On Wednesday, the most critical day of their 11-day mission, spacewalking astronauts performed a complicated and risky operation that NASA compared to a heart transplant, boosting the satellite's electrical capacity by replacing its power control unit.
On two earlier spacewalks, astronaut teams added two new solar-power arrays, the wing-like structures on either side of Hubble, capable of delivering more power to the station.
Thursday's spacewalk by Jim Newman and Mike Massimino was the payoff, adding the largest of several instruments that will take advantage of Hubble's new muscle.
Newman, making the sixth spacewalk of his career, secured himself to the end of the shuttle's 50-foot robotic arm, where he was moved about by astronaut Nancy Currie, operating the arm from inside the shuttle.
Newman was to carry the new camera to the telescope while riding the arm.
"Good to be back on the arm, Nance. It looks like a beautiful night for a spacewalk," Newman said to Currie.
The $75 million Advanced Camera for Surveys will give astronomers 10 times the optical power they now have using Hubble's Wide Field-Planetary Camera, itself a priceless tool in helping cosmologists rewrite their textbooks on the age, composition and destiny of the universe.
Since it takes billions of years for light from distant galaxies to reach Hubble, the telescope photographs distant sights as they existed eons ago.
With this new camera, scientists hope they will be able to see back to the early days of star formation.
Scientists also hope to for some insight into the mysterious nature of dark energy, which seems to be accelerating the expansion of the universe, long assumed to be slowing down.
Hubble, launched in 1990, has been secured to Columbia's cargo bay since Sunday.
Once the last of the five ambitious spacewalks planned for this mission is complete, Hubble will be released back into its own orbit, more than 350 miles above Earth.
Hubble managers at NASA's Goddard Space Flight Center in Maryland expect to complete their tests of all the new equipment in about three weeks.
"The first images should be ready for public release sometime in late April," said Holland Ford, the principle investigator for the Hubble program.
Columbia, skippered by veteran astronaut Scott Altman and carrying a crew of seven, is to land at the Kennedy Space Center on Tuesday.
By Broward Liston