Which design feature was specifically added to the Hubble Space Telescope to allow astronauts to service it in orbit?

The Hubble Space Telescope is one of astronomy's most iconic instruments, but its design journey was filled with challenges and innovations. This poll explores the fascinating product design decisions behind this revolutionary observatory that has changed our understanding of the cosmos since its launch in 1990. Test your knowledge about how engineering constraints, scientific requirements, and practical considerations shaped this remarkable scientific tool.

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Handrails and foot restraint attachment points
Self-healing polymer coating on the exterior
Retractable solar panels that fold into the body
Automated robotic repair arms