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Old 11-03-2019, 01:21 AM
Shalmanese is offline
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What's the cheapest way to bring something from LEO back to earth?


Assume we manage to tow an asteroid from outer space into LEO and we establish a robotic mining colony there to extract platinum and nickel. How do we get the minerals from LEO down to earth affordably while also not turning them into high velocity projectile bombs?

Do we currently have theoretical plans for how to bring large amounts of material down from LEO in an economical manner that allows us to recover the material and integrate it into our supply chains?

Last edited by Shalmanese; 11-03-2019 at 01:23 AM.
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Old 11-03-2019, 01:31 AM
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Well, if it's metal, it doesn't need a soft landing. In principle you could build disposable heat shields and have the metal chunks make controlled craters in a target zone on land.

In reality, you mentioned a key precondition. A robotic mining colony. Really sophisticated robots, right? So advanced that the same software and hardware backend allows for robots that build other robots on earth, right? This makes the robots dirt cheap, right?

Well, why not have the same robots mine for materials on earth? They could work in deep mines, mines that are too hot for humans and full of safety hazards that clever robots have no trouble with.

Some metals, such as platinum and iridium, are extremely rare on earth. In that case, you could build large shuttle rockets, similar to the SpaceX BFR - robots would build them - and soft land a few dozen tons of metal per round-trip. Everything else, robots would mine on earth.
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Old 11-03-2019, 01:38 AM
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Heat shields and parachutes have worked well and were inexpensive. Big chunks of metal don't need a very soft landing or that much heat protection so the method should be less expensive than when sending humans back to earth.
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Old 11-03-2019, 09:51 AM
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Heat shields and parachutes have worked well and were inexpensive. Big chunks of metal don't need a very soft landing or that much heat protection so the method should be less expensive than when sending humans back to earth.
Right. And one cost savings is to leave the parachutes off. Let the whole assembly hit a higher terminal velocity relative to it's aerodynamic profile.
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Old 11-03-2019, 02:00 PM
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Right. And one cost savings is to leave the parachutes off. Let the whole assembly hit a higher terminal velocity relative to it's aerodynamic profile.
You need some control or a heavier heat shield to keep it from staying at hypersonic speeds on the way down. And the result of a misplaced landing or failure to reduce velocity creates enormous economical and safety risks. Parachutes only help to mitigate those risks. Cost was the object here, assuming we don't just want massive fireballs falling out of the sky then heat shields and parachutes are the way to go. For a higher cost the material could be shaped into a controllable aerodynamic shape where the landing spot can be more selective, even if it doesn't need a soft landing like a human craft.
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Old 11-03-2019, 03:31 PM
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Right. And one cost savings is to leave the parachutes off. Let the whole assembly hit a higher terminal velocity relative to it's aerodynamic profile.
I expect that the cost of the parachutes is less than the value of the metal that would be burned up without one. If so, the parachutes are a good investment.
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Old 11-03-2019, 05:15 PM
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I expect that the cost of the parachutes is less than the value of the metal that would be burned up without one. If so, the parachutes are a good investment.
That would probably depend on where the parachutes come from. If they have to be shipped up from Earth, then the cost of launches could make them more expensive.
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Old 11-06-2019, 01:36 PM
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I expect that the cost of the parachutes is less than the value of the metal that would be burned up without one. If so, the parachutes are a good investment.
Sigh.

DO you really, *REALLY* think that a parachute will help prevent part of the metal from burning up?
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Old 11-06-2019, 04:25 PM
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Right, the parachute can only be deployed once the big burning phase is over. Look at old Apollo films and such. Big hot ride until it slows down. Then pop the chute. Pop it earlier and the chute burns.

A chute is good for making sure the pod doesn't go too deep into the ground on impact. It also allows better visual tracking if the radio goes dead. And the chute itself might be easier to spot after landing.
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Old 11-03-2019, 10:10 AM
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Maxim 11: Everything is air-droppable at least once.

Last edited by DesertDog; 11-03-2019 at 10:11 AM.
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Old 11-03-2019, 10:20 AM
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....we establish a robotic mining colony there to extract platinum and nickel. How do we get the minerals from LEO down to earth...
Not sure I understand the question completely. Minerals and Ores both have the sought metal in them but the Ores have them in concentrations economic for extractions.

