What groundbreaking product design feature allowed NASA to correct the Hubble Space Telescope's initially flawed main mirror without bringing it back to Earth?

The Hubble Space Telescope represents one of astronomy's greatest product design achievements. Launched in 1990, this orbital observatory overcame significant early challenges to become a cornerstone of modern astronomical discovery. This trivia question explores a fascinating aspect of Hubble's innovative design that astronomers and space enthusiasts might know, but casual observers might miss.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

Corrective Optics Space Telescope Axial Replacement (COSTAR) system that installed corrective mirrors
Automated self-healing nanopolymer coating that gradually reshaped the mirror surface
Remote-controlled laser etching system that recalibrated the mirror's curvature
Adaptive fluid lens technology that compensated for the spherical aberration