The Niven Bubble

[Geode]

Take an iron-nickel asteroid, core it, insert a chunk of ice into the core, seal the opening.

 

Now, using solar mirrors, heat the asteroid, rotating it slowly so as to achieve some uniformity of heating.

 

What's supposed to happen is that the ice within becomes liquid as the mirrors heat the rock, which migrates through the mass of the asteroid. The liquid becomes steam, steam pressure forces the now-molten body to adopt a spherical shape and the mirrors are removed. The thing cools, retaining its spherical shape.

 

I read about this a long time ago in a science fiction book by Larry Niven and Jerry Pournelle. They didn't call it the Niven Bubble, that's my doing.

 

Anyone know anything about this? I read something else last week that suggests it won't work unless the metals are foamed. I have no idea what that means, I'll try to retrieve the source and post. Is an iron-nickel body the only sort the above scheme would/might work on? Any other thoughts?

 

 

Geode

[ed84c]

It would be easy to melt an asteroid made from Ni and Fe using earth lasers.

[Ophiolite]

Anyone know anything about this? I read something else last week that suggests it won't work unless the metals are foamed. I have no idea what that means' date=' I'll try to retrieve the source and post. Is an iron-nickel body the only sort the above scheme would/might work on? Any other thoughts?

Geode[/quote']An interesting idea. I used to read Niven avidly, but I don't recall this one.

 

I assume the foaming refers to penetration of the Fe/Ni by steam, so that it becomes porous and of overall lower density. If this is a pre-requisite for the process to work then my guess is that is related to reducing the viscosity of the melt, though that should have more of an impact upon timing than success or failure.

 

I can't see it working with the stony meteorites (chondrites and achondrites) for two reasons.

1. Many/most/all of them are thought to be structurally weak, being agglomerations of particles rather than unitary bodies.

2. As the asteroid was heated it would be subject to partial melting (where certain minerals would melt while their neighbours did not). This would further reduce its integrity and provide a route for the escape of the steam.

 

Now, why would you want to do this?

[Geode]

Ophiolite wrote: Now, why would you want to do this?

 

Orbital habitat/generation ship. That was the first thing I thought of when I read this.

 

I wish I remember what book I'd found this in. It wasn't a short-story compilation, or it wasn't all short stories. Most of the work, as I recall (I read this 17 years ago) was speculative stuff about returning to the moon, powering aircraft from orbit, and so on.

 

I was taken with the idea, it seemed that it would make a good setting for a story, if nothing else, and I got maybe 20 pages done before stopping (ran out of plot, I hate it when that happens). I eventually found a suitable ending, and lost the calculations I'd done regarding the size and internal this and that. I scanned the web again looking for info when I happened across a piece of something last week stating that it probably wouldn't work at all for stony asteroids, for reasons cited, and wouldn't be cost efficient for metallic bodies.

 

Back to hollowing the thing out 'normally'.

 

 

Geode

[Tigerbeam]

It's called Tiamet, it was made in the part of Larry Niven's known space series, and is referenced in a number of his stories. The main purpose of it is to make a habitat in it, spin it, thus creating an enviroment with gravity. Niven speculated that childbirth would not be possible in zero gravity, and the society of belters living in the asteroid belt would value Tiamet, as they would not have to visit Earth just to have children.

 

I know Niven, i just don't know physics.

[[Tycho?]]

It would be easy to melt an asteroid made from Ni and Fe using earth lasers.

 

Are you joking? To melt an entire asteroid of any size big enough to live in would take an enourmous amount of energy, our lasers are just not that powerful yet.