Light smoke was reported aboard the International Space Station and the three residents of the station were wearing protective gear, reports have said.
The three astronauts pulled an alarm and donned protective gear after smelling a foul odor that turned out to be an unknown vapor, reports quoted NASA as saying.
Initial reports said there was light smoke aboard the orbiting lab 220 miles above earth.
The development, ABC News reported, happened soon after space shuttle Atlantis pulled away on Sunday to return to earth.
The ISS is expecting heavy traffic, something similar to rush hour.
On Monday, a Russian Soyuz rocket carrying two new station crew members and the world's first female space tourist -- Anousheh Ansari -- blasted off.
Ansari, along with two of the station's current inhabitants, is slated to return to earth on September 28.
Meanwhile, Atlantis is scheduled to land at the Kennedy Space Center in Florida on Wednesday.