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Setting the scene
By 1990, ground-based telescopes were limited by Earth's atmosphere, which blurs images and blocks ultraviolet and infrared light. Astronomers had dreamed of a space telescope since the 1940s—Lyman Spitzer proposed one in 1946. NASA and the European Space Agency collaborated on the Large Space Telescope, renamed for astronomer Edwin Hubble, who discovered the expanding universe. The telescope was designed to orbit above the atmosphere, providing unprecedented clarity. Construction began in 1978, with a 7.9-foot primary mirror polished to exquisite precision.
What happened
The Hubble Space Telescope launched aboard Space Shuttle Discovery on April 24, 1990. It was deployed the next day into orbit 340 miles above Earth. Initial excitement turned to horror when the first images came back blurry—Hubble had spherical aberration. The mirror had been ground to the wrong shape, off by 2 microns (1/50th the width of a human hair). The error was caused by a faulty measuring device during manufacturing. NASA faced embarrassment and criticism. The flaw was correctable, and in December 1993, astronauts on STS-61 installed corrective optics (COSTAR) during a dramatic spacewalk mission.
Why it still matters
After repair, Hubble revolutionized astronomy. It has made over 1.5 million observations, including determining the age of the universe (13.8 billion years), discovering dark energy's accelerating expansion, and capturing iconic images like the Pillars of Creation and Hubble Deep Field. Hubble's data has led to over 20,000 scientific papers. The telescope, expected to last 15 years, has operated for over 34 years. It demonstrated the value of servicing space telescopes and paved the way for the James Webb Space Telescope. Hubble transformed our understanding of the cosmos and brought the universe's beauty to the public, making it one of NASA's most successful missions.
Background
Servicing missions later corrected its initial optical flaw.