STS-125 mission specialists Mike Good and Mike Massimino began the mission’s second spacewalk at 8:49 a.m. EDT.
Massimino and Good will spend the bulk of their time replacing the Hubble Space Telescope’s three rate sensing units. Each unit is part of a rate gyro assembly, which senses vehicle motion and provides rate data to help point the telescope precisely for its science observations.
After the new rate sensor units are installed, Massimino and Good are scheduled to perform the first half of the mission’s battery replacement work. They will be working in the telescope’s bay 2 to replace the first of two battery modules. Each module weighs 460 pounds (210 kilograms) and contains three batteries, providing electrical power to support Hubble operations during the night portion of its orbit. The second battery module will be installed during the fifth and final spacewalk.
Today’s spacewalk is scheduled to last 6.5 hours.