from the nothing-is-lighter-than-*nothing* dept.
A vacuum airship made of a homogenous material cannot withstand the atmospheric pressure on Earth for any material humans have yet discovered, which can be proven using the critical buckling load of a sphere. However, from an initial analysis of the vacuum airship structure and relationship to atmospheric conditions, Mars appears to have an atmosphere in which the operation of a vacuum airship would not only be possible, but beneficial over a conventional balloon or dirigible. In addition, a multi-layer approach, in conjunction with a lattice, would circumvent the buckling problems of a single homogenous shell. The lattice used to support the two layers of the vacuum airship shell can be made, using modulation of the lengths of the members, to fit the curvature of the vacuum airship precisely by following an atlas approach to the modulation.
The Martian atmosphere has a pressure to density ratio that is very beneficial to the operation of a vacuum airship; this is a result of the high average molecular weight of the atmosphere (relative to other planets in the solar system) and the temperature of the atmosphere, the trend for which can be observed from the ideal gas law. Through a more in-depth analysis of the vacuum airship model, it can be shown that the vacuum airship may theoretically carry more than twice as much payload as a modeled dirigible of the same size, a 40-meter radius, in the Martian atmosphere.
NASA Innovative Advanced Concepts (NIAC) Program. NBF.
(Score: 2) by richtopia on Tuesday April 18 2017, @10:02PM (5 children)
I never realized this was a real concept before. I wonder what the lifting capacity would be on Mars; yes there is less atmospheric pressure to implode the vacuum airship, but there is also less atmosphere to provide buoyancy force.
https://en.wikipedia.org/wiki/Vacuum_airship [wikipedia.org]
(Score: 2) by Fluffeh on Wednesday April 19 2017, @03:28AM (4 children)
Given the pressure there, which is from memory somewhere around 1% of sea-level pressure here on Earth, propulsion would also be somewhat difficult - there's not much to push as exhaust unless you are making it yourself (read rockets to give you acceleration) so even if you were to lift something, moving it anywhere once you lifted it would be cute.
(Score: 2) by takyon on Wednesday April 19 2017, @04:25AM (2 children)
Sounds like a job for EmDrive.
But reeling it into the realm of the real... what about ion drives [wikipedia.org]? They are not supposed to work in the presence of atmosphere, but maybe VASIMR [wikipedia.org] is different.
The proposal suggests using solar panels on the surface of the airship to power electric motors. Maybe it can remain aloft forever. But if EmDrive was real, both options would require no propellant, unlike an ion drive. If the EmDrive magic was refined to maximum hype levels [nextbigfuture.com], it would be the superior choice.
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(Score: 2) by Fluffeh on Wednesday April 19 2017, @06:03AM
Yeah, the EMDrive would work - if it does work :P
Part of the problem with using an Ion Drive though is due to the extreme velocities that it expels the propellant (why they are so efficient in the first place) would create all sorts of wake issues behind the craft - possibly in a dangerous manner to the craft itself even in a very thin atmosphere. I'm not sure though. I'm not saying it is impossible - just that thrust will be very hard. A propeller won't work much at all - there's 100 times less air to grab (and push) but also what is pushed will move easier due to the air it is pushed into not having the same outward pressure.
Maybe harvesting the ice, then using water as a propellant to create the thrust would work - but again, that means carrying loads of heavy fuel as thrust.
(Score: 2) by PinkyGigglebrain on Wednesday April 19 2017, @07:17AM
Something like this might work well on Mars
https://en.wikipedia.org/wiki/Ionocraft [wikipedia.org]
The are aka "Lifters". In a nutshell they use high voltage to create thrust. I recall NASA evaluated using them in satellites but it didn't work out for reasons I don't remember. For thrust just point them sideways.
And here are instructions to build one yourself if so inclined
http://www.instructables.com/id/High-Voltage-Lifter-Ionocraft/ [instructables.com]
"Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."
(Score: 0) by Anonymous Coward on Wednesday April 19 2017, @06:17PM
I'm not sure that's a big deal, really -- you just put much bigger fans on the same motor. Thrust, drag, and buoyancy all scale with atmospheric density, so while the thing will be freaking big for a given payload capacity, it shouldn't take inordinate power to push through the thin atmosphere at blimp-like airspeeds. (Of course, blimp-like airspeeds may be a problem if you need to travel upwind...)
I'm not sure what the scaling law for payload vs. length looks like -- obviously total buoyancy scales with the cube of length, but you have to subtract the structural weight, and I don't know how that varies. Should be no worse than squared, though, right? So if you figure thrust, drag, and payload all scale linearly with density, and with the square of length, then you can just scale an Earth blimp up 10x in every direction. And since they say their vacuum airship design can carry more payload for a fixed size, it would be a smaller envelope for the same payload, thus less drag, and either less thrust required, or more speed available.
(I'm sceptical of the whole vacuum-airship thing -- the idea of being able to repair it and re-evacuate with no need for a supply of lifting gas is nice, but I'm suspicious of how much damage the "lattice" can take before field repairs become impossible. Patching a blimp, on the other hand, is trivial for small punctures, and manageable for large tears; same goes for damage to the envelope in a semi-rigid airship, although a damaged keel puts you in the same fix as the vacuum airship.)