Also, you say that the robotic colony extracts the metals. If they have already extracted the metal, why wouldn’t they just send the metal to earth ? Why are they sending the minerals ?

Also, I think while robotics maybe advanced enough to make this look reasonable, mining and metallurgy is very primitive to do any sort of extraction in space. Most of the ore processing on earth relies on gravity separation, water washing, heating things up or reducing them with other chemicals - things that you cannot do in space based on today’s technology.
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Old 11-03-2019, 10:27 AM
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A...tow an asteroid from outer space into LEO and we establish a robotic mining colony there to extract platinum and nickel...
If we had the technology to do these things, the last step would be trivial by comparison. Reentry (or entry) from LEO just takes a tiny bit of delta-V, and heat shield and structural integrity to make sure it doesn't burn up or break up during reentry.

Actually it won't even matter if they broke up, as long as they don't burn up. Just designate a remote desert as a target area, and drop lumps of metal onto it. It'll get mixed up sand and dirt, but we've got robots that can refine metals, right?
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Old 11-03-2019, 01:03 PM
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Plus, of course, a big part of why you'd want to mine asteroids is to get the raw materials to make more space infrastructure. Why go to the trouble of sending it down here at all, when it's more useful up there?
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Old 11-03-2019, 01:34 PM
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Plus, of course, a big part of why you'd want to mine asteroids is to get the raw materials to make more space infrastructure. Why go to the trouble of sending it down here at all, when it's more useful up there?
Some metals are going to be more valuable on Earth than in space. For example, relative to Earth, asteroids have more platinum-group metals and there's likely to be very limited use for them in constructing space habitats and other infrustructure. But there are many industrial uses for them and probably would be more if their prices come down somewhat. The factories that use those metals are on Earth, not in space.
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Old 11-03-2019, 07:07 PM
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If the asteroids have water or some such suitable gas or fluid, you can use it to actively cool the Heat shield of the vessel bringing it.

Similar cooling techniques are used in cooling gas turbines blades in +2000F temperatures. The surface is made porous by drilling holes and the cooling fluid is made to flow outward through these holes (pores).

https://en.m.wikipedia.org/wiki/Turbine_blade#Cooling
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Old 11-04-2019, 12:18 AM
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If the asteroids have water or some such suitable gas or fluid, you can use it to actively cool the Heat shield of the vessel bringing it.
Only undiffrentiated asteroids would have any meaningful water. Only nickle-iron core fragments from blasted diffrentiated asteroids would have reasonably enriched sidreophile elements. (Undiffrentiated asteroids would have higher concentrations than in a random handful of Earth soil, but very unlikely enough of a concentration to make landing the thing on Earth profitable. But then again, you can almost 100% likely say the same about core chunks. It would probably always be cheaper and easier to make mines multiple miles deep in the Earth's crust.)
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Old 11-03-2019, 07:18 PM
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Bring it back on SpaceX Starships, which would presumably be coming back with 50 ton load capacity. Most of the time I would imagine those rockets going up full and coming back empty, so why not load them with gold and platinum first?

if they fly 10 times a month, you could bring back 500 tons of material per month.
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Old 11-03-2019, 10:02 PM
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you could bring back 500 tons of material per month.
That sounds like a big number, but it is very small compared to the size of most industries. The US steel industry alone, for instance, produces 7000 tons a month. The Chinese steel produces 1,000,000 tons a month.

Space metals would require millions of tons monthly to be economically viable.
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Old 11-03-2019, 10:24 PM
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What about all that space-mined helium? Seems like you would want to bring the tanks back in one piece.
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Old 11-03-2019, 10:50 PM
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That sounds like a big number, but it is very small compared to the size of most industries. The US steel industry alone, for instance, produces 7000 tons a month. The Chinese steel produces 1,000,000 tons a month.

Space metals would require millions of tons monthly to be economically viable.
2017 global production platinum: 8 million ounces. https://www.thebalance.com/the-10-bi...ducers-2339736 Or 400 tons, at 10 troy oz to the pound.

