Its exquisite images have graced the pages of astronomy books and calendars all over the world and provided astronomers with invaluable information on the mysteries of the universe.
Now, after 19 years orbiting hundreds of miles above Earth's surface, the Hubble Space Telescope is getting its fifth and final makeover, with a slate of new instruments and repairs scheduled that will restore and expand some of the iconic telescope's capabilities.
The astronaut crew that will give Hubble its tune-up will launch aboard the space shuttle Atlantis on May 11 for an 11-day mission. The excitement over the mission and Hubble's capabilities afterward is palpable among NASA scientists.
"If we are successful, [Hubble] will be more powerful and robust than ever before and it will continue to enable world-class science for at least another five years," said Ed Weiler, associate administrator of NASA's Science Mission Directorate in Washington, D.C.
With those added five years, "we'll be entering our second quarter century on Hubble — that's not bad for a mission we hoped would last 10 to 15 years," Weiler added.
In those five extra years, scientists will use Hubble to peer back closer to the beginning of the universe, look for more exoplanets and try to help solve the mysteries of dark matter and dark energy.
Hubble is badly in need of the repairs and upgrades planned for this month.
"It's been seven years since we've serviced the Hubble Space Telescope," said David Leckrone, Hubble project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. That's "twice as long as we should go in terms of servicing intervals. As a consequence of that, over the last few years, we've seen significant deterioration within the set of scientific instruments that we provide to the astronomical community."
One of the instruments the astronauts will try to fix is Hubble's Advanced Camera for Surveys (ACS), which has been hobbled in recent years. It has three so-called channels, which each act as a separate instrument and have different capabilities: the wide-field channel (the most heavily-used), the high-resolution channel, and the solar blind channel.
Scientists can choose which they want to use based on the kind of science they want to do. But currently on the solar blind channel is working.
"In a sense the ACS is still working, but only on one of its three channels," Leckrone said.
The spacecraft's Space Telescope Imaging Spectrograph (STIS) also has three channels, none of which are currently working. If time allows, the astronauts will try to revive its three channels.
The STIS and ACS repairs are complicated circuitry work not designed to be done in space, so mission scientists can't be sure how the repairs will turn out, though they are optimistic about the chances.
But, if the team can't complete the ACS repairs, then the instrument will still be left with the solar blind channel, "so we should be no worse off there than we were before," said Hubble project manager Preston Burch, of NASA's Goddard Space Flight Center in Greenbelt, Md.
Also, the brand new Cosmic Origins Spectrograph will augment STIS's capabilities; it has 2 channels, one for near ultraviolet observations and one for far UV. COS can also stand-in for STIS if can't get it repaired
Also joining the Hubble instrument team will be the Wide Field Camera 3, which will replace the Wide Field Planetary Camera 2 and complement ACS's observing capabilities (it can also observe in the same wavelengths of light as ACS if ACS can't be repaired).
Wide Field Planetary Camera 2 "has been operating like a champ for about 15 years now, but it is getting a little bit long in the tooth and will be replaced on this mission," Leckrone said.
All of these instruments are "tremendously important tools to be used for a broad variety of astronomical investigations," Leckrone said.
When this servicing mission is complete (and if all goes according to plan), "Hubble will be at the apex of its capabilities," Leckrone added "It will never have been better before than it will be at that point."
What will Hubble do now?
Once its newly-tricked out, Hubble will be able to take even more images and continue to add to our knowledge of the universe.
In the nearly two decades it has been operational, Hubble has contributed considerably to our understanding of the universe.
In an essay in the Jan. 1 issue of the journal Nature, astronomer Julianne Dalcanton, of the University of Washington, discussed some of the contributions Hubble has made, including: refined distance scales in the universe (by monitoring Cepheid variable stars); the life cycle of stars (including the first observations of proto-planetary disks around stars); a better understanding of black holes and their role in the formation of galaxies; the formation of the first galaxies (through the Hubble Deep Field and Ultra Deep Field); and the general age, composition and size of the universe .
"We have reformulated so many different areas of astronomy," Leckrone said. "There is no area of modern astronomical research that hasn't been profoundly affected and changed by Hubble."
With its new components, Hubble will continue to do science in these many of these areas, with the hopes of shedding even more light on the dark spots of space.
Hubble will further investigate the architecture of the universe, as well as the structure of individual galaxies.
"Hubble will look all the way from the nursery to the old age of galaxies," Leckrone said.
When Hubble took its first look back in time, scientists expected to see infant galaxies, because it was thought to take at least a billion years for galaxies to form.
"And lo and behold, what did we see? Did we see the first babies coming out of the birth canal? No, we saw three-year-olds, five-year-olds, ten-year-olds, we saw galaxies already well-formed at a billion, two billion years, which implied that the universe didn't read the same textbooks and decided to get its act together much, much, much earlier than any physicist thought it could," Weiler said.
With the Ultra Deep Field, Hubble was able to spy on galaxies that formed when the universe was only about 700 million years old. With the new Wide Field Camera 3's infrared channel, astronomers will be able to take another survey and stretch our view even further (before the James Webb Space Telescope takes over in this arena).
"I guess you could now call it an Ultra Ultra Deep Field, which hopefully will press back another couple of hundred million years, and we'll perhaps see even earlier fledgling galaxies that emitted their light within, say, 500 million years of the Big Bang," Leckrone said.
Within galaxies, Hubble will investigate how stars are born.
"It's not just something that happened long ago and stopped, continually stars are being born within galaxies and they evolve, burn out their nuclear fuel and ultimately die," Leckrone said. "And understanding that whole process is something that we are now capable of doing, not only in our own galaxy, but in other galaxies as well as we study stellar populations."
Hubble will also likely extend its unexpected contributions to the study and search for exoplanets.
"Hubble surprised everybody by being able to actually observe the atmospheres of planets around other stars and get information about their chemical composition and structure," Leckrone said. "We never expected to be able to do that, but we will continue to do that in a very serious way after this mission."
The telescope will also continue its quest to help solve the mysterious entities of dark matter and dark energy.
"Hubble will of course continue to survey supernovae going off in the distant cosmos to try to narrow down the uncertainty in the quantitative understanding of the magnitude of dark energy," Leckrone said.
But as stunning as the findings of any of these efforts might be, mission controllers say it's probably something unexpected that might be Hubble's triumph in its last few years.
Beginning of the end
Hubble won't be taking pictures again immediately after its facelift, but from the time the astronauts release Hubble back into orbit, "you can start a clock at that point," and expect that after nine or 10 weeks its instruments will be "back up and running and ready for science," Leckrone said.
Mission scientists are aiming to have the first public release of images in early September, he added.
How long the telescope will last after that isn't known for sure, and depends on how Hubble holds up with no more astronauts coming to fix it and whether astronomers are still interested in using it.
"The five years we think we have a good shot at," Burch said. "I would think there's probably a very good prospect of even seven years, like we've currently gone past."