[extropy-chat] balloon stations at the edge of space

[Dan Clemmensen]

John K Clark wrote:

>"Mike Lorrey" <mlorrey at yahoo.com> Wrote:
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>>Vacuum balloons, while a nice SF fantasy, are not physically practical
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>How about using a conventional balloon to get up to 150,000 feet or so and
>then start your vacuum pump to get rid of the air in the vacuum balloon. It
>wouldn't have to be nearly as strong or heavy as one launched at sea level.
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>  John K Clark     jonkc at att.net
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But the advantage of vacuum over hydrogen at high altitude is 
negligible. The balloon is supported by differential pressure, not 
absolute pressure. For a given volume of balloon, you need a much 
smaller amount of hydrogen at 100K feet than at sea level. If I recall 
correctly, the same mass of hydrogen will provide the same lift, 
independently of the pressure of the outside atmosphere. That's why a 
stratospheric balloon is empty on the ground, but swells to a sphere at 
its maximum altitude.

The problem is not going to be mass, but volume. The project uses three 
types of balloons: the ascender, the station, and the orbiter. The 
ascender and station are primarily flotation devices. The orbiter can 
apparently float at the altitude of the station (nominally 140K feet) 
but depends increasingly on aerodynamic lift to replace flotation as it 
ascends to the top of the atmosphere. This means lift and drag forces 
must be counterbalanced. Eventually, lift and drag go away and we are in 
a pure ion thrust regime, but this thrust must also be counterbalanced. 
So, will it take less mass to maintain the shape with hydrogen pressure, 
or with structural elements?