Author Topic: Lake Matthew - 2036  (Read 28339 times)

Offline Elmar Moelzer

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Re: Lake Matthew - 2036
« Reply #40 on: 04/12/2016 01:14 AM »
The main point was that it is possible to build nuclear reactors with a weight low enough to be feasible. It does not have to weight "hundreds of tons". Neither me nor Robobeat were suggesting to use an actual NERVA reactor for this. That said, there are trimodal nuclear rocket engines that are based on NERVA type reactors that switch modes to generate electric power from the same reactor and they are fairly compact as well and don't melt.
Regarding the problem of having a nuclear reactor sitting in a lake... People here were discussing the use of nuclear bombs to do this. Obviously a nuclear reactor would be preferable. They are generally very safe.
Either way, this discussion is in danger of getting too off topic for this thread.
« Last Edit: 04/12/2016 02:34 AM by Elmar Moelzer »

Offline gospacex

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Re: Lake Matthew - 2036
« Reply #41 on: 04/12/2016 01:40 AM »
The main point was that it is possible to build nuclear reactors with a weight low enough to be feasible. The point was that it does not have to weight "hundreds of tons".

No, it is not possible to build a gigawatt reactor which weighs "just a few tons".

Offline RocketmanUS

Re: Lake Matthew - 2036
« Reply #42 on: 04/12/2016 02:09 AM »
Then heat transfer to the air inside the dome from water fountain in lake from the deep water . Water that is cooled by the air is now on the surface of the lake?
Cooled water would be transferred first to the exterior of the dome.  Eventually it would flow to the lake, completing the loop.
Are you saying once the air is heated by the water fountain the water is then used by the people and to water the plants? later the water is filtered and sent back to the lake?
Mars and beyond, human exploration
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Offline Robotbeat

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Re: Lake Matthew - 2036
« Reply #43 on: 04/12/2016 02:10 AM »
The main point was that it is possible to build nuclear reactors with a weight low enough to be feasible. The point was that it does not have to weight "hundreds of tons".

No, it is not possible to build a gigawatt reactor which weighs "just a few tons".
Here's one:
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Offline Robotbeat

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Re: Lake Matthew - 2036
« Reply #44 on: 04/12/2016 02:14 AM »
Building a 1 GWe nuke plant on Mars is arguably further out of our technical grasp than diverting a very small asteroid. 
What makes you think that? Nuclear reactors can be very compact and small. They can even be their own way to get there (NERVA), The bigger issue with nuclear plants in space is the political resistance to them.
A 1 gigawatt nuclear reactor core Weighs hundreds of tons and requires huge amounts of cooling.
NERVA is a nuclear reactor core, output multiple GW and had a mass of just a few tons. Almost a gigawatt per ton for some designs. And we actually tested NERVA, so it's not like this overall idea is ridiculous. You could land a 10-20ton Gigawatt reactor on Mars on a typical human-rated lander design.

NERVA at full power doesn't melt only because it rejects heat in the exhaust. ...
In this case, you'd use water or some other fluid to reject heat instead of exhaust. Same idea, but you'd use a higher mass flow (but similar volume flow). If you actually read my whole post, I literally said that. gotcha avoided
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Offline Elmar Moelzer

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Re: Lake Matthew - 2036
« Reply #45 on: 04/12/2016 02:45 AM »
I think the highest power to weight ratio was 2 tons per GW, or so. That included shielding, nozzle turbopumps and plumbing.
They were quite efficient. They could even reduce the coolant?LH2 fuel flow in half and still produce half the thrust without the whole system failing. That would still be 2 GW thermal... Considering all that, 1 GW thermal should be possible with less than 10 tons even including some plumbing for a water based cooling cycle.

