[TML] A new tourist ship design

[Timothy Little]

On Sun, Jan 13, 2008 at 12:48:30PM +0100, Knapp wrote:
> As I understand gravity (not well) I thought that if you had one g
> it would fade with the square of the distance.

Natural gravity does in such situations, yes.  Artificial gravity
might not.


> So this would give the air the same depth as on the Earth.

If it did fade as the inverse square, no.  Inverse-square means
quarter acceleration at twice the distance.  For Earth, that "twice
the distance" is more than 6000 kilometres.  For a 500m ball, it's
quarter the acceleration at 500m, and all the air escapes within
seconds.  The fall-off would have to be a lot slower than inverse
square.


> If a ship can do 6g for weeks then that should be no problem right,
> power is there?

It may be a problem.  According to a thermodynamics text I have,
nearly 90% of Earth's heat radiated to space comes from the
stratosphere, at an effective height of about 30 km averaged over a
range of far-IR wavelengths.  A ball of 30km radius radiating at 250 K
emits about 2500 GW.  That's quite a lot of power, though it is within
Traveller starship capabilities.

A trickier problem is that the atmosphere will have a mass of more
than a billion tonnes.  It will almost certainly outmass the ship
itself.


> If you are near a sun it should heat the air the same as it does on
> Earth.

Unfortunately no.  Little sunlight is absorbed by the air (about 10%
average).  Most is either scattered or passes through to the ground.
The warm ground radiates low frequency IR, which the atmosphere can
absorb.  In the lower atmosphere, convection also plays a role.  The
atmosphere radiates IR both into space and back to the ground.

Using that 2500 GW figure above, the surface would need to deliver
about 800 kW/m^2 into the air.  Sunlight provides less than 1 kW/m^2.

So unlike Earth, heat from the surface will have negligible effect on
the atmosphere.  The ship would have to directly replenish heat in the
air, somehow, without cooking the surface.


> This is a sphere and is that not what you are implying with one above
> and one below;  A grid of grave balls?

My view is that the artificial gravity only applies between the
plates, apart from some edge effects that very quickly fall off with
distance.  So to retain an atmosphere IMTU with grav plates, you'd
need a shell of grav plates above the atmosphere as well as in the
"ground".


> The whole idea is a bit crazy and I liked it because it does seem to
> be within the rules.

Oh yes, it is crazy and I like it :-)


- Tim