The most symmetrical, spherical man-made objects are the four fused quartz spheres made for the Gravity Probe B satellite (GP-B for short). This satellite experiment verified some predictions of General Relativity to new levels of accuracy and required four rotating very accurately spherical fused quartz spheres to act as gyroscopes. The almost perfect fused quartz spheres are coated with superconducting niobium:
GYROSCOPE FACTSThe gyroscopes are electrically suspended with only 0.001 inch clearance from the housing walls.
Sphericity is less than 40 atomic layers from perfect
Size- 3.81 centimeter (1.5-inch) diameter
Composition- Homogeneous fused quartz
Coating- Niobium (uniform layer 1,270 nanometers thick)
Spin Rate- Between 5,000 Ð 10,000 RPM
Polishing the Perfect Sphere
Challenge: Polishing a fused quartz sphere with standard methods creates "hills and valleys," destroying sphericity.
Solution: Create a tetrahedral lapping and polishing machine that brushes the sphere with micro-inch abrasive slurry in random variations.
Result: Each fused quartz sphere deviates less than one micro-inch from peak to valley (25 nm), making them the roundest objects ever created on Earth.
Bonus Fact: In September 2004, GP-B received a certificate from Guinness World Records Limited, acknowledging that the GP-B gyroscope rotors had been entered into the Guinness Database of World Records. The certificate reads as follows:
"The most spherical man-made objects are the fused quartz gyroscopic rotors onboard the Gravity Probe B Spacecraft operated by NASA and Stanford University. Their average departure from mathematically perfect sphericity is only of their diameter."
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