Saturday, October 26, 2013

Expansive Zero Gravity Atmosphere Concepts Gaining Social Momentum

The Virga comic series has recently hit the (virtual) shelves, and it offers quite a vision of a world that continues seemingly infinitely in all directions, and yet is filled with air that a human can breathe.  This is an installation onto the Virga series by Karl Schroeder, a Canadian science fiction author.  At the time of writing this, Virga comics 1 through 3 are out, and I'm rather excited to see these vivid illustrations of such a world.  Naturally, I want to make a post that covers where it fits into my own views on such worlds.

I will continue to pick at the parts that I find to be particularly bad abuses of physics, but I should note that I find the comic and series extremely cool overall.  The comic, in fact, touched on a few elements of a mixed gravity (my own term) world.  This is a very new kind of environment that is being described, and the author has done a great service by working to popularize it.

Birds and Fishes

The Virga comic portrays fishes with wings.  Even Gerard O'Neill, in his book The High Frontier talked a good deal about fish, which I did discuss on Space Exploration Stack Exchange.  Other people were apparently interested in zero gravity dolphins, which I have to admit, was a little shocking.

(image copyright Virga Comics, used as fair use here
this is from Comic 3 which can be purchased from Comixology for $1.99)

And I feel like the odd one out, thinking that birds would be considerably more interesting.  Of course, my visions hinge around the "friction buffers".  In my own vision of the gravity balloon, a flying fish that gets caught up in the rotation of a cylinder will not fare well at all.  I have no idea how birds will manage to cope with zero gravity.  Still, I'm satisfied thinking "life will find a way", and imagine that birds will at least figure out how to propel themselves long enough to get to some food.  If they flew into an artificial gravity cylinder, then they would revert to their familiar flying mechanics.  I imagine birds would be quite sensitive to Coriolis forces as well, and learn to use them - getting extra "lift" by flying in the direction opposite of the rotation.  Birds are quite good at minimizing effort on Earth.  I doubt that zero gravity worlds would be comfortable to them, but they're also some of the most adaptable species on Earth.  But that's just my 2 cents.

In addition to the bird-fish in Virga, there are also some illustrations of humans with wings or just plain flippers on their feet.  That's very entertaining to see.  It really brings to life the world that we once thought would be the promise of air travel in the early 20th century.

The author also seems to have done a great deal to realize a vision he talked about in an article written about Virga when the idea was much younger.
"For years I’ve had flashes in my mind’s eye of an endless sky, and of towers and buildings floating in that sky. A particularly persistent image was of a woman standing at a tower window looking out over an ocean of cloud, with no ground beneath the tower."
This vision was basically realized.  I believe this is the exact vision the author had in mind when the comic's sort of castle-scape was drawn.

(image copyright Virga Comics, used as fair use here
this is from Comic 1 which can be purchased from Comixology for $0.99)

Novel Environment Physics

Several phenomenon are referenced in the Virga in-world that are quite unique to a mixed gravity world.  Things that stood out in particular:
  • spin downs, where the ring looses gravity
  • dropping out the bottom of the ring on a air-bike

While I haven't read much of the book series, they very quickly got the plot twist of a spin down in the first book.  This is an event where they stop spinning the ring, and everyone on it loses gravity.  This was reference in the comic, although not specifically illustrated to my knowledge.  This sort of thing is only really thinkable in a mixed gravity world, and so is the dispatch of the air bikes (there may be an official term for these, but I do not know it).  The idea there, is that people launch themselves out the bottom of the ring structure to provide quick access to the larger world.  That makes sense certainly, but it would definitely be a rush as you fall, fall, fall, and then wind up without any ground left to catch you.

(image copyright Virga Comics, used as fair use here
this is from Comic 1 which can be purchased from Comixology for $0.99)

I would have liked to see some mention of false forces in artificial gravity rings, but there's still plenty of material in the series I haven't got to.  I think the "preferred" direction in artificial gravity will be a very huge concept for people who ever live in such a place.  I think it will be almost incomprehensible to them that on Earth people can't distinguish easily between north and south.  But then again, in the free floating space between habitats, none of the 3 dimensions we live in can be distinguished.

There are some other details that are generic to large zero gravity environments too.  For instance, the way people move around sticks out.  The way people structure the beds sticks out.  Also, the ports are often in apparently zero gravity environments.  I think it would be difficult to manage in such an area, but I guess that's the idea, and that the people who live there are quite used to the concept.

These zero gravity artificts strikes me as similar to a particular vision of the future (actually the year 2000) by french artists Jean-Marc Côté and other artists, made for the 1900 World Exhibition in Paris.  These visions show people prancing around the skies in only minimalist wingsuits.   It's well past the year 2000 now, and all we have are wingsuit gliders which can't sustain horizontal travel for more than a few seconds.

