NASA said on Tuesday it will launch a final space shuttle mission to keep the aging, trailblazing Hubble Space Telescope in orbit and operational.
The decision, announced by the chief of the US space agency, Michael Griffin, followed a review of safety concerns and appeals from the scientific community to extend the life of the Hubble.
Without a repair mission, which will likely be carried out in 2008, the telescope would shut down in 2009 or even earlier.
Since it was launched into orbit 16 years ago, the telescope has helped astrophysicists peer deep into the universe free of the distortions from the Earth's atmosphere.
Orbiting 575km above the Earth, the Hubble has enabled scientists to better measure the age and origins of the universe, observe distant supernovas, and identify and study bodies in and outside the solar system.
In 2004, it conveyed pictures of the most distant parts of the universe ever observed by visible light, "the deepest portrait of the visible universe ever achieved by humankind," said the Space Telescope Science Institute.
NASA had scheduled a mission for Hubble in 2003, but scrapped it after the Columbia shuttle disintegrated while returning to Earth.
The accident raised serious safety questions for the NASA space program, particularly with the shuttle's heat shield. Tuesday's announcement comes after two of the last three shuttle missions were judged a success.
Griffin said the decision to go ahead was taken after a painstaking review of safety issues.
"We're not going to risk a crew in order to do a Hubble mission," he told staff at Goddard Space Center in Maryland outside of Washington.
NASA has said previously it was ready to refurbish the telescope as long as the mission did not put the space shuttle crew in jeopardy.
The Hubble mission presents a challenge because the shuttle crew would not be able to seek refuge aboard the orbiting International Space Station if a serious problem arose.
NASA also is faced with a busy schedule of another 15 missions to finish building the space station before retiring the entire shuttle program in 2010, or four missions per year.
A Hubble mission would likely be set for early 2008 and would require a second shuttle to remain at the ready for any rescue mission should the crew face an emergency.
A new mission to the Hubble would replace the telescope's six stabilizing gyroscopes and its batteries to extend its life.
Astronauts would also repair an infrared spectrometer that has been broken since 2004 and install two new instruments, including the Wide Field Camera 3 that would enhance images of dark matter and of the first galaxies that were formed after the Big Bang, the scientific model of the creation of the universe.