( CNN ) -- Tuesday 's space debris incident at the International Space Station was the `` closest anything has come to the space station , '' NASA said Wednesday . Final calculations showed the unknown object passed the space station 1,100 feet away and its source remains a mystery , according to Kelly Humphries , a spokesman at the Johnson Space Center in Houston , Texas . When the unexpected space debris came flying close to the space station Tuesday , it prompted the station 's six astronauts to take shelter inside two Soyuz capsules , NASA said . NASA does not expect any other close calls with this particular debris , said Humphries . Russia 's Interfax news agency said preliminary data on `` the dangerous approach '' shows that the `` trash '' came within about 250 meters ( 820 feet ) of the station . Officials at NASA are investigating what the debris was , NASA spokesman Joshua Buck said . By the time it was spotted , it was `` too late to make an avoidance maneuver , '' so NASA ordered the six crew members to `` shelter in place , '' Buck said . About 7:30 a.m . ET , the crew members climbed into the two Soyuz capsules positioned at the station . NASA determined that the debris would come closest to the station at 8:08 a.m . ET . Three minutes later , at 8:11 a.m . ET , the all-clear was sounded and astronauts were allowed to exit the capsules , Buck said . Buck described the debris as an `` unknown object of unknown size . '' CNN 's Josh Levs contributed to this report .
NEW : The debris comes within 1,100 feet of the space station , NASA said . NEW : The source of the object remains a mystery . Russia 's Interfax news agency said the `` trash '' came within 820 feet . The debris was spotted `` too late to make an avoidance maneuver , '' NASA said .