Offline Stan-1967

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Re: Lake Matthew - 2036
« Reply #46 on: 04/12/2016 02:52 AM »
Building a 1 GWe nuke plant on Mars is arguably further out of our technical grasp than diverting a very small asteroid. 
What makes you think that? Nuclear reactors can be very compact and small. They can even be their own way to get there (NERVA), The bigger issue with nuclear plants in space is the political resistance to them.
A 1 gigawatt nuclear reactor core Weighs hundreds of tons and requires huge amounts of cooling.
NERVA is a nuclear reactor core, output multiple GW and had a mass of just a few tons. Almost a gigawatt per ton for some designs. And we actually tested NERVA, so it's not like this overall idea is ridiculous. You could land a 10-20ton Gigawatt reactor on Mars on a typical human-rated lander design. You would need ~12 tons of fuel if you had perfect burn-up. About 40 tons for a more realistic 40% burn-up. That's not a crazy number, but you'd likely need either an advanced breeder reactor design or highly enriched uranium. 20% burn-up (80 tons) has been demonstrated at this breeder reactor: https://en.wikipedia.org/wiki/Experimental_Breeder_Reactor_II


That's actually the neatest thing about nuclear thermal rockets is how ridiculously power dense. If you can find other uses for it other than wasting a bunch of precious liquid hydrogen with it, you're golden.

You'd cool the reactor with Martian water, recirculating through the bedrock.

You are putting the cart ( cooling water) before the horse ( reactor ).   

A NERVA design is very poor for generation of electricity, and very good at making a lot of thermal energy, which needs very significant flow rates for cooling.   Where are you going to get the initial water for cooling?   Can a NERVA reactor sustain criticality at those power levels for more than a few hours?   Doesn't the high velocity hydrogen erode the reactor interior and limit it's life?  Do you think a liquid will make this even worse? or better?  At the temps of NERVA, the cooling fluid can only be in the channels for a very very short time.   A liquid might undergo cavitation or boiling at the sidewall, and BANG!, your reactor fuel melts.

You are going to have to go fracking on Mars to open up enough underlying bedrock ( better pack a geologist to make sure the rocks will comply ) to somehow bootstrap a water reservoir that wont freeze up due to the freezing bedrock, and the very very large frozen heat sink that is that bedrock.   

Besides, the WSTEWART said they are not thinking of using nuclear.   

« Last Edit: 04/12/2016 03:07 AM by Stan-1967 »

Offline Space Ghost 1962

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Re: Lake Matthew - 2036
« Reply #47 on: 04/12/2016 02:54 AM »
By the sound of it, this "startup" hired lawyers before engineers.
We looked at the physics first, then the engineering, then legal matters.  Might you do the same, in our shoes?

Quote
...anyone who struggled hard with a problem never forgets it...
-Elon Musk

Perhaps you should have started with the chemistry first.

Mars surface averages a pressure of 600 pascals, and an average temperature of 200 K. Water doesn't stay liquid but sublimes from solid to gas. If you were to volatilize it, the incident insolation's UV will crack much of it into hydrogen which will escape to space in about 10 years, and the oxygen will recombine with salts/chlorates to form peroxides/hyperoxides/hypochlorates/hyperchlorates/etc.

So you have to substantially increase temperature/pressure as well as scatter/reflect shortwave UV to form useful water and acceptable vapor pressure. Then, with the salts, we have some aqueous ion issues to deal with, that are different depending where this little miracle is to be performed. Oh, and along the way, you can accidentally create certain toxins and explosives if you aren't careful ...

Oh, and there's geology too.

The heat isn't the problem for this. The chemistry by far is.

Offline LMT

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Re: Lake Matthew - 2036
« Reply #48 on: 04/12/2016 03:37 AM »
Then heat transfer to the air inside the dome from water fountain in lake from the deep water . Water that is cooled by the air is now on the surface of the lake?
Cooled water would be transferred first to the exterior of the dome.  Eventually it would flow to the lake, completing the loop.
Are you saying once the air is heated by the water fountain the water is then used by the people and to water the plants? later the water is filtered and sent back to the lake?
In this scheme the water is treated and heated at the lake, then pumped to the dome, clean.  Some of the water cools in fountains, ponds and streams.  Some water cools in piped tanks having various uses.  Eventually the water is pumped outside the dome, where it's considered greywater. It is not readmitted, but returns instead to the lake.
« Last Edit: 12/14/2016 07:29 PM by LMT »

