A Great Telescope with Blurry Vision

The Hubble Space Telescope was one of the most ambitious scientific projects ever attempted. Unlike telescopes on Earth, Hubble would operate above the atmosphere, where clouds and moving air could not disturb its view. Scientists expected it to transmit remarkably clear images of distant stars and galaxies.

The telescope was launched aboard the space shuttle Discovery in April 1990. At first, the mission appeared successful. Then scientists examined Hubble’s early images and discovered a serious problem. The pictures were sharper than those from many ground telescopes, but they were not as clear as planned.

Tests showed that the main mirror had been made in the wrong shape. Its outer edge was too flat by only 2.2 microns—about one-fiftieth the thickness of a human hair. This tiny error caused light to spread instead of meeting at one point. The result was blurry vision.

The discovery was frustrating and embarrassing for NASA. Hubble had cost a great deal of money, and the public had expected extraordinary results. However, the telescope had one important advantage: engineers had designed it so astronauts could replace equipment in orbit. NASA began planning a correction.

Designing Space Glasses

Engineers needed to understand the mirror’s error with extreme accuracy. Once they knew its exact shape, they could build equipment that produced an opposite optical effect. The solution would work like glasses: it would not change the faulty mirror, but it would correct the light reflected from it.

Two new systems were prepared. The Wide Field and Planetary Camera 2 had corrective optics inside it. Another device, called COSTAR, used small mirrors to correct the light entering three other scientific instruments. COSTAR was about the size of a telephone booth.

The repair involved much more than installing these devices. Astronauts also had to replace solar arrays, gyroscopes, electronic units, and other parts. Every action had to be completed while the telescope moved around Earth hundreds of kilometers above the ground.

NASA created a detailed plan and revised it repeatedly. Astronauts practiced underwater, where floating conditions helped reproduce some aspects of working in space. They trained with special tools and full-sized models. Diagrams showed where equipment was located and how each part should be removed. Four astronauts learned the spacewalking tasks so that two teams could share the work.

Five Difficult Spacewalks

Space shuttle Endeavour launched on December 2, 1993, carrying seven astronauts. Two days later, Claude Nicollier used the shuttle’s robotic arm to capture Hubble and place it in the cargo bay.

The crew then began five spacewalks on five consecutive days. This was an unusually demanding schedule. Each astronaut had to remain cautious because one careless movement could damage the telescope or a spacesuit.

During the first spacewalk, Story Musgrave and Jeffrey Hoffman replaced gyroscopes and electrical units. On the second, Kathryn Thornton and Thomas Akers installed new solar arrays. One old array was damaged and could not be safely returned to Earth, so Thornton released it into space.

On the third spacewalk, Musgrave and Hoffman removed Hubble’s original main camera and promptly installed the improved camera. The next day, Thornton and Akers removed another instrument to make room for COSTAR. Their work required patience: two small electrical connectors initially refused to move. The astronauts adjusted their method and continued.

The fifth spacewalk completed the remaining repairs. Altogether, the teams worked outside for more than 35 hours. Ground controllers checked each electrical connection and verified that the new equipment was operational.

Waiting for the Results

The crew released Hubble on December 10. Three days later, Endeavour returned safely to Earth. Yet the most important question remained unanswered: had the correction actually worked?

Scientists needed several weeks to prepare the telescope and examine its first new images. In January 1994, NASA presented the results. The difference was dramatic. Stars that had appeared as unclear circles were now shown as sharp points of light. Images of the galaxy M100 demonstrated that Hubble’s planned performance had been restored.

The repair changed the outlook for the entire project. Instead of becoming a famous failure, Hubble developed into one of history’s most influential scientific instruments. Later servicing missions continued to renew its equipment and extend its useful lifetime.

The 1993 mission also demonstrated the value of careful planning and teamwork. Hundreds of people contributed: scientists measured the mirror, engineers designed the correction, trainers reproduced difficult conditions, astronauts performed the repairs, and controllers supervised the work from Earth.

Hubble’s problem could not be solved by one brilliant idea alone. Success depended on reliable information, repeated practice, timely decisions, and people who could respond calmly when a plan did not work perfectly. A mistake smaller than the width of a human hair had damaged the telescope’s vision. Human cooperation gave it a clear view of the universe.