The team was asked to fix a spectrograph that can, among other things, measure the chemical composition of distant objects in the cosmos. To accomplish this, Massimino had to remove more than 110 small screws which, with huge space gloves, proved to be a tedious, time-consuming task.
At one point, Houston sent Massimino back to the space shuttle's airlock to refill the oxygen in his backpack. In the end, the astronauts wrapped up what was scheduled as a 6½-hour spacewalk after eight hours.
On Saturday, astronauts Grunsfeld and Feustel whipped through what was supposed to be the toughest spacewalk of the mission with remarkable ease.
The two replaced an old instrument with the new Cosmic Origins Spectrograph, and then repaired a broken camera deep inside the telescope, removing blown circuit boards that were never meant to be taken off in orbit.
Massimino and Good were working on the telescope's Space Telescope Imaging Spectrograph, or STIS. They had the very challenging task of replacing a low-voltage power supply board, which contains a failed power converter. That meant taking out the 110-plus very small screws -- and not letting any of those screws float away -- to accomplish the repair.
STIS has been in "safe mode" since August 2004, when its power supply failed. Massimino, during training on the ground, managed to perform the task in 40 minutes.
The spacewalkers also were scheduled to install one of two new protective thermal insulation panels to protect Hubble from space junk.
Spacewalking to fix the Hubble Space Telescope is hard work, especially when the shoe doesn't fit. If your feet hurt nothing is fun. Ask any woman who has to smile while wearing 4-inch heels.
Good struggled with an ill-fitting boot on his first spacewalk last week, and a team on the ground at Mission Control sent up suggestions to adjust the fit.
"Once pressurized, you should be able to pull your foot back in the boot away from the pressure point on the top of the foot," wrote astronaut Rex Walheim to Good.
Walheim said he has chased boot pain issues in spacesuits for more than seven years.
A fifth and final spacewalk is set for Monday, and the Hubble telescope will be released Tuesday from Atlantis, with a landing planned, if weather cooperates at the Kennedy Space Center Friday.
The new discoveries from the improved Hubble Space Telescope won't be revealed for months. This last mission to Hubble cost more than $1 billion.