Offline Robotbeat

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Re: Lake Matthew - 2036
« Reply #49 on: 04/12/2016 04:15 AM »
Building a 1 GWe nuke plant on Mars is arguably further out of our technical grasp than diverting a very small asteroid. 
What makes you think that? Nuclear reactors can be very compact and small. They can even be their own way to get there (NERVA), The bigger issue with nuclear plants in space is the political resistance to them.
A 1 gigawatt nuclear reactor core Weighs hundreds of tons and requires huge amounts of cooling.
NERVA is a nuclear reactor core, output multiple GW and had a mass of just a few tons. Almost a gigawatt per ton for some designs. And we actually tested NERVA, so it's not like this overall idea is ridiculous. You could land a 10-20ton Gigawatt reactor on Mars on a typical human-rated lander design. You would need ~12 tons of fuel if you had perfect burn-up. About 40 tons for a more realistic 40% burn-up. That's not a crazy number, but you'd likely need either an advanced breeder reactor design or highly enriched uranium. 20% burn-up (80 tons) has been demonstrated at this breeder reactor: https://en.wikipedia.org/wiki/Experimental_Breeder_Reactor_II


That's actually the neatest thing about nuclear thermal rockets is how ridiculously power dense. If you can find other uses for it other than wasting a bunch of precious liquid hydrogen with it, you're golden.

You'd cool the reactor with Martian water, recirculating through the bedrock.

You are putting the cart ( cooling water) before the horse ( reactor ).   

A NERVA design is very poor for generation of electricity, and very good at making a lot of thermal energy, which needs very significant flow rates for cooling.   Where are you going to get the initial water for cooling?
Same place you'd get any water on Mars.
Quote
Can a NERVA reactor sustain criticality at those power levels for more than a few hours?
Probably not, just showing that landing a 3GWt reactor on Mars (not including coolant) is not crazy from a mass perspective. It could, in principle, be done.
Quote
Doesn't the high velocity hydrogen erode the reactor interior and limit it's life?
It's mostly the extreme high temperatures, which would be unnecessary if you are using a bunch of water for coolant instead. Also, far, far higher mass flow would mean lower velocity
Quote
Do you think a liquid will make this even worse? or better?  At the temps of NERVA, the cooling fluid can only be in the channels for a very very short time.   A liquid might undergo cavitation or boiling at the sidewall, and BANG!, your reactor fuel melts.
Not saying you could literally do this with any old NTR reactor, just that NTR reactors show what CAN be done as far as mass per thermal power if you have plentiful coolant.

You are going to have to go fracking on Mars to open up enough underlying bedrock ( better pack a geologist to make sure the rocks will comply ) to somehow bootstrap a water reservoir that wont freeze up due to the freezing bedrock, and the very very large frozen heat sink that is that bedrock.[/quote]Not saying it's easy, just that it's possible. Nothing on Mars is easy.

Quote
Besides, the WSTEWART said they are not thinking of using nuclear.
Initially in this thread they said he's (or she's) not thinking of nuclear /explosives/. I took that to mean a nuclear reactor is possible, and didn't dig into the website. If not nuclear at all, then either an impactor or geothermal. Anyway, I'm not particularly taken by their idea, just pointing out what is feasible as far as an energy source. Once you get enough water to cool a large reactor (could be high pressure steam, not just boiling the water) and can reliably-enough circulate it, then you can harness a huge amount of heat energy without having to land much mass.
« Last Edit: 04/12/2016 04:17 AM by Robotbeat »
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Offline Robotbeat

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Re: Lake Matthew - 2036
« Reply #50 on: 04/12/2016 04:21 AM »
... If you were to volatilize it, the incident insolation's UV will crack much of it into hydrogen which will escape to space in about 10 years, and the oxygen will recombine with salts/chlorates to form peroxides/hyperoxides/hypochlorates/hyperchlorates/etc....
"much of it"...

...this is not a very well-thought-out critique of terraforming. A wet climate lasted on Mars for a quite long time. It's going to take more than just some hand-waving to say it's impossible.
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Offline LMT

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Re: Lake Matthew - 2036
« Reply #51 on: 04/12/2016 04:31 AM »
Quote from: Space Ghost 1962
Mars surface averages a pressure of 600 pascals, and an average temperature of 200 K.
Stopping at your first assertive statement.  It doesn't apply to the Lake Matthew scheme because this scheme takes advantage of a low-elevation site, one having significantly higher atmospheric pressure and, per the methods, persistent heat. 

