this post was submitted on 02 Dec 2023
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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
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.
Simple: bucket of lava, bucket of water, repeat.
Grabs a bucket. Quick, to the lava depository!