Galaxy IV

Galaxy IV was a model HS-601 satellite built by Hughes Space and Communications Company (HSC). The satellite, which carried a payload of both C band and K_u band transponders, was launched on June 24, 1993 and operated by PanAmSat Corporation.

Control of Galaxy IV was lost on May 19, 1998 when the satellite's primary control processor failed. The backup control processor had suffered a previously undetected anomaly, and PanAmSat was not able to regain control of the spacecraft. Galaxy IV was declared a loss on May 20, 1998. Failure of the primary control processor was attributed to tin whisker growth, a phenomenon in which tendrils grow from solder, causing an electrical short circuit. Engineers believe that a hole developed in the conformal wax coating over the solder, allowing whiskers to develop. The satellite manufacturer, Hughes, has replaced pure tin plating with nickel to alleviate the problem in newer designs, adding 45 to 90 kg per payload.

The loss of this satellite was very disruptive to telecommunications in the United States. Pagers were affected greatly; service was not restored for days. Wire news services, like Reuters, were also affected. The TV network CBS had to use alternate means of transmitting its programs, as did NPR.

At the time of failure, Galaxy IV was in geostationary orbit at 99°W. This orbital slot was briefly occupied by Galaxy 4R, and is now occupied by the Galaxy VI satellite. Galaxy IV remains in space.

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