(Score: 0) by Anonymous Coward on Tuesday April 18 2017, @10:32PM (3 children)
"Through a more in-depth analysis"
we assume, also, then, that the superior displacment of the mars atmosphere will also yields some subtile weather and ... air? changes.
it is, i believe, thank god? possible to "inflate" a "vacuum deligerable" on mars to influence an approaching storm(*). however, a constant, yaerlong vacuum displacement of the mars athmosphere might be considered as "climate change" by the yet undiscovered marsians?
well, cool, what can i say?
(*) mathematically, the vacuum derigible would represent a hole in the dynamic solar powered heated mars athmosphere?
(Score: 2) by deadstick on Tuesday April 18 2017, @10:53PM (2 children)
Quit bogarting.
(Score: 0) by Anonymous Coward on Tuesday April 18 2017, @11:07PM
Hey there, bogart
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What would you do now
(Score: 0) by Anonymous Coward on Wednesday April 19 2017, @03:43PM
What?
(Score: 0) by Anonymous Coward on Wednesday April 19 2017, @12:29AM (5 children)
Airships need hangers when the weather gets rough.
(Score: 2) by bob_super on Wednesday April 19 2017, @01:46AM
In most states, it's still legal to get a proper abortion.
(Score: 2) by takyon on Wednesday April 19 2017, @01:56AM
The initial hangars might have to be excavated caves, until such time that industrial production on Mars takes off.
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(Score: 2) by tibman on Wednesday April 19 2017, @02:38AM
Airship hangers on Mars might need reinforced underground bunkers for when the weather gets rough.
SN won't survive on lurkers alone. Write comments.
(Score: 2) by PinkyGigglebrain on Wednesday April 19 2017, @07:28AM (1 child)
Wind on Mars is not really that powerful, the atmosphere is too thin to really do much but move the really fine particles of dirt around.
None of the Mars rovers would be able to handle a really windy day on Earth but they have no trouble with the sand storms on Mars.
(That was one of my few criticisms of "The Martian", A sand storm would not have been enough of a threat to the crew to abort the mission.)
"Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."
(Score: 2) by AndyTheAbsurd on Wednesday April 19 2017, @02:54PM
The author of "The Martian" was actually aware of this - but left it in, because without a reason for the other astronauts to abandon Watney, there was no story. (I learned this from the interview he did with the StarShipSofa podcast [starshipsofa.com]. IIRC, there were a few other scientific inaccuracies as well, but this was the most glaring.)
Please note my username before responding. You may have been trolled.
(Score: 2) by esperto123 on Wednesday April 19 2017, @01:09AM (1 child)
Reading this I've just imagined a ship arriving compressed and then expanding into a bucky ball, like that toy, it would cool.
(Score: 2) by kaszz on Wednesday April 19 2017, @02:18AM
It might be the way to land on Mars actually. Eliminating the need for a risky SpaceX booster type landing.
(Score: 2, Interesting) by khallow on Wednesday April 19 2017, @06:04AM (6 children)
Instead, fill it with hydrogen. The atmosphere of Mars is mostly CO2. That means the average molecular mass is around 44. Hydrogen is 2. You will get more than 95% of the lifting power of pure vacuum with hydrogen at equal pressure to the atmosphere. So almost the same lift with far less structure (latex and mylar balloons on Earth already operate at pressures and temperatures similar to summer on Mars.
(Score: 1) by khallow on Wednesday April 19 2017, @01:02PM
(Score: 2) by Rivenaleem on Wednesday April 19 2017, @01:31PM (1 child)
Is there not sufficient O2 in Mars's atmosphere to make the highly combustible Hydrogen still a highly risky choice?
(Score: 2, Informative) by khallow on Wednesday April 19 2017, @02:34PM
Is there not sufficient O2 in Mars's atmosphere to make the highly combustible Hydrogen still a highly risky choice?
No. For starters, the much lower pressure just by itself would make even a pure oxygen atmosphere considerably safer than Earth's atmosphere. And actual oxygen content of the martian atmosphere is 0.15% which is way below any threshold of risk.
The real danger from combustion would be hydrogen reacting with human breathable atmosphere in habitats or perhaps the vehicle's interior. There are a variety of designs where that could be a problem.
(Score: 2) by AndyTheAbsurd on Wednesday April 19 2017, @02:58PM (2 children)
You have to add mass and structure to prevent the balloon from collapsing due to atmospheric pressure pushing in. 0.01 atmospheres or less, isn't much
Well, surface pressure on Mars is just 0.00628 atmospheres, so no problem, right?
Please note my username before responding. You may have been trolled.
(Score: 0) by Anonymous Coward on Wednesday April 19 2017, @06:26PM
Averaged over the whole surface, maybe. At the bottom of Hellas it's about twice that.
(Score: 1) by khallow on Thursday April 20 2017, @04:45AM
Well, surface pressure on Mars is just 0.00628 atmospheres, so no problem, right?
Still is a problem. Pressure to resist deflation may be much lower, but so is the lift. Meanwhile with hydrogen, you get more than 95% of the lift without that internal structure. Plus we've already flown gas-filled balloons under near Martian conditions and the balloon can expand as it rises to maintain the lift.