There are few fears worse than having to confront a fire incident inside a pressurized space vehicle in microgravity orbiting 230 miles above Earth, so there's little doubt that when the International Space Station crew reported smelling smoke late on Tuesday, concern would have been high.
PHOTOS: Astronauts Watch Spectacular Spacecraft Reentry
But fortunately, through the professional response of the astronauts and cosmonauts in space and the rapid response of mission controllers on the ground, the source of the smoke was quickly identified before there was any threat to the six-man crew.
"In line with standard protocol, flight controllers at mission control in Houston followed emergency procedures to isolate the Russian segment ventilation system," NASA said in a statement. "Expedition 40 commander Steve Swanson reported that the smoke quickly subsided and the crew was not in any danger."
The source of the smoke was the Water Dispensing and Heating Unit, which is used for water reclamation purposes and is located in the Russian Zvezda service module. The unit was powered down, removed and replaced with a spare. As reported by the Associated Press, there was a similar problem in 2009.