(CNN) -- The debris spotted floating away from space shuttle Discovery has been preliminarily identified as a thermal clip from the shuttle's brake system, NASA said Friday.
Also, lighting conditions tricked astronauts into thinking there was a "bump" along the edge of the shuttle's rudder, agency officials added.
It is not immediately clear why the thermal clip fell off the shuttle.
The clip -- one of three on the rudder speed brake -- protects the brake during launch and ascent.
The problem will not affect Saturday's planned landing, NASA spokesman Rob Navias said.
Discovery is expected to land at 11:15 a.m. Saturday at the Kennedy Space Center in Florida.
Meanwhile, NASA imagery experts said what astronauts had described as a "bump" along the edge of the shuttle's rudder was just a trick of lighting. Watch what it looks like »
Astronauts said they noticed a shiny, rectangular object, about a foot to a foot and a half long, floating from behind the rear portion of the right wing. Shortly afterward, they said they noticed the bump on the left-side trailing edge of the rudder.
Both issues arose during routine testing of the steering jets and during an examination of the flight control system -- standard day-before-landing tests.
The seven-person Discovery crew arrived at the international space station on June 2, bringing with them the Japanese Pressurized Module, the second and largest component of the Japan Aerospace Exploration Agency's Kibo laboratory. The module is the size of a bus, NASA said.
The billion-dollar Kibo -- which means "hope" in Japanese -- is Japan's first human space facility, more than 20 years in the making. Watch one of the mission's three spacewalks »
The crew also brought parts, including a gas-liquid separator, urine collector bags and filters, to fix a problematic toilet aboard the space station.
And they dropped off a new station crew member, Greg Chamitoff, who traded places with Expedition 17 Flight Engineer Garrett Reisman, who is returning home on the Discovery after a three-month stay on the outpost.