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For Calliban re link to video by Isaac Arthur celebrating 11 years of creating videos...
Thanks for providing that link! The video is chock full of inspiration!
I had time enough for about half of it, and will return to finish later.
The idea of a tether across a LaGrange point is ** definitely ** interesting. We could use that technique today, at L1, to see if helps to stabilize the orbit. The cable wouldn't need to be massive, because if it starts to stretch toward braking, propulsion can be enlisted to save it.
Speaking of tethers.... I think it was SpaceNut ??? who posted a link about the new Haven-1 habitat. I noted that the video in one of the links shows a possible tethered artificial gravity experiments at phase 4 of the proposed timeline. Interestingly, the experiment would be done without a crew on board. Wimpy!
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For Calliban re report on methane at MakeMake...
Thanks for this interesting report ... In light of your conversation with Void about making habitats from such bodies, and considering the amount of mass available, humans might be able to create a fairly sizable community ( Isaac Arthur's vision).
I found time to watch the entire series you showed us, featuring Isaac Arthur's celebration of 11 years producing his future vision videos. That is an impressive collection. That is world class computer animation harnessed in support of vision that seems (to me at least) well tuned to what is possible as we humans currently understand physics.
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Isaac Arthur is without a doubt, one of the greatest futurists of our time.
Void spent some time researching the use of water ice as a building material. The colder ice gets, the stronger it becomes. On icy moons and dwarf planets, ice could serve as a structural material for buildings and dugouts. Insulation would be needed to prevent heat from habitable spaces from draining into ice walls. For free space habitats, cosmic ray shielding dominates the total mass budget. Ice is one of the most efficient shielding materials that we know.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re post on atmospheric engine...
Thanks for this interesting post, with the link to a site where an overview of the citation is available.
I read the overview, and noted what appear to be links to additional resources.
The overview confirmed my suspicion... there must be (and is) a second energy input to the machine.
The energy of hot water is an input, and it may be the greater in terms of joules, but there is another energy input which I ** think ** is needed to provide the low pressure side of the machine. Perhaps some of the energy developed by the machine is consumed in performing the low pressure function. You and Void are keeping content flowing in the forum, until the next Starship flight in mid-October. If you have time, and the inclination, you have shown the ability to create images that are helpful in understanding concepts.
In hopes you might be willing to build up a collection on engines of this type, I will create a topic dedicated to it.
We might develop some interest among our still active members, and potentially there might be non-member readers who would be interested. What temperature is the water from a fission power plant? Right now (as far as I know) all such a water is allowed to deliver thermal energy to the atmosphere and to ground water. I wonder if engines of this time might be useful adjunct to fission power plants, to capture a bit of the otherwise wasted heat.
Update after watching the Wikipedia animation for a while. I think I can see where that ** extra ** energy is coming from. The piston is pushing the atmosphere up the cylinder, thus storing energy in the Earth's atmosphere. When the steam inlet is closed and the chamber is vented the atmosphere exerts it's force, driving the piston down and pulling the rocker arm down with it, which pulls water up from below ground (in the original application).
I still would like to see an explanation of how the system you proposed would work. We have no one in group right now who can create animation, or rather, admits to knowing how to create animation. I could probably to something with blender, but I'm booked for weeks on other projects.
If we have a member who would like to learn how to create animation for educational purposes, this is a good application.
Update later: I subsequently realized you are NOT talking about the classic 1700's design, as shown in the Wikipedia article. That machine used steam created by boiling water to lift the piston against the atmosphere. In the concept you've hinted might be possible, a partial vacuum is (apparently) created under the piston, so that the atmosphere forces the piston down. It is the mechanism that creates the partial vacuum that may require a second source of energy, as suggested by the article at the link you provided. In any case, we have a topic available if this is something you would like to explore further.
How we (or anyone) might be able to obtain mechanical power from hot (not boiling) water will surely be of interest to forum members and readers. There's a ** lot ** of hot water inside the Earth.
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For Calliban re low temperature liquid...
Quoting:
The atmospheric steam engine uses heat at temperature <100°C, to raise steam in a boiler under vacuum. The condenser has a temperature of 30°C and a pressure of 4KPa. The low temperature difference between hot a cold side, mean that this heat engine is relatively inefficient. At 100°C boiler temperature, theortical efficiency is 25%. This drops to 10% for a boiler temperature of 69°C. Real efficiency in a practical device would be lower than this, perhaps 6-15% in a steady flow turbine system. This has led to relatively little interest in the atmospheric steam engine.
I'm hoping you'll follow up on this idea... Mars has a lower air pressure, so water will boil at a lower temperature.
On Earth, we might see the same effect by operating at a high altitude.
What I'm trying to understand is the idea of placing a low pressure area (somehow) so that non-boiling water can deliver useful mechanical energy.
If there is a way to do this, we should be able to make an apparatus to test in the kitchen with a pot of hot water.
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The Carnot efficiency is an upper bound upon what can be done, from classical thermodynamics. The disparity between what actually can be done and what that upper bound is, is usually quite large: around a factor of 2.
Carnot efficiency is 1 - Tcold/Thot, where the temperatures must be in absolute units.
These low pressure concepts are attractive ONLY if you can tolerate the low inherent energy conversion efficiency. Crudely factor 2 below Carnot efficiency.
Sorry, but that's just the way it is. There have been NO observed exceptions to classical thermodynamics for about 300 years now!
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For Calliban re liquid air propulsion...
https://newmars.com/forums/viewtopic.ph … 59#p234559
In the post above, in one of Terraformer's topics, you commented upon the possible use of liquid air as an energy storage medium.
Not everyone in the NewMars membership would be able to design an actual Real Universe implementation of this energy storage method, but I'm hoping you might have time to work out what a tug that uses it might look like. Radiators to pull thermal energy from ocean water (or fresh water inland) would presumably be inside the hull, and filters would be needed to keep debris from entering and clogging the radiators. Pumps of some kind would be required to pull water into the radiator section. Pipes would be required to convey liquid air from storage to the radiator subsystem and then on to motors able to take advantage of gas produced by the radiator subsystem.
In a recent post by kbd512 in the same topic, kbd512 provides some details about the operating requirements for a marine tug, and a liquid air system would need to match the capability of a diesel powered vessel, including power delivered and duration of that power.
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For Calliban re post on kite and liquid air...
https://newmars.com/forums/viewtopic.ph … 17#p234717
kbd512 showed us examples of both test and production versions of the large kite puller for vessels, in the Sunday meeting.
I'm inspired by your latest observations to inquire again about the practical engineering that is needed to implement a liquid air solution for any vehicle. The transfer of thermal energy from the environment to the store of liquid air is something (it seems to me) will require some significant engineering effort, and extremely precise manufacturing. If you have time, please add a post or two about how that might actually be done. Humans have a lot of experience delivering thermal energy to the air, and heat pumps show how to pull thermal energy from the air.
Feeding liquid air into the outdoors coils of a heat pump system would be a practical example of how such a system might be used. I would imagine that freezing of water in the outside air might be a problem to be solved.
Feeding liquid air into the coils of a water immersion heat transfer system might lead to freezing of the water unless flow is managed carefully, such as with computer control.
In short, I think there are probably good reasons why this technology has not been developed to date.
The talent available in this forum might be able to show the way.
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