World dishes join comet probe search party

Drawing of Contour approaching a comet

(CNN) -- Numerous radar and optical observatories around the world have joined NASA's Deep Space Network stations in looking for a $159 million spacecraft, which disappeared as it attempted to leave Earth orbit.

In such an emergency, the Comet Nucleus Tour (Contour) probe was supposed to point one of its four antennas toward Earth on Friday, the day after it went silent.

But hours after an onboard computer should have given the command to move the antenna, "no signal has been received," the space agency said in a statement late Friday.

Mission controllers sent radio commands Thursday morning for Contour to conduct an engine burn, hoping to nudge the octagonal spacecraft out of a highly elliptical orbit and into a trajectory to encounter two or three comets in the coming years.

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The spacecraft was too low for Deep Space Network antennas in the United States, Australia and Spain to track Contour during the burn, about 140 miles (225 kilometers) above the Indian Ocean.

Contour technicians at the Johns Hopkins University Applied Physics Laboratory expected to regain contact less than an hour later. Hearing nothing, they tried to find the 1-ton vessel along predicted trajectories had the thruster firing gone as planned.

"We're looking at the nominal path, as if the burn occurred," Contour mission director Robert Farquhar said late Thursday. "We're working on the assumption that the motor fired, and the team is putting its priority there."

In the meantime, Contour controllers scrambled to try different strategies to re-establish contact with the solar-powered vessel, which had been "parked" in Earth orbit since July.

"We're trying to send commands to the spacecraft to switch between its two transmitters and use different onboard antennas, in case they turned off for some reason," Farquhar said.

"But we really won't know what happened until we contact it."

The Contour mission was designed and managed for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.