The 14-day mission will feature four spacewalks to help install the S6 truss segment to the starboard, or right, side of the station and the deployment of its solar arrays. The truss is a high-tech girder structure made up of 11 segments and is the 361-foot-long backbone of the space station. The truss includes the fourth pair of solar array wings and electronics that convert sunlight to power for the orbiting laboratory. Altogether, the station’s arrays can generate as much as 120 kilowatts of usable electricity, which is enough to provide about forty-two 2,800-square-foot homes with power. The addition of the S6 truss segment provides nearly twice the amount of power for station science, an increase from 15 kilowatts to 30 kilowatts. The flight also will replace a failed unit for a system that converts urine to potable water. The entire Water Recovery System was delivered and installed during Endeavour’s STS-126 mission in November 2008. Astronauts were able to coax it into use by performing in-flight maintenance, but a distillation unit failed after Endeavour's departure. Discovery will fly one heat shield tile underneath its left wing that will have a bump raised 0.25 inches so that heating effects are monitored at about Mach 15 during reentry, when the smooth, laminar flow of air close to the shuttle’s surface becomes turbulent or is disrupted.
Detailed Supplementary Objectives (DSOs) and life sciences investigations are also flown on the STS-119 mission. A DSO is a NASA-sponsored investigation performed by Space Shuttle crewmembers, who serve as the test subjects. These studies required minimal crew time, power and stowage. Biomedical DSOs focus on operational concerns, including space motion sickness, cardiovascular deconditioning, muscle loss, changes in coordination and balance strategies, radiation exposure, pharmacokinetics and changes in the body's biochemistry.
This mission is projected to be fourteen days in duration. STS-119 is the 125th space shuttle flight, the 28th flight to the station, the 36th flight for Discovery and the first flight for 2009. The shuttle also will deliver the first Japan Aerospace Exploration Agency’s resident station crew member and bring back a U.S. astronaut after more than three months aboard the orbiting laboratory.