After years of delays and debate about whether the risks to astronauts outweigh the scientific benefits, the space shuttle Atlantis launches on May 11, on a final repair mission to the Hubble Space Telescope.

The repairs and upgrades will make it possible for astronomers to see deeper into space and help them understand more about the origins and makeup of the universe. The work will also allow the space telescope to continue to operate for at least five more years.

Bill Harris, an astrophysicist at McMaster University in Hamilton, Ont., says outcry from the international community of scientists helped push NASA to complete the repairs instead of abandoning the deteriorating space telescope.

"The scientific value is enormous," he said.

Repairs to the Hubble, which has already undergone four major maintenance missions, have been a long time coming. The space telescope's most powerful camera has been broken for two years, and its main spectograph, which measures light wavelengths, has been busted for five years.

The controversy over what to do with the deteriorating telescope began when former NASA administrator Sean O'Keefe decided to cancel repairs and eventually abandon it.

O'Keefe cited safety concerns — the Hubble telescope is too far away from the nearest space station for astronauts to return there and await rescue in the event of an emergency. They would have to wait at the telescope, where supplies would run out within 28 days.

Decision was reversed

NASA was under increased public scrutiny after seven astronauts were killed when the Columbia space shuttle burned up during re-entry into the atmosphere.

In 2006, O'Keefe's successor Michael Griffin reversed the decision to abandon Hubble. NASA drafted a plan to have a second rescue shuttle prepared to launch from Cape Canaveral in the event of an emergency during the repair mission. This will be the first time NASA has taken such a safety precaution.

If the rescue shuttle were to be deployed, it would reach the Hubble telescope within days. The rescue shuttle would then grasp the repair shuttle using a robotic arm, allowing astronauts to move from one shuttle to the other and return to Earth.

The Hubble telescope has made many important scientific discoveries possible. Using data it has collected, scientists have confirmed the existence of black holes, estimated the age of universe at about 13.7 billion years, and discovered dark energy, a mysterious substance that some scientists think allows the universe to expand.

The Hubble telescope has also helped popularize space research. Images taken by Hubble have made the front pages of magazines and newspapers, sparking public interest and garnering support for research funding.

A high-powered telescope in space allows scientists to observe the universe without the blurring effects of the atmosphere. Comparing pictures taken by Hubble to pictures taken by telescopes on Earth is like a near-sighted person putting on glasses for the first time, Harris says.

Hubble a hard act to follow

That this is to be the final repair on Hubble before a new generation of telescopes replaces it is troubling for scientists, Harris says. So far, none of the telescopes that have been proposed to replace Hubble can perfectly match its technology.

"It's going to change the emphasis of astronomy in a fairly big way," Harris says.

The Hubble telescope is vital to Harris's work. When he found out repairs on the telescope's main camera were going to be delayed two years ago, he had to scrap plans to research a nearby giant elliptical galaxy.

Harris is glad the repair mission will extend Hubble's operation for a few more years, but he says he's concerned about what will happen after that.

"We'll have to either design a kind of replacement telescope from scratch, or just figure out more clever and more powerful ways to do something like that from the ground," he said.

Hubble was designed to require maintenance missions from time to time. But the high-powered camera and spectograph weren't designed to be taken apart at all, let alone in space.

To fix them, astronauts will have to remove more than 100 tiny screws to access a computer card. It will take five space walks over 11 days to make all the scheduled repairs and upgrades.

Four of Atlantis's seven crew members have been on previous Hubble repair missions. Commander Scott D. Altman also led maintenance to the telescope in 2002.

For these astronauts, this job will have broader implications than fixing Hubble for the last time — it's also the last flight Atlantis will ever take.

The U.S. plans to retire its fleet of space shuttles next year, after repairs to the International Space Station are completed. NASA is shelving the shuttle program to make way for future missions to the moon and to Mars.