During the morning of day 11, astronauts Jett and Ferguson tested Atlantis' reaction control thrusters and practiced for landing using on-board computers.
The thrusters will be used to position the shuttle during re-entry.

The crew also took some time for interviews, with Ferguson telling the media that everyone on board was looking forward to landing. "
I think we all, thus far, feel pretty good about the job that we did," Ferguson said. "
We are looking forward to a successful re-entry and landing sometime tomorrow."

Following the interviews, the crew continued their preparations for re-entry by stowing unnecessary equipment and other tasks prior to landing.
However, the crew informed the Mission Control Center later in the day that, following the test of the reaction control system, an object was seen moving in a co-orbital path with the Orbiter.
The astronauts spotted the object using an on-board TV camera, but unfortunately the resolution of the images was not high enough to identify the object.

The images were sent down to the MCC for further analysis by flight controllers, who were concerned about the possibility that the object may have come off Atlantis, and as such wished to identify the object.
The most likely scenario was that the object was benign, such as ice or a piece of shimstock (observed earlier in the flight protruding from the heat shield) that may have shaken loose.
However, the possibility remained that the object may be of critical importance, such as a tile from the Orbiter's thermal protection system, and the Mission Control Center asked Atlantis' crew to power up the shuttle's robotic arm ready to reinspect the orbiter, and drew up plans for a series of tests which took place on flight day 12 to determine whether the shuttle was safe for re-entry.
This extra inspection, added to poor weather forecasts predicted for the Shuttle Landing Facility for Wednesday, and the de-orbit burn and landing were delayed by a day.
During the morning of day 11, astronauts Jett and Ferguson tested Atlantis' reaction control thrusters and practiced for landing using on-board computers. The thrusters will be used to position the shuttle during re-entry.
The crew also took some time for interviews, with Ferguson telling the media that everyone on board was looking forward to landing. "I think we all, thus far, feel pretty good about the job that we did," Ferguson said. "We are looking forward to a successful re-entry and landing sometime tomorrow."
Following the interviews, the crew continued their preparations for re-entry by stowing unnecessary equipment and other tasks prior to landing. However, the crew informed the Mission Control Center later in the day that, following the test of the reaction control system, an object was seen moving in a co-orbital path with the Orbiter. The astronauts spotted the object using an on-board TV camera, but unfortunately the resolution of the images was not high enough to identify the object.
The images were sent down to the MCC for further analysis by flight controllers, who were concerned about the possibility that the object may have come off Atlantis, and as such wished to identify the object. The most likely scenario was that the object was benign, such as ice or a piece of shimstock (observed earlier in the flight protruding from the heat shield) that may have shaken loose. However, the possibility remained that the object may be of critical importance, such as a tile from the Orbiter's thermal protection system, and the Mission Control Center asked Atlantis' crew to power up the shuttle's robotic arm ready to reinspect the orbiter, and drew up plans for a series of tests which took place on flight day 12 to determine whether the shuttle was safe for re-entry. This extra inspection, added to poor weather forecasts predicted for the Shuttle Landing Facility for Wednesday, and the de-orbit burn and landing were delayed by a day.
STS-115