The problem, described as an anomaly that surfaced during routine testing of a steering engine, caused the space agency to delay the Wide-field Infrared Survey Explorer mission by at least one day. But inclement weather expected throughout the weekend in California could push the launch back several more days.
The steering engine is designed to place the spacecraft into orbit 326 miles above the Earth. Over the next year, the craft's telescope will scan the near region of space in the infrared part of the electromagnetic spectrum, searching for asteroids and failed stars that are too dim and cold to see in ordinary light.
Because infrared instruments can detect even the minimal emissions of heat from very cold objects, WISE is expected to unmask tens of thousands of asteroids and possibly even a giant planet that some astronomers believe could be hiding beyond the orbit of Pluto.