Launch from Cape Canaveral (KSC); landing at Cape Canaveral (KSC); ISS-20-12A.1 SH-LSM ITS-P5; mission Celsius.

Liftoff was originally scheduled for December 07, 2006, but that attempt was canceled due to a low cloud ceiling.

The main goals of the mission were delivery and attachment of the International Space Station's P5 truss segment, a major rewiring of the station's power system. The shuttle also carried a Spacehab Logistics Module to resupply the ISS, and an Integrated Cargo Carrier with four sub-satellites, which were deployed after undocking from the ISS: the ANDE technology demonstrator, developed by the Naval Research Laboratory, and three CubeSats (RAFT-1 and MARScom for the United States Naval Academy, and MEPSI 2A/2B for DARPA). It was the first Shuttle mission to deploy satellites since STS-113 in 2002.

Following a two days solo flight the Discovery docked to the ISS. During the next eight days the crew performed common work with the ISS expedition 14. Sunita Williams was tranferred to the ISS and Thomas Reiter to the crew of STS-116 for returning to the Earth.

The first EVA by Robert Curbeam and Christer Fuglesang occured on December 12, 2006 (6h 36m) to align and connect the P5 truss segment to P4. They also replaced a faulty video camera attached to the S1 truss. Since they worked ahead of the time-line, the two astronauts were also able to complete some get-ahead tasks.

On December 13, 2006, the crew attempted retraction of the P6 port-side solar array. Problems with the array folding due to 'kinks' and 'billows' led the controllers to redeploy the array (from about 40% retracted). There then followed a series of more than 40 commands to furl and unfurl the arrays in an effort to get them properly aligned and folded. The retraction efforts were abandoned for the day.

The second EVA was performed by Robert Curbeam and Christer Fuglesang on December 14, 2006 (5h 00m) to reconfigure power on channels 2 and 3 of the station's electrical system.

The third EVA by Robert Curbeam and Sunita Williams was conducted on December 16, 2006 (7h 31m) to reconfigure power on channels 1 and 4 of the station's electrical system. As an "add-on task" to the EVA, astronauts Robert Curbeam and Sunita Williams also continued work on the retraction of a sticking solar array, enabling the retraction of another six sections of the P6 array. At the end of the EVA there were another 11 "bays", or 35% left to retract.

The fourth and unplanned EVA by Robert Curbeam and Christer Fuglesang was performed on December 18, 2006 (6h 38m) to fully retract the array.

The first landing opportunity at Kennedy Space Center was abandoned due to unfavorable weather conditions.

Sunita Williams landed on June 22, 2007 at 19:49 UTC with STS-117.