Hubble at 30: The Telescope Built to Be Fixed

When the Hubble Space Telescope sent back its first pictures in 1990, the stars were blurred. Its primary mirror had a production error: its edges were too flat by 0.003 mm, enough to cause the optical flaw called spherical aberration. The mirror could not be repaired in orbit. Hubble was saved anyway, because of a decision made in 1983: it would be maintained by astronauts in space.

"Trying to do stellar observations from Earth is like trying to do birdwatching from the bottom of a lake." — James B. Odom, Hubble program manager 1983–1990

From an idea to a launch

The first concrete plan for a telescope above the atmosphere's blurring came from Princeton astronomer Lyman S. Spitzer in 1946, eleven years before Sputnik. In 1962 the National Academy of Sciences recommended Earth-orbiting telescopes. NASA launched four Orbiting Astronomical Observatories between 1966 and 1972, only two of them successful; the last, Copernicus, used a 32-inch (80-cm) telescope for ultraviolet observations from 1972 to 1981.

NASA proposed a Large Space Telescope in 1972, and Congress funded it five years later. It was to have a 94-inch (2.4-meter) primary mirror, observe mainly in visible and ultraviolet light, last 15 years, and ride the still-unfinished Space Shuttle in 1983. In 1983 the plan to bring it back to Earth for refurbishment gave way to repairs by spacewalking astronauts, and it was renamed for astronomer Edwin P. Hubble, with launch set for October 1986. The Challenger accident that January grounded the Shuttle, and Hubble waited until 1990.

Lyman Spitzer. Image from NASA's page.

Hubble's major components. Image from NASA's page.

Engineers working on the primary mirror. Image from NASA's page.

On April 24, 1990, Space Shuttle Discovery (STS-31) carried the 24,000-pound telescope to an unusually high 380-mile orbit, with five instruments aboard. Steven Hawley lifted it out with the robotic arm and released it once its solar arrays and antennas had unfolded. Bruce McCandless and Kathryn Sullivan waited suited up in the airlock in case a spacewalk was needed — which made them probably the only two interested parties who did not see the release. The Shuttle stayed 50 miles away for three days in case of trouble; none came.

Hubble released during STS-31. Image from NASA's page.

A star that should have been a single point of light, from the first Wide Field/Planetary Camera. Image from NASA's page.

The fix

Because the error in the mirror was precisely known, engineers designed corrective mirrors that astronauts could install on the first servicing mission, already planned. In December 1993 the crew of STS-61 made an unprecedented five spacewalks. They installed COSTAR, a corrective-optics unit, in place of the High-Speed Photometer — giving up one instrument so the others could work as designed — replaced the original camera with an upgraded WF/PC-2, and fitted stiffer solar arrays to stop vibrations the first pair caused. Within a month, Hubble's images showed the telescope was back to its expected capability.

Kathryn Thornton and Thomas Akers installing COSTAR. Image from NASA's page.

The core of galaxy M100, before and after the first servicing mission. Image from NASA's page.

Four more visits

The last visit almost did not happen. After the 2003 Columbia accident, NASA approved only Shuttle flights to the safe haven of the International Space Station. On the National Academy of Sciences' advice it reversed that in 2005, and the flight went in 2009 — four years past Hubble's original 15-year design life. It was expected to keep the telescope working through 2014; at its 30th anniversary, Hubble was still going strong.

Michael Massimino and Michael Good repairing STIS on the final servicing mission. Image from NASA's page.

Hubble after its final release, STS-125. Image from NASA's page.

Across the five missions, 16 astronauts made 23 spacewalks totaling more than 165 hours — just under seven days. Beyond what its data did for astronomy — scientists rewrote textbooks — Hubble proved the value of building a space observatory that can be maintained.

Thirty years of pictures

The Cat's Eye Nebula, NGC 6543, 1995. Image from NASA's page.

Eta Carinae, 1996. Image from NASA's page.

Barred spiral galaxy NGC 1300, 2005. Image from NASA's page.

The 20th anniversary image, in the Carina Nebula. Image from NASA's page.

The 25th anniversary image: star cluster Westerlund 2. Image from NASA's page.

One of the 30th anniversary images: spiral galaxy UGC 2885. Image from NASA's page.

Sources

• NASA, 30 Years Ago: Hubble Launched to Unlock the Secrets of the Universe. The Odom quotation is from Kathryn D. Sullivan, Handprints on Hubble: An Astronaut's Story of Invention (Smithsonian Institution, 2019), as cited there.