For gold, it's roughly 2500-3000 tonnes a year. https://www.gold.org/about-gold/gold.../how-much-gold

Neodymium is a bit more common, with a mine in Australia producing around 10,500 tonnes a year. https://investingnews.com/daily/reso...ing-countries/

This assumes we don't find a diamond asteroid, perhaps as a chunk of some gas giant core. Edit, the point is, if certain minerals are more readily found in their pure states in space, being restricted to 50 tons at a time may not be a dealbreaker.

What would a large deposit of Helium-3 go for?

Last edited by Gray Ghost; 11-03-2019 at 10:51 PM.
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Old 11-04-2019, 01:27 AM
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What would a large deposit of Helium-3 go for?
The price on Earth is about $12000 per gram right now, and it's not getting any cheaper. Obviously unloading a large deposit would depress the price by a significant factor.

Last edited by DPRK; 11-04-2019 at 01:28 AM.
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Old 11-04-2019, 11:32 AM
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The price on Earth is about $12000 per gram right now, and it's not getting any cheaper. Obviously unloading a large deposit would depress the price by a significant factor.
I'm not sure how you can have a large deposit of He-3. It's a noble gas with a boiling point of 3.2 Kelvin. There's only so much of it that can be trapped in rock. A surface exposed to the solar wind accumulates He-3 but we're talking tens of ppb (parts per billion). Meaning you need to process a thousand tons of regolith to get maybe one ounce (30 grams) of He-3.
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Old 11-24-2019, 09:49 PM
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Edit, the point is, if certain minerals are more readily found in their pure states in space, being restricted to 50 tons at a time may not be a dealbreaker.
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The stuff we might bring back to Earth has to be very valuable. Gold, Platinum, other extremely rare elemenfs. We only produce 2500 tons per year or so worldwide. That 500 starship loads per year.
The problem is the overhead cost of mining in space. Millions of tons would be needed to cover the costs of operations to make the price of space minerals comparable to what's available on earth.
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Old 11-25-2019, 03:58 PM
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The problem is the overhead cost of mining in space. Millions of tons would be needed to cover the costs of operations to make the price of space minerals comparable to what's available on earth.
This is only true if all the stuff that's mined is being brought back to Earth. But what about the case where almost everything mined (water, carbon, iron, aluminum, etc.) is being used in space and a relatively small amount of stuff that can't be used up there comes out as a byproduct or for very little additional cost. It might be worthwhile to bring some of that byproduct (e.g. platinum or perhaps some rare earth elements such as neodymium) back if it can be done cheaply enough.

However, not gold. For that, you just store it in an "orbital vault" and sell pieces of paper giving ownership to a certain amount of space-gold. It wouldn't be all that different than how a lot of gold is owned right now.
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Old 11-04-2019, 12:03 PM
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That sounds like a big number, but it is very small compared to the size of most industries. The US steel industry alone, for instance, produces 7000 tons
Missing some zeroes there. Like 3.
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Old 11-04-2019, 12:31 PM
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"Belters" is a common science fiction term (especially in Niven's Known Space series) for humans who live in the asteroid belt, with an industry built primarily around mining. "Groundhogs" is presumably derogatory slang for humans who live on (and probably have never left) Earth.
I'm aware of who Belters are in SF. I was asking who they were in the real world. The answer is they don't exist and will probably never exist.
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Old 11-05-2019, 10:41 PM
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I'm aware of who Belters are in SF. I was asking who they were in the real world. The answer is they don't exist and will probably never exist.
"If a senior scientist says something is impossible, they're probably wrong."
--One of AE Clarke's Laws.

The OP assumed the existence of technologies to push asteroids around and robotically mine them. I figured the existence of such technologies implies changed human societies, so why not use the Niven model? It's essentially economic: what's profitable will happen.

No, Belters don't yet exist, and neither do fusion drives. I'll not bet against either.
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Old 11-24-2019, 09:41 PM
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Missing some zeroes there. Like 3.
No, 7000 per month is correct. The post is in response to 500 ton capacity being available on current SpaceEx vehicles returning.

https://tradingeconomics.com/united-...eel-production
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Old 11-04-2019, 01:35 PM
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That sounds like a big number, but it is very small compared to the size of most industries. The US steel industry alone, for instance, produces 7000 tons a month. The Chinese steel produces 1,000,000 tons a month.

