Step by Step
1
Launch and the mirror flaw
Hubble launched in April 1990, but its primary mirror had been ground to the wrong shape, causing spherical aberration and blurry initial images.
2
The fix and ongoing servicing
Servicing Mission 1 in 1993 installed COSTAR (Corrective Optics Space Telescope Axial Replacement), effectively correcting the flaw. Hubble received five servicing missions in total over its operational lifetime.
3
Technical specs and key discoveries
Hubble orbits at 547 km altitude, observing in ultraviolet, visible, and near-infrared wavelengths. Its key discoveries include determining the age of the universe (about 13.8 billion years), confirming the accelerating expansion of the universe (dark energy), finding that black holes exist at the centers of most galaxies, and observing solar system formation processes.
4
The Hubble Deep Field and legacy
The Hubble Deep Field (1995), a 10-day exposure of a tiny, seemingly empty patch of sky, revealed thousands of previously unseen galaxies. Hubble remains operational as of 2026, working alongside its successor, the James Webb Space Telescope.
Applied Walkthrough
1
When Hubble launched in April 1990, astronomers quickly discovered its primary mirror had been ground to the wrong shape, causing blurry images due to spherical aberration — a serious early setback for the mission.
2
In 1993, a dedicated servicing mission installed COSTAR, effectively correcting the flaw and unlocking Hubble's full potential — the first of five total servicing missions that would keep the telescope operating and improving over its decades-long lifetime.
3
Once corrected, Hubble went on to make landmark discoveries: determining the universe's age at about 13.8 billion years, confirming the universe's accelerating expansion (evidence for dark energy), and finding that supermassive black holes reside at the centers of most galaxies.
4
Perhaps most strikingly, the 1995 Hubble Deep Field — a 10-day exposure of what looked like an empty patch of sky — revealed thousands of previously unknown galaxies, cementing Hubble's legacy as one of the most transformative scientific instruments ever built, and one that remains operational even today, working alongside its newer counterpart, JWST.
Exam Application
Exams test whether you know Hubble's early mirror flaw and how it was corrected, whether you know Hubble's key scientific discoveries, and whether you know the significance of the Hubble Deep Field.
⚠ Common Trap
The most common trap is assuming Hubble's mirror flaw meant the mission was a failure — the 1993 servicing mission successfully corrected the issue with COSTAR, after which Hubble went on to become one of the most scientifically productive instruments in history, making it a story of successful recovery rather than failure.
✓ Quick Self-Check
1. What problem did Hubble's mirror have at launch, and what caused it?
Spherical aberration, caused by the mirror being ground to the wrong shape.
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2. What corrected this flaw, and when?
COSTAR, installed during Servicing Mission 1 in 1993.
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3. Name two major discoveries made using Hubble.
Any two of: the age of the universe, accelerating expansion (dark energy), black holes in most galaxies, solar system formation.
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4. What was the Hubble Deep Field, and what did it reveal?
A 10-day exposure of a tiny patch of sky (1995), revealing thousands of previously unseen galaxies.
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5. What wavelengths does Hubble observe in?
Ultraviolet, visible, and near-infrared.
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