[extropy-chat] The other space program

Charlie Stross charlie at antipope.org
Sun Aug 15 10:38:14 UTC 2004

On 12 Aug 2004, at 18:48, Adrian Tymes wrote:

> --- Eugen Leitl <eugen at leitl.org> wrote:
>> Who's going to build the microwave
>> stations on the ground to
>> track the craft as it goes around the Earth?
> I generally agree with most of your objections here,
> but this one can easily be solved: solar panels (or
> cells on the craft's skin), or a fleet of microwave
> satellites launched by traditional means.
>> The Dark Sky station is as close to LEO as
>> SpaceshipOne. I.e., not at all.
> *shrugs*  Doesn't mean it isn't useful in its own
> right.  If they can solve the engineering issues of
> floating serious payload at high altitudes...floating
> cities, anyone?

Sure. Until ...

1. The neighbours on the ground get a bit annoyed about the city 
blocking all their sunlight

2. The neighbours on the ground who you've just drifted over point out 
that under existing international law they have sovereignty over their 
head space, and would you mind implementing their shari'a legal code 

(For the sake of point (2) above, assume the neighbours have SAMs or an 
ABM system)

3. The higher you float your city, the lower the density of the 
surrounding air. Therefore the volume of lift gas you need to displace 
your own mass in air also increases. When you're so high that 
atmospheric pressure is around 1% of sea level, your aerostat needs to 
hold 100 times the volume it encloses at sea level. The kind of 
altitude these folks are talking about implies kilometre-plus diameter 
gas cells, just to hold up something as massive as a 747. If you want a 
floating city, you either have to have gas cells the size of continents 
or float it down in the troposphere where the pressure's higher but 
there's nasty weather to contend with.

(See http://www.mypage.bluewin.ch/airshipsimon/design.html for a basic 
overview of how an aerostat works.)

-- Charlie

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