One of the most universally agreed upon greatest telescopes of all time started out as a near failure.

The $1.5 billion Hubble Space Telescope was deployed in 1990 to great expectations, but the first images returned were smudgier than expected. Hubble's main mirror, 2.4 meters (8 feet) across, was misshapen by a fraction of a hair's width. Astronauts visited Hubble in 1993 to install corrective mirrors -- glasses, essentially -- and Hubble assumed its rightful position in the telescope hierarchy.

The mirror is not big by telescope standards. Hubble's advantage is that it is situated in space, above Earth's blurring atmosphere.

"That immediately made the sharpest pictures ever," Tucker says.

With its array of cameras and sensors, Hubble has peered into the farthest reaches of the universe. Hubble has shown the world that the smallest patches of sky are full of galaxies and revealed dusty star-forming regions that may resemble earlier versions of this solar system.

Hubble is a joint project of NASA and the European Space Agency.

The observatory's design has helped keep the orbiting observatory in the forefront of discovery throughout its lifetime. Hubble's parts are easily removed and replaced, so each time astronauts pay Hubble a visit, they can install an even more powerful instrument.

Most recently, astronauts installed a new primary camera and fixed Hubble’s nonworking infrared camera.

The orbiting observatory is better than ever.