Spaceships--how much IS a power point

[Agemegos]

Originally Posted by whswhs

That's exactly the one. Though I haven't read it in a long time and I'm not 100% sure about the composition.

It seems I had misremembered: the rescuers got drunk because they weren't used to so much oxygen.

[YankeeGamer]

I'm not findig any of the math or logic here unconvincing. Order of magnitude guess is fine. Every comment here is good for the worldbuilding.

The water froze out first, of course, and there's rime in the soil. I think that there's plenty of places where decent amounts of liquid, and later solid, atmosphere could pool, but most will be coating the lowlands and the ocean.

I was going to have the major civilization--the one sending out Enterprise--in Colorado, but perhaps I need to move it to a spot closer to either the ocean or an endorheic basin.

It's been about 300 years that Earth has been on its odyssey through interstellar space.

Every comment is greatly appreciated; THANKS

And I just realized something. Ice is everywhere, and can be utilized to get oxygen. With nitrogen not as abundant, their cities might have a low pressure oxygen atmosphere instead of oxygen-nitrogen. Some significant problems, but solvable for a mostly TL 9 society.

EDIT: The Great Divide Basin includes Colorado :)

[weby]

One powerpoint is 30 minutes to 2 hours of boredom listening to someone drone on about some boring topi.. oh.. space ships Power Point.. :)

The way I calculate the power plant effect of spaceships is based on the given effect of beam weapons for the same size ships.

The weapons have given output energy and the rate of fire 1/20 seconds. Thus the energy that that beam weapon needs/second is the output/20/efficiency.

Since the "improved" versions of the beam weapons fire at double speed for the same energy in power points, that change is then seemingly the efficiency change. (Doubling of efficiency in that one TL change)

Gurps take on Beam weapons has been that they are mostly 25-50% efficient, thus I have used 50% for the "improved" and 25% for base models.

That means that the energy is output energy/20/.25(base) output energy/10/.5(improved) that are the same number: energy/5.

Thus SM 13 beamweapon at 100Gj needs 20 giga watts. Thus the 15000 ton powerplant would produce 20 gigawatts if fission(1 SM 13 power point), 40 gigawatts if fusion(2 SM 13 power points) and so on.

If you use different assumptions for the beam weapon efficiency, you get slightly different values, but for realistic values you are likely within *1.5 to /1.5 range of those energy values.

[Agemegos]

Originally Posted by cptbutton

It is on Gutenberg.org:

A Pail Of Air

At the end they are getting contacted by a higher tech enclave with atomic reactors in Los Alamos.

Since they could only go as far as they could with the air in a tankless suit, they would eventually have died when there was no more coal or food within a few minutes distance.

Well, I can imagine a portable gadget that used the heat from burning coals to melt, evaporate, and warm oxygen from a reserve of oxygen ice for breathing, which would extend their foraging range. But the engineering experimentation to build it would be rather dangerous. And anyway, that would only postpone the day when they ran out of food and fuel; it would not put them in a position to actually grow food or fuel.

It is interesting to note that Leiber has the layer of solid oxygen on top of the layer of solid nitrogen. He has them layered in the order in which they freeze, as though ices always sink. And indeed solid nitrogen is 25% denser than liquid nitrogen. But solid nitrogen is less dense than liquid oxygen, so as the nitrogen froze out of the liquid mixture the liquid would become denser, and at some point the solid nitrogen would start floating to the top. When eventually the oceans froze you'd end up with the oxygen in a eutectic mixture with nitrogen, frozen solid with at least some nitrogen above it.

Furthermore, as Anthony pointed out, geothermal flux would prevent things from getting cold enough for helium to condense to a liquid.

As the world coled the sequence of events would be roughly

1. 290 K Everything goes dark.
2. 273 K Water vapour rains and snows out.
3. 195 K carbon dioxide freezes out without becoming liquid.
4. 90.2 K Oxygen rains out, flowing to the ocean and endorheic lakes, there to form a liquid layer over a base of water ice.
5. 87.3 K Argon rains out, only about 100mm of it or less.
6. 83.8 K Argon freezes and sinks.
7. 77.4 K Nitrogen rains out and flows to the seas and lakes, where it mixes in to turn the oceans and lakes to liquid air.
8. < 63 K Nitrogen starts freezing (at the ocean surface) and initially sinks. That raises the proportion of oxygen in the remaining ocean liquid, which becomes denser.
9. The oceans reach a density of 1 040 kg/m³ and "turn over". Nitrogen ice not securely attached to the bottom floats to the top.
10. Further nitrogen freezes at the surface but floats there, forming a surface pack of nitrogen ice that grows thicker, leaving the liquid to become steadily richer in oxygen.
11. < 54 K The liquid under the ice-pack reaches the eutectic ratio of oxygen to nitrogen at about the same time that it reaches the freezing point of the eutectic mixture. The oceans and lakes freeze solid.
12. Temperature falls towards 35 K, ever more slowly.

