demanbmore t1_j9ti1co wrote
Reply to comment by zephyer19 in Could they move ice from the planets to Earth? by zephyer19
Can't catapult people into space - the forces generated by the catapult system exceed 10,000g. People can usually handle about 9g before bad things start to happen and will become mush well before hitting 10,000g. Pretty much restricted to non-compressible things if we're going to launch them via catapult.
And then there's the return trip, deceleration, landing or splashdown, etc. All of these things require energy and are replete with opportunities for catastrophic failure. And you'd need thousands of ships returning each day to get any meaningful amount of water (see below).
As far as where to put the salt, back in the ocean is fine. It's simply not possible to remove so much fresh water from the oceans that putting the salt removed back into the oceans will make a significant (or really even noticeable) difference. Sure, the actual dumping points will be impacted, but the oceans generally will not be.
Here's the basic math:
The average person used 3,800 liters per day of water. Let's say that we learn to reduce that by 75% (which is highly unlikely). That takes it down to about 1,000 liters per day per person, or 8 trillion liters per day worldwide. Now let's assume we want to get 10% of that from extraterrestrial sources - that's 8 hundred-million liters of water a day, every day, which is 8 hundred million kgs brought in each day every day (or 8 hundred thousand metric tons). The largest payload we can launch currently from Earth in one launch is about 17 metric tons. Granted, we're not launching from Earth is we're harvesting ice off-planet, so let's assume we can (somehow) launch 100 times the amount from somewhere else (a silly assumption, but we'll doit anyway). So now we can lift (from Mars or wherever) 1,700 metric tons of ice/water on one launch. To supply just 10% of the GREATLY reduced water consumption needs of the Earth under these incredibly favorable and ridiculous assumptions, we'd need about 500 unbelievably huge ships (each one carrying a payload measuring 1,700m x 1,700m x 1,700m, or nearly 5 billion cubic meters) delivering ice/water each day, every day. The Astrodome - a huge stadium that fits 68,000 people, is only 1.2 million cubic meters in volume, meaning we'd need to bring over 4,166 Astrodomes worth of water just to meet 10% of the needs (again assuming great reduction from current usage). And somehow we'd need to launch enough ships, parts, people, fuel, etc. to carry on this mission.
And even if this was a one-time project to just add to the water supply on Earth, the new water would immediately join the same water cycle as the existing water, so we'd have to be desalinizing and or decontaminating the newly arrived water as well.
Nothing changes the bottom line - it will always be easier and cheaper and more environmental friendly to deal with the water already on Earth than to try to get a meaningful amount from elsewhere.
zephyer19 OP t1_j9u7k3v wrote
Well, the catapult is for equipment, mainly satellites. If it works, no telling what they have develop out of it later.
I totally disagree about putting salt back in.
Enough countries start desalination then that much more salt well go into the ocean.
Are you taking into account population growth? Loss of water resources? That some areas are becoming deserts? Loss of aquifers?
I live along a river in Montana that is known for white water and trout fishing. Many houses have been built by the river the last ten years and drop in water levels on the river had been noted.
The major conclusion is houses, like mine have their own well and has dried out the area, so water is flowing from the river to our wells.
As one man said, "How many straws can you put in the glass before the glass is dry?
Developing technology to go get water may not be cheap, easy, or even all that practical but, we may not have a choice.
demanbmore t1_j9ubkhl wrote
Sure, stick enough new straws in an ancient aquifer that takes decades to centuries to recharge and you'll drain it dry. Nothing noteworthy there. But so what? That just means there's not enough water to go around in your part of the world, it doesn't mean the amount of water in the world has decreased. It's just not going downstream in the river like it used to. The fix there is not to drag water in from outer space and drop it upstream from you and all the other houses. The fix is in recognizing that in your area, there's not enough resources to go around and some sort of restrictions are called for. If the community is unwilling to do that, they may face a choice between spending millions to get water from somewhere within a few hundred miles or spending trillions to get water from a few hundred million miles away. That's the difference between making a deal with some Canadian water authority and building canals or pipes to increase supply, or building and launching hundreds of spacecraft on some decades long mission to drop a bunch of icebergs upriver (that will eventually flow downstream and then you'll need to repeat the cycle again and again).