Space metals would require millions of tons monthly to be economically viable.
No one is going to bring iron ore or steel to Earth. It's far too inexpensive to warrant asteroid mining. We'll mine those things for sure, hut we'll use them in space, not on Earth.

The stuff we might bring back to Earth has to be very valuable. Gold, Platinum, other extremely rare elemenfs. We only produce 2500 tons per year or so worldwide. That 500 starship loads per year.

Platinum is even better. Annual platinum production is only about 150 tonnes. Platinum is currently about $30,000 per kilo. So a single Starship load could bring back about $23 million in platinum, which would more than pay for the entire flight.

I can imagine an economy like this: A space mining company finds a gold and platinum rich asteroid, and begins processing. They ship the stuff back to a depot in low Earth orbit, then simply offer a discounted spot price for anyone who wants to buy it from orbit. Let the market figure out the best way to return it to Earth. Some company might come up with a fantastic method for returning it cheaply and make a fortune, Others like SpaceX realize that after each satellite launch mission they could rendezvous with the depot, pick up a load of metal, and bring it back for extra profit.

But ultimately, we don't know how it will work. Once a market has been established there will be innovation and competition for ways to use the materials in space or on Earth. We are certain to be surprised by what this market ultimately looks like.
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Old 11-04-2019, 04:13 PM
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So a single Starship load could bring back about $23 million in platinum, which would more than pay for the entire flight.
Your math is off. 50,000 kg * $30,000/kg = $1.5 billion.

Also, as far as I know Starship should be able to land with ~100 t payload. It may require launching without a payload, though. Either way, the launch costs will be negligible compared to that quantity of platinum (or gold).
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Old 11-03-2019, 09:40 PM
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Even if you're sending up Starships anyway, it'll still be cheaper to just crater the metal than to bring it back gently. Whatever system the Starship uses for landings, it won't be designed for that kind of cargo load.
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Old 11-04-2019, 01:22 PM
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Even if you're sending up Starships anyway, it'll still be cheaper to just crater the metal than to bring it back gently. Whatever system the Starship uses for landings, it won't be designed for that kind of cargo load.
Starship is designed to land with 50 tons of cargo, as I understand it. My point is that if they are coming back and landing empty, it's a freebie to load them up with expensive stuff first.

Just letting the stuff fall to Earth is not free. They would have to be encased in some sort of heat shield, which presumably would have to be manufactured in space from the slag of the asteroid or something, then you'd need a de-orbit burn, then you'd have recovery operations.

With a Starship, you just land the stuff, and you're done. If your ship was coming back empty anyway, it's a free ride other than docking in space - which you'd have to do to prep the stuff for a re-entry anyway.

For very large quantities that exceed the limits and availability of current rocket transport, sure. Find a big open desert and drop the stuff on it.
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Old 11-03-2019, 11:12 PM
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Oh, and cheapest way to deorbit the stuff is probably to process some of it, and expel the slag as a reaction drive to deorbit the ore.

Spin a silica blanket around the product. Maybe deploy some high drag apparatus that deploys after reentry? I was thinking of solid helical fins on the payload, so the payload could spin down like a seed pod?
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Old 11-04-2019, 01:15 AM
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I think we're overanalyzing. Built the rentry vehicles out of the core material with very high surface area to weight. Air resistance to slow the object, spread over a large area, means much less heat and less loss. Note the SpaceX boosters fall from a great height and only have to use their rockets to slow down when they are close to landing, since they are essentially empty cans with a high drag compared to weight, so a low terminal velocity. heck, build them shaped like giant windmills so they float to ground at a moderate speed spinning like a maple seed.
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Old 11-04-2019, 01:50 AM
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Assume we manage to tow an asteroid from outer space into LEO and we establish a robotic mining colony there to extract platinum and nickel.
Who thinks Belters will allow groundhogs to grab their resources? If they do, wouldn't the tech implicit in asteroid-towing also be sufficient to assure soft landings in a gravity well? Easier, why not fashion vast parachutes and massive heat shields from asteroid detritus? Use the rest of the detritus to fabricate outer-space infrastructure.
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Old 11-04-2019, 05:40 AM
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Who thinks Belters will allow groundhogs to grab their resources?
Who are these Belters of which you speak?