[YankeeGamer]

Originally Posted by Agemegos

Well, I can imagine a portable gadget that used the heat from burning coals to melt, evaporate, and warm oxygen from a reserve of oxygen ice for breathing, which would extend their foraging range. But the engineering experimentation to build it would be rather dangerous. And anyway, that would increase their foraging range and postpone the day when they ran out of food and fuel, but it would not put them in a position to actually grow food or fuel.

It is interesting to note that Leiber has the layer of solid oxygen on top of the layer of solid nitrogen. He has them layered in the order in which they freeze, as though ices always sink. And indeed solid nitrogen is 25% denser than liquid nitrogen. But solid nitrogen is less dense than liquid oxygen, so as the nitrogen froze out of the liquid mixture the liquid would become denser, and at some point the solid nitrogen would start floating to the top. When eventually the oceans froze you'd end up with the oxygen in a eutectic mixture with nitrogen, frozen solid with at least some nitrogen above it.

As the world coled tht sequence of events would be roughly

1. Everything goes dark.
2. Water vapour rains and snows out.
3. Carbon dioxide freezes out without becoming liquid.
4. Argon rains out, only about 100mm of it or less.
5. Oxygen rains out, flowing to the ocean and endorheic lakes, there to form a liquid layer over a base of water ice.
6. Argon freezes.
7. Nitrogen rains out and flows to the seas and lakes, where it mixes in to turn the oceans and lakes to liquid air.
8. Nitrogen starts freezing (at the ocean surface) and initially sinks. That raises the proportion of oxygen in the remaining ocean liquid, which becomes denser.
9. The oceans reach a density of 1 040 kg/m³ and "turn over". Nitrogen ice not securely attached to the bottom floats to the top.
10. Further nitrogen freezes at the surface but floats there, forming a surface pack of nitrogen ice that grows thicker, leaving the liquid to become steadily richer in oxygen.
11. The liquid under the ice-pack reaches the eutectic ratio of oxygen to nitrogen at about the same time that it reaches the freezing point of the eutectic mixture. The oceans and lakes freeze solid.
12. Temperature falls towards 35 K, ever more slowly.

Furthermore, as Anthony pointed out, geothermal flux would prevent things from getting cold enough for helium to condense to a liquid.

WOW! That is an incredibly useful summary condensed in one place. The science of Enterpris's world is clearer to me. Once again, THANKS!
What would the proportions of the eutectic mix be?
Oxygen is easy to get--plenty of ice all over Colorado--but if nitrogen is a bit harder to get, their air might have a smaller percentage of nitrogen than Earth's air now.

[Agemegos]

Originally Posted by YankeeGamer

What would the proportions of the eutectic mix be?

To my very great amazement someone has actually determined it, using x-ray crystallography. Here is the phase diagram. It looks at though the eutectic mix is about 23% or 24% nitrogen.

From the phase diagram we can also work out that nitrogen will start freezing out of the liquid air at 60 K and that the eutectic melt will freeze at 50 K.

We can get a bit more specific about the sequence of events that forms the new environment.

• 290 K Everything goes dark. Global circulation of the atmosphere falters and halts.
• 273 K Water vapour rains and snows out.
• Lakes and oceans freeze over, then freeze through. Global circulation of ocean water falters and halts. Expansion of ice produces bulges over the formerly deep water.
• 195 K carbon dioxide freezes out without becoming liquid.
• 90.2 K Oxygen rains out, flowing to the ocean and endorheic lakes, there to form a liquid layer over a base of water ice.
• 87.3 K Argon rains out, only about 100mm of it or less.
• 83.8 K Argon freezes and sinks.
• 77.4 K Nitrogen rains out and flows to the seas and lakes, where it mixes in to turn the oceans and lakes to liquid air.
• 60 K Nitrogen starts freezing (at the ocean surface) and initially sinks. That raises the proportion of oxygen in the remaining ocean liquid, which becomes denser.
• The oceans reach a density of 1 040 kg/m³ and "turn over". Nitrogen ice not securely attached to the bottom floats to the top.
• Further nitrogen freezes at the surface but floats there, forming a surface pack of nitrogen ice that grows thicker, leaving the liquid to become steadily richer in oxygen.
• 50 K The liquid under the ice-pack reaches the eutectic ratio of oxygen to nitrogen at about the same time that it reaches the freezing point of the eutectic mixture. The oceans and lakes freeze solid.
• Temperature falls towards 35 K, ever more slowly.

