, and radiators only affect firing rate, but for a single large blast, you only need a sufficient heat sink.

So when you said thrust, it seems you meant high dry mass. [snip]

Quote

Asteroid mining never pays for the expenses unless the expenses are ALREADY paid.

QED: people already living in massive rotating space habitats with constant 1g acceleration scifi spaceships that either do not use propellant or are ridiculously efficient with it.

I really have no idea what you meant here, and I cannot even formulate a guess as to how those two statements are linked.

The QED of the second statement seems to indicate that the point of this thread was to show  "people already living in massive rotating space habitats with constant 1g acceleration scifi spaceships that either do not use propellant or are ridiculously efficient with it", but I suspect you meant what the abbreviation  "eg" (or maybe "ie") means. [snip]

Edited December 7, 2020 by Vanamonde

[Meecrob]

[snip]

This forum is a cool place precisely because people who are knowledgeable about topics are willing to explain them rather than drop a wiki link.

Edited December 7, 2020 by Vanamonde

[YNM]

15 hours ago, Meecrob said:

This forum is a cool place precisely because people who are knowledgeable about topics are willing to explain them rather than drop a wiki link.

And it's not like we only have our imagination to play with anymore, like it would be for someone in the victorian era to imagine space travel - we have 5 robotic sample return mission (Genesis, Stardust, Hayabusa, Hayabusa2, OSIRIS-REx) from asteroids, comets and solar wind, 4 robotic sample return mission (Luna 16,  20,  24 and Chang'e 5) and 6 manned (Apollo 11, 12, 14, 15, 16, 17) from the Moon, and one sample prepared for Mars (taken with Mars 2020 rover). If you really want to plan ahead, then use the realistic data we've gathered.

Edited December 7, 2020 by Vanamonde

[Spacescifi]

9 hours ago, YNM said:

And it's not like we only have our imagination to play with anymore, like it would be for someone in the victorian era to imagine space travel - we have 5 robotic sample return mission (Genesis, Stardust, Hayabusa, Hayabusa2, OSIRIS-REx) from asteroids, comets and solar wind, 4 robotic sample return mission (Luna 16,  20,  24 and Chang'e 5) and 6 manned (Apollo 11, 12, 14, 15, 16, 17) from the Moon, and one sample prepared for Mars (taken with Mars 2020 rover). If you really want to plan ahead, then use the realistic data we've gathered.

 

Is it not obvious that I have?

Asteroid mining is most profitable when man already is living in space with large populations.

Which itself makes little sense...unless in a scifi setting with overpopulation due to long life span or a ruined homeworld.

Any scifi setting must have scifi abilities that make whatever they do viable and reasonable.

Manned asteroid mining will only make sense when it does.

Robotic is a given, but also boring for scifi.

Edited December 7, 2020 by Spacescifi

[YNM]

1 hour ago, Spacescifi said:

Asteroid mining is most profitable when man already is living in space with large populations.

Which itself makes little sense...unless in a scifi setting with overpopulation due to long life span or a ruined homeworld.

Any scifi setting must have scifi abilities that make whatever they do viable and reasonable.

Manned asteroid mining will only make sense when it does.

Robotic is a given, but also boring for scifi.

I'd wager more that space exploration is partly motivated by trying to solve looming problems back at home, or a way to show the world what they can really do. For example, autonomous robotic missions and equipments shows that you can solve problems related to labour shortage all on your own without resorting to foreign labour (we still have a way to go before having autonomous probes, most are still pre-programmed, but autonomous equipments are coming in). Manned space exploration shows that you can do the same back on Earth too, regardless of the terrain or environment (even if said environment involves extreme coldness or thin atmospheres at high altitude). If you can go and aim at an asteroid tens to hundreds of millions of kilometres away and come back, you could probably aim any part of the Earth's surface (and beneath) as easily. If your outpost on another celestial body can survive with very few resource input, largely relying on recycling and highly-efficient processes, that means you can do the same back on Earth as well.

Living in space in large proportions, while it would take quite a while to, is a likelihood we might have to get to. It's clear that interest in finally keeping a permanent presence on another celestial body is now present, with new players in the 'space race' starting to gain a pace. The surface of the Earth might change a lot in the coming decades, making many places not quite ideally habitable. And while there's a lot of surface of the Earth, there's only so much of it before you run into another party. While elemental resource scarcity are currently far away, and it's likely to remain as such, land scarcity is a different story altogether. Keeping your potential future space plots in hand would be needed in short timescales, before we finally do run out of space down here. At least expect it to be the case after we've scrambled for Antarctica or something.

Edited December 7, 2020 by YNM

[Vanamonde]

A personal argument has been removed from this thread. Please stick to the subject rather than attack each other personally, and do not carry over arguments from one thread into another.