What critical flaw was discovered in the Hubble Space Telescope shortly after its 1990 launch that required a major repair mission?

The Hubble Space Telescope is one of astronomy's most celebrated instruments, but it wasn't always perfect. Shortly after its launch in 1990, astronomers discovered a serious flaw that threatened the entire mission. This poll tests your knowledge about one of the most famous product recalls in astronomical history - when NASA had to fix their $1.5 billion space telescope while it was already orbiting Earth.

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The primary mirror was ground to the wrong shape, causing spherical aberration
Solar panels failed to fully deploy, providing insufficient power
The main camera's sensor was installed backward, inverting all images
Faulty gyroscopes prevented proper alignment and targeting