On Wet Stars, 4 of 5

           Conversation between N. Hellerstein and G. David Nordley:

 

NH:

But a 10,000 km torus does provide room for a great big honking particle accelerator; any use for that?

 

GDN:

On could use it to push small starships up to near relativistic speeds, to deal with external issues.

 

NH:

To scout out an approaching nebula, I suppose. How much use would the particle beam be for asteroid and meteor defense? Or would that be a misuse of a precision technology? What asteroid defenses do you propose?

 

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NH:

Iain Banks noted, in “The Algebraist”, that the core of an all-liquid world will experience microgee. Any use for that?

GDN:

Well, the space station advocates believe there are all sorts of uses for microgee.   A hollow diamond sphere at the center would have essentially zero g throughout its volume, just as the electric field within a charged metal sphere is zero.

NH:

So, a room-temperature shirtsleeve zero-gee drydock. Excellent! I suppose they’ll build ships in it; so call them “Eggs”. But these Eggs need propulsion and Wet Net access to stay at the core despite whatever currents there are.

 

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NH:

Speaking of which... I am concerned that the wet star is too light to hold its hydrogen. How badly will it leak? Can keeping sufficient magnetosphere and oxygen keep it wet, or will it constantly have to absorb comets?

 

GDN:

At the 30K starlight equilibrium temperature (the surface for a thin atmosphere, the tropopause for a thick one) the mean molecular velocity of monatomic hydrogen is 0.852 km/s and molecular hydrogen is 0.6.   So it will leak a little, but not much.   Helium’s is 0.426, so one would expect the atmospher to become helium enriched with time.   Heavier gasses would freeze out before they get high enough to be subject to Jean’s evaporation.   It would lose a lot of this gas, even with a protective magnetic field, in stellar periastron passes, of course.

 

NH:

Suppose it takes a 1,000,000 year jaunt between stars. How much water will it lose? How does it go about ingesting new water? Earlier versions of the Wet Star were Neptune-sized and didn’t mind plowing into an ice ring one bit. But now that it’s Europa-sized and has vulnerable necessary surface structures, it’ll have to eat more daintily. Dock a comet at the tip of an elevator cable and sip its water down? Or will dropping comets onto the poles do?

And as for excess helium; give that as reaction mass to the gravity tug?

 

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NH:

And let’s not forget the gravity-tug. How big should it be?

 

GDN:

I thought I gave you a point design for that.   What kind of delta V do you want, and how fast do you want to get it?

 

NH:

Okay, here’s the mission: Nemo was built in Kuiper Belt orbit (or to be precise it was melted and stocked): lately its inhabitants, all 100 billion of them, want out from solar system politics. They plan to slingshot past Jupiter and head out into interstellar space; and they’re willing to take 100 Earth years until encounter. How big a tug would they need? And can they keep the tug after Jupiter encounter?

So they slingshot past Jupiter and are heading to Alpha Centauri. How long will it take them to get there? Suppose that half-way there they see that Alpha’s boring, Proxima’s the star to visit. How big a tug moon do they need to change course?