Ground controllers in California say they've been unable to communicate with NASA's long-lived Deep Impact spacecraft, last heard from in August.

Deep Impact mission controllers at the space agency's Jet Propulsion Laboratory in Pasadena, Calif., said they would make ongoing attempts to uplink commands to re-establish communications with the spacecraft.

The last communication with the comet-hunting spacecraft was on Aug. 8, when an anomaly generated by the spacecraft's software may have left its computers in a condition where they are continuously rebooting themselves, controllers said Tuesday.

In that state, the computers would not be able to command the vehicle's thrusters to fire and hold the spacecraft's attitude, they said. That may be making attempts to re-establish communications more difficult because the orientation of the spacecraft's antennas is unknown, JPL said.

Deep Impact, launched in January 2005, is NASA's most-traveled, deep-space comet hunter, successfully completing both its original mission and a subsequent extended mission.

To date, Deep Impact has traveled about 4.7 billion miles in space.