Bear in mind that the oceans have a catchment (including their surfaces) that is only about 50% larger than their surfaces, so the thickness of the sheet of oxygen-nitrogen ices that forms over them is only about 50% greater than the thickness of the air column if solidified. But endorheic lakes are often much, much smaller than the internal drainage basins they drain. So the frozen air sheets over and around endorheic lakes can be a lot thicker. But remember that they won't fill any higher than their sills: they will overflow rather than stack material higher than their sill heights. This is because the atmosphere will mostly rain out as a liquid.

Leiber seems to have overlooked the liquid phase in A Pail of Air, and considered that the atmosphere would fall out as snow.

• His frozen oxygen can be shovelled, rather than being a rock-forming mineral.
• He has the oxygen ice on top of the nitrogen ice instead of forming a layer of nitrogen-oxygen eutectic under the buoyant nitrogen ice.
• Los Alamos seems to have access to oxygen and water ices. I would expect that the significant elevation and ample drainage that put it in the New Mexico high desert would mean that the water and air would drain away in their liquid phases.

[Agemegos]

Originally Posted by YankeeGamer

The science of Enterpris's world is clearer to me.

There are going to be a lot of very interesting things going on in the vicinities of volcanoes, seafloor spreading zones, and other geothermal hot-spots. If volcanic activity on the real Earth can maintain magma domes, lava lakes, and volcanic eruptions I suppose that not only will those phenomena continue, but that there will also be water domes, steam volcanoes, and possibly even polynyas.

I'm trying to envision the structure that forms around a volcanic vent, where water, nitrogen and oxygen melt at successively greater distances, trickle downslope to the heat, boil, are blown off into vacuum by their vapour pressures, and sublime to ices in a bullseye arrangement. I think the eutectic melts first, undermining the nitrogen ice sheet above it and producing a treacherous zone of unsupported ground, overhangs, and jumbled terrain of collapsed cavern roofs. I'm very uncertain about the scale, though. Part of the heat diffusion is conduction through the crust, part is radiant, and part is carried outwards as sensible and latent heat by a succession of drafts of vapour, the water boiling oxygen as it freezes into ice, etc.

[Anthony]

The thermal conductivity of ice appears to be in the range 2-4W/m/K (exact numbers seem hard to find), which means at a geothermal flux of .087W/m^2 requires a temperature change of .02-.04K/m, or 20-40K/km. This may prevent the deepest parts of the ocean from freezing, and will certainly prevent it around vents.

The other issue is time. If you have water at 273K under a kilometer of ice, and then a surface temperature of 35K, using a median transfer rate of 3W/m/K, transfer rate winds up as 3W/m/K * 238K / 1000M = 0.714W/m^2. The heat of fusion of water is about 333MJ/m^3, which works out to a freezing rate of 0.07m/yr (for an arbitrary depth, time to freeze is about 7,000 years * depth in km^2. This overstates the freezing rate because the surface temperature won't immediately drop to 35K and the water will actually cool below 273K; if we only use a 200K difference we wind up at about 0.6W/m^2)

Heat transfer from the cooling oceans should prevent surface temperature from reaching liquid nitrogen temperatures until the rate has dropped below 0.9W/m, which will take several thousand years.

The earth's crust has similar thermal conductivity to ice, but does not have the distinct phase change so it takes less time and energy to cool.

[Agemegos]

Originally Posted by Anthony

The earth's crust has similar thermal conductivity to ice, but does not have the distinct phase change so it takes less time and energy to cool.

Does that suggest that there will be epochs in which first oxygen and then nitrogen evaporate over the oceans and rain out over the continents?

If the land surface reaches 60K while the sea ice is warmer than 77.4 K nitrogen will form an ice cap over the land and former shallow oceans while the sea ice becomes covered with a shallow sea of oxygen. When the surface finally reaches 54 K you will have highlands of low-density nitrogen ice (some of it overlying rock, other parts overlying water ice) and level lowlands of dense oxygen ice overlying water ice (with a magma of liquid water at great depth). But it seems to me that that might be too large a range of temperatures to expect.

It seems to me that ice volcanoes ought to be limited by the fact that ice in a crack is more dense than the ice surrounding it, so that the pressure of the ice on a buried water chamber cannot be sufficient to raise water to the ice surface. But perhaps that doesn't apply to high-pressure phases of water ice.

[Anthony]

Originally Posted by Agemegos

Does that suggest that there will be epochs in which first oxygen and then nitrogen evaporate over the oceans and rain out over the continents?

Maybe? I'm an amateur speculating.