Filled with Space

[Rufius]

Curious about other peoples thoughts on the plausibility of vacuum lift dirigibles. Take a rigid frame, put a non permeable membrane around it, expose it to open space, seal it, and then drop it into an atmosphere. Such a vehicle would have minimal energy requirements, solar panels could keep electric motors running for thrust and life support. It wouldn't be fast or much to look at, except for me, (I have a thing for dirigibles), but it's endurance would be unlimited. It would serve well as an observation or exploration platform for covert ops on lower tech worlds if built of radio translucent materials etc. It would be relatively cheap to build.
Big negatives I can think of are it's large size, and the fact that any puncture would result in an extremely rapid, and likely catastrophic loss of lift.
Just curious about other thoughts or problems I haven't forseen. Seems like a fun addition to an adventure.

 

[tjoneslo]

The big problem with the vacuum balloon is the air pressure problem. You need a rigid hull capable of withstanding full atmospheric pressure. Most balloons use Hydrogen or Helium at full atmospheric pressure so the hull can be much lighter. Doing that isn't hard, but since you want it to fly, it needs to be very light. And that can be a challenge.

The issue of altering lift go do up or down is not addressed by your design. Having a vacuum pump on board is a simple solution. It's simpler than having a supply of hydrogen/Helium and/or ballast, but still has power requirements.

You should google Montgolfier balloon. The idea here is you can seal the hull and use solar radiation to provide/alter the lift for your balloon.

 

[Rufius]

Thanks for the input, I will look up your balloon, the ability to change altitude wouldn't be a big deal. Access to and from could be subordinate craft or even grav belts. And I guess I was being lazy with the airframe. I figured a material with sufficient strength, (tec 15 has to have some awesome stuff right) it could still be flexible and stretched over a rigid frame and withstand the pressure. I was also considering it as an emergency option.
You are trapped on a dead ship in a decaying orbit, you have x,y, and z in your cargo hold etc.

 

[Whipsnade]

Curious about other peoples thoughts on the plausibility of vacuum lift dirigibles.

There is no plausibility of vacuum lift dirigibles.

However, that does not preclude you from using them in your setting.

 

[aramis]

There is no plausibility of vacuum lift dirigibles.

However, that does not preclude you from using them in your setting.

Wrong.

0.1 mm aluminum can hold against 2 atm difference if braced (pressure test for the Apollo LM was >+2 Atm; it was only 0.012mm thick). Thanks to the square cube law, it's plausible at certain relatively large sizes, where the volume has grown by the x^1.5 over the surface area, and the monocoque frame is still survivable.

They are quite plausible. But they are big.... the mass needs to be kept below 1.3 kg/m^3 at STP; Helium masses 0.178 kg/m^3 at STP, so needs to be kept below 1.28kg/m^3.

The Square Cube law is our friend. THe aluminum shell needs to only be the same thickness, provided it's braced, no matter the volume enclosed, and goes up as a SA:V^2/3. THe total load is a function of SA*Pressure, and the frame strength as a function of cross section of the members...

In simpler language, as it gets bigger, the volume goes up faster than the needed structure.
And an aluminum skinned dirigible IS doable, so it's plausible, barely, to make a sufficiently large dirigible with a vacuum instead of a pressurized interior.

 

[Whipsnade]

Wrong.

Assembled in space and than "lowered" into the atmosphere as the OP suggests?

Also, while increasing the size helps with the structural issues, increasing the size increases control and propulsion issues. Eventually you end with an "island in the sky" that no number of solar panels and propellers can control.

 

[atpollard]

For whatever it might be worth, I saw a parametric study of Blimps vs Rigid Airships that indicated that up to about the largest US Navy Blimp sizes, a blimp is cheaper than a Rigid Airship and for larger sizes, a Rigid Airship becomes cheaper.

The application to this topic is that there is probably a similar minimum size where vacuum is cheaper, but it will probably be larger than the largest Rigid Airship ever built ... so the first question becomes: Do you need a ship that large?

 

[atpollard]

Personally, I like a world with an exotic atmosphere (like Venus) where regular air at STP could be a lifting gas.

 

[whartung]

Is there a really dramatic benefit in lift and management of a vacuum airship vs a H/He airship?

The idea of having to shuttle them down from space seems kind of a management pain compared to inflating with hydrogen or helium.

How much extra lift capacity does a vacuum ship have over a comparably Hydrogen ship?

 

[aramis]

Is there a really dramatic benefit in lift and management of a vacuum airship vs a H/He airship?

The idea of having to shuttle them down from space seems kind of a management pain compared to inflating with hydrogen or helium.

How much extra lift capacity does a vacuum ship have over a comparably Hydrogen ship?

Lift: not really. The vacuum dirigible has about 1% more lift per cubic meter,

Management, kind of. It's easily managed, but it's going to require perfect maintenance... because...

Safety - no Any failure of the vacuum bubble is catastrophic.

It's doable, at a sufficient size, but it's not advisable. It's the kind of thing done by bored millionaires because they can, just to show off.

 

[Whipsnade]

It's doable...

Does "doable" equate "plausible"?

... not advisable...

Does "not advisable" equate "plausible"?

It's the kind of thing done by bored millionaires because they can, just to show off.

There's your answer, Rufius. It can be done, but for no other reason than bragging rights.

Some noble, scion, or dilettante is going to own one for the same reason some people have gold plated Monopoly games or mink trimmed umbrellas.

 

[aramis]

Does "doable" equate "plausible"?

Yes.
Or, at least, the antonyms of both (implausible and undoable) are effectively synonymous in use, and denotationally, plausibility is a huge subset of doability.

Plausibilty is not denotationally about advisability; it's about reasonably believable; scientific plausibility merely requires not breaking known axia of physics and/or chemistry.

It's quite plausible that my next door neighbor could freak out and kill me. It's neither advisable nor likely.

 

[Spartan159]

I just saw something but words fail me. o:

 

[Enoki]

One clear advantage of having a H / He filled envelope is that if you develop a leak and the pressure differential is small or nonexistent, you aren't going to lose lift rapidly. A vacuum filled hull will rapidly fill with atmosphere if punctured, even in a small way. That will, in turn, cause a rapid loss of lifting capacity.