Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > Transhuman Space

Reply
 
Thread Tools Display Modes
Old 10-17-2013, 11:00 AM   #1
tantric
Banned
 
tantric's Avatar
 
Join Date: Mar 2005
Location: Athens, GA
Default Could you bubble-wrap a planet?

This could go in Geek Culture, but it's relevant to THS, too. Would it be possible to build a bubble around a planet to trap an atmosphere? How about one with selective permeability, maybe with an algae layer, for Venus (O2 only goes under).
tantric is offline   Reply With Quote
Old 10-17-2013, 01:47 PM   #2
johndallman
 
Join Date: Oct 2010
Location: Cambridge, UK
Default Re: Could you bubble-wrap a planet?

The problem is the astounding amount of material you'd need. The surface area of Earth is roughly 5x10^8 square km, 5x10^14 square metres. Taking 10 grams per square metre as a rough weight, that's five billion tons of membrane. You deal with much more material in terraforming, but not all at once, and not as one piece without (many) holes in it.
johndallman is offline   Reply With Quote
Old 10-17-2013, 02:35 PM   #3
smurf
Banned
 
Join Date: Jun 2005
Location: Bristol
Default Re: Could you bubble-wrap a planet?

No only wrap it in chewing and bubble gum. And that won't come off!
smurf is offline   Reply With Quote
Old 10-17-2013, 05:37 PM   #4
tantric
Banned
 
tantric's Avatar
 
Join Date: Mar 2005
Location: Athens, GA
Default Re: Could you bubble-wrap a planet?

I'm wondering if it could be grown in some situations. All you really need is CO2, H2O and sunlight. Atmospheric microbes with gas bags and really long cilia/filaments. And lots of extra DNA that doesn't turn on until later in the game.

Also, I have this image in my mind of looking up at night and seeing a giant soap bubble with a blue and green moon in it. *Sigh*
tantric is offline   Reply With Quote
Old 10-17-2013, 06:13 PM   #5
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Could you bubble-wrap a planet?

The problem is that it's essentially impossible to make the bubble wrap strong enough to not leak and tear, at which point the bubble wrap winds up on the ground with the atmosphere outside.
__________________
My GURPS site and Blog.
Anthony is online now   Reply With Quote
Old 10-17-2013, 08:18 PM   #6
Agemegos
 
Agemegos's Avatar
 
Join Date: May 2005
Location: Oz
Default Re: Could you bubble-wrap a planet?

Let's dirty up the back of an envelope.

We're looking up into the sky to see a bubble-wrapped moon. So let's check the figures for bubble-wrapping The Moon.

The purpose of this bubble-wrapping is to keep an atmosphere in where none belongs, which means that the air tends to go outward, which means that the pressure is greater than the weight of the air. The atmosphere enclosed pushes upward on the envelope and tends to support it. The envelope doesn't nave to support its own weight. That's good: it tells us that we don't need to worry about buckling. It also tells us that the bubble is supported by air pressure inside it, not hung off sky-hooks. That's terrific.

In order that the bubble stay where it is (as opposed to sink lower down and compress the atmosphere further, or bulge out and let the pressure drop, we need the weight of the envelope plus tension in the envelope to be equal to the unbalanced pressure of the atmosphere. We'll take the pressure above the envelope to be negligible, and the atmosphere below the envelope to be no more than 25% oxygen (to prevent a fire hazard) and no less than 10 kPa pp(O2) (so that it will support human respiration). That gives us an unbalanced pressure of at least 40 kPa on the envelope.

The surface gravity on the Moon is about 1.5 N/kg, so to provide the necessary compression to the envelope contents by weight alone would require 40000 N/m^2 divided by 1.5 N/kg = 27 tonnes per square metre. The density of the envelope material would be somewhere between that of polythene and that of diamond so that means an envelope thickness of about 8 to 28 metres. If you make it any thicker than that of reasonable material and you would have to support it somehow (perhaps with a denser atmosphere, though there are limits to that), and if you make it any thinner you will need tension in the envelope to hold it down. How transparent is 8 metres of diamondoid? How transparent is 28 metres of polythene?

The Moon's surface area is 3.8 * 10^7 square kilometres, which is 3.8 * 10^13 square metres. At 27 tonnes per square metre that is 10^15 tonnes. One quadrillion tonnes of transparent wrapping material.

Okay, so let's see how much tension will help.

A great circle of the Moon has a length of 1.1 * 10^7 m and an area of 9.5 * 10^13 m^2. With a pressure of 40 kPa that's about 3.8 * 10^17 N spread around 1.1 * 10^7 metres. Call it 3.4 * 10^10 N/m. The tensile strength of polythene is about 25 MPa and that of diamond about 60 GPa. A polythene envelope would need to be at least 1.4 kilometres thick to withstand the pressure (and then its weight would make the tension irrelevant). But 0.57 m of diamondoid could do it.

Allowing an order of magnitude for safety in the tension element (tearing would be catastrophic) we're in the region of a 3.6-metre thick diamondoid envelope restraining the air 40% by weight and 60% by tension, massing a total of 400 trillion tonnes. The structure is supported by an atmosphere of at least 0.4 bar contained within it: without that there it will collapse.


As is always the case with self-supporting structures, the real engineering difficulty is in getting the envelope and air into place without having both in place to support or constrain each other while you get them into place. I do not fancy building a centring for this dome.

Last edited by Agemegos; 10-17-2013 at 09:50 PM.
Agemegos is offline   Reply With Quote
Old 10-17-2013, 08:22 PM   #7
Flyndaran
Untagged
 
Join Date: Oct 2004
Location: Forest Grove, Beaverton, Oregon
Default Re: Could you bubble-wrap a planet?

For your image, you would only need a bubble so big as to look like it covered the planet from a human's perspective. That would make the problem orders of magnitude simpler.
__________________
Beware, poor communication skills. No offense intended. If offended, it just means that I failed my writing skill check.
Flyndaran is offline   Reply With Quote
Old 10-17-2013, 08:27 PM   #8
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Could you bubble-wrap a planet?

Your other option, which is easier, is that you don't need a single bubble. Bubbles in the kilometer range shouldn't be too difficult, and just build enough bubbles to cover the entire surface.
__________________
My GURPS site and Blog.
Anthony is online now   Reply With Quote
Old 10-17-2013, 08:44 PM   #9
Agemegos
 
Agemegos's Avatar
 
Join Date: May 2005
Location: Oz
Default Re: Could you bubble-wrap a planet?

Quote:
Originally Posted by Anthony View Post
Your other option, which is easier, is that you don't need a single bubble. Bubbles in the kilometer range shouldn't be too difficult, and just build enough bubbles to cover the entire surface.
Now you're talking about something scaleable and extensible, and which would not be subject to catastrophic failures. Have you no soul?
Agemegos is offline   Reply With Quote
Old 10-17-2013, 09:24 PM   #10
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Could you bubble-wrap a planet?

Quote:
Originally Posted by Agemegos View Post
Now you're talking about something scaleable and extensible, and which would not be subject to catastrophic failures. Have you no soul?
True, I apologize and retract my suggestion. And in penance, I will point out that GURPS Traveller: Rim of Fire has a bubble-wrapped planet.
__________________
My GURPS site and Blog.
Anthony is online now   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 11:37 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2022, vBulletin Solutions, Inc.