CAPE CANAVERAL, Fla. — Two spacewalking astronauts worked on a leaky radiator system outside the International Space Station today, just hours after barely dodging a menacing piece of orbiting junk.

NASA ordered the space station to change position Wednesday evening to avoid a fragment from a communication satellite that was destroyed in a high-speed collision three years ago.

Thrusters on a docked Russian supply ship were fired to move the orbiting lab out of harm’s way. But a computer error caused the thrusters to malfunction and the space station did not reach the desired altitude. NASA officials said the space station and its six residents were safe despite their lower-than-intended orbit.

Space station commander Sunita Williams and Japanese astronaut Akihiko Hoshide successfully rerouted ammonia coolant lines and bypassed a radiator believed to be leaking. They isolated the suspect radiator to help flight controllers determine in the coming days whether that, indeed, is the source of the ammonia seepage.