Balloons work by allowing hot air to find a zone where its surroundings match its buoyancy, modified by the weight of the craft surrounding it.
Glass surrounding a vacuum has great resistance to pressure.
Therefore, if you can create a vacuum surrounded by thin but strong (doped, obviously) glass, would you not have one hell of a lovely, non-explosive balloon?
Hard to get back down, I admit, but if you had a craft heavy enough to cruise along at a relatively low altitude, then you could come up with options…
metapundit
/ August 28, 2007And with a fairly catastrophic failure mode! I could see somebody like JP Aerospace (http://www.jpaerospace.com/) using this though – vacuum based balloons ought to be able to go higher than “light gas” balloons, right?
alex
/ August 28, 2007Yes, you would, and these items exist. They’re called “Dewars” and they’re used to capture and hold very cold liquids (liquid N2, O2, etc.) since they don’t conduct heat very well through the vacuum. When they break they have a mild tendency to implode rather than explode. Usually they just crack though, even when they are made out of high durability glass (such as pyrex).
However, since glass is much much denser than air, you would have a hell of a time getting it to float in air at all. Maybe if you backfilled it with Helium instead you might be able to get it to float, but it would not be easy.
happycrow
/ August 28, 2007Hrm. I wonder what might be light enough to do the job?
alex
/ August 28, 2007It has to be lightweight and be a good gas barrier, otherwise the outside atmosphere slowly leaks into the vacuum and fills it up. Aerogels and Xerogels might work though.
James
/ August 28, 2007I remember reading about a proposed exploration vehicle for non-terrestrial planets. The idea was to build a lightweight structure while still in the vacuum of space that looks a lot like a hot-air balloon. Then, with very lightweight rockets you could slow the craft down just enough to float in the outer atmosphere to act as a platform for launching multiple smaller craft without the need to ‘burn them in’ from orbit. The problem is still the material to build it with. Even in a light gas there is almost no way to prevent leakage.
Alex
/ August 28, 2007Good breakthroughs have been made to prevent light gas leakage depending upon what you want to pay for. A combination of metalized mylar and polymer nanocomposites/multi-layer polymer barriers can yield an almost impervious gas barrier. These materials are in use today and will probably be in use for the high-altitude airships that are under consideration by several organizations.
I would presume if the exploration vehicle described above ever comes to be that they would use things like this to make the baloons in situ once the outer atmosphere “orbiter” is set up.
James
/ August 28, 2007I volunteer to open a bar on one of them……
happycrow
/ August 28, 2007And I volunteer to whip up space fajitas.