If you still want to make some point about pressure and temperature, first consider and describe the effect which persistent heat would have on the triple-point findings presented in Fig. 5 of Haberle et al., "On the possibility of liquid water on present-day Mars".
« Last Edit: 12/14/2016 07:29 PM by LMT »

Offline Space Ghost 1962

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Re: Lake Matthew - 2036
« Reply #52 on: 04/12/2016 05:07 AM »
... If you were to volatilize it, the incident insolation's UV will crack much of it into hydrogen which will escape to space in about 10 years, and the oxygen will recombine with salts/chlorates to form peroxides/hyperoxides/hypochlorates/hyperchlorates/etc....
"much of it"...

...this is not a very well-thought-out critique of terraforming. A wet climate lasted on Mars for a quite long time. It's going to take more than just some hand-waving to say it's impossible.

Yes I know, the fact that I didn't reconcile the past few million years or more paleo-Mars environment to the current in a single fcking post, it wasn't complete.

In a nutshell, the huge Tharsis volcanos have a huge eruption that causes the mantle to shift to one side and the dynamo shuts down, we lose magnetic field except for crustals, the RTI of the E/M fields create a vortex effect that lets the solar wind brush off 97% of the atmosphere as well as half the water with the remaining being submerged into the soil. Hundreds of thousands of years of UV penetrate and dissociate molecules creating halogen speciation of highly oxidative volatiles and reductive salts of varying metals.

So to undo that, you have to reverse the process. Once you have an aqueous environment on the surface, then you need to "unload" the accumulated energy that is collected in the chemical potentials that have been accumulated in highly concentrated ways.

Perhaps I should patent/IPR protect them before spouting forth? That seems to be the clear point of this thread.

Robotbeat, did that take you any further? If you'd like, visit LPSC next time and there are a few dozen scientists that spend their entire lifetimes on the study of this stuff.

Quote from: Space Ghost 1962
Mars surface averages a pressure of 600 pascals, and an average temperature of 200 K.
Stopping at your first assertive statement.  It doesn't apply to the Lake Matthew scheme because this scheme takes advantage of a low-elevation site, one having significantly higher atmospheric pressure and, per the methods, persistent heat. 

Sure, we can venture into my favorite location on Mars, the Hellas Basin, but a)it's unreachable by current EDL and b) has other undesirable aspects, some of which you've dismisses by stopping with my "first assertion". Am not impressed. You'll also find your ability to heat will be highly degraded by the same means you use to exploit in the first place, so your evasion of one characteristic causes a contradiction in another way.

Quote
If you still want to make some point about pressure and temperature, first consider and describe the effect which persistent heat would have on the triple-point findings presented in Fig. 5 of Haberle et al., "On the possibility of liquid water on present-day Mars".

That point has limited use as you know. A better way to use it would be in subterranean caverns or lava tubes. But then there are easy ways to exploit them without your scheme, which would have more efficacy because it could be employed many sites on Mars, and ones more "popular" for exploration.

Offline Stan-1967

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Re: Lake Matthew - 2036
« Reply #53 on: 04/12/2016 05:33 AM »

Snip...

Hundreds of thousands of years of UV penetrate and dissociate molecules creating halogen speciation of highly oxidative volatiles and reductive salts of varying metals.

So to undo that, you have to reverse the process. Once you have an aqueous environment on the surface, then you need to "unload" the accumulated energy that is collected in the chemical potentials that have been accumulated in highly concentrated ways.

Snip...


I want to open the first electroplating shop on Mars.  ( under a heated dome...with no EPA to monitor my metals discharge to the local POTW)   But I seriously wonder if electrowinning of metals on Mars has ever been proposed as an ISRU method?   

Offline LMT

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Re: Lake Matthew - 2036
« Reply #54 on: 04/12/2016 06:45 AM »
Quote from: LMT
If you still want to make some point about pressure and temperature, first consider and describe the effect which persistent heat would have on the triple-point findings presented in Fig. 5 of Haberle et al., "On the possibility of liquid water on present-day Mars".
Quote from: Space Ghost 1962
That point has limited use as you know. A better way to use it would be in subterranean caverns or lava tubes. But then there are easy ways to exploit them without your scheme, which would have more efficacy because it could be employed many sites on Mars, and ones more "popular" for exploration.

No, you've glossed over the first point, which is a most salient point. 