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If they do, wouldn't the tech implicit in asteroid-towing also be sufficient to assure soft landings in a gravity well?
Not at all. It's much easier to push things around in orbit than to soft land on a high gravity planet.

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Easier, why not fashion vast parachutes and massive heat shields from asteroid detritus?
Parachutes are usually made of nylon although probably could be made of other polymers. How do you easily make polymers from the stuff found in asteroids? Some asteroids have lots of carbon, but it's not in the form of monomers.

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Use the rest of the detritus to fabricate outer-space infrastructure.
Detritus is stuff that you can't use for anything except reaction mass. Anything you can use to make space infrastructure is not detritus. Iron, aluminum, copper and some other metals are useful for that. They're far more valuable in space than they are on Earth. The only metals you want to bring down to Earth are ones that aren't very useful for infrastructure but are valuable on Earth.

Last edited by dtilque; 11-04-2019 at 05:41 AM.
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Old 11-04-2019, 08:00 AM
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Parachutes are usually made of nylon although probably could be made of other polymers. How do you easily make polymers from the stuff found in asteroids? Some asteroids have lots of carbon, but it's not in the form of monomers.
Glass can be spun into fibers. That includes all sorts of silicate compounds. Bright S (silicacaseous) asteroids are the asteroids closest to earth.

ETA: Silicates can also be used for heat shields.

Last edited by TriPolar; 11-04-2019 at 08:01 AM.
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Old 11-04-2019, 07:22 AM
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"Belters" is a common science fiction term (especially in Niven's Known Space series) for humans who live in the asteroid belt, with an industry built primarily around mining. "Groundhogs" is presumably derogatory slang for humans who live on (and probably have never left) Earth.
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Old 11-04-2019, 07:58 AM
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Here's a whacko idea for slowing down items dropped from LEO without using heat shields or parachutes.



Laser Propulsion.



I worked on Arthur Kantrowitz' plan to send things up from the Earth (actually, he suggested elevated spots, like plateaus and mountaintops) to LEO by using a series of pulses from ground-based lasers. This was NOT using light pressure -- the light pulse would evaporate a metered amount of ablative material (ice, ideally), and the succeeding pulse would feed energy into it via inverse bremstrahlung that would expand it and provide oomph, something called a Laser Sustained Detonation wave*.

If it works going up, it would work as well going down. Even better, arguably, because you only have to slow the descent, not push the whole load against gravity.

The great part is that it's basically a rocket that doesn't use explosive and dangerous materials, and all the heavy parts get to stay on the ground. The problem is that you have to be extremely careful in your aiming. And you use an awesome amount of power, since the lasers involved aren't very efficient. But they might be able to fix that.


The idea of ground-to-orbit laser propulsion of this sort has been used in science fiction for decades -- Jerry Pournelle's High Justice; Michel Kube-McDowell's The Quiet Pools, Dean Ing's The Big Lifters, and my own The Flight of the Hans Pfaall.


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






*I'm sure the acronym LSD is pure purely fortuitous.
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Old 11-04-2019, 10:35 AM
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Here's a whacko idea for slowing down items dropped from LEO without using heat shields or parachutes.



Laser Propulsion.



I worked on Arthur Kantrowitz' plan to send things up from the Earth (actually, he suggested elevated spots, like plateaus and mountaintops) to LEO by using a series of pulses from ground-based lasers. This was NOT using light pressure -- the light pulse would evaporate a metered amount of ablative material (ice, ideally), and the succeeding pulse would feed energy into it via inverse bremstrahlung that would expand it and provide oomph, something called a Laser Sustained Detonation wave*....
I've seen the videos of the small rigs using the tech to climb a tower or wire. CRACK-CRACK-CRACK-CRACK. How do they address the eye safety issues and what's the largest size they ever lifted with the tech?
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Old 11-04-2019, 12:30 PM
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I've seen the videos of the small rigs using the tech to climb a tower or wire. CRACK-CRACK-CRACK-CRACK. How do they address the eye safety issues and what's the largest size they ever lifted with the tech?
We used to zap dime-sized pieces of acetal plastic in our lab. as far as I know, the biggest item that's been lifted "in the wild" is one of Leik Myrabo's "Apollo Lightcraft", which are about the size of a volleyball and probably weigh about a pound. He shot them up into the sky using a pulsed carbon dioxide laser at White Sands. When they shut off the laser and it fell, they caught it in a net. Of course, that's only for testing -- they envisioned sending up a three-man crew or equivalent, eventually.

