Experts and officials have ruled out any terrorist hand in the break-up of American space shuttle Columbia, which killed India-born astronaut Kalpana Chawla and six of her colleagues on Saturday.
They said the Columbia was at an altitude of 200,700 feet travelling at six or seven times the speed of sound when it apparently broke up and no missile is known to have that range.
An expert said the United States is trying to develop that kind of technology but it is still at an experimental stage.
The concerns about terrorist threat were raised as an Israeli astronaut was among the crewmembers.
There was unprecedented security at the time of take off from the Kennedy Space Centre at 1039 EST (2119 IST) on January 16.