An artist's concept of Galaxy 7. Photo: Boeing Satellite Systems

For the third time in two years an American-made telecommunications satellite has spun out of control in geostationary orbit after its computer brain malfunctioned due to a design flaw.

The latest casualty of a phenomenon plaguing craft built by Boeing Satellite Systems -- formerly Hughes Space and Communications -- is PanAmSat's Galaxy 7, which went dark on Wednesday and won't be recovered.

The craft was launched in October 1992 with an expected 12-year life to provide television distribution and other telecommunication services across the entire United States and Caribbean. It was recently moved to a backup role in PanAmSat's satellite fleet with the new, more powerful Galaxy 11 craft assuming its original slot at 91 degrees West longitude above the equator some 22,300 miles up. Galaxy 7 had been maneuvered to 125 degrees West where it had been working part-time.

"PanAmSat took decisive action early on to assure the highest levels of service and reliability across our fleet. As a result, none of our full-time customers will be affected by the Galaxy 7 failure," said R. Douglas Kahn, President and CEO of PanAmSat. "We remain focused on expanding our 21-satellite global network and are confident in the continued performance of our Boeing 601 spacecraft in orbit."

The spacecraft lost its backup Spacecraft Control Processor (SCP) at 1:29 p.m. EST (1829 GMT) on Wednesday, effectively allowing the spacecraft fall out of its correct attitude and causing the solar arrays to lose track of Sun, thus draining the satellite of its power.

Two SCPs are in each Boeing 601-model spacecraft, but only one is required for operation of the satellite. The SCPs oversee the attitude control systems and the pointing of the solar arrays and antennas.

Problems with SCPs in 601 satellites are electrical shorts caused by internal tin-plated relay latching switches that act as on/off switches within the processors.

Investigators have found that under certain conditions, a tiny, crystalline structure, less than the width of a human hair, can grow and bridge a relay terminal to its case, causing an electrical short.

Galaxy 7's primary SCP failed in June 1998, one month after sister-satellite Galaxy 4 became the first craft to fail because of electrical shorts, wiping out communications and pager services across the U.S. for days before customers were switched to alternate satellites.

Another Boeing-built communications satellite went out of service in August when the Mexican Solidaridad 1 lost its backup SCP.

Engineers have solved the electrical shorts in newer Boeing satellites by replacing the tin-plated switches with nickel-plated switches.

PanAmSat also announced Friday that their PAS-4 satellite that serves the Indian Ocean and surrounding regions lost its primary SCP in November 1998. Its reign over the Indian Ocean is scheduled to be taken over by PAS-10, once it is launched next spring.

Yet another satellite built by Boeing is also running without backup -- DirecTV's DBS-1 direct-to-home broadcast satellite is relying on its second SCP.

PanAmSat says it intends to file an insurance claim for the loss of Galaxy 7, which is worth around $130 million to the telecommunications giant. The satellite used 24 C-band and 24 Ku-band transponders to broadcast its telecommunications services.