As far as salt goes - there's about 321 million cubic miles of ocean water in the world. There's about 14 million cubic miles of all other water combined - fresh water, water locked in glaciers and ice sheets, and groundwater. That's a 23:1 ratio of ocean water to all other water combined. At most, there's about 2.2 million cubic miles of non-ice locked freshwater, a 146:1 ratio of ocean water to fresh water. If we desalinated enough ocean water to double the amount of available freshwater, we'd have extracted salt from only 0.68% of the ocean. Drop that back in the ocean - it won't even be noticed (expect the immediate areas where the salt goes back in). And then keep in mind that all this additional freshwater we extracted through desalinization just gets back to the oceans in the normal water cycle, so it very quickly "rebalances" and is unchanged from before the desalinization.
Population growth, aquifer exhaustion, etc. - those are resource allocation issues, not "bring water in from Mars" issues. Drought in one area or another isn't due to not having enough water on the planet, it's due to regional weather (climate), land use, and resource use, planning and conservation. There's plenty of places that deal with too much water for their needs, but it's super expensive to get that water from there to you (but still far cheaper than space harvesting).
There's no amount of space ice-gathering or ocean desalinization that will help your river, well and aquifer issues without transporting that water upstream from you (and then upstream from whoever is upstream from them, etc.). You're not suffering from a lack of water generally, you're suffering from uncontrolled growth overwhelming an ecosystem (specifically an aquifer) that has existed without issues for likely millions and millions of years. It's past the time to stop building houses along that river and dropping wells, at least if the water flow in the river is important.
zephyer19 OP t1_j9v6ci3 wrote
And when all of that runs out, then what?
We are already seeing its effects on places like El Salvador. People leaving there and coming here because they can't raise crops.
I did hear an interesting story on today's NPR's Here and Now and indoor farming.
demanbmore t1_j9v7382 wrote
You've hit the nail right on the head in your response. What we need to do is get water to El Salvador. If you don't want people leaving El Salvador, it is much much much much much much much much easier and cheaper to get water from the Atlantic Ocean or the pacific Ocean or even the Indian Ocean or the Arctic Ocean, desalinate it, and pipe it or ship it to El Salvador then it could ever be to get that water from a planet hundreds of millions of miles away. The water on earth isn't disappearing or running out. It just moves around. There's no place for it to go other than somewhere else on the planet. Solutions like urban indoor farming, reduce water consumption locally and have a role in solving this problem. But trying to build some sort of infrastructure to transport trillions and trillions and trillions of gallons of water over months or years long journeys from other planets do not. I'm not understanding where you're coming from. You have a solution in search of a problem, and honestly, it's not much of a solution.
zephyer19 OP t1_j9vi6l7 wrote
I hear a lot about desalination. Nobody answers the question about salt really.
What if you don't have the water to ship around?
demanbmore t1_j9vj57l wrote
The answer is dump it back in the ocean. I get you don't like that answer, but that's the answer.
And you can pull a practically unlimited amount of water out of the oceans. Any amount humans can conceivably need.
zephyer19 OP t1_j9w230y wrote
Can't put in too much salt, can't put in too much plastic, can't put in too many chemicals...
Is the ocean just one big sewer?
Anyway, thanks for answering the question with science.
demanbmore t1_j9xyt6a wrote
You're jumping to conclusions and making assertions way beyond what I'm saying. We're not ADDING salt to the oceans, we're just putting back what we took out. That has nothing to do with dumping plastics or other wastes in the ocean. Things would be very different if we mined salt from Mars and dumped that into our oceans - that would be adding things that didn't come from it just a few days or weeks ago. And understand that all the freshwater we removed would make its way back to the oceans too - that's how the water cycle works. That's the beauty of desalinization - we're just borrowing the freshwater from the ocean for a brief period of time again and again and again, which is what the normal process of evaporation, rainfall/snowfall, and runoff does constantly. The reason desalinization isn't practiced more often is because its energy intensive and expensive, but it's far less energy intensive and expensive as building a fleet of interplanetary mining and transfer ships.
zephyer19 OP t1_j9ypbew wrote
The Caspian Sea. Once it was the 4th largest body of fresh water in the world.
Now it has been badly shrunken and is very polluted and becoming too salty to support life and it isn't the only lake.
The Great Salt Lake and the Dead Sea are vanishing. Of course, that water could not be used for anything but, the winds blow and blows the salt across cities and agricultural lands.
The water does not always make it way back.
That is really bad for agricultural land, killing it off and increasing the problems.
Ocean life is struggling now, reefs are dying, fish stocks depleted. Now you want to increase the amount of salt.
Anyway, I can see if being able to get ice from other planets and finding a way to process it could be helpful in future space stations and exploration.
Even if my opinion is the dumbest thing you have ever read, I thank you for the informed conversation.
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