The lightcraft differed from the ablation method we were using in that there was no material to be ablated -- the bottom part of the craft and a special ring around the outside were highly polished mirrors that focused the light onto a sample of air and used the ambient atmosphere as the material heated. Obviously, this would only work as long as the atmosphere held out. The idea was to get the craft moving to the necessary velocity while still in the atmosphere. Since you can continuously feed in energy, it's not like Jules Verne's cannon in From the Earth to the Moon. You don't need one big acceleration at the start, squishing your payload into jelly.

According to https://en.wikipedia.org/wiki/Leik_Myrabo, the record flight was 10.5 seconds and achieving a height of 72 meters (236 feet).

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


we were working o a beam about 6" in diameter for our own efforts when the plug got pulled on the project.
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The makers of the GoPro have to come out with a model called the "Quid"

Last edited by CalMeacham; 11-04-2019 at 12:30 PM.
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Old 11-04-2019, 10:51 AM
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I worked on Arthur Kantrowitz' plan to send things up from the Earth (actually, he suggested elevated spots, like plateaus and mountaintops)...
That's why we need to buy Venezuela now with it's value bottomed out.
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Old 11-04-2019, 12:29 PM
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Here are statistics on global steel production:
https://en.wikipedia.org/wiki/List_o...eel_production
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Old 11-04-2019, 03:39 PM
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Ah, OK, Starship is designed to be able to take 50 tons on a round-trip, but some trips will be one-way deliveries (putting satellites into orbit), so you're thinking that you might as well take a cargo down, too.

The problem there is that "space" is not all one place. If you're launching a satellite, you're going to be in whatever orbit that satellite needed to be in to do whatever job it does. And that's probably a very different orbit than the orbit of your platinum depot. And changing orbits can be just as expensive as going into orbit to begin with.
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Old 11-04-2019, 04:15 PM
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Ah, OK, Starship is designed to be able to take 50 tons on a round-trip, but some trips will be one-way deliveries (putting satellites into orbit), so you're thinking that you might as well take a cargo down, too.

The problem there is that "space" is not all one place. If you're launching a satellite, you're going to be in whatever orbit that satellite needed to be in to do whatever job it does. And that's probably a very different orbit than the orbit of your platinum depot. And changing orbits can be just as expensive as going into orbit to begin with.
Oh for sure. But remember the economics here - A starship flight may eventually only cost a couple of million dollars. It might even make economic sense to fly dedicated missions up to the depot just to bring back gold and platinum.

You know, when we talk about how to do things in the future we always talk about it in sort of 'clean room' terms in the sense of debating the cheapest, best technology, etc. But that's not really the way things evolve. We never account for the complexity of how markets actually develop.

For example, here's a scenario that could lead to a 'spaceship only' transportation system - a company like SpaceX builds 10 starships per year (their planned rate, btw). These things are reusable, so after two years they have an inventory of 20. After three years, 30. If each one is good for 100 flights, they now have a capacity for 1000 flights per year while maintaining a fleet of 30. Maybe there is an initial market for that, but other entrants plus an eventual downturn in demand causes a large glut of rockets. By now (say, 10-15 years from now) the reusable rocket business is pretty reliable, and rocket flights are routine. Every day sees the launch of several rockets around the world.

Now a space mining company, which used a cheap starship flight to send a 100 ton miner to a metal rich asteroid, contemplates how to exploit its find. Bringing it back too fast will simply crater the market. It has to be brought back slowly enough to allow demand for the now-cheaper metal to grow as new uses are found.

