Hubble’s problem and fix
On June 25, 1990, astronomers learned that the space telescope’s images were out of focus. Why? The main mirror had been ground to the wrong shape! Fortunately, because engineers knew what went wrong, they were able to design new optical components with the same error but reversed.
And the upgrades continued. In 1997, astronauts replaced instruments, repaired thermal insulation, and boosted Hubble’s orbit. In 1999, a different group replaced all six gyroscopes, a Fine Guidance Sensor, and thermal-insulation blankets. March 2002 saw the installation of a new main camera. During this mission, astronauts also replaced the solar arrays with new ones two-thirds as large that provided 30 percent more power.
Best. Telescope. Ever.
What really sets Hubble apart, however, is the astounding research scientists have conducted with it. The pictures are nice (and some even important), but let’s face it: The images Hubble has produced are the icing on the cake. Astronomers know it’s Hubble’s data that rocks our universe. Need proof?
In December 1995, the Hubble mission team pointed the telescope toward a small spot in the constellation Ursa Major. Earthbound telescopes showed nothing there. But after 342 exposures over 10 days, the resulting image — the Hubble Deep Field — shocked the world. It contained some 3,000 objects, nearly all distant, previously invisible galaxies. This and subsequent “deep field” images have revealed far more galaxies than astronomers thought existed, including some that existed when the universe was less than a billion years old.
In January 1999, Hubble imaged what was, up to that time, the most powerful explosion ever recorded. This optical counterpart to a massive gamma-ray burst identified the host galaxy and the cause: the collapse of a stellar core due to a supernova explosion.
Also in 1999, astronomers using Hubble completed an eight-year survey of Cepheid variable stars, those whose periods correspond to their real brightnesses. The results revealed that the Hubble constant — the expansion rate of the universe — is 70 kilometers per second per megaparsec, a number within 5 percent of the current value.