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#51 2025-07-30 01:25:37
- Calliban
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- From: Northern England, UK
- Registered: 2019-08-18
- Posts: 4,397
Re: Shell Worlds
One thing I don't quite understand about TARS is how it can remain stationary. When a rotating system releases a payload, both the accelerator and projectile recieve equal linear momentum. Does TARS use sunlight pressure to correct its orbital position after a launch? It isn't clear to me. Another problem is that centrifugal forces will be huge unless spin radius is enormous. This limits the type of payload that such a system can accelerate.
"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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#52 2025-09-19 11:09:07
- Void
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- Registered: 2011-12-29
- Posts: 9,905
Re: Shell Worlds
An article about TARS: https://www.msn.com/en-us/news/technolo … r-AA1MrlT5 Quote:
Spacecraft launcher 'TARS' could take humanity to another star system
Story by Aparna Parameswaran • 6d •
3 min read
Ending Pending 
Last edited by Void (2025-09-19 11:10:42)
Be careful what you wish for.
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#53 2026-09-18 09:25:59
- Terraformer
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- From: The Fortunate Isles
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Re: Shell Worlds
Wondering about the use of a shellworld as a radiator. Build a large shell around a dwarf planet / moon and let atmospheric convection carry heat up to it, allowing for very large habitats without a particularly complex cooling system.
Use what is abundant and build to last
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#54 2026-09-18 13:10:15
- Void
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Re: Shell Worlds
No one else has responded Terraformer, so I will give it a try.
A shell world with a double shell and "Gravity Drains", and a moon in orbit where volatile substances can be stored: 
Gravity Drains are there so that if a gas escapes, it may settle into the drains and then be pumped back into the shell. It is not guaranteed that an escaped gas will immediately leave a small worlds gravity well, especially if it exits a 1 millibar pressure. So, we may hope to recover much of a gas leak.
We also want to avoid a atmosphere freezing to the underside of a shell. Or it's top side. Low pressure helps with that.
So, an N2/O2 atmosphere of 1 millibar may or may not be enough pressure to lift the outer shell. If not then perhaps additional means of support are required such as a higher pressure or more gravity wells to support the outer shell over the inner shell.
The sun's heat and also produced industrial heat might be able to maintain a non-condensing situation for each shell.
Then if desired air vented from the lower shell into the upper shell might be a way to cool the inner part, then when the cold air settles into the gravity well, you can compress it back into the lower shell.
This may need more work.
1 millibar prevents atmosphere condensing as a liquid on the outer shell, but does not prevent it to condense into a solid.
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Freezing Point of Nitrogen Gas at 1mbar
At 1mbar (0.001atm), nitrogen does not freeze at the same temperature as at 1atm. The freezing point of nitrogen is strongly pressure‑dependent because the gas–solid equilibrium is governed by the triple point and the solid–gas (sublimation) curve.Key facts from the nitrogen phase diagram
scientifically.blog
scientifically.blog
+1Triple point: 63.15K (−210.00°C, −346.00°F) at 12.55kPa (≈125.5mbar).
Below this pressure, nitrogen cannot exist as a stable liquid; it transitions directly from gas to solid (sublimation) at the solid–gas equilibrium temperature.
At 1mbar, the solid–gas equilibrium temperature is slightly lower than the triple point temperature, because the sublimation curve slopes downward with decreasing pressure.
Estimated value at 1mbar
Using the nitrogen sublimation curve data from NIST/TRC
wtt-lite.nist.gov
wtt-lite.nist.gov
, the solid–gas equilibrium temperature at 1mbar is about 62.0K (≈−211.15°C, ≈−348.07°F). This is roughly 1.15K lower than the triple point temperature.Why it’s lower
The sublimation curve for nitrogen has a negative slope in the low‑pressure region, meaning that as pressure drops below the triple point, the temperature at which solid and gas coexist decreases. This is a general property of most substances: the solid–gas equilibrium temperature changes with pressure according to the Clausius–Clapeyron relation.Summary table
Pressure Phase equilibrium temp
Notes125.5mbar (triple point) 63.15K
Liquid, solid, gas in equilibrium1mbar ~62.0K
Solid–gas equilibrium (sublimation)Practical note: At 1mbar, nitrogen gas will sublime into solid nitrogen at ~62K, not at the −210°C value quoted for 1atm
scientifically.blog
scientifically.blog
+1
. This is important for cryogenic and vacuum systems, where low pressures can shift phase boundaries significantly.
So what you might want on the outer shell is something like insulating flaps that can move and regulate the rate of thermal losses.
Around the Orbit of Pluto, sunshine might avoid condensation, but then what of the poles, even if it is rotating?
Ceres? Not a problem, I expect.
Hope I have not annoyed you.
Ending Pending :-)
Last edited by Void (2026-09-18 13:27:12)
Be careful what you wish for.
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