There are other mining companies exploiting other asteroids, and they have the same problem. So they collectively realize that an answer is to restrict supply to Earth, much like OPEC. And the easiest way to do that is to start a lobbying campaign to make 'direct drop' return of cargo illegal, siting dangers to wildlife and people. Then you get laws passed against it, essentially giving the rocket companies a monopoly on metal transportation from orbit.

Sure, it's more expensive than it needed to be, but in this case that's a feature. Now space metal is being fed into the economy at a nice controlled rate designed to optimize profit as the price inevitably declines.

Of course, I could make up an equally plausible scenario for a future in which rockets are forbidden to bring back such cargo. For instance, if current cartels and mining interests put massive pressure on politicians to advocate a 'Space materials are for space' campaign, making it illegal to use space-based minerals on Earth. Too much disruption to existing markets. A real world example would be deBeers and other existing diamond mining concerns lobbying to make lab-grown diamonds carry an etched marking identifying them as 'not authentic'.

It's like the typical debates we have regarding the best place to colonize. We talk about Mar's better gravity than the moon, the moon is closer, Mars has an atmosphere and could one day be terraformed, whatever. In fact, there is only one criterion for the best place to colonize first: The place where there is profit to be made doing so. Nothing else matters. Until we identify a source of profit, we won't be colonizing anything in space. The math doesn't work.
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Old 11-04-2019, 05:39 PM
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The heat of re-entry is essentially the re=entry vehicle compressing the air ahead of it. Compress a gas, it gets hot. Compress it with a projectile going 17,000mph and it gets really hot. Thanks to Newton's laws, conservation of energy means the velocity of the mass is converted into heat, and the vehicle's speed - it's kinetic energy - is translated into heat. That's why anything with a high amount of air resistance - and empty can - will create less heat. The kinetic energy of a ton of nickel spread over 20 square meters will be the same as a blob a meter square - but will compress 20 times as much air 9approximately) and so the same energy over a wider area means less temperature increase overall.

(I would consider a shape like a globe simply because then aerodynamics doesn't matter - but if there's a way to make it autorotate to change the face presented to the heat of re-entry - a spinning globe - even better. Maybe we should drop volleys of giant nickel wiffle-balls into Death Valley.

Last edited by md2000; 11-04-2019 at 05:40 PM.
  #47  
Old 11-05-2019, 01:12 PM
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(I would consider a shape like a globe simply because then aerodynamics doesn't matter - but if there's a way to make it autorotate to change the face presented to the heat of re-entry - a spinning globe - even better. Maybe we should drop volleys of giant nickel wiffle-balls into Death Valley.
Spinning is bad for hitting the target zone. This is a curve ball on a grand scale.

The shape of the Mercury->Apollo capsules was really good. Highly stable, only the bottom needed shielding, predictable landing spot. Gordo nailed his landing the best of the Mercury flights. Despite losing a bunch of automatic attitude control and such and having to fire the retros on Glenn's count. Landed within 4 miles of the recovery ship. (Which is not the actual target but is a good measure of accuracy.)

Figure a 20 mile radius for unmanned, heavy blobs of metal. That's a pretty big area. If was a sphere, figure at least a 50 mile radius. And you have to have good tracking to figure out where it landed. You don't want to search an area that big. Radio tracking on a hot, rotating sphere coming out of the upper atmosphere isn't easy. It's trivial with a cone shape.
  #48  
Old 11-05-2019, 06:11 AM
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...we establish a robotic mining colony there to extract platinum and nickel. How do we get the minerals from LEO down to earth affordably while also not turning them into high velocity projectile bombs?...
See this page by a JPL physicist: "Rule 2: There is no commodity resource in space that could be sold profitably on Earth": https://caseyhandmer.wordpress.com/2...ions-in-space/
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Old 11-05-2019, 06:22 AM
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I'm glad the moon has not devolved into a robotic mining colony like some people were predicting would already be the case by 2015 or 2020 or whenever.
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Old 11-05-2019, 01:30 PM
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I'm glad the moon has not devolved into a robotic mining colony like some people were predicting would already be the case by 2015 or 2020 or whenever.
Why?
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