So.
« Last Edit: 12/14/2016 07:28 PM by LMT »

Offline MikeAtkinson

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Re: Lake Matthew - 2036
« Reply #55 on: 04/12/2016 07:28 AM »
It would be easier to redirect a near Mars asteroid of the equivalent size.

I'm going to agree with this and abondon my previous thoughts of pulling it off the surface of Phobos.   This will mean the impactor can be much smaller, as its velocity wil be much higher.  All the orbit needs is to be adjusted to intercept Mars.   Any list of asteroids with close passes to Mars in the 2-4 years prior to the 2036 target date?

And also hit Mars in the right spot.

For a Mars orbit crossing asteroid the delta-v required can be arbitrarily small, as long as you are in no hurry.

Offline MikeAtkinson

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Re: Lake Matthew - 2036
« Reply #56 on: 04/12/2016 08:07 AM »
Quote from: Space Ghost 1962
Mars surface averages a pressure of 600 pascals, and an average temperature of 200 K.
Stopping at your first assertive statement.  It doesn't apply to the Lake Matthew scheme because this scheme takes advantage of a low-elevation site, one having significantly higher atmospheric pressure and, per the methods, persistent heat. 

Presumably you are thinking of the Hellas basin which has pressure of 1155 Pa (11.55 mbar, 0.17 psi, or 0.01 atm).

Offline Alf Fass

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Re: Lake Matthew - 2036
« Reply #57 on: 04/12/2016 08:09 AM »
Reading through it seems pretty obvious that the proposal is to drop a rock into Hellas Basin and rely on enough of the heat generated staying in the bedrock to maintain a lake of liquid water in the resulting crater.


If you smack an asteroid into Mars a lot of the energy released is going to go straight up and out, so I'll assume only 10% of the energy released is going to stay at the point of impact, so to get the quintillion (10^18) Joules at the site you'll need an impact event that actually releases 10 quintillion Joules. working on an impact velocity of 30 km/s the rock would mass over 20 million tons. It actually requires quite modest velocity changes - on the order of 100 m/s - to change the direct of an asteroid on a suitable orbit enough to hit a planet.

If we use some sort of solar thermal system using water in the rock as propellant and achieve an exhaust velocity of 3000 m/s you'd need to expend around 700,000 tons to achieve that 100 m/s delta V.  The energy in the exhaust would be 3.15 x 10^15 J, if the acceleration took 5 years that gives a power requirement of 20 mW, so a solar concentrator of 40,000 m^2 at Mars orbit assuming 100% efficiency, I would think 40% efficiency more realistic, so a 25 acre concentrator.

I don't see that happening for less than several hundred tons of gear attached to the asteroid.

Well, unless they got really, really lucky with the right rock in the right place at the right time.


The claim is for 4 million m^3 of habitable volume for 100 tons delivered to the Martian surface, that's a sphere with a hundred meters radius and a surface area of 126,000 m^2, (using the best possible shape to minimize the surface area of the containment envelope), for a hundred ton envelope that gives an areal density of 800g/m^2, something with a density of 1g/cc would be 0.8mm thick. I don't see how using ISRU is going to get you a robust strategy to manufacture more than a hundred tons of envelope from manufacturing infrastructure weighing 100 tons.

Finally; I wonder if Harness Dickey know that their name is being used to label them as the architects of this proposal, I would have expected them to include their logo if that were the case.
« Last Edit: 04/12/2016 08:24 AM by Alf Fass »
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Offline R7

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Re: Lake Matthew - 2036
« Reply #58 on: 04/12/2016 08:11 AM »
Any idea on the velocity at perigee?

~4.3km/s using vis-viva equation.
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Offline Elmar Moelzer

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Re: Lake Matthew - 2036
« Reply #59 on: 04/12/2016 08:34 AM »
How about crashing not one big asteroid, but many, many small ones? Certainly, more of their volume would evaporate upon re- entry, but probably not that bad with the thin Martian atmosphere. If you had a lot of relatively small water asteroids, you could also increase the amount of water vapor in the atmosphere, which would increase the green house effect. Redirecting lot of small asteroids might actually be easier than one big one, since you can use relatively small, mass produced satellites. The biggest problem would probably finding suitable candidates.

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