Turns out it’d be a dissapointingly small sphere:
US annual defence budget = $800 billion
2% = $16 billion
Obsidian cost per kg = $5
Total kg in budget = 3.2 billion kg
Density of obsidian = 2.6 g/cm3 = 2600 kg/m3
Total volume of sphere = 3.2b/2600 = 1230769 m3
Volume of sphere = 4/3 π r^3
Radius = (3V/4π)^(1/3) = 66.48 m
The sphere would only stand at 133m tall, I propose we instead utilise the entire defence budget for a much more skyscraper like 490m tall orb
ignores engineering and construction cost. but we can assume that all people involved would work for free, because its a massive honour
Well that’s assuming it’s completely solid and not hollow. Hollow would probably be pretty huge, although the structural rigidity might not be great. Maybe we make a giant obsidian 3D printer and print it at like 10-15% infill.
An obsidian 3d print is less crazy than you might think. It’s essentially rapidly cooled lava.
Need something to hold the lava, then pressurize it to squeeze it through a nozzle that that has attached cooling units.