 (Public domain images, source)

I find the similarities between these and the Virga comic rather stunning actually.  Sure, the physics and technology itself is different.  But in both we see impossible-seeming air vehicles, and people propelling themselves around with simple flaps.

Intermediate Scale Environments

I was very happy to see a number of creative environments that exist often on the scale beyond a single artificial gravity ring.  In Schroeder's vision, the Virga world has many small suns (really fusion reactors) which define a nation, which then consists of many gravity habitats.  If I am to take the expanse of such an area to be defined by the path length of photons in the atmosphere, this is quite large.  Actually, the heat would be intolerable near the sun itself because it would entail huge intensities, which would heat the air, which would cause other problems.  But I'm not determined to ruin everything.

Aside from the "suns" there are lots of other structures depicted.  In particular, green things that look like they have bushes growing on them, which I can only assume are some type of growing platform.  In the Virga comic, they portray many artifical gravity rings hanging from these structures.  This is very cool, as it represents a sub-scale to the "suns" or "nation" scale.  Larger than the suns/nations, there's still the air circulation patern in the Virga world.  I completely agree that this is sci-fi gold, because there's so much potential expanse to this world.  The scales that are or could be at work in a science fiction world are:
  • The individual rotating ring / cylinder
  • A cluster of rings, possibly tied together
  • Suns/nation level which spans the distance light can travel
  • Circulation patters, which are the largest grouping in super-large habitats
  • The gravity balloon itself
  • Possibly multiple gravity balloons within a solar system
The author did mention the possibility of the final scale somewhere in his online writings, but it's not central to the Virga story at all.
"Circulation is necessary because otherwise you run the risk of having the atmosphere condense and then freeze onto the outer skin of the sphere.  (This will only occur if it's orbiting in the outer part of a star system, of course--but in my books Virga does just that.)"
So in essence, this just fills in one scale of the hierarchy of the organization of such a place.

(image copyright Virga Comics, used as fair use here
this is from Comic 1 which can be purchased from Comixology for $0.99)

The Remaining Problems

Displayed front-and-center on the cover of the first Virga comic, probably the most iconic image of the series, is a man riding an air bike counter-rotation around the surface of an artificial gravity ring.

There's only one problem with this - it would never work that way.  I know, the idea is that the rotating structure "drags" the air with it, or something like that.  The only problem is, we already have models for this type of fluid mechanics problem, and it does exactly not do that.  I've written several posts on the fluid mechanics of the issue, and I've not seen a single thing that refutes the basic estimates of power dissipation per unit area, or the consequences of that.  In fact, the worlds portrayed in Virga are not "smooth" in the thermal-hydraulic sense at all.  They consist of macroscopic imperfections, otherwise known as buildings.  These would only add to the massive stirring of the atmosphere in that environment.  Not only would such a craft be unmanageable in the situation portrayed, but so would walking.

I don't know what kind of scale these illustrations are tying themselves to.  It seems pretty indefensible to imagine that they're much less than 500 meters in diameter.  The calculation is then simple.  Acceleration is v^2/r, and that equals to one Earth gravity.  Relative to the ambient air, that results in 110 mph.  Even if we were as generous as possible to the concept, we must somehow imagine that the airflow transitions from one stream which is at rest to another stream at this velocity.

Could the Idea Catch On?

Virga represents one extreme.  As I covered in my last post, there is a fairly specific limit to how large of a habitable area you could create with this type of method, and this science fiction world isn't far from that.  The scales and the simple expanse of the world are beyond our ability to think clearly about.  There's a meaningful place for this type of thought.  Particularly since this is a fully 3D world, the transportation limitations aren't actually any greater than Earth itself, in spite of being so many orders of magnitude more expansive.

On the other extreme, there's another reason to promote the concept of expansive zero gravity space habitats.  That's because they have good near-term prospects for space development.  The sales pitch is that we can pick a nice asteroid, walk in, and then just "put up the wall paper".  In practice, it's a little bit more complicated of course, but that description is quite an honest summation.  Asteroids of the relevant size might have enough fissures to allow us to venture straight into their center, unimpeded.  Then, even if we exert a pressure on the walls we're assured stability due to the fact that gravity itself would be sufficient to hold against the pressure.  Sure, there's a great deal of exploration and then analysis which would be requisite before we ever think about doing this, but it's something that can have safety demonstrated before hand, and it's something that can scale up to significant sizes for a significant number of people, all the while being in the depths of space.

The key to all of this, both the large and the small, is the prospect of a habitable environment which is sometimes zero gravity and sometimes artificial gravity - mixed gravity.  The smallest habitat within an asteroid with the "wallpaper" model may only host a small tube of low gravity and frustrating Coriolis forces.  But you can hop off of that to do work in zero gravity.

I come at this from the perspective of space advocacy.  The sci-fi world of Virga is the fantasy part of the spectrum, but the basic concept of a mixed gravity world are the same.  It's also really really cool.

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